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Composting Composting Document Transcript

  • COMPOSTING Page 2 ACKNOWLEDGEMENT I am very thankful to Dr. Aruna Joshi for her constant support and valuable guidance for preparation of my seminar. I am also thankful to my friends for valuable suggestions. Mr. Sourabh M. Kulkarni. M. Tech (Environmental engg). Roll No. 112020016.
  • COMPOSTING Page 3 Index- Sr no Description Page no Remark 1 Introduction 4 2 History of composting. 4 3 Compost. 5 4 Composting processes. 6 5 Microbiology of composting. 6 6 Fate of pathogens. 9 7 Ingradients in composting. 10 8 Various methods of composting. 12 9 Steps in composting. 18 10 References 20
  • COMPOSTING Page 4 INTRODUCTION- Composting can generally described as a thermophillic aerobic decomposition process. Solid substrates are degraded over a period of weeks ,by a succession of microbial population to form a dark brown, granular, humus like end product sometimes described as “loamy”. This compost can be used beneficially as a soil conditioner, improving the characteristics of both excessively clayey and sandy soils. The advantages of composting do not lie simply in the production of a soil conditioner. It can be a viable method of domestic refuse disposal. The composting of domestic refuse in Europe has received significant attention since the 1920s. It is less popular in the USA because there is less demand for soil conditioner. The typical refuse soil refuse composition is not as suitable, and alternative means of disposal appear more economically attractive. A range of materials, from municipal refuse and paper to sewage sludge and mixtures of these, can be composed. The primary objective of composting in most cases is to convert an unstable, potentially offensive material into a stable end product. In contrast to stabilise degradable, potentially offensive material, composting is an aerobic process. The composting process is an environmentally sound and beneficial means of recycling organic materials and not a means of waste disposal. It is important to view compostable materials as usable and not as waste requiring disposal. A major portion of municipal solid wastes in India contain up to 70% by weight of organic materials. In addition, certain industrial by-products-those from food processing, agricultural and paper industries – are mostly composed of organic materials. HISTORY OF COMPOSTING- Composting was somewhat modernized beginning in the 1920s in Europe as a tool for organic farming. The first industrial station for the transformation of urban organic materials into compost was set up in Wels/Austria in the year 1921.The early personages most cited for propounding composting within farming are for the German-speaking world Rudolf Steiner, founder of a farming method called biodynamics, and Annie Francé-Harrar, who was appointed on behalf of the government in Mexico and supported the country 1950–1958 to set up a large humus organization in the fight against erosion and soil degradation. In the English-speaking world it was Sir Albert Howard who worked extensively in India on sustainable practices and Lady Eve Balfour who was a huge proponent of composting. Composting was imported to America by various followers of these early European movements in the form of persons such as J.I. Rodale (founder of Rodale Organic Gardening), E.E. Pfeiffer (who developed scientific practices in biodynamic farming), Paul Keene (founder of Walnut Acres in Pennsylvania), and Scott and Helen Nearing (who inspired the back-to-land movement of the 1960s). Coincidentally, some of these personages met briefly in India - all were quite influential in the U.S. from the 1960s into the 1980s. There are many modern proponents of rapid composting that attempt to correct some of the perceived problems associated with traditional, slow composting. Many advocate that compost can be made in 2 to 3 weeks. Many such short processes involve a few changes to traditional methods, including smaller, more homogenized pieces in the compost, controlling
  • COMPOSTING Page 5 carbon to nitrogen (CN) ratio at 30 to 1 or less, and monitoring the moisture level more carefully. However, none of these parameters differ significantly from early writings of Howard and Balfour, suggesting that in fact modern composting has not made significant advances over the traditional methods that take a few months to work. For this reason and others, many modern scientists who deal with carbon transformations are sceptical that there is a "super-charged" way to get nature to make compost rapidly. They also point to the fact that it is the structure of the natural molecules - such as carbohydrates, proteins, and cellulose - that really dictate the rate at which microbial-mediated transformations are possible.Some cities such as Seattle and San Francisco require food and yard waste to be sorted for composting. COMPOST- It is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming. At its most essential, the process of composting requires simply piling up waste outdoors and waiting a year or more. Modern, methodical composting is a multi-step, closely monitored process with measured inputs of water, air and carbon- and nitrogen-rich materials. The decomposition process is aided by shredding the plant matter, adding water and ensuring proper aeration by regularly turning the mixture. Worms and fungi further break up the material. Aerobic bacteria manage the chemical process by converting the inputs into heat, carbon dioxide and ammonium. The ammonium is further converted by bacteria into plant-nourishing nitrites and nitrates through the process of nitrification. Compost can be rich in nutrients. It is used in gardens, landscaping, horticulture, and agriculture. The compost itself is beneficial for the land in many ways, including as a soil conditioner, a fertilizer, addition of vital humus or humic acids, and as a natural pesticide for soil. In ecosystems, compost is useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover. Organic ingredients intended for composting can alternatively be used to generate biogas through anaerobic digestion. Anaerobic digestion is fast overtaking composting in some parts of the world including central Europe as a primary means of downcycling waste organic matter.
  • COMPOSTING Page 6 COMPOSTING PROCESSES - Microorganisms such as bacteria, fungi and actinomycetes as well as larger organisms such as insects and earthworms play an active role in decomposing the organic materials. As microorganisms begin to decompose the organic material, they break down organic matter and produce carbon dioxide, water, heat and humus (the relatively stable organic end product). This humus end product is compost. MICROBIOLOGY OF COMPOSTING- Biodegradable material is decomposed naturally by mesophilic microorganisms which initially utilise the most readily degradable carbohydrates and proteins. When such material is gathered into heap, the insulating effect leads to a conservation of heat and rise in temperature. The maximum temperature achieved and time taken to achieve it depends on many process parameters including composition of organic wastes, availability of nutrients, moisture content, size of heap, particle size and degree of aeration and agitation. This processes is devide into four stages. Mesophilic, thermophilic, cooling and maturation or curing. Mesophilic or moderate-temperature phase: Compost bacteria combine carbon with oxygen to produce carbon dioxide and energy. The microorganisms for reproduction and growth use some of the energy and the rest is generated as heat. When a pile of organic refuse begins to undergo the composting process, mesophilic bacteria proliferate, raising the temperature of the composting mass up to 44oC. This is the first stage of the composting process. These mesophilic bacteria can include E. coli and other bacteria from the human intestinal tract, but these soon become increasingly inhibited by the temperature, as the thermophilic bacteria take over in the transition range of 44-52oC.  Thermophilic or high-temperature phase: In the second stage of the process, the thermophilic microorganisms are very active and produce heat. This stage can continue up to about 70o C, although such high temperatures are neither common nor desirable in compost. This heating stage takes place rather quickly and may last only a few days, weeks, or months. It tends to remain localized in the upper portion of a compost pile where the fresh material is being added, whereas in batch compost, the entire composting mass may be thermophilic all at once. After the thermophilic heating period, the manure will appear to have been digested, but the coarser organic material will not be digested. This is when the third stage of composting, i.e., the cooling phase, takes place.  Cooling phase: During this phase, the microorganisms that were replaced by the thermophiles migrate back into the compost and digest the more resistant organic materials. Fungi and macroorganisms such as earthworms and sow bugs that break the coarser elements down into humus also move back in.
  • COMPOSTING Page 7  Maturation or curing phase: The final stage of the composting process is called curing, ageing, or maturing stage, and is a long and important one. A long curing period (e.g., a year after the thermophilic stage) adds a safety net for pathogen destruction. Many pathogens have a limited period of viability in the soil, and the longer they are subjected to the microbiological competition of the compost pile, the more likely they will die a swift death. Immature compost can be harmful to plants. Uncured compost can, for example, produce phytotoxins (i.e., substances toxic to plants), robbing the soil of oxygen and nitrogen and contain high levels of organic acids. CHEMICAL PROCESSES - Several factors determine the chemical environment for composting. These include the presence of an adequate carbon food/energy source, a balanced amount of nutrients, the correct amount of water, adequate oxygen, appropriate pH and the absence of toxic constituents that could inhibit microbial activity. A brief description of each of these factors is given below.  Carbon/energy source: For their carbon/energy source, microorganisms in the composting process rely on carbon in the organic material, unlike higher plants that rely on carbon dioxide and sunlight. Since most municipal and agricultural organics and yard trimmings contain an adequate amount of biodegradable forms of carbon, it is not a limiting factor in the composting process. As more easily degradable forms of carbon are decomposed, a small portion of the carbon is converted into microbial cells, and a significant portion is converted to carbon dioxide and lost to the atmosphere. As the composting process progresses,the loss of carbon results in a decrease in weight and volume of the feedstock.  Nutrients: Among the plant nutrients (i.e., nitrogen, phosphorous and potassium), nitrogen is of greatest concern, because it is lacking in some plant materials. The carbon-nitrogen ratio, which is established on the basis of available carbon rather than total carbon, is considered critical in determining the rate of decomposition. Leaves, for example, are a good source for carbon, and fresh grass, manure and slaughter house waste are the sources of nitrogen. To aid the decomposition process, the bulk of the organic matter should be carbon with just enough nitrogen. In general, an initial ratio of 30:1(C:N or Carbon: Nitrogen) is considered ideal. Higher ratios tend to retard the process of decomposition, while ratios below 25:1 may result in odour problems. Finished compost should have ratios of 15 to 20:1. Adding 3 – 4 kg of nitrogen material for every 100 kg of carbon should be satisfactory for efficient and rapid composting. To lower the carbon to nitrogen ratios, nitrogen-rich materials such as yard trimmings, animal manures, or bio-solids are often added. Adding partially decomposed or composted materials (with a lower carbon: nitrogen ratio) as inoculums may also lower the ratio. As the temperature in the compost pile rises and carbon- nitrogen ratio falls below 25:1, the nitrogen in the fertilizer is lost as gas (ammonia) to the atmosphere. The composting process slows, if there is not enough nitrogen, and too much nitrogen may cause the generation of ammonia gas, which can create unpleasant odours.
  • COMPOSTING Page 8  Moisture- Water is an essential part of all forms of life, and the microorganisms living in a compost pile are no exception. Since most compostable materials have lower than ideal water content, i.e., 50 to 60% of total weight, the composting process may be slower than desired, if water is not added. However, it should not be high enough to create excessive free flow of water and movement caused by gravity.Excessive moisture and flowing water from leachate, which creates potential liquid waste management problems including water and air pollution (e.g., odour). For example, excess moisture impedes oxygen transfer to the microbial cells, can increase the possibility of developing anaerobic conditions and may lead to rotting and obnoxious odours. Controlling the size of piles can minimize evaporation from compost piles, as piles with larger volumes have less evaporating surface/unit volume than smaller piles. The water added must be thoroughly mixed so that the organic fraction in the bulk of the material is uniformly wetted and composted under ideal conditions. Properly wetted compost has the consistency of a wet sponge. Systems that facilitate the uniform addition of water at any point in the composting process are preferable.  Oxygen: Composting is considered as an aerobic process. Decomposition can occur under both aerobic (requiring oxygen) and anaerobic (in the absence of oxygen) conditions. The compost pile should have enough void space to allow free air movement so that oxygen from the atmosphere can enter the pile and the carbon dioxide and other gases emitted can be exhausted to the atmosphere. To maintain aerobic conditions, in which decomposition occurs at a fast rate, the compost pile is mechanically aerated or turned frequently to expose the microbes to the atmosphere and to create more air spaces by fluffing up the pile. 10 to 15% oxygen concentration is considered adequate, although a concentration as low as 5% may be sufficient for leaves. While higher concentrations of oxygen will not negatively affect the composting process, circulation of an excessive amount of air can cause problems. For example, excess air removes heat, which cools the pile and also promotes excess evaporation. In other words, excess air slows down the rate of composting. Excess aeration is also an added expense that increases production costs.  pH: The pH factor affects the amount of nutrients available for the microorganisms, the solubility of heavy metals and the overall metabolic activity of the microorganisms. A pH between 6 and 8 is considered optimum, and it can be adjusted upward by the addition of lime, or downward with sulphur, although such additions are normally not necessary. The composting process itself produces carbon dioxide, which, when combined with water, produces carbonic acid, which could lower the pH of the compost. As the composting process progresses, the final pH vary, depending on the specific type of feedstock used and operating conditions. Wide swings in pH are unusual since organic materials are naturally well buffered with respect of pH changes.
  • COMPOSTING Page 9 PHYSICAL PROCESSES-  Particle size: Smaller particles usually have more surface area per unit weight, they facilitate more microbial activity on their surfaces, which leads to rapid decomposition. The optimum particle size has enough surface area for rapid microbial activity and also enough void space to allow air to circulate for microbial respiration.  Temperature: Composting can occur at a range of temperatures, and the optimum temperature range is between 32 and 60oC. Temperatures above 65oC are not ideal for composting as thermal destruction of cell proteins kills the organisms. Similarly, temperatures below the minimum required for a group of organisms affect the metabolic activity (i.e., regulatory machinery) of the cells. When compost is at a temperature greater than 55oC for at least three days, pathogen destruction occurs. It is important that all portions of the compost material are exposed to such temperatures to ensure pathogen destruction throughout the compost. Attaining and maintaining 55oC for three days is not difficult for in vessel composting system. However, to achieve pathogen destruction with windrow composting systems, the 55oC temperature level must be maintained for a minimum of 15 days. The longer duration and increased turning are necessary to achieve uniform pathogen destruction in the entire pile.  Mixing: Mixing of feedstock, water and inoculants is important and is done by running or mixing the piles after composting has begun. Mixing and agitation distribute moisture and air evenly, and promote the breakdown of compost clumps. Excessive agitation of open vessels or piles, however, can cool them and retard microbial activity. FATE OF PATHOGENS DURING COMPOSTING- The thermophilic nature of composting process is widely claimed to be effective in reducing the number of viable organisms present. The temperature is the most critical factor. A temperature in excess of 56deg c will usually be sufficient to inactivate 99% or more of E- coli, faecal streptococci and salmonella spp. Polio virus is also destroyed at similar temperatures in as short a time as thirty minutes. At higher temperatures even better pathogen removal is obtained. For example, mycobacterium tuberculosis will be killed by a temperature of 65deg c after fifteen days exposure. Some of the thermophilic fungi are classified as secondary pathogens. This means that they may infect individuals who are already infected by other pathogens or who are particularly susceptible to respiratory complaints. Airborne spores of Aspergillus fumigates are frequently found in the vicinity of composting windrows. A number of antigenic substances having a microbiological origin may also be found associated with the dust particles. Aspergillus flavus, which produces aflatoxin , a potent human carcinogen, may be found in composting processes,
  • COMPOSTING Page 10 Any adverse effects caused by the composting organisms themselves are likely to be highly localised, so that there will be no threat to residential areas. INGRADIENTS - Composting organisms require four equally important things to work effectively:  Carbon — for energy; the microbial oxidation of carbon produces the heat o High carbon materials tend to be brown and dry.  Nitrogen — to grow and reproduce more organisms to oxidize the carbon. o High nitrogen materials tend to be green (or colorful, such as fruits and vegetables) and wet.  Oxygen — for oxidizing the carbon, the decomposition process.  Water — in the right amounts to maintain activity without causing anaerobic conditions. Materials in a compost pile. Certain ratios of these materials will provide beneficial bacteria with the nutrients to work at a rate that will heat up the pile. In that process much water will be released as vapor ("steam"), and the oxygen will be quickly depleted, explaining the need to actively manage the pile. The hotter the pile gets, the more often added air and water is necessary; the air/water balance is critical to maintaining high temperatures (135°-160° Fahrenheit) until the materials are broken down. At the same time, too much air or water also slows the process, as does too much carbon (or too little nitrogen). The most efficient composting occurs with a carbon:nitrogen mix of about 30 to 1. Nearly all plant and animal materials have both carbon and nitrogen, but amounts vary widely, with characteristics noted above (dry/wet, brown/green). Fresh grass clippings have an average ratio of about 15 to 1 and dry autumn leaves about 50 to 1 depending on species. Mixing equal parts by volume approximates the ideal C:N range. Few individual situations will provide the ideal mix of materials at any point in time. Observation of amounts, and consideration of different materials as a pile is built over time, can quickly achieve a workable technique for the individual situation.
  • COMPOSTING Page 11 Urine People excrete far more of certain water-soluble plant nutrients (nitrogen, phosphorus, potassium) in urine than in faeces. Human urine can be used directly as fertilizer or it can be put onto compost. Adding a healthy person's urine to compost usually will increase temperatures and therefore increase its ability to destroy pathogens and unwanted seeds. Urine from a person with no obvious symptoms of infection is generally much more sanitary than fresh faeces. Unlike faeces, urine doesn't attract disease-spreading flies (such as house flies or blow flies), and it doesn't contain the most hardy of pathogens, such as parasitic worm eggs. Urine usually does not stink for long, particularly when it is fresh, diluted, or put on sorbents. Urine is primarily composed of water and urea. Although metabolites of urea are nitrogen fertilizers, it is easy to over-fertilize with urine creating too much ammonia for plants to absorb, acidic conditions, or other phytotoxicity. Manure and bedding On many farms, the basic composting ingredients are manure generated on the farm and bedding. Straw and sawdust are common bedding materials. Non-traditional bedding materials are also used, including newspaper and chopped cardboard. The amount of manure composted on a livestock farm is often determined by cleaning schedules, land availability, and weather conditions. Each type of manure has its own physical, chemical, and biological characteristics. Cattle and horse manures, when mixed with bedding, possess good qualities for composting. Swine manure, which is very wet and usually not mixed with bedding material, must be mixed with straw or similar raw materials. Poultry manure also must be blended with carbonaceous materials - those low in nitrogen preferred, such as sawdust or straw. Micro-organisms - With the proper mixture of water, oxygen, carbon, and nitrogen, micro-organisms are allowed to break down organic matter to produce compost. The composting process is dependant on micro-organisms to break down organic matter into compost. There are many types of microorganisms found in active compost of which the most common are:  Bacteria- The most numerous of all the micro organisms found in compost.  Actinomycetes- Necessary for breaking down paper products such as newspaper, bark, etc.  Fungi- Molds and yeast help break down materials that bacteria cannot, especially lignin in woody material.  Protozoa- Help consume bacteria, fungi and micro organic particulates.  Rotifers- Rotifers help control populations of bacteria and small protozoans. In addition, earthworms not only ingest partly-composted material, but also continually re- create aeration and drainage tunnels as they move through the compost A lack of a healthy micro-organism community is the main reason why composting processes are slow in landfills with environmental factors such as lack of oxygen, nutrients or water being the cause of the depleted biological community.
  • COMPOSTING Page 12 VARIOUS METHODS OF COMPOSTING - 1) THE INDIAN BANGLORE METHOD - This method of composting was developed at Bangalore in India by Acharya (1939). The method is basically recommended when night soil and refuse are used for preparing the compost. The method overcomes many of the disadvantages of the Indore method such as problem of heap protection from adverse weather, nutrient losses due to high winds / strong sun rays, frequent turning requirements, fly nuisance etc. but the time involved in production of a finished compost is much longer. The method is suitable for areas with scanty rainfall. Preparation of the pit Trenches or pits about one metre deep are dug; the breadth and length of the trenches can be made depending on the availability of land and the type of material to be composted. The selection of site for the pits is made as in the Indore method. The trenches should preferably have sloping walls and a floor of 90-cm slope to prevent water logging. Filling the pit Organic residues and night soil are put in alternate layers and, after filling, the pit is covered with a 15-20 cm thick layer of refuse. The materials are allowed to remain in the pit without turning and watering for three months. During this period, the material settles down due to reduction in volume of the biomass and additional night soil and refuse are placed on top in alternate layers and plastered or covered with mud or earth to prevent loss of moisture and breeding of flies. After the initial aerobic composting which is for about eight to ten days, the material undergoes anaerobic decomposition at a very slow rate and it takes about six to eight months to obtain the finished product. 2) THE INDIAN INDOOR METHOD – An important advance in the practice of composting was made at Indore in India by Howard during the period 1924 to 1926. The traditional procedure was systematized into a method of composting now known as the ‘Indore method’. Raw materials The raw materials used are mixed plant residues, animal dung and urine, earth, wood ash and water. All organic material wastes available on a farm such as weeds, stalks, stems, fallen leaves, prunings, chaff, fodder leftovers and so on, are collected and stacked in a pile. Hard woody material like cotton or pigeon pea stalks and stubble are first spread on the farm road and crushed under vehicles such as tractors or bullock carts before being piled. Such hard materials should in any case not exceed ten percent of the total plant residues. Green materials, which are soft and succulent, are allowed to wilt for two to three days to remove excess moisture before stacking; they tend to pack closely if they are stacked in the fresh state. The mixture of different kinds of organic material residues ensures a more efficient decomposition. While stacking, each type of material is spread in layers about 15 centimetres thick until the heap is about one and a half metres high. The heap is then cut into vertical slices and about 20-25 kilograms are put under the feet of cattle in the shed as bedding for the
  • COMPOSTING Page 13 night. The next morning the bedding, along with the dung and urine and urine-earth, is taken to the pits where the composting is to be done. A) Pit method Site and pit dimension: The site selected for the compost pit should be at high level so that no rainwater gets in during the monsoon season; it should be near to the cattle shed and a water source. A temporary shed may be constructed over it to protect the compost from heavy rainfall. The pit should be about 1 m deep, 1.5-2 m wide and of any suitable length. Filling the pit: The material brought from the cattle shed is spread evenly in the pit in layers of 10-15 cm. On each layer is spread a slurry made with 4.5 kg dung, 3.5 kg urine-earth and 4.5 kg of inoculum taken from a 15 day-old composting pit. Sufficient quantity of water is sprinkled over the material in the pit to wet it. The pit is filled in this way, layer by layer, and it should not take longer than one week to fill. Care should be taken to avoid compacting the material in any way. Turning: The material is turned three times during the whole period of composting; the first time 15 days after filling the pit, the second after another 15 days and the third after another month. At each turning, the material is mixed thoroughly, moistened with water and replaced in the pit. B) Heap method - Site and heap dimensions: During rainy seasons or in regions with heavy rainfall, the compost may be prepared in heaps above ground and protected by a shed. The basic Indore pile is about 2 m wide at the base, 1.5 m high and 2 m long. The sides are tapered so that the top is about 0.5 m narrower in width than the base. A small bund is sometimes built around the pile to protect it from wind,which tends to dry the heap. Forming the heap: The heap is usually started with a 20 cm layer of carbonaceous material such as leaves, hay, straw, sawdust, wood chips and chopped corn stalks. This is then covered with 10 cm of nitrogenous material such as fresh grass, weeds or garden plant residues, fresh or dry manure or digested sewage sludge. The pattern of 20 cm carbonaceous material and 10 cm of nitrogenous material is followed until the pile is 1.5 m high and the material is normally wetted so that it may feel damp but not soggy. The pile is sometimes covered with soil or hay to retain heat and is turned at six- and twelve-week intervals. In the Republic of Korea, heaps are covered with thin plastic sheets to retain heat and prevent insect breeding. If materials are limited, the alternate layers can be added as they become available. Also, all materials may be mixed together in the pile if one is careful to maintain the proper proportions. Shredding the
  • COMPOSTING Page 14 material speeds up decomposition considerably; most materials can be shredded by running over them several times a rotary mower. When sufficient nitrogenous material is not available, a green manure or leguminous crop like sun hemp is grown on the fermenting heap by sowing seeds after the first turning. The green matter is then turned in at the time of the second mixing. The process takes about four months to complete. 3) In-Vessel Composting- In-vessel composting refers to a group of methods which confine the composting materials within a building, container, or vessel. In-vessel methods rely on a variety of forced aeration and mechanical turning techniques to speed up the composting process. Many methods combine techniques from the windrow and aerated pile methods in an attempt to overcome the deficiencies and exploit the attributes of each method. There are a variety of in-vessel methods with different combinations of vessels, aeration devices, and turning mechanisms. The few methods discussed here have either been used or proposed for farm composting. They also serve as good examples of the types of invessel systems available. There are various methods of In-vessel composting-  Bin composting.  Rotating Drums.  Transferable Containers.  Reactangular agited beds. 4) Windrow Composting- Turned Windrows - Windrow composting consists of placing the mixture of raw materials in long narrow piles or windrows which are agitated or turned on a regular basis. The turning operation mixes the composting materials and enhances passive aeration. Typically the windrows are initially from 3 feet high for dense materials like manures to 12 feet high for fluffy materials like leaves. The width varies from 10 to 20 feet. The equipment used for turning determines the size, shape, and spacing of the windrows. Bucket loaders with a long reach can build high windrows. Turning machines produce low, wide windrows. Windrows aerate primarily by natural or passive air movement (convection and gaseous diffusion). The rate of air exchange depends on the porosity of the windrow. Therefore, the size of a windrow that can be effectively aerated is determined by its porosity. A light fluffy windrow of leaves can be much larger than a wet dense windrow containing manure. If the windrow is too large, anaerobic zones occur near its centre which release odours when the windrow is turned. On the other hand, small windrows lose heat quickly and may not achieve temperatures high enough to evaporate moisture and kill pathogens and weed seeds. For small to moderate scale operations, turning can be accomplished with a front end loader or a bucket loader on a tractor. The loader simply lifts the materials from the windrow and spills them down again, mixing the materials and reforming the mixture into a loose windrow. The loader can exchange material from the bottom of the windrow with material on the top by forming a new windrow next to the old one. This needs to be done without driving onto the windrow in order to minimize compaction. Windrows turned with a bucket loader
  • COMPOSTING Page 15 are often constructed in closely spaced pairs and then combined after the windrows shrink in size. If additional mixing of the materials is desired, a loader can also be used in combination with a manure spreader. A number of specialized machines have been developed for turning windrows. These machines greatly reduce the time and labour involved, mix the materials thoroughly, and produce a more uniform compost. Some of these machines are designed to attach to farm tractors or front-end loaders; others are self-propelled. A few machines also have the capability of loading trucks or wagons from the windrow. It is very important to maintain a schedule of turning. The frequency of turning depends on the rate of decomposition, the moisture content and porosity of the materials, and the desired composting time. Because the decomposition rate is greatest at the start of the process, the frequency of turning decreases as the windrow ages. Easily degradable or highnitrogen mixes may require daily turnings at the start of the process. As the process continues, the turning frequency can be reduced to a single turning per week. By the end of the first week of composting, the windrow height diminishes appreciably and by the end of the second week it may be as low as 2 feet. It may be prudent to combine two windrows at this stage and continue the turning schedule as before. Consolidation of windrows is a good wintertime practice to retain the heat generated during composting. This is one of the advantages of windrow composting. It is a versatile system that can be adjusted to different conditions caused by seasonal changes. With the windrow method, the active composting stage generally lasts three to nine weeks depending upon the nature of the materials and the frequency of turning. Eight weeks is a common period for manure composting operations. If three weeks is the goal, the windrow requires turning once or twice per day during the first week and every three to five days thereafter. Passively Aerated Windrows- The method, passively aerated windrow system, eliminates the need for turning by supplying air to the composting materials through perforated pipes embedded in each windrow. The pipe ends are open. Air flows into the pipes and through the windrow because of the chimney effect created as the hot gases rise upward out of the windrow. The windrows should be 3-4 feet high, built on top of a base of straw, peat moss, or finished compost to absorb moisture and insulate the windrow. The covering layer of peat or compost also insulates the windrow; discourages flies; and helps to retain moisture, odour, and ammonia. The plastic pipe is similar to that used for septic system leach fields with two rows of 1/2-inch diameter holes drilled in the pipe. In many aerated pile applications, the pipe holes are oriented downward to minimize plugging and allow condensate to drain. However, some researchers recommend that the holes face upwards. Windrows are generally formed by the procedures described for the aerated static pile method. Because the raw materials are not turned after the windrows are formed, they must be thoroughly mixed before they are placed in the windrow. Avoid compacting the mix of materials while constructing the windrow. Aeration pipes are placed on top of the
  • COMPOSTING Page 16 peat/compost base. When the composting period is completed, the pipes are simply pulled out, and the base material is mixed with the compost. This method of composting has been studied and used in Canada for composting seafood wastes with peat moss, manure slurries with peat moss, and solid manure with straw or wood shavings. Manure from dairy, beef, swine, and sheep operations has been used. 5) VERMICOMPOSTING - Preparing vermicompost- Materials - breeder worms, a wooden bed and organic wastes. • The bed should be 2 1/2 ft. high x 4 ft. wide x any length desired. Apply worms for every part of waste. • Sieving and shredding- Decomposition can be accelerated by shredding raw materials into small pieces. • Blending- Carbonaceous substances like sawdust, paper and straw can be mixed with nitrogen rich materials such as sewage sludge, biogas slurry and fish scraps to obtain a near optimum C/N ratio of 30:1 / 40:1. A varied mixture of substances produces good quality compost, rich in major and micro nutrients. • Half digestion- The raw materials should be kept in piles and the temperature allowed to reach 50-55oC. The piles should remain at this temperature for 7 to 10 days. • Moisture, temperature and pH- The optimum moisture level for maintaining aerobic conditions is 40-45%. Proper moisture and aeration can be maintained by mixing fibrous with nitrogen rich materials. The temperature of the piles should be within 28- 30oC. Higher or lower temperatures will reduce the activity of micro flora and earthworms. The height of the bed can help control the rise in temperature. The pH of the raw material should not exceed 6.5 to 7. After about a month the compost is ready. It will be black, granular, lightweight and humusrich. To facilitate separating the worms from the compost, stop watering two to three days before emptying the beds. This will force about 80% of the worms to the bottom of the bed. The rest of the worms can be removed by hand. The vermicompost is then ready for application.
  • COMPOSTING Page 17 Vermicompost- Vermicompost is the product of composting utilizing various species of worms, usually red wigglers, white worms, and earthworms to create a heterogeneous mixture of decomposing vegetable or food waste (not to include meat, dairy, fats, or oils), bedding materials, and vermicast. Vermicast, also known as worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by species of earthworm. This type of composting is sometimes suggested as a feasible indoor composting method The earthworm species (or composting worms) most often used are Red Wigglers (Eisenia foetida or Eisenia andrei), though European nightcrawlers (Eisenia hortensis) could also be used. Red wigglers are recommended by most vermiculture experts, as they have some of the best appetites and breed very quickly. Users refer to European nightcrawlers by a variety of other names, including dendrobaenas, dendras, and Belgian nightcrawlers. Containing water-soluble nutrients, vermicompost is a nutrient-rich organic fertilizer and soil conditioner in a form that is relatively easy for plants to absorb. Worm castings are sometimes used as an organic fertilizer. Because the earthworms grind and uniformly mix minerals in simple forms, plants need only minimal effort to obtain them. The worms' digestive systems also add beneficial microbes to help create a "living" soil environment for plants. Vermicompost tea has been shown to cause a 173.5% increase in plant growth by mass over plants grown without castings. These results were seen with only 10% addition of castings to produce these results. VERMICOMPOST
  • COMPOSTING Page 18 STEPS OF COMPOSTING- There are five basic steps involved in all composting practices, namely preparation, digestion, curing, screening or finishing, and storage or disposal. However, differences (among various composting processes) may occur in the method of digestion or in the amount of preparation and the finished product. Preparation- The preparation phase of composting involves several steps, and these depend upon the sophistication of the plant and the amount of resource recovery practiced. A typical preparation process, however, may include activities such as the sorting of recyclable materials, the removal of non-combustibles, the shredding, pulping, grinding and the adding of water sludge. The separation of other non-compostable recyclable materials like glass, metal, rag, plastic, rubber and paper may be accomplished by either hand or mechanical means. Since the refuse characteristics vary from one load to the next, a final step in the preparation phase of composting may be to adjust the moisture and nitrogen content of the solid waste to be composted. The optimum moisture content ranges from 45 to 55% of wet weight, while the optimum carbon to nitrogen ratio should be below 30%. The moisture and nutrient adjustments can be accomplished most efficiently through the addition of raw waste water sludge. This increases the volume of composted material by 6 to 10%, in addition to accelerating the composting operation and producing a better final product in terms of nutrient contents. Digestion- Digestion techniques are the most unique feature of the various composting processes and may vary from the backyard composting process to the highly controlled mechanical digester. Composting systems fall into the following two categories (i) Window composting in open windrows (ii) Mechanical composting in enclosed digestion chambers. Curing- During curing, the compost becomes biologically stable, with microbial activity occurring at a slower rate than that during actual composting. Curing piles may be either force-aerated or passive aerated with occasional turning. As the pile cures, the microorganisms generate less heat and the pile begins to cool. Cooling is merely a sign of reduced microbial activity, which can result from lack of moisture, inadequate oxygen within the pile, nutrient imbalance or the completion of the composting process. Curing may take from a few days to several months to complete.The cured compost is then marketed. Screening or finishing- Compost is screened or finished to meet the market specifications. Sometimes, this processing is done before the compost is cured. One or two screening steps and additional grindings are used to propagate the compost for markets. During the composting operation, the compostable fraction separated from the non-compostable fraction, through screens, undergoes a significant size reduction. The non-compostable fraction retained on the coarse screen is sent to the landfill, while the compostable materials retained on finer screens may be returned to the beginning of the composting process to allow further composting.
  • COMPOSTING Page 19 The screened compost may contain inert particles such as glass or plastic that may have passed through the screen. The amount of such inert materials depends on feedstock processing before composting and the composting technology used. To successfully remove the foreign matter and recover the maximum compost by screening, the moisture content should be below 50%. Drying should be allowed only after the compost has sufficiently cured. If screening takes place before curing is complete, moisture addition may be necessary to cure the compost. The screen size used is determined by market specifications of particle size. Storage or disposal - In the final analysis, regardless of the efficiency of the composting process, the success or failure of the operation depends upon the method of disposal. Even when a good market for compost exists, provision must be still made for storage.
  • COMPOSTING Page 20 REFERENCES- • www.hdra.org.ok • On firm composting methods by R.V. Mishra and R. N. Roy.FAO, Rome. • http://en.wikipedia.org/wiki/Compost • http://www.vegweb.com/composting • Microbiology and chemistry for environmental scientists and engineers, Second edition. J. N. Lester and J.W. Birkett. Taylor and Francis gro.
  • COMPOSTING Page 21 VARIOUS METHODS OF COMPOSTING- The Indore method- The Indore method involves putting layers of different materials on top of each other to form a heap. First, make a base 1 metre (m) wide and 3m long, with twigs and cane shoots that are
  • COMPOSTING Page 22 difficult to decompose. This allows ventilation which is important for the survival of micro- organisms. Then the layering is as follows:  10 centimetres (cm) of material which is difficult to decompose, for example  maize stalks. Then sprinkle with water.  10cm of material which is easy to decompose, such as fruit and vegetable  scraps.  2cm of animal manure (if available).  A thin layer of soil from the surface of cropped land to obtain the microorganisms  needed for the composting process.  Repeat these layers until the heap reaches 1m to 1.5 m high.  Cover with grass or leaves (such as banana leaves) to prevent water  loss. Complete this process within one week. After 2 to 3 weeks the heap should be taken apart and rebuilt. This is because the materials do not all decompose evenly. Again, a layer of coarse material should be laid down first. The material which was on the outside of the heap and has not decomposed, should be placed into the middle of the new heap and watered. This should then be covered with the remaining material. The original layered structure is lost. After another three weeks this process may have to be repeated depending on how much the heap has decomposed. Full decomposition should take 3 months. Urine (diluted with 4 parts water) sprinkled over the layers of soil can accelerate the process of decomposition. Urine also adds valuable nutrients to the compost. Ash in small quantities also acts as an accelerator and can be sprinkled over each layer of soil. However, too much urine or ash can be destructive to the microorganisms in the heap. Advantages: The Indore method produces compost in a short space of time and the process can be controlled. Weed seeds and diseases are killed. Disadvantages: The Indore method requires a lot of water and is very labour intensive. It works best when you have a lot of material to use all at once. The Bangalore method-
  • COMPOSTING Page 23 The Bangalore method is a popular method of composting. A few days after completing a heap, it is covered with mud or damp grass so that it is closed off from the outside air. This allows ‘anaerobic’ micro-organisms (that do not need air) to decompose the heap. The heap should be 1m to 1.5m high, 1m wide and 3m long. The method for building the heap is as follows:  10cm layer of material that is difficult to decompose (stalks and crop  residues). Then sprinkle with water.  10cm of material that is easy to decompose (fruit and vegetable wastes).  2cm of animal manure (if available).  A thin layer of soil from the surface of cropped land to obtain.  the micro-organisms needed for the composting process.  Repeat these layers until the heap reaches 1 to 1.5m high  Cover with wet clay, mud or  damp grass Advantages: The Bangalore method uses less water and labour than other methods as turning is not required. Disadvantages: Weed seeds and diseases can survive due to the low temperature. The process of decomposition cannot be controlled. Experience of composting is needed as the process is more complex than other heap methods. Uses Compost is generally recommended as an additive to soil, or other matrices such as coir and peat, as a tilth improver, supplying humus and nutrients. It provides a rich growing medium, or a porous, absorbent material that holds moisture and soluble minerals, providing the support and nutrients in which plants can flourish, although it is rarely used alone, being primarily mixed with soil, sand, grit, bark chips, vermiculite, perlite, or clay granules to produce loam. Compost can be tilled directly into the soil or growing medium to boost the level of organic matter and the overall fertility of the soil. Compost that is ready to be used as an additive is dark brown or even black with an earthy smell. Generally, direct seeding into a compost is not recommended due to the speed with which it may dry and the possible presence of phytotoxins that may inhibit germination, and the possible tie up of nitrogen by incompletely decomposed lignin.It is very common to see blends of 20–30% compost used for transplanting seedlings at cotyledon stage or later.
  • COMPOSTING Page 24 Destroying pathogens, seeds, or unwanted plants - Composting can destroy pathogens or unwanted seeds. Unwanted living plants (or weeds) can be discouraged by covering with mulch/compost. The "microbial pesticides" in compost may include thermophiles and mesophiles, however certain composting detritivores such as black soldier fly larvae and redworms, also reduce many pathogens. Thermophilic (high-temperature) composting is well known to destroy many seeds and nearly all types of pathogens (exceptions may include prions). However, thermophilic composting requires a fair amount of material, around a cubic meter. Destruction of pathogens would only take place in the high temperature zone in the center and not in the outer fringes—it is therefore a questionable practice if the intent is to kill pathogens. The sanitizing qualities of (thermophilic) composting are desirable where there is a high likelihood of pathogens, such as with manure. Applications include humanure composting or the deep litter technique. FATE OF PATHOGENS DURING COMPOSTING- The thermophilic nature of composting process is widely claimed to be effective in reducing the number of viable organisms present. The temperature is the most critical factor. A temperature in excess of 56deg c will usually be sufficient to inactivate 99% or more of E- coli, faecal streptococci and salmonella spp. Polio virus is also destroyed at similar temperatures in as short a time as thirty minutes. At higher temperatures even better pathogen removal is obtained. For example, mycobacterium tuberculosis will be killed by a temperature of 65deg c after fifteen days exposure. Some of the thermophilic fungi are classified as secondary pathogens. This means that they may infect individuals who are already infected by other pathogens or who are particularly susceptible to respiratory complaints. Airborne spores of Aspergillus fumigates are frequently found in the vicinity of composting windrows. A number of antigenic substances having a microbiological origin may also be found associated with the dust particles. Aspergillus
  • COMPOSTING Page 25 flavus, which produces aflatoxin , a potent human carcinogen, may be found in composting processes, Any adverse effects caused by the composting organisms themselves are likely to be highly localised, so that there will be no threat to residential areas.
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