Feedstock synthesis

Operation

Step 2: Preparing Feedstock.

This step refers to the changes made to the feedstocks’ physical and chemical characteristics in order to provide optimal conditions for active composting. This may involve grinding to change particle size, blending to ensure the feedstocks are homogeneous
, or adding amendments or other materials to adjust physical or chemical characteristics of the feedstocks.  A Deer compact wheel loader 624K of 4 m3 capacity uplift the feedstock and the bulk agent (sawdust). After that place them in large mixer with vertical augers to grind them.

Step 3: Active zone

Once the feedstocks have been amended and mixed with other materials, they are placed into the Areated static pile pile that has dimension of H= 1.5 m , W= 3m, L= 17m where active composting takes place. There are 8 piles will be constructed, each pile handle 75m3 weekly.  Total area and calculations for piles are in appendix A.

When the optimal oxygen, moisture, and nutrient levels are present, the biological activity can raise the feedstock mixture’s temperature from ambient levels into the 55 to 65°C range within 24 hours. Most pathogenic bacteria, viruses, and parasites are inactivated when exposed to temperatures in excess of 55°C for 3 or more consecutive days.  However, the temperatures encountered during active composting can also cause large quantities of water to evaporate from the composting piles. If this loss of moisture is not properly managed, and the moisture content of the material is allowed to drop below the optimal range (i.e., 55 to 65%), then the microorganisms are impeded, and the composting process slows down. If feedstocks are allowed to dry out too much (i.e., less than 40% moisture), they may also become a source of dust, increasing the risk of fires and causing health issues for site staff and visitors.

Step 4: Curing.

This step involves microorganisms converting carbon into carbon dioxide and humus, and nitrogen into nitrates, which is a much slower biological process. Microorganisms begin to decompose more complex organic structures, such as the lignins and cellulose contained in paper, wood, and plants, and stable humic substances are formed in the curing piles. Climatic conditions are also relevant, because curing activities generally occur outdoors. Since ambient temperatures directly affect the level of biological activity, the curing step may be partially or completely interrupted by cold, winter temperatures as microorganisms in the curing piles become dormant. If there are pockets of cold temperatures, the curing step can take 8 to 12 months.  In this process, only need is a space to cure composite as windrows.

Step 5: Final Screening.

This step involves refining the cured compost before it is sold or used so that it is a more suitable soil amendment. Most commonly, this involves passing the material over 1- to 1.25-cm screens to remove oversized materials, such as large compost particles, stones, and uncomposted bulking agents (which can be reused in the active composting step). Screening can also remove some of the remaining physical contaminants that may be present, such as glass or metal pieces.

Step 7: Storing.

Properly storing the finished compost product is the final step of the composting process. Whether compost is in bulk form or placed in bags, it should be stored in a manner that prevents dust or odours from developing, and prevents contamination of the product from weeds, leachate, or other contaminants. For example, large stockpiles of finished compost can become a source of odours if they are saturated with rainfall, and can quickly become infested by weeds. Fire prevention and control should also be considered in finished product storage areas, since compost can be a fuel source.

Composite Management Parameters






oxygen concentration:

The oxygen exists and permeates through the air voids between individual particles within the composting pile Oxygen consumption is highest during the first two to three weeks of active composting, when bacteria populations are at their largest, and is then reduced as the size of the microorganism populations decline later in the active composting step and during curing. Since oxygen demand cannot easily be measured
in the field, the oxygen concentration (also referred to as oxygen levels and oxygen content) in the
compost pile’s pore spaces is used as a monitoring and control parameter. Oxygen concentrations can be measured in a matter of seconds using probes that are manually inserted into the pile. The target oxygen concentration during all stages of the composting process is 13 to 18%. Moreover, corrective action should be taken when oxygen falls below 10%.  In this project there is distribution piping air systems with blower and controller to manage and documented temperature of composite.

Photo 1 : Specialized instruments are used to measure oxygen levels in compost
Piles:








Free Air Space, and Particle Size and Structure:

In composting, three controlled parameters are directly correlated to oxygen concentrations and decomposition rate time:

 Generally, FAS of 40 to 60% is required during the active composting step. It is possible to measure FAS in a compost sample, but the procedure requires the use of specialized instruments that are generally too cumbersome to be used in the field on a regular basis. Instead, bulk density is often used as an indicator of FAS. For example, the bulk density of feedstocks and amendments processed in an actively aerated composting system should be in the range of 475 to 590 kilograms per cubic metre (kg/m3 ). Don’t know how to test it.

The Size of individual particles affects the rate of decomposition. Smaller particles have a greater surface area relative to their volume, and more surface area means more of the material is exposed to microorganisms. Particles should typically be between 3 and50 mm in size.

Carbon to Nitrogen Ratio:

The optimal C: N ratio for the active composting step is between 25:1 and 30:1. If a material’s C:N ratio is less than 20:1, then the available carbon may be fully consumed before all the nitrogen is stabilized, and the surplus nitrogen can be converted to ammonia and lost as a gaseous emission. If the C:N ratio is higher, the composting process
proceeds, but at a slower pace, since the microorganism’s population size is limited by the lack of nitrogen. Since the C:N ratio of feedstocks does not always fall within the ideal range, it is a normal practice to blend several feedstocks together, or add amendments to feedstocks prior to the active composting step. For instance, a feedstock containing a large concentration of nitrogen, like food waste or green grass, would be mixed with one that contains a high concentration of carbon, like woodchips or newsprint, to arrive at a mixture with a C:N ratio in the optimal range. In fact, a compost recipe defines the relative quantities of feedstocks and other materials needed to achieve a mixture with the optimum C: N ratio, moisture content, and bulk density. Recipe development is an iterative process. Spreadsheets and commercially available software can be used for efficiencies. In this project the available bulking agent is sawdust that has a C: N ratio of 200-400:1.


Moisture Content:

Generally, outdoor systems tend to operate at the lower 55 to 60% range, but that may vary based on local climatic conditions. During the curing step, moisture levels are typically maintained between 45 and 55%, while during storage, moisture levels are typically in the 40 to 45% range.  less than 40% microorganism populations is inhibited, resulting in slower active composting and or curing. more than 65%), there is a risk that too much of the pore space between individual particles fills with water, which can prevent the efficient movement of air and lead to anaerobic conditions and unpleasant odours.

Moisture content is initially adjusted while preparing feedstocks for active composting by blending wet and dry feedstocks and amendments together. If the mixture of feedstocks and amendments is still too dry, potable water can be added. Moisture content is expressed as a percentage-by-weight basis. Accurate moisture content measurements
normally require drying samples of a material in a laboratory using specialized drying ovens. However, these drying methods can be approximated in the field using a microwave oven or a device used to measure moisture in wheat and barley grains (e.g., Koster Moisture Tester). The experience of various facility operators has shown that moisture probes commonly used for soils and wood do not provide consistently accurate results in compost.