In this article we will discuss about:- 1. Kinetics of Composting 2. Moisture Content Essential for Composting 3. Design Criteria for Building a Compost Heap 4. Practical Applications of Composting.
Kinetics of Composting:
The aerobic composting of all the municipal refuse plants are operated on aerobic process.
Biochemistry:
The biochemistry or the rate at which organic matter decomposes is affected by the carbon-nitrogen relationship of the organic matter, moisture content, temperature, availability of oxygen, and the pH. The effects of these environmental factors on the decomposition of organic matter will help one to better understand the composting process.
The biochemical reactions during composting are ate also influenced by the moisture content of the organic matter. The optimum moisture content should be 100%, but this is impractical because the composting systems are based on the principle of dry handling. The maximum moisture content, therefore, is predicated on the ability of the composted material to be stacked.
The optimum moisture content for greatest decomposition should be maintained between 50 and 60% (wet weight). Moisture content above 60% causes compaction of the material and also fills the voids with water, thus reducing the amount of air present. This may cause anaerobic conditions to occur, giving off foul odors and slowing down the decomposition process.
If this occurs, it is necessary to mix the compost in order to supply oxygen and restore the process to aerobic conditions.
Under aerobic conditions, it is also important for the composted material to form interstices which entrap air when the windrow is formed or the material is mixed. If these spaces are filled with water, no oxygen is available to the organisms. If composting is to be done anaerobically, a high moisture content is a desirable condition and can be obtained by saturating the windrow before sealing.
If the moisture content falls below 50%, high temperatures occur in the center of the pile. The high temperatures begin to destroy the microorganisms, seriously curtailing the decomposition process. The problem can be corrected by adding water to the organic matter to raise its moisture content.
Carbon-Nitrogen Balance:
Carbon to nitrogen ratio controls the rate at which composting proceeds. As composting begins, the microorganisms require carbon as a source of energy for growth and nitrogen for protein synthesis.
A C/N ratio above this range results in a slowdown of the composting process. If the carbon is present in a form highly resistant to bacterial attack, the C/N ratio can exceed the optimum level indicated. Examples of material that have a large percentage of carbon in a resistant form are paper, fiber, wood, and straw. The C/N ratio and hence the time required for composting can be lowered by adding a nitrogen source such as manure or activated sludge.
A low C/N ratio results in the loss of nitrogen as ammonia. The loss of nitrogen is not detrimental to the composting process, one should attempt to conserve the nitrogen as a soil nutrient.
Ideal C : N Ratio in Heap:
The art of making successful compost is largely associated with achieving a correct C : N balance. 30 parts carbon to 1 part nitrogen is ideal which reduces to 10-15:1 when turned into mature content. Fine grass mowings on their own will produce a treacly mass result, so straw, leaves or, possibly, cardboard would be good companions. If you include too much woody material such as bark and pruning’s without balancing this with sufficient green matter, the pile may not heat up at all.
A compost heap, in fact, is somewhere between a bonfire and nature’s own method of decomposition, which is a slow rotting process culminating in incorporation by worms into the soil when breakdown is completed. By speeding up the decomposition process one can increase a soil’s fertility very quickly, especially by making a well aerated heap where oxygen-loving organisms can flourish.
As composting proceeds, the C/N ratio continuously decreases with time, since the nitrogen remains relatively constant and the carbon is released as carbon dioxide gas. The compost is considered ripened once the C/N is lowered to a value between 12 and 20.
Moisture Content Essential for Composting:
Moisture is essential for microbial activity. In a dry summer the heap will definitely need some, preferably, added every so often while you are constructing it. Ingredients should be pretty damp. Too much moisture is unlikely at the time of making the heap, but it should be protected from rain with polythene on top.
Indore Composting Method:
The Indore Composing Method is an ideal system of preparing organic manure or compost which replaces chemical fertilizers and enhances the crop-yield, without any ill side- effects.
Stalks of cotton, maize, millet and the pulses (Ideally they should be chopped to a particle size below 2 inches) are used. Start building the heaps by laying a lattice of old branches at the bottom. Divide the base area of the heap into a 6 (roughly equal) transverse sections, five of which are filled and one left vacant. Make each section of 7 layers of 9 inch thickness. In a 9 inch layer, have 4 inches of dry waste, 3 inches of green weeds and leaves, 2 inches of manure and a sprinkling of urine-earth-wood ash.
Make ventilation holes after completing two layers of a section. Take a 6-8 ft long pole with a 2 inch diameter and probe vertically through the working, gradually increasing the size of the hole to 4 inches by waggling the pole. See that the pole remains in its position and ensure that the air-vent continues to the top of the completed section. The first pole should be at a distance of not more than 2 feet from the heap, with a maximum distance of 4 feet between two successive holes.
Continue building of the section up to a height of 5 feet, after establishing the air vents. Build five sections in the similar manner, leaving the sixth one vacant (The sixth one is utilized while turning the heap). Water the heap, lightly, just after completion and again the next morning.
The central portion of the compost heap gets heated to its maximum temperature, within one week of its completion. The material in the cooler region composts slowly and the weeds, seeds and diseased material may not be completely decomposed. Hence, it is vital to turn the heap so that the cooler top, bottom and sides get mixed back into the middle of the new heap, once the temperature at the centre begins to drop. Turning also facilitates thorough mixing of the ingredients and their aeration.
Carry out the first turning two weeks after construction of the heap. Put the top 9 inches from section 5 into the floor of section 6, mixing it in the process. Cover it with the next 9 inch layer and water it. Reestablish the air vents before proceeding further. Switch section 4 to Section 5, once Section 5 is completely turned over into Section 6. Keep turning over each section into the next one, leaving Section -1 blank.
Carry out the second turning after 3 weeks. A third turning is realized only if the original materials are recognizable, after 9 weeks. It takes around 12 weeks for final composting, though a little longer during monsoons. The final product has a pliable texture, an earthy smell and is dark brown or grey in colour. This matured compost is half of its original volume as it simply shrinks due to the cooling process.
Ingredients to Avoid:
Organic material that should not be included in a compost pile like:
(i) Residue from crops that have been sprayed with pesticides or herbicides;
(ii) Material diseased with rusts and viruses;
(iii) Meat scraps from the kitchen unless the compost heap is well protected from flies and vermin;
(iv) Material with hard prickles or thorns;
(v) Persistent perennial weeds, to avoid any chance of these weed spreading they should be killed, burning or spreading out in the sun so that they dry out completely are two methods for achieving this.
1. Para-Toxics:
Materials, which definitely should not find their way into your heap include all metals, rubbers, glass and plastics – even so – called biodegradable plastic will endure for many years. Large quantities of newspaper and cardboard will greatly slow the rotting process.
Also inadvisable is diseased plant material, such as brassica stalks infected with club root, or white rot on onions, leeks or garlic. Potato blight, however, can be safely composted. If your heap does not meet these criteria it is safest to burn suspicious material.
2. Temperature:
Temperature is a key environmental factor and indicates the amount of biological activity taking place. The temperature within a compost pile is affected by moisture content, oxygen availability, and microbial activity. A drop in the temperature may indicate the material needs to be moistened or aerated or that the decomposition is in a late stage of activity.
3. Oxygen Availability:
Oxygen is essential to maintain aerobic conditions. An ample supply of atmospheric oxygen throughout the compost pile at all times is necessary. Oxygen can be incorporated into windrows by turning or by thoroughly mixing with mechanical means. The windrow should be turned once every 3 to 4 days to maintain aerobic conditions.
Oxygen is added to enclosed digesters through continuous tumbling, stirring action, or through forced aeration. It is difficult to determine the true oxygen requirement because it is influenced by temperature, moisture content, and the bacterial population. It may be done by using the chemical oxygen demand (COD) as a means of measurement.
4. pH:
During the decomposition process, changes in pH occur. At initial stage the material is slightly acidic because as composting proceeds, acid-forming bacteria cause the compost to become more acidic, thus lowering the pH. The microbes in the compost then begin to metabolize the inorganic nitrogen to ammonium nitrogen, causing the pH to rise rapidly.
At this stage the compost becomes alkaline. As decomposition continues, the ammonia may be released to the atmosphere or converted to nitrates. The nitrates are lost by leaching or by denitrifying bacteria, rendering the compost nearly neutral or slightly alkaline.
Microbes Involved in Composting:
Transformation of biological material is carried out by microbial flora. They requires moisture, heat and, depending on the type of production operation chosen, air. A single gram of compost will contain up to a billion bacteria, 100 million actinomycetes, a million fungi, algae, protozoa and others in their hundreds of thousands.
Activators of Biodegradation:
Animal manure is used to enhance the heating process; it must be fresh rather than already rotted. Fresh manure activates by seeding the heap with bacteria. If enough is added it will also bring a lot of heat into the compost heap. This can be very useful in winter when it is cold and there is a shortage of green matter to engender heat.
The right bacteria can also be introduced by adding some of last time’s compost as the heap is constructed. Commercial activators are unnecessary if the above conditions are met, but you might find it interesting to experiment with herbal products, which definitely make a difference. Packaged bacterial activators are also available but since the types of bacteria at work vary with the temperature, air conditions and other factors, these may be of limited use.
Composting is the conversion of biodegradable organic matter to a stable product called humus. The microbes involved include bacteria, fungi, and actinomycetes. During aerobic composting there is a continual change in the qualitative and quantitative nature of the microbial population. At first, fungi and acid-producing bacteria appear, causing the temperature to rise (mesophilic range). When the temperature rises above 40°C, these microbes are replaced by thermophilic bacteria, actinomycetes, and thermophilic fungi.
i. Bacteria:
Both mesophilic and thermophilic bacteria play an important role in the composting process. The mesophilic bacteria predominate during the initial and final phases of decomposition when temperatures are below 40°C.
ii. Actinomycetes:
They exist in the thermophilic region and they utilize hemicellulose but not cellulose. Thermophilic actinomycetes are capable of decomposting cellulose. Thermophilic actinomycetes can grow at temperatures up to 72°C.
iii. Fungi:
They appear in both the mesophilic and the thermophilic stages of composting, mesophilic fungi utilize the simple carbon substrates as their source of food. During the late stages of decomposition they utilize some cellulose and hemicellulose. Thermophilic fungi are less temperature tolerant than the thermophilic bacteria or actinomycetes. They operate in the range of 40°C to 60°C. Above 60°C, thermophilic fungi will die off.
Design Criteria for Building a Compost Heap:
During designing there are a number of factors which influence the process like, the type of amount of compost to be treated, the climate, land availability and handling.
i. Type and Amount of Compost:
The type and amount of compost to be treated is the first factor that must be considered. The type of compost will depend upon the livestock produced and the compost collection system employed.
In order to build a managed compost heap sufficient organic material must be collected together. It may be possible to collect some of the material needed for the compost heap, such as soil or crop residues, on the day of building the heap. However, the majority of the organic ingredients, e.g., kitchen compost, have to be collected on a regular or day-to-day basis.
The materials collected before the day of composting need to be kept dry, cool and without ready air circulation. This will reduce decomposition. Putrescible material should be kept covered to prevent fly breeding. Suitable ways to keep the material dry would be to cover with banana leaves or a grass thatch.
ii. The Climate:
Since temperature and moisture affect the composting process, climatic conditions must be taken into account. For example, if a composting pile fails to heat up it may be due to either too much or not enough moisture. In extreme cases it may be desirable to add some sort of protective roof over the windrow. A protective cover will keep the rain and snow off of the windrow, prevent the hot sun from drying out the pile, and also retain much of the heat within the pile during cold weather.
iii. Availability of Land:
While designing for composting operation the factor of land availability should be considered. One should calculate the amount of land required for windrowing, curing the compost, and storing the finished product. The amount of land required, although relatively small, will depend upon the size of the operation and the size of the windrows constructed.
Spacing of the piles may be determined from the proposed mixing procedures and the space required for maneuvering when turning and stacking. The amount of land needed should be doubled to account for contingencies, such as the inability to finish the compost on schedule due to equipment breakdown or inclement weather. The space is also needed for curing and storing the compost. Since compost is generally applied to the fields in the spring and the fall, at least six months of storage space should be provided.
iv. Handling:
Generally speaking, composting can be carried out without the use of specialized equipment. In most cases, a front-end loader can be used to collect the manure, transport it and spread it into layers to construct the windrow. Manure spreaders are also useful for spreading the manure to form windrows.
Many households and farms or small holdings will have a site where organic compost is piled up as it becomes available. This unmanaged heap will produce compost. However, the compost takes a very long time to develop and will be of inferior quality to compost produced in a managed heap.
A managed compost heap requires considerably more planning and labour. However, the compost produced under this controlled system will be available for use far sooner than that from an unmanaged heap; nutrient loss will be kept to a minimum and, due to the heat production during the composting process, many weed seeds and disease organisms will be killed. Consequently, for many people the production of a reliably high quality compost justifies the extra work.
Practical Applications of Composting:
Although composting is not widely used as a means of treating livestock composts, there are some farmers that are using it quite successfully. Whether or not composting fits into one’s compost handling scheme is dependent upon the availability of labor, the degree of mechanization that can be afforded, whether the compost should be treated as a liquid or a solid, and how one plans to utilize the end products.