Composting is the biological decomposition and stabilization of organic substrates, under conditions that allow development of thermophilic temperatures as a result of biologically produced heat, to produce a final product that is stable, free of pathogens and plant seeds, and can be beneficially applied to land.
Aerobic composting is the decomposition of organic substrates in the presence of oxygen air (Fig. 2.1). The main products of biological metabolism are carbon dioxide, water, and heat. Anaerobic composting is the biological decomposition of organic substrates in the absence of air. Metabolic end products of anaerobic decomposition are methane, carbon dioxide, and numerous low molecular weight intermediates such as organic acids and alcohols. Anaerobic composting releases significantly less energy per amount of organic decomposed compared to aerobic composting. Also, anaerobic composting has a higher odor potential because of the nature of many intermediate metabolites. For these reasons almost all engineered compost systems are aerobic (Haug, 1993). Therefore this thesis deals with aerobic composting systems because of their commercial importance to man.The purpose of composting has traditionally been to biologically convert putrescible organics into a stabilized form and to destroy organisms pathogenic to humans. Organic composts can accomplish a number of beneficial purposes when applied to the land. First, compost can serve as a source of organic matter for maintaining or building supplies of soil humus, necessary for proper soil structure and moisture holding capacity. Second, compost can improve the growth and vigor of crops in commercial agriculture and home related uses. Stable compost can reduce plant pathogens and improve plant resistance to disease. Colonization by beneficial microorganisms during the latter stages of composting appears to be responsible for inducing disease suppression. Third, compost contains valuable nutrients including nitrogen, phosphorus and a variety of essential trace elements. The nutrient content of compost is related to the quality of the original organic substrate. However, most composts are too low in nutrients to be classified as fertilizers. Their main use is as a soil conditioner, mulch, top dressing, or organic base with fertilizer amendments.
Latent phase, which corresponds to the time necessary for the microorganisms to acclimatize and colonize in the new environment in the compost heap.Growth phase, which is characterized by the rise of biologically produced temperature to mesophilic level.Thermophilic phase, in which the temperature rises to the highest level. This is the phase where waste stabilization and pathogen destruction are most effective. Maturation phase, where the temperature decreases to mesophilic and, consequently, ambient levels. A secondary fermentation takes place which is slow and favors humification; that is, the transformation of some complex organics to humic colloids closely associated with minerals (iron, calcium, nitrogen etc.) and finally to humus. Nitrification reactions, in which ammonia (a by-product from waste stabilization) is biologically oxidized to become nitrite (NO2) and finally nitrate (NO3), also takes place.
Nutrient balance The most important nutrient parameter is the carbon/nitrogen or C/N ratio. The organisms involved in stabilization of organic matter utilize about 30 parts of carbon for each part of nitrogen and hence an initial C/N ratio of 30 is most favorable for composting. Research workers have reported the optimum value to range 26-31 depending upon other environmental conditions. Particle sizeThe particle size of composting materials should be as small as possible so as to allow for efficient aeration and to be easily decomposed by the bacteria, fungi and actinomycetes. Therefore, MSW and agricultural residues, such as aquatic weeds and straw, should be shredded into small pieces prior to being composted. Moisture controlThe moisture tends to occupy the free air space between the particles. Hence, when the moisture content is very high, anaerobic conditions set in. However, the composting mass should have certain minimum moisture content in it for the organisms to survive. The optimum moisture content is known to be between 50 to 60%. Higher moisture content may be required while composting straw and strong fibrous material which soften the fibre and fills the large pore spaces. Aeration requirementIt is necessary to ensure that oxygen is supplied throughout the mass and aerobic activity is maintained. During the decomposition, the oxygen gets depleted and has to be continuously replenished. This can be achieved either by turning of windrows or by supplying compressed air. During the turning, it is necessary to bring inner mass to the outer surface and to transfer the outer waste to the inner portion. Temperature Various studies have shown that the activity of cellulose enzyme reduces at more than 70oC and the optimum temperature range for nitrification is 30o to 50oC beyond which nitrogen loss is known to occur. The high temperature also helps in destruction of some common pathogens and parasites. Heat death of a cell means thermal inactivation of its enzymes. Without enzymatic activity a cell cannot function and will die. Pathogens are also destroyed or controlled by: competition with other microbes, antagonistic relationship, antibiotic of inhibiting substances produced by microbes and time of survival (Haug, 1993). But temperature is the only factor that operator can measure and control during composting. Hence, US Environmental Protection Agency recommended 53oC for 5 days, 55oC for 2 days and 70oC for 30 minutes for destruction of pathogens.
Long, narrow piles agitated/turned regularlyAeration by natural/passive air movementBetter suited to larger volumesComposting time: 3-6 months
Aeration provided by static blowersCan shorten composting time to 3-5 weeksBetter suited for larger volumesMay not be suited to wastes that need mixing during composting, like food wastesDifficult to adjust moisture content during composting if neededOdour control difficult with positive aerationLess land area require than windows, still labor intensive
Rotation mixes, aerates compost mixSecond stage curing/composting neededFood waste grinding and mixing needed with bulking agent prior to feeding drumComposting time: 21 days
Tropical Species (EichhorniaCrassipes)Occurs in lakes, slowly moving rivers and swampsKnown for its production abilities and removal of pollutants from waterCan double its size in 5 days
Water hyacinth, cattle (Cow) manure and saw dust were used for preparation of different waste mixtures. Water hyacinth was collected form the lakes situated in the IITG campus. Cattle manure was obtained from dairy farm near the campus. Saw dust was purchased from nearby saw mill. The compost was prepared with different proportioning of waste composition as described in Table 3.1. Five trials (Trial 1, 2, 3, 4 and 5) were performed on pile composting of water hyacinth in combination with cattle manure and saw dust as a bulking agent.
The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. When the frequency of the IR is the same as the vibrational frequency of a bond, absorption occurs. Examination of the transmitted light reveals how much energy was absorbed at each frequency (or wavelength). This can be achieved by scanning the wavelength range using a monochromator. Alternatively, the whole wavelength range is measured at once using a Fourier transform instrument and then a transmittance or absorbance spectrum is generated using a dedicated procedure. Analysis of the position, shape and intensity of peaks in this spectrum reveals details about the molecular structure of the sample.
TGA is a process that utilizes heat and stoichiometry ratios to determine the percent by mass of a solute. Analysis is carried out by raising the temperature of the sample gradually and plotting weight (percentage) against temperature. The temperature in many testing methods routinely reaches 1000°C or greater. After the data are obtained, curve smoothing and other operations may be done to find the exact points of inflection.
The methods of differential thermal analysis and thermogravimetry have been used in parallel for thermal investigations of analytical precipitates. This double method possesses obviously the advantage that the same thermal change can be observed and characterized by the loss of weight and the change of temperature simultaneously, the two sets of measurements checking each other, or indicating by differences of results some changes which could not otherwise have been observed. In addition, the differential thermal analysis method completes the thermogravimetry measurements in the case when no loss of weight occurs. On the basis of thermogravimetry results, accurate quantitative conclusions may be drawn, which can scarcely be made with thermograms obtained by differential thermal analysis.
The basic principle underlying this technique is that when the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it than the reference to maintain both at the same temperature. Whether less or more heat must flow to the sample depends on whether the process is exothermic or endothermic. For example, as a solid sample melts to a liquid it will require more heat flowing to the sample to increase its temperature at the same rate as the reference. This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid. Likewise, as the sample undergoes exothermic processes (such as crystallization) less heat is required to raise the sample temperature. By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. DSC may also be used to observe more subtle physical changes, such as glass transitions. It is widely used in industrial settings as a quality control instrument due to its applicability in evaluating sample purity and for studying polymer curing.
Spectroscopic and Thermal Analysis of Composting during Agitated Pile and Rotary Drum Composting
SPECTROSCOPIC ANDTHERMAL ANALYSIS OF COMPOSTING DURING AGITATED PILE AND ROTARY DRUM
ABSTRACTWater hyacinth (Eichhornia crassipes) has infested vastwetlands, and has caused major problems in the region viz.reducing fish population, blocking irrigation canals andaverting navigation, damaging rice fields, eutrophication etc.Composting can be one of the suitable options formanagement and disposal of this free floating weed, as theprocess is ecologically sound and economically viable, andhelps in reducing large quantities of organic wastes. Chemicalanalyses used in previous studies to determine the quality andstability of compost is time consuming and unreliable.Therefore, the aim of this study is to employ modernspectroscopic and thermal analyses during agitated pile androtary drum composting of water hyacinth and its differentwaste combinations with cattle manure and sawdust. Duringphase 1 of the project, samples were prepared by pile anddrum composting techniques. In phase 2, spectroscopic andthermal analysis of these collected samples will be done.
MATERIAL FLOW FOR CONVENTIONAL COMPOSTING PROCESS C, N, Inorganic, Humic substances, CompostingPathogens, Weed Mixing Curing Inorganic micro- Processseeds, Microbes organisms
PHASES IN COMPOSTING PROCESS • Time necessary for microorganisms toLatent phase colonize in new environment • Rise of biologically produced temperature to Growth phase mesophilic levelThermophilic • Temperature rises to highest level phase • Temperature decreases to mesophlilic and, Maturation phase consequently ambient levels
PATTERNS OF TEMPERATURE ANDMICROBIAL GROWTH DURING COMPOSTING
ENVIRONMENTALREQUIREMENTS Nutrient balance Particle size • Organisms involved in stabilization of • Particle size of composting materials organic matter utilize about 30 parts of C should be as small as possible so as to for each part of N allow for efficient aeration Moisture control Aeration requirement • Optimum moisture content is known to be • Necessary to ensure that oxygen is between 50-60% supplied throughout the mass and aerobic activity is maintained Temperature • Optimum temperature varies for different feedstocks or materials. However, most data indicate it to be between 50-600C
TYPES OF COMPOSTING Composting Open Process Reactor ProcessAgitated Pile Static Pile / Vertical Flow Horizontal/Inclined Non-flow (Batch) (Windrow) Aerated Pile
ENVIRONMENTAL PROBLEMSConsidered to be world’s worst aquatic plantsAbility to reproduce exponentially interferes withagricultural and infrastructural projectsCan present many problems for fishermenBlamed for reduction of biodiversityLow oxygen conditions create breading conditions formosquito vectors of malaria, encephalitis and filariasis
POTENTIAL UTILIZATIONAs a phytoremediation agent • Ability to grow in heavily polluted water together with its capacity for metal ion accumulation makes it suitable for treating wastewatersPower alcohol production • Relatively high content of hemicellulose indicates it could be a good source of hemicellulose for bioconversionBiogas production • Possibility of converting water hyacinth to biogas has also emerged as an area of major interest for many yearsAnimal fodder/fish feed • High water and mineral content of water hyacinth indicates that the nutrients in water hyacinth are suitable to some animals
COMPOST MATERIAL Water Hyacinth Cattle Sawdust Manure
SPECTROSCOPIC TECHNIQUES IN COMPOSTINGYear Raw Material Spectroscopic Technique 1990 Cattle manure FTIR 1998 Pig manure FTIR 2003 Municipal Solid Waste Thermal analysis 2003 Olive Mill wastes FTIR 2005 Sewage sludge and green plant waste FTIR 2007 Winery and Distillery residues Thermal analysis 2009 Olive mill residues FTIR & DSC
PHASE IISpectrocopic and Thermal analysis of samplesAgitated Pile – Samples from day 0, 18 and 30 to beanalyzedRotary Drum – Samples from day 0, 12 and 20 to beanalyzed5 different waste combinations will be testedTotal 30 samples to be analyzed by FTIR, TGA, DTGand DSC
REFERENCES1. Gunnarsson, C.C., Petersen, C.M., 2007. Water hyacinths as a resource in agriculture and energy production:A literature review. Waste Management 27, 117-129.2. Hsu, J.H., Lo, S.L., 1999. Chemical and spectroscopic analysis of organic matter transformations during composting of pig manure. Environ. Pollut. 104, 189–196.3. Haug, R.T., 1993. The practical handbook of composting engineering. Lewis publishers.4. Jouraiphy, A., Amir, S., El Gharous, M., Revel, J-C., Hafidi, M., 2005. Chemical and spectroscopic analysis of organic matter transformation during composting of sewage sludge and green plant waste. International Biodeterioration & Biodegradation 56, 101-108.5. Kalamdhad, A., Ali, M., Khwairakpam, M., & Kazmi, A. (2009). Organic metter transformation during rtary drum composting. Dynamic Soil, Dynamic Plant.
THANK Presentation by – Shreyas Nangalia YOU 09012227