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  • 1. 10 CHAPTER II LITERATURE REVIEW2.1 INTRODUCTIONComposting is a controlled process for the rapid decomposition of waste in stack(Biddlestone& Gray 1988). The stack contains a variety of stages of a food chainwhich consists of microflora and macrofauna (Table 2.1). However, microflora suchas bacteria, actinomycetes and fungi play an important role in the real compostingprocess (Day & Shaw 2001). Table2.1Microflora and macrofauna in the composting process Bacteria, Actinomycetes Microflora Fungi, Algae Protozoa Macrofauna Mites, ant,Termites, millipede, Spider, beetle, earthworm Source: Biddlestone& Gray 1988During the process of composting, microorganisms convert organic materials intocarbon dioxide, biomass, heat energy and a final product which resembles humus. Themain component of organic material is carbohydrates (example cellulose), protein,lipids and lignin. Through the coupling reaction of microorganisms, complex organiccompounds will be decomposed into smaller molecules which can be utilized by
  • 2. 11microbial cell (Golueke 1991). The metabolism of microbes results in the increase oftemperature in the compost stack because the heat released by metabolism of microbesis captured faster than that released to the environment (Miller 1991). The increase intemperature will enhance the degradation process (Biddlestone& Gray 1988).2.2 THEMICROBIOLOGYOF COMPOSTINGIt has long been known that composting is primarily a microbiological process. If onehas the chance to read the work by(Waksman et al.1939), most likely he will getimpressed with the amount of knowledge about the microbiology of the process thatalready existed by that time. The understanding that composting is, above all, amicrobiological process is of paramount importance since this is actually the basis forgood process management (Finstein 1980, de Bertoldiet al. 1983,Golueke 1991). Thiswas one of the strongest basis for the development of the rutgers system ofcomposting (Finstein 1980), where process rate is controlled by maintenance of anappropriate process temperature by forced aeration and it has been one of the guidingprinciples in most of the composting systems available nowadays. Although smallanimals like earthworms or small insects can be found in composting, most of theorganic matter degradation is carried out by microbes. There are three main groupsofmicrobes involvednamely bacteria, fungi and actinomycetes which may befacultative or strict aerobic (Huang et al. 2000).They may have individual preferentialsubstrates andenvironmental conditions for growth.The materials subjectedforcomposting usually contain an indigenous population of microorganisms derived fromthe atmosphere, water or soil (Gray &Bidlestone 1973). Once materials are piled forcomposting, feeding of this microbiological population on the substrates leadto theproduction of heat and is accumulation in the pile, causing process temperature to rise(Finsteinet al. 1987a.,Rynket al. 1992).Microbial activity and the resulting heatgeneration trigger a change in the environmental conditions and substrate compositionalong process time, which in turn causes a succession of mixture ofmicrobialpopulations to occur (Waksman et al. 1939, Gray &Bidlestone 1973,Silveira1999,Tiquiaet al. 2002,Nakasakiet al. 2005, Klammeret al. 2008,Chroniet al.2009).Microbial populations can be subdivided by the temperature ranges of theiractivity: i)psychrophiles, preferring temperatures below 20ºC; ii) mesophiles, for a
  • 3. 12temperature range in between 20ºC and 40ºC; and iii) thermophiles, above 40ºC (Gray&Bidlestone 1973).2.3 BIOPROCESS COMPOSTINGMicroorganisms require carbon material, macronutrient such as nitrogen, phosphorusand potassium and other few side elements for their growth. Carbon is the mainenergy source for microorganisms while small constituents from carbon will beinserted into the cell. Some of the energy formed will be used for microbialmetabolism and the rest of it will be released as heat. Nitrogen is an important elementfor microorganism because it is a component of protein, nucleic acid, amino acid,enzymes, and co-enzymes which are needed for development and cell function(Golueke 1991). During composting, the carbon source which is dissolved and biodegradablesuch as monosaccharide, starch and lipid will be used by microorganism in the earlystage of composting. pH value will decrease because the organic acid formed as aresult of microbial decomposition compound during the process of degradation.Microorganisms will later start the process of protein degradation, resulting inammonia being released and rise in pH value. After the biodegradable source ofcarbon is used up, the compound which takes more time for biodegradable such ascellulose, hemicellulose and lignin will undergo biodegradable and part of it will beconverted into humus (Crawford 1983). Ammonia formed will undergo different process depending on the condition ofcompost mixture. For example, if it is possible to be dissolved (example NH4+) will belater immobilized by microorganisms by using ammonium as nitrogen source andsubsequently changing it back to organic nitrogen. At temperature below 40 0C andalso at a suitable ventilation, ammonia is possible to be converted to nitrate (NO3-) bynitrating bacteria. During nitration, nitrating bacteria will lower down pH caused bythe released oh hydrogen ion. The process can be simplified as follows:Nitrosomonasbacteria: 2NH4++ 3O22NO2-+ 4H+ + 2H20
  • 4. 13Nitrobacterbacteria: 2NO2- + O22NO3-The lack of oxygen will cause the microorganisms to utilize nitrate as oxygen sourcewhich will cause the occurrence of denitration and halts nitration. At a highertemperature and pH exceeding 7.5, ammonia can be vaporized and released (Sanchez-Monederoet al. 2001). Microorganisms have the tendency to utilize organic molecule which isdissolved in water. If the moist content falls below the critical level, the microbialactivity will decrease and it will be dormant (not active temporarily). On the contrary,high moisture content will cause the ventilation of compost to be less efficient,causing leaching of nutrient and the process to be anaerobic (Golueke 1991).Humidity is also important is the storage of energy in the stack of compost (Schaub&Leonard 1996). Composting process can be either more aerobic or more anaerobic. Thedecomposition is faster and lesser foul if the process is more aerobic. This conditionresults in a process which is more aerobic to be conducive in order to stabilize thelarger scaled waste. Biochemical equation for an aerobic process in shown as below(Day & Shaw 2001; Polprasert 1989):Organic material + O2+ aerobic microbes CO2 + NH3 + H20 + Product + Energy On the other hand, a more anaerobic process is easier and less costly althoughthe degradation is time consuming and more have more foul. The biochemicalequation for an anaerobic process is shown below (Day & Shaw 2001; Polprasert1989):Organic material + anaerobic microbes CO2 + NH3 + H2S + Product + Energy + CH4Composting is a microbiological process which relies on the increase and decrease oftemperature.Day and Shaw (2001) stated that microorganisms in a compost stack isdivided into three categories, namely cryophilic or psychrophilic (0-250C),
  • 5. 14mesophylic (25-45 0C) and thermophylic (>45 0C). Generally, mesophylic andthermophylic microorganisms are prone to domination in stack compost. Thetemperature profile for composting is shown as in Figure 2.1. At optimum condition,composting will go through three phases namely, mesophylic phase, thermophylicphase (happens from few days to few months) and cooling and maturation phase (canhappen for few months). Figure2.1 Profile of Temperature and Microbial Growth in Compost Stack Source: Polprasert 1989The period of each phase relies on natural factors or the condition of organic materialwhich is compost and the effectiveness of the process which is determined by degreeof ventilation and stirring (Golueke 1991). The addition of starting compost caneliminate long mesophylic phase and hence speeding up the composting process(Agamuthuet al. 2000). The active composting phase is considered ended when themixture temperature is stabilized and reaching atmospheric temperature (Sanchez-Monederoet al. 2001). The population of microorganisms in the stack also changesduring the composting process as portrayed in Figure 2.2.
  • 6. 15 When composting is not done properly, the breeding and spread of pathogenscan occur. According to Federal Biosolid Technical Regulation, U.S., to reduce therisk of pathogens, limit system (windrow) is compulsory to have a minimumtemperature of 55 0C at a compost stack for 15 days, whereas the minimumtemperature of 55 0C in the reactor for 3 days (Day & Shaw 2001). Figure2.2The Change in Overall Population of Microorganisms (total of bacteria,actinomycetes and fungi) during Sludge-saw dust Composting. Source: Day & Shaw 20012.4 SUITABLE MATERIALS FOR COMPOSTINGAny waste material with high organic matter content is a potential replacement usedfor centuries to stabilize human and animal wastes.Recently it has been used forsewage sludge,industrial wastes (e.g. food, pulp & paper),yard and gardenwastes.Municipal solid wastes (up to 70% organic matter by weight),softprunings,clippings, leaves, woody prunings (finely shredded),straw based farmyard and horsemanure, pure wool jumpers, paper shredded mixed with grass cuttings are usedsparingly.Kitchen waste includes waste from fruit, peelings, teabags, egg shells and
  • 7. 16bedding from vegetarian pets such as rabbits.When selecting materials for yourcompost, avoidusing coal ash, metal, glass and plastic, nappies,the roots of persistentweeds like bindweed and couch grass, leaves with persistent disease such asblackspot,meat or fish and cooked food, especially meat as this attracts vermin (homecomposting).2.5 COMPOSTING SYSTEMComposting system can be classified into reactor and non-reactor. There are two typesof non-reactor system namely long rows (windrow): stirred system and air staticsystem. Long rows refer to stirred system which is usually done manually. In an airstatic system, sludge is piled on a perforated pipe. Air will be forced by aircompressor into the perforated pipe so that there is direct contact between sludge andair in order to activate the microbes (Hassounehet al. 1999).In a reactor system,compost will be circled by container (reactor) and the flow of substance will bedirected according to reactor design. The reactor is usually closed even though thereare researches which uses open reactor system (Papadimitriou et al. 1997). For avertical reactor, raw materials are inserted from the top of the reactor while air issupplied from the bottom so that all substances get sufficient air. In general, reactor isused for organic material without sludge. In a horizontal reactor, the reactor is placed in a horizontal or slightly inclinedwith small gradient so as to ease the flow of substances in a reactor. The direction offeed and air feed is opposite in order to maximize the contact time. The final compostis collected near the air nozzle (Hassounehet al. 1999). Table 2.2 shows the summaryof composting system of commercial scale. A non-reactor system is less costly butrequires a bigger space (Furhacker&Haberl 1995;Haug 1993). Although it is costlyand requires skilled labor, the reactor system has a good control which makes it moresuitable for sludge composting in a larger quantity (Bhamidimarri&Pandey 1996;Haug 1993). In order to increase process efficiency and to reduce cost, only activecomposting is usually carried out on reactor system while maturation process iscarried out on limit system (Furhacker&Haberl 1995; Vourinen&Shaharinen 1997).
  • 8. 172.5.1 RotatingDrumReactorinCompostingRotating drum reactor has been long used in composting field either by batch orcontinuous in a large and small scale. Compared to the batch process, continuousprocess has the ability to manage a larger quantity of material and eliminate themesophilic phase (Schulze 1962). Table 2.2 .Commercial-scale composting systemDecomposing system System’s Information CategoryRotating row Not a Reactor A long narrow piles is rotated regularly and passively ventilated.Static and passive stack Not a Reactor Free standing piles is turned occasionallyventilation or not at all and aerated without the aid of passive ventilation.Static pile and long row Not a Reactor Piles and the long row with the help ofwith the help of passive passive air like perforated pipe andair forced-air plenum.Aerated piles and bins Not a Reactor Short barrels and free standing piles with forced ventilation and without rotated.Stack, long row and Not a Reactor Long row or free standing piles or shortbarrel with turnaround barrel forced air system. Material will beand ventilation fixed or sometimes rotated.Stirred horizontal layers Reactor Material will be composed in long layers with a turnaround narrow, usually with forced ventilation and continuous movement.Aerated containers Reactor Material will be included in various containers with forced ventilation.Aerated-stirred Reactor The commercial container stirred, aeratedcontainers by force and material is moved continuously.Silo or reactor tower Reactor Forced air system that leads to the movement of material vertically from top to bottom.Rotating drum Reactor Drum is rotated slowly to stir the material permanently or intermittently and move the material through the system. Source: Rynk& Richard 2001
  • 9. 18Rotating drum reactor differs in size, design and process management. Rotating drumreactor has common basic technique which is to increase decomposition by mixing upthe materials in the reactor (Rynk& Richard 2011). Rotating drum reactor (RDB) is a complex multiphase reaction system Figure2.3 which includes substrate layer, head space gas, and drum wall. In general,substrate layer covers 10%-40% of bioreactor volume (Hardin et al. 2000). Schulze(1962) filled up 67% of RDB’s volume during composting of sewage sludge. RDB isusually rotated to 2-3 rpm although there are values as low as 3 revolutions per dayand there were also revolution values as high as 40-50 reported before. Drum maycontain internal blades in order to increase mixing action caused by rotation (Hardin etal. 2000).Figure 2.3 Showing the multiple phase and matter and energy flow in a rotating drum reactor. Source: Hardin et al. 2000In a composting process, rotation functions as to expose the materials to fresh air toincrease oxygen and also to release heat and product gases from decomposition.Forced ventilation is commonly used to supply fresh air and to eliminate gaseousproducts. In a few cases, a short drum can obtain sufficient air by exchange of passiveair through the opening at the end. When forced ventilation is carried out, air will bedirected to compost or the opposite side of where the compost is fed to the output.
  • 10. 19 Drum system are needed for composting less homogeneous materials such asmunicipal waste.These drums are of diameter 3 m or more and have a length of morethan 50 m. Some drums can be used in parallel.Smaller drum system can be used tofeed a more homogeneous as excrement, dead animals and leftover food. This unitrange is from 1.5 to 3 m in diameter and 3 to 15 m long. Rotating drum reactor has ashorter retention time of 3 to 5 days. In practice, the drum works on the early stages ofcomposting. Material removed from the drum is usually cured in the limit, an aeratedpile composting system or second composting system. Drum starts feed composting quickly and uniformly in a high and controlledtemperature environment. Drum is effective especially to homogenize heterogeneousmixture such as municipal waste. Lack of ventilation causes the production of anorganic acid and a decrease in pH in the drum. This is why drum is used in earlystages of composting. In few cases, composting time is extended to a few weeks andthis in turns allows aerobic degradation of many acids with the decrease in ventilationrate. In other cases, compost will reach maturity after 3 to 5 days in the drum. Thematerials released from this short retention time may be useful on only certainapplications for example application on soil during winter and autumn.However,according to compost maturity analysis, the period of several weeks isnecessary in agriculture application (Rynk& Richard 2001). One of the important features of rotating drum reactor is its ability to producegranulate products. In industries such as fertilizer, the granulation process issuccessfully done in rotating drum reactor (Walker et al. 2003; Hanafiet al. 2000).Granulate products are important in order to reduce dust and this will minimize therisk of material loss, inhalation and blast. It also improves the flow, is manageable,increasedensity and speeds up the mixing of materials (Ivesonet al. 2001).2.5.1.1 RotatorComposter Design and Description Used in This StudyRotator composter reactor system as shown in Figure 2.4 consists of 3 maincomponents. There are rotator drum, air compressor and gas absorber. Rotator drumsfunctionally facilitated with 3 phase motor. There are 8 inner blades with length of 5
  • 11. 20cm each in order to enhance the mixing in the reactor. On the other hand, aircompressor functionsas to provide air to the reactor, hence the function of gasabsorber is to absorb gas and air resulting from the process inside the reactor.Absorber used in this reactor is charcoal. The characteristic of each components of thereactor is as shown in Table 2.3. Mixing of palm oil mill effluents (POME) and emptyfruit bunches (EFB) is inserted through the feeding part. Figure 2.4Rotatorcomposter reactor system Table 2.3 Rotatorcomposter reactor system specificationsRotator Composter SystemMaterial Stainless steelLength 3mDiameter 0.6 mInitial active volume 0.4 m3Maximum rotation 2 rpm (rotation per minute) To be continued…
  • 12. 21Continued…Air CompressorModel SWAN DR 115Ability 122 liter/minSpeed 1450 rpm (rotation per minute)Cycle 50 HzMotorModel CHENTA, TaiwanVolt 400 VCurrent 9.1 ACycle 3.50 Hz2.5.2 Bin-compostingThis type of composting can be done easily even at home provided that there isenough space to install the composter. The composter can be installed in the garden oron a balcony. Composter is a simple box, made of wood or plastic that can also behome-made. It has a lid to prevent rodent and other animals from eating the compostfeedstock and is in contact with soil to enhance biological activity.In general, yardtrimmings, preferably shredded and food waste can be added to the composter.Nevertheless, a few restrictions on what kind of organic waste should be put in thecomposter must be observed. Meat, fish, dairy products and sanitary material (e.g.diapers) are to be avoided because they are likely to attract vermin. Besides that, thetemperature in the compost heap is usually too low to kill potential pathogens presentin such waste and contamination must be avoided (USEPAEnviro.com2006).Composter can be more sophisticated: the composter might have a forcedaeration system or be automatically turned on. It might also have an odor-controlsystem as well as a leachate collection system. In this study, the composter size is90cm high and its width is 60. The composter has system of natural ventilation at itsbottom and the plasticcompost bin is made of dark color so as to absorb as much heat
  • 13. 22from the Sun as seen in Figure 2.5. Through access doors at thebottom, the finishedcompost can be moved out. The organic waste was poured from the upper part ofthecomposter and it involves waste collected from wet market with removed noncomposting materials(such as plastics, metal etc.) which has been chopped orshredded into smaller sizes for faster decomposition andhas been well mixed. Figure 2.5 Bin composter2.5.2.1 Types of compost binsThere are several types of compost bins available as follows. Description of each binis explained in details. 1. Worm BinsWorm composting is unique because it uses only food scraps and not yard waste. It isideal for people with very small yards or with no yard. Plastic storage bins with holesdrilled on the bottom and on the sides are good for starting out. Homemade wood binsare easy to make. Manufactured bins with layers help in separating worms fromcompost work reasonably well and can be kept indoors but they can be expensive(Compost Bins). 2. HeapsThis is the simplest composting method.However, compost in a heap may take upmore space than a bin. It is not recommended for food scraps as four-legged critters
  • 14. 23are likely to visit looking for a meal. To keep it from drying out in summer and gettingtoo wet during the winter, a heap or open pile should be covered (Compost Bins). 3. HoopsThis type of bin is not costly and can be made from lengths of wire fencing or fromwoodenpallets. Hoops are enclosed and are tidier than a heap andcan be moved andcovered easily.However, they are generally not animal resistant. Hoops are easy totake apartand reassemble when turning or removing compost (Compost Bins). 4. Tumbler or SpinnerThese self-contained barrels, drums or balls rotate for easy mixing and fastdecomposition. They are more costly than other systems. Although most models areeasy to turn, end-over-end models can be nearly impossible to turn and poorlybalanced when they are full. Tumblers and spinners are suitable for small spaces andare usually animal resistant. Since they must be loaded in batches, you will either haveto store fresh materials or use two tumblers. The materials in one will be decomposingwhile the other is being loaded (Compost Bins). 5. Multi Bin SystemThis is a great system for a household or community space generating a significantamount of waste. It is efficient,allowing you to have three working piles at differentstages of decomposition. It is easy to turn and harvest. This style bin can be madeanimal resistant (Compost Bins). 6. One Bin SystemA one-bin system canbe square, circular or cone shapedand can be commercial orhomemade. Most commercial bins have lids andgood ventilation.They are of animalresistant.These bins are good for smaller yardswhere there is a small amountofmaterial to be composted. Bins aid inmoisture and heat retention. Manyprefer theneat appearance of enclosed bins.Although some have small doors near the base,turningthe material and/or removing the compost typicallyrequires lifting the bin upand over the material and reloading it (Compost Bins).
  • 15. 24 Figure 2.6 Types of compost bins2.6 OPTIMUM FACTORS FOR THE COMPOSTING PROCESSComposting process control is very important in order to achieve a short processingtime at a lower cost, consistent results and free from pathogens and odour (deBertoldiet al. 1985). The composting of sludge is controlled by few factors such astemperature, ratio of C to N (C/N), moisture content, free air space, pH, ventilation,rotation and material adapter like stools, wood dust, flying ash and etc. These factorsrely on each other (Figure 2.7) (Campbell et al. 1990). Figure 2.7 Schematic of granulation process Source: Iveson et al. 2001
  • 16. 252.6.1 TemperatureTemperature in the composting material is a function of the rate of heat evolution andheat loss to the environment (Miller 1992; Liang et al. 2003). The temperature in thecompost pile is very important to be controlled because it affects metabolism andmicrobial population (Liang et al. 2003; Campbell et al. 1990). Temperatures between30 and 50 0C increase microbial activity based on the highest oxygen consumption (deBertoldiet al. 1983). Temperature below 20 0C and more than 60 0C is proven todecrease microbial activity (Liang et al. 2003). However, the normal operatingtemperature range used are as follows: >55 0C to maximize sanitation, 45-55 0C to 0maximizebiodegradation rate and 35-45 C to maximize microbial diversity(Stentiford1996). For sludge composting, temperature was found to be responsible forsludge drying (Buchanan et al. 1999; Walker et al. 1999). Figure 2.8. Major Factors which affect decomposition in composting Source: Campbell et al. 1990
  • 17. 262.6.2 Ratio of C to NSewage sludge with a low C/N ratio causes ammonia to become steam andtemperature to not reach thermophilic temperatures (Qiao& Ho 1997). The highammonia emissions can also cause toxicity in microbes and reduce the rate ofbiodegradation of cellulose (Shin &Jeong 1996). Available carbon source such asgreen waste and sucrose is added to sludge to improve the C/N ratio (Qiao& Ho1997). When C/N ratio exceeds 35, microorganisms must go through a long lifecycleto oxidize excessive carbon to a suitable C/N ratio for their metabolic process to beachieved (de Bertoldiet al. 1983). This causes the composting process to becomelonger. Additional resources for nitrogen source such as stool or urea will reduce thecomposting time and cause the end result to be better as the ground adapter material(Hackett et al. 1999; Jokelaet al. 1997). At optimum conditions, thermophilic phase in stack is achieved in ashortertime and dehydration of material will be more effective (Jokelaet al. 1997;Walker et al. 1999). Metcalf and Eddy (1991) mentioned that excellent C/N ratio is ofrange 25- 35. In a larger scale, C/N ratio of 43 can also be considered sincethermophilic temperature can be achieved within 24 hours and rate of waterelimination is high (Jokelaet al. 1997). Sludge composting and solid waste from farmusing ventilated limits with C/N ratio of about 18 was found not to hinder degradationof microbes (Tiquia& Tam 2001). Table 2.4 shows the early C/N ratio for a fewcomposting process.
  • 18. 27 Table2.4 Initial ratio of C/N used in variety composting processes. Sludge Suitable Ratio Composting References materials of Time, day C:N Pulp and Paper Mill Flying ash 70 245 Hackett et al. 1999 Pig Farms Waste 18 77 Tiquia& Tam 2000 Olive Mill Solid waste 27 60 Papadimitriou et al. of olive industry 1997 Sewage Waste 25 50 Pera et al. 1991 Cow Dung Peat moss 16 20 Yu et al. 1991 Cow Dung Paper 18 20 Yu et al. 1991 Wood dust 25 18 Liao et al. 1997 Pig faeces Peat moss 16 14 Lau et al. 1992 Grape residue Chicken manure 14 25 Ferrer et al. 2001 Vinasse (sugar industry) Cotton residue 19 70 Diaz et al. 2002Gelatin-grenetine industry Urea and wood 30 55 Hoyos et al. 2002 dust Olive Mill Cotton residue 23 182 Paredes et al. 2002 Sewage Sugar, clay, and 13 50 Qiao& Ho 1997 wood dust Paper Mill Domesticated 64 168 Charest & poultry waste Beauchamp 2002 Source: Hackett et al. 1999 &Jokelaet al. 1997 2.6.3 Moisture Content and Free Air Space Sludge differs from organic materials because it does not contain fibre and is not capable of supporting high moisture content. When the free space in compost is filled with water, sludge will have a weaker structure and acts like a plastic. This will cause aerobic composting to stop and oxygen transfer will be prohibited. Aerobic composting will occur when the spaces are filled with air. There are five methods of lowering down moisture content of sludge which are recycling of materials that have been composted, the addition of bulking agents such as wood dust, the fixed use of agitation for compost aeration,addition of dry adapter and lastly, the drying of sludge before being composted (Buchanan et al. 1999).
  • 19. 28 Liang et al. (2003) mentioned that moisture content is to be given morepriority for monitoring compared to temperature in order to increase microbialactivity. Optimum moisture content will fasten oxygen transfer hence increasingmicrobial activity, fastens decomposition and reduces odour (Goldstein 2002; Liang etal. 2003; Schaub& Leonard 1996; Tiquiaet al. 1996). An optimum moisture content isneeded to overcome early cooling problems and also to avoid increase in bulk density(Goldstein 2002). Liang et al. (2003) mentioned that the minimum moisture contentfor sludge-saw dust composting is 50% in order to obtain microorganisms exceeding1.0 mg g-1 hour-1. According to Metcalf and Eddy (1991), moisture content cannotexceed 60% for non-reactor system and 65% for reactor system. Goldstein (2002)stated that optimum moisture content for composting mixture of sludge and wood dustin aerated static pile is 55-65%. Table 2.5 shows the initial moisture content for fewcomposting processes. Moisture content (MC) and free air space (FAS) affect the air movement andoxygen transfer in decomposing materials. Free air space is defined as ratio of gasvolume to total volume. Free air space is closely related to other physicalcharacteristics such as porosity (the ratio of vacant space volume with total volume),structure and bulk density. Biddlestone and Gray (1988) reported that the minimalporosity is 30%. Optimal bulk density for sewage sludge composting using reactorsystem and non-reactor system are 400-500 kg/m3 and 475-593 kg/m3respectively(Goldstein 2002; Schulze 1962). Haug (1993) combined free air space (%), porosity(P, %) and MC (%) through the following equation: FAS = P (1 - ) ----- (1)Whereby, P = 100 (1 - ) ----- (2)Where is bulk density (g cm-1) and is the particle density (g cm-1). Combiningequation (1) and (2) results in,
  • 20. 29 FAS = 100 (1 - )( 1 - ) ----- (3)Rearranging equation (3), MC = 100 - ( ) ----- (4)Moisture content (%) can be expressed in terms of FAS (%). Free air space ofcompost can be increased by adapter materials such as recyclable compost productand bulking agents such as saw dust. There are evidences stating that minimummoisture content for certain materials are related to the percentage of minimum freeair space.Ventilation is difficult to attain in the initial stage of decomposition beforesteaming is carried outfordrying the mixture andtoincrease the volume of space.Addition of adapter materials can speed up the rate of composting process (Buchananet al. 1999). Table2.5 Initial moisture of various composting processSludge Adapter Initial Composting Reference Materials moisture time, day content, %Pulp and Fly ash 53 245 Hackett et al.paper mill 1999Pig Farms Waste 65 77 Tiquia& Tam 2000Olive Mill Solid waste of 51 60 Papadimitriou et olive fruit al. 1997 industrySewage Waste 62 50 Pera et al. 1991Cow Dung Peat moss 64 20 Yu et al. 1991Cow Dung Paper 69 20 Yu et al 1991Fish waste Wood dust 60 18 Liao et al. 1997Sewage Glucose + wood 59 50 Qiao& Ho 1997 dust + clayPig Faeces Peat moss 66-69 14 Lau et al. 1997Gelatine- Urea and Sawdust 71 55 Hoyos et al. 2002grenetineindustry
  • 21. 302.6.4 pHpH values are important since they play a huge role in affecting the soil acidity as wellas composting process. An optimal pH value for sludge composting is in between 6 to9 (Metcalf & Eddy 1991). If the pH is too alkaline, this will result in extreme rise intemperature which will lead to death of bacteria and volatilization of ammonia. WhenpH values are not in this range, bacterial activity will experience retardation anddegeneration will slow down or stop entirely (Schaub& Leonard 1996). Addition ofmaterials such as cotton waste and fly ash to the sludge will increase its pH value(Diaz et al. 2002; Hackett et al. 1999). Table 2.6 shows the pH value for fewcomposting processes. Table2.6 Initial pH value for multiple composting processSludge Adapter Initial pH Composting Reference material value time, daysPulp and Fly ash 8.9 245 Hackett et al.paper mill 1999Pig Farms Waste 8.6 77 Tiquia& Tam 2000Olive Mill Solid waste of 7.2 60 Papadimitriou olive fruit et al. 1997 industrySewage Waste 7.0 50 Pera et al. 1991Sewage Glucose + 7.0 50 Qiao& Ho wood dust + 1997 clayPaper Mill chicken 7.5 168 Charest & droppings Beauchamp 20022.6.5 AerationAeration is required for metabolic heat production from aerobic microbial. However,excessive air supply rate will increase cost and cause loss of heat from the compostpile while too little ventilation will cause anaerobic process (Polprasert 1989). In
  • 22. 31addition, aeration is important to remove the main waste product, carbon dioxide andwater (Haug 1993). Table 2.7 shows the rate of aeration in few composting processes. Failure in aeration system can cause a slow decomposition, a process with highodour, a delay in achieving maximum temperature, a lower maximum temperature andlow rate of water removal (Diaz et al 2002; Ferreret al. 2001; Haug 1993). Accordingto Campbell et al. (1990), aeration rate depends on biodegradation properties ofcompost mixture. The harder the biodegradation, the lower the rate of optimum airrequired. For sludge composting, the proposed value is between 300-700 m3 air/tonesof volatile compounds (VC)/days (Biddlestone& Gray 1988; Schulze 1962). Dailyaeration with rate exceeding 1 000 m3 air/min tones of (VC)/days will cause coolingeffect in composting (Campbell et al. 1990; Lau et al. 1992). Aeration is carried out either through natural passive air movement or byforced air. Passive aeration uses absorbing and natural air movement. Forced airdepends on the fan to move the air through composting materials. There is apossibility of a third mode which is pure oxygen gas being injected into the reactor(Rynk& Richard 2001). Natural aeration or passive occur when there is diffusion and natural airmovement. Natural or passive aeration is driven by at least three mechanisms namelymolecular diffusion, wind and thermal convection. Oxygen is absorbed into thematerial because there is more oxygen in the outer than in the compost media. On theother hand, carbon dioxide will diffuse out. However, this process is slow and mightgive an impact to the aerated pile. If the compost pile is exposed, oxygen transfer iscarried out by the wind (Haug 1993). Thermal convection is the main mechanism in most passive aerationcomposting system. Heat generated from the composting process raises thetemperature of the gas causes a reduction in the density of the material.Hot gas movesout of the composting process, creating space and the cold outside air will enter.Ventilation rate is determined by the temperature difference between the gas in theambient air and the air flow resistance of compost media. Thus, the actual air flow in
  • 23. 32the compost heap is dependent on the production of heat to drive the heat convectionand the existence of the physical structure of the porous media in compost (Rynket al.1992). Forced aeration can be supplied in a positive or negative way. Positive forcedaeration is forcing air into the compost material while negative forced aeration issucking the air out of the compost material. Positive forced aeration is good for airmovement while negative aerationis suitable for inhaling the odour (Rynk& Richard2001). Forced aeration can be performed continuously or intermittently depending onthe requirements of the process.Continuous aeration can reduce the rate of air flow,reduce temperature fluctuations and oxygen.However, continuous aeration will causethe slope of the composting environment, causing extreme drying and cold areas thatremain in the air in (Rynk& Richard 2001). Aeration can also be suppliedintermittently so that the maximum temperature in the process can be achieved forlonger time and final compost will be safer (Lau et al. 1992).2.6.6 RotationRotation can be conducted using the front loading tractor. Rotation providesventilation, reduced particle size, ensuring that the material experiences the highesttemperature, renewing microbial activity, increasing porosity and producing a moreuniform compost heap (Biddlestone& Gray 1991; Diaz et al. 2002; Hackett et al.1999; Thambirajah&Kuthubutheen 1989). It is also the primary mechanism foraeration and temperature control systems for composting using bounds (Tiquiaet al.1997). Heap of pile which is rotated experiences reduction in volume by 55 to 72%(Larneyet al. 2000). The loss is found in mass of C, K and Na (Tiquiaet al. 2002).Maturation process is achieved at a faster rate for composting of faeces by rotation(Tiquiaet al. 1997).
  • 24. 33 The rate of rotation also contributes to the effectiveness of composting. It issuggested that inversion of 3-4 days in a week is necessary for composting (Tiquia etal. 1997; Wong et al. 2001). High frequency of rotation leads to electricalconductivity and low NH4-N content and also a low rate of thermophilic phasebecause of heat loss by evaporation and volatilization of ammonia in the stack (Wonget al. 2001). The disadvantages of using front loading are that it takes a longer time anduses a large space (Biddlestone& Gray 1991; Tiquia& Tam 1998). Rotation can alsobe carried out in rotating drum. The main function of rotation in composting is that itexposes materials to fresh air, increases oxygen and dissipates the heat and gas fromthe product of composting (Rynk& Richard 2001). Rotation in the rotating drum can also reduce air pollution (Tiquia& Tam1998) and ease the mixing process. However, the rate of rotation has to be minimizedbecause frequent rotation will produce large lumps. In the composting of sludge-waste, the rotation of rotating drum was carried out for 5 minutes after the materialswere added and also 5 minutes before the materials were removed (Schulze 1962). Inthe research by Smarset al. (2001), the rotation was limited to only 10-20 minutes perday.2.6.7 Adapting MaterialsAdapting materials such as sawdust, paper, fruit waste and etc. greatly influence thedecomposition process for active composting, maturation and storage(Eklind&Kirchman 2000). There are two types of adapter namely structural adapterand energyadapter. Structural adapter acts as a bulk weight reduction and increases airspace thereby improving its aeration. Energy adapter increases the amount ofbiodegradable organic matter in the compost mixture (Liao et al. 1997). Adaptermaterials are necessary in composting because they influence the pH, C/N ratio,humid content and air supply to aerobic bacteria (Golueke 1991). Therefore, adaptermaterials are significant in improving microbial degradation process and also inproducing good quality compost so as to ensure its compatibility as fertilizer and soil
  • 25. 34adapter (Liao et al. 1997). The release of ammonia from mass of compost has beenreduced by addition of woody material, peat and vermiculate (Bhamidimarri&Pandey1996; Liao et al. 1997; Qiao& Ho 1997). Coal fly ash is found to reduce the potentialof the metal reactions (availability) in sewage sludge composting (Wong et al. 1997). Composting studyofvinasse (sludge sugar industry) mixture and grape residuewas performed in the reactor system. Increase in amount of vinasse (0-40% wetweight) was studied for 43 days. The increase in quantity of vinasse did not affect thepH value. Evolution of organic materials show higher loss and higher capability ofbiodegradation when vinasse mixture having a lesser volume. Loss of Nitrogenincreased when quantity of vinasseinin the mixture increased. The optimum rate ofvinassewas found to be in between 10-20% (Diaz et al. 2002). Composting ofvinasseand cotton waste was carried out by adding vinasse (0-80% mass) in thereactor for 23 days. It was found that 20-30% of vinasse is the optimum conditionsince the final product was of good quality, higher rate of biodegradation and theminimum loss of N (Diaz et al. 2003). Ash was mixed at 0-50% (dry weight) together with sewage sludge andcomposted for three months. The emission of carbon dioxide for every amount of ashwas found to be similar except for 50% of ash. However, the emission of carbondioxide experienced a reduction as the quantity of ash was increased. This indicated adecrease in microbial activity. The increment in content of salt and pH was believed tocause this inhibition. Rise in more than 25% (dry weight) resulted in a decrease in thegrowth of thermophilic bacteria and the production of carbon dioxide.Dry ash oflesser than 25% in amount is compatible for composting of ash-sludge (Fang et al.1999; Wong et al. 1995; Wong et al. 1997). Shin and Jeong (1996) have reported studies of food waste composting withvarious amounts of paper of 33%, 50% and 67% (wet weight). Mixture whichcontained 33% of paper was found to have inhibitory impairment due to excessiverelease of ammonia. From this study, it was found that the highest degradation ofcellulose is 61% when the paper content in the mixture is high.
  • 26. 35 One of the commonly used adapter materials in the composting process iswood waste such as sawdust and bark.Wood waste takes a longer time to bebiodegradedand is usually burned to be disposed. There are numerous studies on reuseand recycling of sawdust such as making fuel, liquid absorbent, building additives andetc. Wood waste is less suitable as a soil adapter since its C/N ratio is high. However,by adding nitrogen source such as sludge, wood waste can be converted into soiladapter materials (Siddiqui&Alam 1990). The use of wood waste as an adapter material in the composting processappears to increase the porosity, ability to hold nutrients, reducing odour andenhancing its energy when applied at the appropriate amount (Bhamadimarri&Pandey1996; Liao et al. 1994; Tiquia& Tam 2000). Wood waste was found to have theability to reduce pathogens more effectively compared to other agricultural wasteduring composting of sewage sludge (de Sales-Papa 2002). The difference incomposition of different wood tissues from species to species resultsintheinconsistentrate of decomposition of wood dust on every different species. Liao et al. (1997)reported that sawdust from hardwood is more readily biodegradable compared tosawdust from softwood. Sawdust from hardwood is better inholding nitrogen.However, it produces a higher concentration of phenol during the process ofcomposting. In sewage sludge composting, usage of sawdust is more suitable as a bulkingagent compared to hay and grass (Furhacker&Haberl 1995). Waste wood has thehighest reduction of organic matter, dries the sludge and reduces pathogens comparedto other materials (de Sales-Papa 2002). In swine waste composting, wood waste ispartially decomposedin swine waste providing sufficient empty air space and thusallowing delivery of oxygen to the microorganisms (Tiquia& Tam 1998).Bhamadimarri&Pandey 1996 reported that wood dust has the ability to absorbmoisture, providing carbon source, withhold nutrients and providing the appropriateporosity in the compost pile. Furhacker and Haberl (1995) reported that volume of wood waste must bemore than 33% in sewage sludge composting using rotating drum. If the density of the
  • 27. 36sludge and wood waste is estimated to be 700 kg/m3and 100 kg/m3 respectively, thenthe minimum amount of wood waste needed is 10%.Liao et al. (1994) havecarried outthe composting of fish waste by using 25%, 33% and 50% by weight of sawdust. Theend result had a C/N ratio of less than 20 except for when sawdust of 50% was used.The pH value of compost with sawdust of 50% is lower than the others because of lowammonia content.2.7 COMPOST MATURATIONAccording to Commision of the European Communities (CEC 1986), compost is theproduct of a stable composting process and free from pathogens which is beneficialfor plant growth. It has undergone an early and fast decomposition process and alsothe process of humification. Humification is the process of partial conversion of theoriginal material into humus which is a humicsubstance andis relatively inert(Tuomelaet al. 2000). The usage of immature compost will prevent the uptake of nutrientsby themicrobial population which will further cause nitrogen deficiency in plants. Other thancontributing to excess of carbon source, the presence of phytotoxicitymaterials such asammonia and organic acid will speed up the decomposition process of immaturecompost which in turn will have a negative impact to the soil and plants. Plantsinteract with the retarded environment by lowering down metabolic rate, decrease inroot respiration, drop in nutrient absorption and lowers down the synthesis andtransport of gibrelin and cytokinins (Jimenez & Garcia 1989). According to Jimenez and Garcia (1989), the techniques of observing compostmaturity is divided into five namely,physical tests, microbial activity research,methods of compost humic fractions, chemical method and biological method. Thephysical test includes observation of physical characteristics of compost mixture suchas its temperature, odour and colour. Microbial activity research includes counting oftotal microorganisms, respirometric research, biochemistry parameters for microbialactivity and analysis of biodegradable material. On the other hand, method of composthumic fraction covers chromatography test and photocalorimetric method. Chemical
  • 28. 37method includes C/N ratio (solid state), pH, cation exchange capacity and the presenceof nitrate and nitrite. Example of biological method is the test of germination of seedto detectphytotocity. The maturation process greatly depends on the composting materials and noton the type of system (reactor or non-reactor) used (de Bertoldiet al. 1983).Faeces-straw composting in rotary rotating drum requires three months of composting forcompost maturation using the row system (Vourinen&Shaharinen 1997). Furhackerand Haberl (1995) composted sewage sludge with wood chips for 4 to 5 days and thematuration process took 6 months. Composting of paper industry sludge with faecesusing row system failed to undergo maturation after 6 months based on C/N ratio andcalometric test (Charest & Beauchamp 2002). Table 2.7 shows the time taken forcomposting process in multiple systems. Table2.7Duration of composting process for combination of systems and materialsSystem Mixture Range of Usual Maturation composting composting time timeStatic stack Leaves 2-3 years 2 years - Livestock manure 6 months – 2 1 year - yearsAerated static Sludge + wood 3-5 weeks 4 weeks 1-2 monthspile waste Leaves 6 months-1 9 months 4 monthsBounds, yearirregular Livestock manure 4-8 months 6 months 1-2 monthsroundBounds with Livestock manure 10-12 weeks - 1-2 monthspassive Fish waste + peatventilation 8-10 weeks - 1-2 monthsStirred layer Sludge+compound 2-4 weeks 3 weeks 1-2 months waste or Faeces+wood dustRotating Sludge and/or 3-8 days - 2 monthsdrum solid waste Source: Carr et al. 1995
  • 29. 382.8 COMPOST AS SOIL ADAPTER MATERIALThe addition of direct waste into the soil will cause a change in the ecosystem of thegrowing plant. The waste which is not composted and added to the soilcausesmicroflorato decompose them and produce transition metabolites which willinhibit the growth. In addition, a tussle between microorganisms and soil nitrogen, ahigh carbon to nitrogen ratio and the production of ammonia in the soil will occur (deBertoldiet. al 1983). These conditions can be improved by the production of goodcompost. Compost releases nutrients at a slower rate (Keeling et al. 1994; Maeda et al.2003).Sikora and Enkiri (2000) described the rate of mineralization of sludge compostto beabout 9.3% to 29% of the total nitrogen.Composting has many uses in the field ofagronomic, horticulture and forestry. It can be used for field crops, tree seedlings,plants in the greenhouse, nursery plants, flowers and herbs grown on the land. It canalso be used to maintain organic matter, structure and fertility of agricultural land, tosupport urban landscape, to reclaim abandoned land such as mining areas, to create alandscape and to close the landfill space (Rynk 1992). Function of compost in the soil and in the relationship of the land-plantinteraction is different with conventional fertilizer even though compost has nutrientslike N, P, and K. The main purpose is not to enrich the soil compost with this elementbut isto supply humus and improve soil structure (de Bertoldiet. al 1983). Humus is anorganic material that is relatively stable. It is very important in maintaining good soilstructure, especially in fine-textured soils.It increases the cation exchange capacity,resulting in the loss of elements such as potassium, calcium, and magnesium (Tisdale& Nelson 1975). Application of sludge-waste composting in city has found to improvesoil-water content, water holding capacity, saturated hydraulic conductivity,compression, aggregation, total porosity and pore size distribution(Aggelides&Londra 2000; Yadavet al. 2002). Atiyehet al. (2001) stated the potentialof compost to supress soil-borne plant pathogen. Table 2.8 indicates the various typesof compost quality which is produced from sludge. Compost is easier to be applied tosoil, easily maintained, easily stored and transported as compared to sludge/waste
  • 30. 39without composted. It is also a soil medium adapter which is not costly (Hackett et al.1999; Van Heerdenet al. 2002). Table 2.8 Quality of compost of sludge for soil adapter materialsType of Adapter Organic N, % P, K, Note Referencesludge Materials Material ppm ppm %Gelatin Wood dust 55-58 2.4- 2000- 4000 No odour Hoyosetindustry 4.3 3000 0- for final al. 2002 4200 compost 0Paper Livestock 53-58 0.7- 2600- 3000 Achieved Clarest&industry manure 0.9 3700 - compost of Beaucham 4000 B Standard p 2002Pulp and Fly ash 58-63 Not 100- 870- Application Hackett etpaper stated 119 970 for 15m3/ha al. 1999industry to improve soil nutrientSewage Horse Not 1.1- 9600- 8200 Addition of Warman& droppings stated 1.2 16000 - compost Termeer 9400 and peat 1996 improves tree growthOlive Cotton 36-88 1.4 - Not Not Adapter Paredes etindustry waste/corn 1.7 stated state materials al. 2002 stalk d influences compost productSugar Grape Not 1.8- 32 1700 Suitable Madejonindustry waste/cott stated 2.7 000 0- with et al. 2001 on waste 2000 moderate 0 compost dose application2.8.1 Plant growth and factors affecting itGrowth is interpreted as a progressive development of an organism.Plant growth canbe referred as the development of a specific organ or the whole plant. Growth can be
  • 31. 40expressed within the definition of dry weight, length, height or diameter. The factorswhich affect plant can be divided into two namely genetic and environmental (Tisdale& Nelson 1975). Environmental factors which are important in affecting plant growth aretemperature, moisture content, energy radians, atmospheric composition, gas contentin the soil, soil reaction, biotic factors and supply of mineral elements.Temperaturehas a direct impact on plant functions such as photosynthesis, respiration, cell wallpermeability, absorption of water and nutrients, transpiration, enzyme activity andprotein coagulation. Water is required for construction of carbohydrates, maintainingprotoplasm hydration and also as a tool for food and mineral elementstranslocation.When the temperature or water content is not optimal, then plant growthwill decrease.Plants will generally grow well in low light intensity than in high lightintensity.However, plants vary in their response to light. Air content consisting ofsulphurdioxide, carbon monoxide and hydrofluoric acid can cause toxicity in plants(Tisdale & Nelson 1973). Among the mineral elements which are essential in plant growth are nitrogen,phosphorus and potassium. Nitrogen is an important plant nutrient. It is absorbed byplants in the form of nitrates although it can also be absorbed in the form ofammonium ion and urea.When adequate nitrogen is supplied, plant growth occurswell and are coloured green.However, when the supply of nitrogen is in excess, it cancause slow plant maturity, causing plant fibers to become softer and more susceptibleto disease and insect attack.Lack of nitrogen causes the plant to be retarded andyellowish.Initially, the process of plant becoming yellowish will strike the bottom ofthe plant, followed by parts of plants. When nitrogen deficiency is more critical, plantscan also die. Phosphorus is absorbed by plants in the form of ions in the form oforthophosphate, H2PO4- and dissolved organic phosphate. Phosphorus plays asignificant role in plant root development. It also accelerates the maturation of plants,increase the quality of product and resistance to disease.Phosphorus deficiency willalso retard the overall growth.Plants absorb potassium in the form of K+. Potassium
  • 32. 41deficiency is most easily detected by inhibition of leaf characteristics.In addition,potassium deficiency causes the plant growth to be reduced, reduced resistance todisease, degradation of roots and reduction in photosynthesis. The other importantfeatures of potassium are that it maintains an appropriate water-plant relationship andplant metabolism (Tidale& Nelson 1975). Soil structure greatly influences the development of roots and the shoot ofplants. The higher the bulk density of the soil, the more compact the soil will be,causing weakened soil structure and smaller air space. High soil bulk density resultsinmechanical resistance to root penetration to increase.This condition usually affects therate of oxygen absorption into the soil porous space and root respiration is directlyassociated with the gas supply is adequate and continuous.Water holding capacity ofcompost/soil shows the maximum moisture that can be supported by the dry soil atstandard conditions.The value of water holding capacity is essential to determine themoisture needed for plant growth. Porous area/porosity is the volume fraction ofsoil/compost that is not filled by a solid material. Porous space is important for air andwater movement in the soil (Iswaran 1980). In addition, the amount of oxygen in the soil is also important for plant growth.Soil reaction (soil acidity, pH) affect plant growth by influencing the availability ofcertain elements needed for plant growth.At acidic pH, the reaction capacity ofphosphate, manganese and molybdenum were found to decrease.When nitrogen inammoniacal form is applied on the surface of the soil at a pH above 7, the ammoniawill be lost due to volatilization.In addition, the disease from the soil can also becaused by neutral-alkaline soil conditions. There are many biotic factors that will limitplant growth for farming operations and shows the potential threat to reduce the crop,if not to the destruction of the crops. Imbalance of available nutrients can also increasethe incidence of disease and insect infestation (Tisdale & Nelson 1973).2.8.2 Effect of various amount of compost on plant growthCompost affects physical, chemical and biological characteristics of soil byinfluencing the permeability, porosity and structure, as well as the redistribution of
  • 33. 42movement and transportof nutrients.Therefore, the occurrence of some of the activitiesand biosynthetic microbial degradation results in improvement of soil fertility,particularly in terms of the supply of nutrients to plants.Nutrient intake occurs atrhizosphere (zone encircling the land and influenced by plant roots) and it isstimulated by microbial metabolites. Microbial metabolites are capable of influencingor enhancing the influence of the enzymes in plants.Composting improves mineralnutrition, protein synthesis and carbon assimilation and increases the production of theentire plant.In addition, the roots will produce more exudates to the soil. Thus,composting is a new source of energy that stimulates the growth and microbialprocesses and subsequently, the metabolism and plant growth (Figure 2.9)(Tomatietal. 1996). Soil reactions to the application of compost depends on a number of factorsincluding the type of compost and composition, level and application method, soilproperties and weather conditions (Abdel-Sabour& Abo El-Seoud 1996). Pinamontietal. (1997) reported that ornament plants were found to grow well with a mix of 50%sewage sludge compost and bark.Hountinet al. (1995) reported that the application ofcompost with peat shrimp waste exceeding 240 tonnes/ha also showed no increase inthe development of barley.However, Klock (1997) reported that trees namelyImpatienand Snapdragoncan grow fertilein 100% composted sewage sludge togetherwith farm waste.Applications of droppings on sandy soil can improve crop productionof plantation Brassica parachinensis andBrassica chinensiscompared to sandy soilsalone and treatment with synthetic chemical fertilizers (Wong & Wong 1987).Composting of sewage sludge is also found to increase the yield of corn andgrain(Abdel-Sabour& Abo El-Seoud 1996).
  • 34. 43 Figure 2.9 Influence of compost on plant system Source: Tomati et al. 19962.9 GENERATED SOLID WASTETotal solid waste that is generated in Peninsular Malaysia is increasing from day today. The average of solid waste produced can be divided into 45.0 percent food, 24.0percent plastic, 7.0 percent paper, 6.0 percent steel, 3.0 percent glasses and etc. (NinthMalaysia Plan). Generation rate of these solid waste differ depending on types of area,total population and occupation or business (Agumuthu 2001).
  • 35. 442.10 DOMESTIC WASTESolid wastes that are produced everyday are result of thrown waste of domestic andhousing sectors. There are specific categories that have been identified in producingthese solid waste including housing waste, commercial waste, construction waste,environmental waste and etc. These waste producedare mainly from housing wasteswhich includes food waste, papers, plastic which are in the forms of solid, semi-solid,or liquid.Organic materials are easy to decompose, decay at a faster rate and extractodd odour that can disrupt public peace (Agumuthu 2001).2.10.1 Housing WasteHousing waste produced from activities done by individual in every home are also informs of solid, semi-solid and liquid. Most of these housing wastes consist of foodwaste, papers, boxes, plastic and aluminum which are easily decomposed and decayed(Agumuthu 2001).2.10.2 Business WasteThese types of wastes are a result of business activities, management and trading.These wastesare usually in forms of solid/semi-solid and are easily disposed throughcombustion. Examples of businesswaste are business premises waste and officeutilities such as papers, files, stationeries, plastic and etc. (Agumuthu 2001).2.10.3 Industrial WasteAlmost half of waste from industrial sectors and factories exist in forms of solid andliquid. Examples of industrial waste include wood, plastic, scrap metal, sheet metaland etc. Generally, these industrial wastes are divided into two parts, which are dangerand non-danger wastes. Danger wastes usually contain chemical substances, biologyprocess waste and also radioactive waste, whereas non-danger waste are of plastics,steel, fiber, and etc. (Agumuthu 2001).
  • 36. 452.10.4 Construction WasteConstructions waste are mainly produced from constructions of new building,construction sites, road repairing work, building renovation, demolition of oldbuilding and etc. Most of the wastes are in solid form such as woods, steel, rock,plaster, concrete and etc.(Agumuthu 2001).2.10.5 Environmental WasteMost of the environmental wastes produced are in forms of solid. Examples includedried leaves, grasses, tree branches, wood and other waste from gardens and landscape(Agumuthu2001).2.11 FACTORS INFLUENCING THE REVENUEOF SOLID WASTEAccording to studies by (Laimanet al. 2005) entitled ‘Revenue and Composition ofSolid Waste’ in Mukim Melaka Tengah, Melaka, there are various factors influencingthe increasing revenue of solid waste. Amongst them are mainly housing type thatinvolves way of living and eating styles in every house namely the high-class, middle-class, and low-class housing. Besides that, according to Yusof(2007) in Comparative Research between theUsage of Soil and Wood Powder on Organically Kitchen Waste Composting System,among the involving factors that influence the generation of solid waste aregeographically, seasonal, attitude of individual and types of residence.2.11.1 Geographical FactorGenerally, the geographical factor of an area or country does affect its weather. Forexample, Malaysia is a country that is situated on the equator line that is alwaysexperiencing moist and hot weather throughout the year. However, the monsoon windthat hit this country will cause the raining season on certain times of the year. On top
  • 37. 46of that, the frequent cooking will increase during these seasons and result in rise offood waste produced than usual.2.11.2 Seasonal FactorSeasonal factor includes the fruitsseasons, festive, vacations/school breaks and etc.Generally, the rate of waste disposal during these seasons will increase and becomethe generated factor of solid waste in Malaysia. The solid wastes produced are foodwastes generated in large quantity from food prepared by the house residence and alsofrom fruit skin waste from the orchards during fruit seasons.2.11.3 Society Attitude FactorThe attitude of the society and public that underestimates the result of increased solidwaste contributes to the increasing generation of solid waste. Generally, the public areunaware of their attitude of throwing rubbish which in real fact is affecting thecleanliness of the environment.2.11.4 Type of Residence FactorThe quality of the environment can easily be affected by the attitude of residence inMalaysia. In studies conducted by Laimanet al.(2005), lifestyles and economic factorscan affect the amount of expenses and eating styles whereby it is proven that thehigher the expensesand the bigger the size of a family, the more solid wastes aregenerated.2.12 SOLID WASTE MANAGEMENTSolid waste management in Malaysia is not systematic and efficient. Generally, thewaste produced will be disposed at the disposal site provided. Five years ago, therewere 230 disposal site set up in this country. However, only 170 disposal sites areregistered to accommodate the rising waste produced. Unfortunately, almost 80% of
  • 38. 47the disposal sites available now will be closed in a period of two to three years in thenear future. There are few methods being applied to overcome the increasing amount ofsolid waste producedin Malaysia such as recycling, composting system of wet waste,and the reduction of reusable waste. For recycling process, either all or some parts ofthe items are being reused again.2.12.1 Disposal SitesSolid waste disposal sites are the easiest and cheapest method used. Generally, thedisposal sites are operated by dumping the wastes into the Earth and thenby buryingthem. These disposal sites are usually situated in places of abandon quarry, miningarea and loan holes. According to Syarina(2007) the disposal sites are divided into twotypes which are sanitary and non-sanitary disposal sites. However, almost all disposalsites in Malaysia are non-sanitary disposal sites. This method requires the waste to betrimmed and compressed inside the ground with heavy-machinery. The surface of thewaste are then sealed with soil to prevent bad odor. However, this method cancontaminate the environment through the diffusion of waste in the ground and then toundergroundwater. On the other hand, sanitary disposal sites are covered withgeotextile fiber to prevent waste diffusion into the underground water.This diffusionwill then be channeled and treated at a diffusion treatment plant.2.12.2 IncineratorIncinerator is a type of solid waste disposal that involves waste combustion. Thismethod will convert the solid waste into heat, gases, vapour, ashes, and chemicals.However, there are few places in the world that has stopped this method due to itsdestructive effect to the environment and also to health. The ashes from the incineratorcontain poisonous materials including lead, mercury and cadmium.
  • 39. 482.12.3 RecycleRecycling is a process ofobtaining or ensuring half of the materials of solid waste canbe reused again. The recycled materials include glasses, plastic, paper product andaluminum can. There are multi types of recycling barrels that can be seen in publicplaces to tell the public the importance of recycling. According to Yusof(2007), thesuccess of recycling can reduce the control cost of handling solid waste andenvironmental pollutions. Malaysia has targeted the rate of recycling to increase by22% in the year 2020.2.12.4 Composting SystemSolid waste in organic form such as plants, food waste and paper products can berecycled using the method of composting system and biological digestion todecompose the organic matter. This method can be easily done and managed toproduce fertilize compost product that can be used in agriculture. This method ofcomposting was practiced before the Second World War. However, it is still notusedtraditionally intoday’sworld (Day et al. 1998).2.13 PALM OIL MILL EFFLUENT SLUDGE (POMES)The market for palm oil industry is continuouslybeing an attractive topic even thoughit is now sold at about one half of its highest price recorded. In Malaysia, palm oilindustry is growing quickly becoming a significant agriculture-based industry. A totalof about 80 million tonnes of palm oil and 57.4 tonnes of palm oil mill effluent(POME) was generated in the year 2009 (MPOB 2009). Malaysian government is alsosupporting the treatment process of palm oil mill effluent (POME) in order togeneratebiogas that can be an alternative source of electricity. Moreover, the palm oil industryprovides a source of livelihood to rural families throughthe government land schemesand private small holders as well as employment opportunities to agriculture workersin estates (Ma et al., 1993).
  • 40. 49 The production of palm oil may result in the generation of huge quantities ofhighly polluting waste water, also called as palm oil mill effluent (POME). Theproperties of POME include thick brownish viscous liquid waste but non-toxic as nochemicalsis added during oil extraction. However, it has an unpleasant odour. POMEis predominantly organic in nature but highly polluting (Ma 2000). Other than that,POME is a colloidal suspension of 95 – 96 % water, 0.6 – 0.7 % oil and 4 – 5 % totalsolids including 2–4% suspended solids originating from mixture of sterilizecondensate, separate sludge and hydrocyclone wastewater (Ahmad et al. 2003).POME has been identified to be one of the major sources of water pollution due to itshigh biochemical oxygen demand (BOD) and chemical oxygen demand (COD)concentrations. Hence, Malaysian government had enacted the Environmental QualityAct (EQA) in 1978 and parameter limits were set for the discharge of POME into theenvironment. The parameter limits are as shown in Table 2.9. Due to the mentioned characteristicsof POME, a wide range of approaches forPOME treatment have been developed to alleviate the pollution problems caused bythe palm oil industry. The conventional treatment technology of POME employed inmost of the palm oil mill factories in Malaysia which is the ponding system ofbiological treatment have been adapted (Chin et al., 1982). However, with theincreasing production in most palm oil mills, the under-sized biological treatment isunable to cope with the increased volume of POME (Ismail 2005). Therefore, a properPOME treatment is needed urgently in order to ensure the sustainable economicgrowth of palm oil industry without neglecting the precious environment. Table 2.9. Characteristic of POME and its respective standard discharge limit by the Malaysian Department of Environment.Parameters Concentration (mg/L) Standard Limit (mg/L)pH 4.7 5-9Oil and Grease 4000 50BOD 2500 100COD 50000 -Total Solids 40500 -Suspended Solids 18000 400
  • 41. 50The global energy demand is growing rapidly and at present time,about 88% of thisdemand is met by fossil fuels. Researches have shown that the energy demand willincrease during this century by a factor of two or three (EIA 2006). At the same time,concentrations of greenhouse gases in the atmosphere is rising rapidly, with CO2emission derived from fossil fuels being the most significant contributor. Therefore,environmental pollution due to the use of fossil fuels as well as their gradual depletionmakes it necessary to find alternative energy and chemical sources which areenvironmental friendly. For fossil fuel-derived energy, reduced environmental impactsby providing a clean fuel from renewable feedstock such as energy crops, organicfractions of municipal solid wastes and agro-industrial wastes is necessary(Chynoweth et al. 2001). Palm oil mill effluent (POME) from palm oil mill wastewater is one of the obvious wastes in Malaysia. In Malaysia, palm oil is utilized forthe production of biodiesel (palm oil methylester or palm oil diesel) for buses and carsand is a major expansion of Malaysian diesel production with 5% palm oil is expectedfor biodiesel production from the year 2006 (Kalam&Masjuki 2002 ;Reijnders&Huijbregts 2008). The production of biogas through anaerobic digestion offers significantadvantages over other forms of bioenergy production. This has been evaluated as oneof the most energy efficient and environmentally beneficial technology for bioenergyproduction (Fehrenbachet al., 2008). The proper control of anaerobic digestion ofPOME treatment will generate gas and renewable energy. Megatet al.,(1989) andBorjaet al.,(1996) had investigated the performance of anaerobic digestion of POME,whereby 62 – 98 % of COD reduction and 34 – 98 % of methane production wasreported depending on feed rate, substrate concentrations and system operation.2.13.1 Anaerobic Digestion in POME TreatmentAnaerobic treatment is the most suitable method for the treatment of effluentscontaining high concentrations of organic carbon (Perez et al., 2001). A wide range ofapproaches have been developed for the POME treatment. This is because anaerobicsystem offers more potential for POME treatment due its high organic content. On theother hand, anaerobic treatment does not require high energy for aeration and
  • 42. 51allowsthe recovery of energy in the form of methane. The conventional way to treatPOME which is widely used in Malaysia is the ponding system. Ma et al., (1993)reported that more than 85% of the palm oil mills in Malaysia have adopted pondingsystem for POME treatment. However, ponding system requires long retentions timeand large treatment facilities because the system usually consist of de-oiling tank,acidification, anaerobic and facultative pond with hydraulic retention time (HRT) of 1,4, 45 and 16 days respectively (Ma &Ong 1985). Another disadvantages by usingponding system as reported by Chin et al., (1996) are the system could not meet theeffluent quality requirement. For instance, COD and BOD5 in the effluent were about1725 and 610 mg/L respectively. Sporadic researches have been performed in order to find approachablesolutions for POME treatment. The main aim of the researchers in POME treatmentnowadays are to shorten the treatmenttime, lessen the land required and at the sametime to collect the useful biogas produced.Borjaet al. (1995) in their research reportedon usage of two stages upflow anaerobic sludge blanket (UASB) system in POMEtreatment. They observed that the optimum organic loading rate (OLR) in order toproduce a good methane yield and COD reduction of greater than 90% is 30g/l.d.COD. In addition, 4.1 g/l.d of acetic acid isproduced at OLR of 16.6.g/l.d.CODat only 0.9 days of hydraulic retention time (HRT). Furthermore, Zhang et al., (2007) examined the integration of biologicalmethod and membrane technology in treating POME. In their study, 43% organicmatter in POME was converted into biogas and COD reduction efficiency reached93% in the expended granular sludge blanket (EGSB) system. Najafpouret al., (2005)demonstrated the use of upflow anaerobic sludge fixed film bioreactor (UASFF) intreating POME. Their study showed a high COD removal of 89% and 97% at HRT of1.5 and 3 days respectively. Besides, the highest organic loading rate (OLR) value of0.346 l.CH4/g. COD removed of methane yield was obtained. The OLR value graduallyincreased from 2.63 to 23.15 g COD/l.d in this study.
  • 43. 52 Table 2.10Literature on POME treatment using variable of anaerobic reactorSystem Influent COD removal HRT Methane Reference COD (COD/mg.L) (h or d) Production (mg/L) (%)UASB 30600 94 6.5d 63 Borja and Banks (1994)Anaerobic 30000- 97.8 40d 54.4 Yacob etPond 40000 al., (2006)AF 25000 80.7 20d 36 Yacob etDigester al., (2005)UASFF 15000– 97 3d 71.9 Najafpour 35000 (2006)CSTR 20000– 80 18d 62.5 Tong and 35000 Jaafar (2005)SBR 11000– 96 20h NM* Chan et 18650 al., (2009)EGSB 79723 91 2d 70 Zhang et al., (2007)UASFF 44300 94 1.5d - 2.2d NM Zinatizade h et al., (2005Anaerobic 25000 93.3 4.7d 63 Ibrahim etContact al., (1984)ProcessFluidised 15000 78 0.25d NM Borja andBed Banks (1995)On top of that,Zinatizadehet al., (2005) studied about the kinetic evaluation of POMEdigestion in high rate upflow sludge fixed film bioreactor. They reported that withHRT ranges between 1 and 6 days, the removal efficiency of COD was between80.6% and 98.6%. The methane production rate was between 0.287 and 0.384l.CH4/g. COD removed. Their study also demonstrated the apparent rate constant, Kcalculated by simplified Monod model which were in the range of 2.9 – 7.41 l.CH4/g.COD. Other literatures on POME treatment using anaerobic treatment is simplified asshown in Table 2.10.
  • 44. 532.14 NITROGEN FIXING BACTERIANitrogen is the most limiting nutrient for increasing crop productivity.Nitrogen is acritical nutrient for virtually all life forms. Input efficiency of nitrogenous fertilizers islow (Prasad et al. 1990) and in turn contributes substantially to environmentalpollution. Nitrogen which is present in the atmosphere occupies about 79% of the air.Plants cannot use nitrogen in its gaseous state (Sing 2005). Many industrial importantcompounds such as ammonia, nitric acids, organic nitrates and cyanides containnitrogen. However its conversion in utilizable form is very less and requires highamount of energy due to presence of triple bond between two N atoms(Singh 2005).Nitrogen fixing microbes (bacteria and blue green algae) has a natural power to bringabout the conversion of N2 into NH3 which is further being incorporated into aminoacids and finally into proteins.Nitrogen must be fixed or combined into eitherammonia, NH3or nitrate, NO3. Specifically, tree legumes (Nitrogen Fixing Trees,NFTs) are valuable in subtropical and tropical agroforestry. They can be integratedinto the agroforestry system to restore nutrient cycling and self-reliance fertility (Craig&Wilkinson 1995). There are many species of Nitrogen Fixing Trees (NFTs) that canprovide numerous useful products and functions including food, wind protection,shade, animal fodder, wood fuel and timber in addition to providing nitrogen to thesystem (MacDicken 1994).Biological nitrogen fixation is the process that changesinert N2into biologically useful NH3. This process is mediated in nature only bybacteria. In legumes and a few other plants, the bacteria lives in small growths on theroots called nodules. Within these nodules nitrogen fixation is done by bacteria andthe NH3 produced is absorbed by the plant. Biological nitrogen fixation can take manyforms in nature, including in blue green algae which is a bacterium, in lichens, and infree-living soil bacteria (Lindemann 2003). An enzyme called nitrogenase performsthis. Nitrogen fixing microorganismsfix nitrogen in five different modes.Through 6biological nitrogen fixation, 180 x 10 tones nitrogen per year is being added to thesoil but this figure is still insufficient to replace completely the use of chemicalfertilizers. Various Nitrogen fixing systems shares this global fixation and theestimated contribution of each component is shown in Table 2.11.
  • 45. 54Table 2.11N-fixing systems share this global fixation and the estimate of contribution of each componentNitrogen fixing system Estimated contribution (kg/h/year)Free living 15Cyanobacteria 7- 80Aossciative Bacteria 36Azolla/Anabaena 4.5-450Frankia 2.0-362Rhizobium-legume 24-5852.14.1 Nitrogen Fixing Bacteria - FrankieNitrogen is a critical nutrient for virtually all lifeforms. We get our nitrogen eitherdirectly or indirectly from plants. While nitrogen makes up about 79% of ouratmosphere, plants cannot use nitrogen in its gaseous state. It first must be fixed orcombined into either ammonia, NH3 or Nitrate, NO3-. The natural nitrogen cycle relieson nitrogen fixing bacteria like those found in the Frankia family of actinobacteria tosupply the fixed nitrogen. Fixed nitrogen is often the limiting factor for growth, bothin your garden and in the general environment. About 15% of the worlds nitrogen fixed naturally is from symbioticrelationships between various species of the Frankia family of actinobacteria and theirhost plants.The plants that form symbiotic relationships with Frankia are calledactinorhizal plants. Scientists have found over 160 plants that host theseactinomycetes including alders, Russian olive, bayberry, sweet fern, bitterbush andcliffrose. The Frankia is able to provide most or all of the host plants nitrogen needs.These nitrogen fixing bacteria and their host plants are often pioneer species on youngnitrogen deficient and disturbed soils such as moraines, volcanic flows and sanddunes. They help in creating a reservoir of nitrogen rich soil that the next wave ofplants can benefit from. Scientists believe that much of the new nitrogen in temperate forests, drychaparral, sand dunes, moraines, and mine waste tailings is as a result of themutualism of Frankia and host plants. They are the main nitrogen fixing relationships
  • 46. 55in large parts of the world and will only become more important as we adjust theclimate change. Figure 2.10.Nitrogen fixing bacteria – Frankie2.14.2 Nitrogen Fixing Trees for AgroforestryNitrogen fixation is a pattern of nutrient cycle which has successfully been used inperennial agriculture for ages. Legumes, which are nitrogen fixers,are of particularimportance in agriculture. The tree legumes (nitrogen fixing trees, hereafter calledNFTs) are especially valuable in subtropical and tropical agroforestry. They can beintegrated into an agroforestry system to restore nutrient cycling and fertility self-reliance. The "pioneer" plants (plants which grow and thrive in harsh, low-fertilityconditions) begin the cycling of nutrients by mining and accumulating availablenutrients. As more nutrients enter the biological system and vegetative cover isestablished, conditions for other non-pioneering species become favorable. Pioneerslike nitrogen fixing trees tend to benefit other forms of life by boosting fertility andmoderating harsh conditions. NFTs are often deep rooted, which allows them to gain access to nutrients insubsoil layers. Their constant leaf drop nourishes soil life, which in turn can supportmore plant life. The extensive root system stabilizes soil, while constantly growing
  • 47. 56and atrophying, adding organic matter to the soil while creating channels for aeration.There are many species of NFTs that can also provide numerous useful products andfunctions, including food, wind protection, shade, animal fodder, fuel wood, livingfence, and timber, in addition to providing nitrogen to the system.2.14.3 Nitrogen: From the Air to the PlantsNitrogen is often referred to as a primary limiting nutrient in plant growth. In anotherphrase, when nitrogen is not available plants stop growing. Although lack of nitrogenis often viewed as a problem, nature has an immense reserve of nitrogen everywhereplants grow, even in the air. Air consists of approximately 80% nitrogen gas (N2),representing about 6400 kg of N above every hectare of land. However, N2 is a stablegas, normally unavailable to plants. Nitrogen fixation, a process by which certainplants "fix" or gather atmospheric N2 and make it biologically available, is anunderlying pattern in nature.2.14.4 How to Use NFTs in a SystemIn the tropics, most of the available nutrients (over 75%) are not in the soil but in theorganic matter. In subtropical and tropical forests, nutrients are constantly cyclingthrough the ecosystem. Aside from enhancing overall fertility by accumulatingnitrogen and other nutrients, NFTs establish readily, grow rapidly, and regrow easilyfrom pruning. They are perfectly suited to jump-start organic matter production on asite, creating an abundant source of nutrient-rich mulch for other plants. Many fast-growing NFTs can be cut back regularly over several years for mulch production. TheNFTs may be integrated into a system in many different ways including clumpplantings, alley cropping, contour hedgerows, shelter belts, or single distributionplantings. As part of a productive system, they can serve many functions:microclimate for shade-loving crops like coffee or citrus (cut back seasonally toencourage fruiting); trellis for vine crops like vanilla, pepper, and yam; mulch banksfor home gardens; and living fence and fodder sources around animal fields.
  • 48. 572.14.5 Literature Review on Nitrogen Fixing Bacteria in CompostingPramanik et al(2006) have studied the effect of organic wastes; cow dung, grass,aquatic weeds and municipal solid waste with lime and microbial moculants onchemical and biochemical properties of vermicompost. In this research, it shows thatcow dung was the best substrate of vermicompostcompared to other organic wastes.Application of lime and inoculation of microorganisms increases the nutrient contentin vermicompost. Besides, Bacillus Polimyxa, the free-living N-fixer, has increasedthe N-content of vermicompost significantly. The results show that the C/N ratio forcow dung was decreased from 18.95 to 12.46 and it was the least C/N ratio reading.Other than that, cow dung recorded the maximum increase in nutrient content of 275%in the vermicompost over its initial reading. Diazotrophs,the potential use of free-living nitrogen fixing bacteria as a sourceof nitrogen nutrition for crops has not been realised in most parts of the world, largelybecause of the inability of the organism to multiply effectively in temperature ofagriculture soils (Keeling 1998). The population ofDiazotrophicwas enhanced 300%over the long term and nitrogen uptake by plants increased by over 100% in the first 2months post 15 gl−1 glucose treatment in compose-grown swards while soluble starch-treated sward growth was inhibited. In addition, a typical field soil similarly treated with glucose failed to respondto the treatment. Contrary, a nitrogen immobilizing effect was observed. It wasconcluded that significant nitrogen fixation and plant N availability was stimulated bythe glucose treatment of compose but the mechanisms of these processes require moreextensive research. Low(2008) studied on the isolation and characterization of nitrogen free fixerbacteria from empty fruit bunches (EFB) of oil palm. In his study, the ability of themicroorganism to fix nitrogen freely was examined by using the N-free mannitol agarmedium. The microorganisms which were able to grow in N-free mannitol agarmedium were considered as free living nitrogen fixing bacteria (Alexander 1977). Themedium used containing carbon source without the supplement of nitrogen. Based on
  • 49. 58C:N ratio, the microorganisms that were able to fix the nitrogen were able to grow onthe medium. In his study, 16 isolates of free living nitrogen fixing microorganismsnamely actinomycetes and bacteria were isolated from the empty fruit bunches (EFB)of oil palm. From 16 isolates, 14 isolates were free living nitrogen actinomycetes and2 isolates were free living nitrogen fixing bacteria. All microorganisms studied wereGram Positive except 2 of the isolates were Gram Negative. Besides, all the isolateswere tested for biochemical properties using Catalase test, Simmon’s-citrate test, triplesugar iron (TSI) test and Voges-Proskauer (VP) Test. From the biochemical propertiesexperiment, 7 of isolates showed positive result for catalase test, 1 isolate showedpositive result for TSI test, 2 isolates showed positive reaction to Simmon’s-citratetest and all the isolates (16 isolate) showed negative results for VP test. From hisstudy, 1 isolate which was named as strain B1 was identified as Azotobacter sp. due tothe formation of cyst structure. The free living nitrogen fixing actinomycetes wererecognized as the slow grower microorganisms (Sylvia et al., 1999). Low(2008) in hisstudy showed that the actinomycetes took an incubation period approximately 10-12days in order to grow well. By having the isolates grown on N-free mannitol agarmedium, it was observed that the free living N-fixing bacteria possessed slimy,glistening and sticky appearance. For free living nitrogen fixing actinomycetes, thecolonies appeared to be white powdery and chalky colonies. In his study, theactinomycetes colonies were observed to be powdery colonies. Other than that, thegram staining results from his study shows that free living nitrogen fixing bacteriacould be of Gram Positive and Gram Negative. However, the free living nitrogenfixing bacteria actinomycetes were mostly Gram Positive with the shape of rod. Cayuela et al,(2009) have done a study on the impact of different N-richanimal wastes on the composting of ligro-cellulosic wastes by a range of classical andnovel methods. The compostwere analyzed using physic-chemical and biochemicalproperties meanwhile two composting mixture was used. Mixture A wasa mixture ofcotton carding wastes, wheat straw and meat meal. On the other hand, Mixture B wasa mixture of cotton carding waste, wheat straw, blood meal and horn and hoof meal.As the result, compost B showed that it contained more problematic organisms and awider variety of other bacteria than compost A. This is because of the high variety of
  • 50. 59N-sources such blood, horn and hoof meals used to make the compost. Bacillus andSphingobacteriumwere found in the sample of compost B after3 days. Gadoriet al.(2003) have done an investigation to examine the performances ofAzospirillumisolates on growth and N uptake of Gailardiapulchella with two nitrogenlevels. This study was aimed to develop N2 fixing inoculants to increase yield of theG. Pulchellaplants using efficient Azospirillumisolates from ornamental plants withdifferent levels of nitrogen. Seven efficient Azospirillumstrains which were OAD-2,OAD-3, OAD-9, OAD-11, OAD-29, OAD-37 and OAD-57 were isolated from theornamental flower plant. As the result, maximum nitrogen uptake showed at the 120DAT (days after transplanting) which was 92.0 kg ha-1 when compared to other stagesof plant growth. Azospirillumstrains OAD-2/ OAD-3/OAD-9/OAD-11 inoculationsalso showed increase in nitrogen uptake than that of inoculation with A. BrasilenseBR-11001 and Azospirillumstrains AOD-5 at all stages of plant growth. Highest Nuptake was recorded in plant receiving Azospirillumstrains OAD-2 + 150 kg N ha-1,which was significantly superior over all other Azospirillumstrains inoculated and notinoculated control plants. Use of Azospirillumas nitrogen fixing inoculants is welldocumented in cereals or non-legume plants. In conclusion, Azospirillumstrains OAD-2 and OAD-11 could be potential N-fixing inoculants for blanket flower G. Pulchellaand other ornamental flower crops after screening them under different field trails. Kumar et al. (2000) have studied on enriching vermicompost by nitrogenfixing and phosphate solubilising bacteria. Three N-fixing which have been choosento be assessed were Azotobacterchroocooccumstrains, Azospirillumlipoferumand thephosphate solubilizing Pseudomonas striata. As the result, it showed an increasingvalue in N and available P contents during the incubation period. Initially, thevermicompost contained only 1.40(g/100g) of N which was increased to 2.72(g/100g)on the 60th day after inoculation with A. Chroococcum. For inoculation of other strainsof Azotobacter, N content increased to 2.53 and 2.50(g/100g). Besides,Azospirilliumlipoferumalso increased N content up to 2.18(g/100g). However, fromthe observation, Azosprilliumlipoferumwas less efficient than Azotobacterstrains. P.Striatacaused a significant effect on the available P content in vermicompost when itwas inoculated alone or with 1%Mossoorie Rock Phosphate (MRP).However,
  • 51. 60 available P content was greater with MRP and P. Striata combination at 60th day which was 1.97(g/100g) compared to 1.52(g/100g) for P. Striataonly. As a conclusion, Azotobacter, Azospirilliumand Pseudomonas inoculation helped inincreasing the N and P contents of vermicompost, androck phosphate was solubilized during composting. In other study, Beauchamp et al (2005) have studied about the isolation of free-living dinitrogen –fixing bacteria and their activity in compost containing de- inking paper sludge. This research founded that two gram-negative N2-fixing isolates were identified as Pseudomonas. The N2-fixing activities increased at each cycle for 3 and 1-year old composts but decreased after two cycles for the 0.5-year old compost. Among these isolated bacteria, only four were found to be able to fix atmospheric N2. After performing the diagnostic test, the N2-fixing bacteria were grown on TSA (Tryptic Soy Alga). However, the isolates from 0.5-year old compost were unable to fix atmospheric N2. This study showed that approximately 5% of the population of DPS composts consisted of free-living N2-fixing bacteria which belong to the Pseudomonas genus. Table 2.12.List of studies found in the literature on nitrogen fixers in composting.Treatment Phosphate Nitrogen Composting N-fixer Referencesystem periodEnriching 1.45 2.73 75 days A.vermin compost Chroococcumby nitrogen 1.40 2.16 A. Lipoferum Vivekfixing & 1.52 1.68 P. Striata Kumar etphosphate 1.97 1.68 P. Striata+ 1% al. 2000solubility MRPbacteria.
  • 52. 61 Table 2.13List of studies found in the literature on nitrogen fixers in composting.Treatment system Initial pH Final T Composting N-fixer Reference C/N C/N C0 Period ratio ratioPlant & animal 30.1 8.1 11.3 70 92 days Bacillus Mariawastes CuzCayuelacomposting:Effects 32.7 7.7 10.9 et al., 2009of the N sources onprocessperformanceIsolation of free- - - 35.6 12- 30 days Pseudomonas Chantal J.living dinitrogen- - - 37.8 25 Beauchampfixing bacteria & - - 36.2 et al., 2005their activity incompostcontaining de-inking papersludge.N-fixing in Cow 6.65 12.46 37 85 days Bacillus P.Pramanikvermicompost of dung Polimyxa et al., 2006biodegradable 18.95organic wastes Grass 6.95 12.93under liming and 21.65microbial Aquatic 6.80 13.35inoculants. weeds 19.96 MSW 7.05 21.77 31.84 2.15 ENERGY BALANCE in COMPOSTING Energy balance is an important consideration in composting. The considerations of energy balance will be discussed below. 2.15.1 Heat balance considerations The solution of coupled heat and mass balance equations in time and in some cases, spatially has provided the basis for most compost process models. The general form adopted for heat and mass balance analysis has been as follows: Accumulation = input − output ± transformation
  • 53. 62Heat balance components in composting models have included sensible heating of thesystem contents, sensible heat of input and output streams, input air, water vapour andany supplementary water, exit gases and vapours, conductive/convective losses,radioactive inputs and losses, latent heat of evaporation of water and biological heatproduction. Biological heat production and latent heat of evaporation of water havebeen shown to be the most significant terms in the heat balance for full-scale systems(Bach et al., 1987). Coefficient (U), which incorporates the combined roles ofconvection, conduction and radiation at system boundaries, has typically beenemployed, although the term conduction is frequently used in this context. Radiationas a separate term has typically been ignored.2.15.2 Energy Balance In Composting ModelsAccumulation = input − output ± transformation (1)Sensible heatingof reactorcontents = (Sensible heat of inlet dry air, sensible and latentheat of inlet water vapour, sensible heat of supplementary water,radiation) -(Sensibleheat of dry exit gas, sensible heat of exit water vapour, conductive/convective losses,radiation losses, latent heat ofevaporation) ±Biologicallygenerated heat. A generalized heat balance model for a representative volume of material inwhich axial heatand moisture variations in the direction of airflow are small andconfigured for sensible heataccumulation as the dependent variable is presentedbelow:d (mcT ) dBVS = GHi - GH0 - UA ( T – Ta ) + Hc (2) dt dtWhere m is the mass of the composting material (kg), c is the specific heat of thecomposting material (kJ/kg.oC), T is the temperature of the composting material (oC),t is the time (s), G is the mass flow rate of air (kg/s), Hi and Ho are the inlet and exitgas enthalpies (kJ/kg), BVS is the mass of biodegradable volatile solids (kg), Hcis the
  • 54. 63heat of combustion of the substrate (kJ/kg), U is the overall heat transfer coefficient(kW/m2. oC), A is the reactor surface area (m2), and Ta is the ambient temperature(oC). Eq. (2) has units of kJ/s (kW). A number of authors have treated mc in Eq. (2) as a constant term (Lieret al.,)resulting in expressions of the following form: dT d ( BVS)mc GH i Hc GH o UA(T Ta) (3) dt dtfrom which the expression for the rate of temperature change is: d ( BVS) GH i H c GH o UA(T Ta )dT dt (4)dt mc Output (sensible heat in exit gases, latent heat of evaporation in water vapour ) Input (sensible heat in air and Output (conductivity , convective , water vapour) radioactive losses )2.16 CO-COMPOSTING OF SOLID WASTE WITH PALM OIL MILLSLUDGE (POMS)Co-composting is the controlled aerobic degradation of organics using more than onematerials(sludge and organic solid waste). Sludge has a high moisture and nitrogencontent while biodegradable solid waste is high in organic carbon and has goodbulking properties (i.e. it allows air to flow and circulate).By combining the two, thebenefits ofeach can be used to optimize the process and the product. For dewateredsludge, a ratio of 1:2 to 1:3 of dewatered sludge to solid waste should be used. Liquidsludge should be used at a ratio of 1:5 to 1:10 of liquid sludge to solid waste. There are two types of Co-composting designs: open and in-vessel. In opencomposting, the mixed material (sludge and solid waste) is piled into long heaps
  • 55. 64called windrows and left to decompose. Windrow piles are turned periodically toprovide oxygen and ensure that all parts of the pile are subjected to the same heattreatment. Windrow piles should be at least 1m high, and should be insulated withcompost or soil to promote an even distribution of heat inside the pile. Depending onthe climate and available space, the facility may be covered to prevent excessevaporation and protection from rain. To adequately treat excreta together with other organic materials in windrows,Who (1989) recommends active windrow co-composting with other organic materialsfor one month at 55-60°C, followed by two to four months curing to stabilize thecompost. This achieves an acceptable level of pathogen killed for targeted healthvalues.In-vessel composting requires controlled moisture and air supply as well asmechanical mixing. Therefore, it is not generally appropriate for decentralizedfacilities. In-vessel composting requires controlled moisture and air supply, as well asmechanical mixing. Therefore, it is not generally appropriate for decentralizedfacilities. Although the composting process seems like a simple, passive technology, awell-working facility requires careful planning and design to avoid failure. A Co-composting facility is only appropriate when there is an available source of well-sorted biodegradable solid waste. Mixed solid waste with plastics and garbage mustfirst be sorted. When done carefully, Co-composting can produce a clean, pleasant,beneficial product that is safe to touch and work with. It is a good way to reduce thepathogen load in sludge. Depending on the climate (rainfall, temperature and wind) the Co-compostingfacility can be built to accommodate the conditions. Since moisture plays an importantrole in the composting process, covered facilities are especially recommended wherethere is heavy rainfall. The facility should be located close to the sources of organicwaste and feacal sludge (to minimize transport) but to minimize trouble, it should notbe too close to homes and businesses. A well-trained staff is necessary for theoperation and maintenance of the facility.
  • 56. 65 Adding excreta especially urine to household organics produces compost witha higher nutrient value (N-P-K) than compost produced only from kitchen and gardenwastes. Co-composting integrates excreta and solid waste management thusoptimizing efficiency. Although the finished compost can be safely handled, care should be takenwhen handling the faecal sludge. Workers should wear protective clothing andappropriate respiratory equipment if the material is found to be dusty. Robust grindersfor shredding large pieces of solid waste (i.e. small branches and coconut shells) andpile turners help to optimize the process, reduce manual labour and ensure a morehomogenous end product. The mixture must be carefully designed so that it has the proper C:N ratio,moisture and oxygen content. If facilities exist, it would be useful to monitor helminthegg inactivation as a proxy measure of sterilization. Maintenance staff must carefullymonitor the quality of the input materials, keep track of the inflows, outflows, turningschedules, and maturing times to ensure a high quality product. Manual turning mustbe done periodically with either a front-end loader or by hand. Forced aerationsystems must be carefully controlled and monitored.