Best Practices in Composting
- • Organic materials to be composted must be separated from non-organics which may be recyclable; reduced in size to increase the surface area which allows for greater biological activity in the material: and mixed thoroughly to get an even distribution of nutrients, moisture, and oxygen. The first separation should be done by the citizens putting out the waste.
- • The organic materials for composting should be taken to a centralized separation system which will further recover recyclable or combustible materials, and the visible inert materials such as plastic and glass, and remove potentially hazardous materials that are visible. Screening mechanisms, magnetic separation, and manual separation may be necessary to accomplish this task. This is followed by size reduction of all materials before the compost process proceeds.
- • Use windrow composting when a system of natural convection and diffusion of oxygen works best for the community. The pile size, porosity, and frequency of turning to manage temperature control and oxygen levels can be altered as necessary to prevent anaerobic digestion. The pile is shaped like a haystack and is usually 300 feet or more long, 4.5-9 feet high, and 9-18 feet wide. This system must be placed on a layer of impermeable soil to prevent contamination of the groundwater. Forced aeration can be used if necessary, but this adds to the cost. This process is usually conducted outside but cannot be covered by a roof.
- • Use an aerated static pile when it is best for the community. It is shaped like the windrow, but it is not mechanically agitated. Process control occurs by use of pressure and/or vacuum-induced aeration using temperature or oxygen as the control variable. Often a layer of wood chips is placed below the pile and also on top of the pile. This process is usually conducted outside but can be covered by a roof.
- • Use an aerated static pile when it is best for the community. The pile is usually 12 feet high and can be placed in a silo or other large building. The original material is fed into the reactor at the top and is distributed evenly. It flows by gravity to the unloading mechanism at the bottom. Pressure aeration causing the airflow to be opposite to the downward material flow is the means of process control.
- • Use a horizontal reactor when it is best for the community. The horizontal reactor avoids the potential problems of high temperature, oxygen levels, and moisture gradients of the vertical reactor by having a short airflow pathway. The agitation system to turn the material is in continuous mode with materials being shredded to expose new surfaces for decomposition.
- • Develop a quality assurance program for the compost by utilizing a proper random sample collection system using multiple samples of sufficient numbers to determine the mean concentration of a specific contaminant in the feedstock and the finished compost product. Metal concentrations, hazardous chemical concentrations, plastic concentrations, and microorganism concentrations and types should be noted. The frequency of sampling and the timing of sampling are essential because different feedstock may be found at different times of the day, week, season, and year. These samples should be mixed thoroughly and homogenized prior to the removal of subsamples for evaluation of different contaminants. Samples should be collected only in clean plastic containers, refrigerated but not frozen, and delivered promptly to the analytic laboratory. Record keeping is absolutely essential at the processing plant and at the laboratory.
- • Establish a market to use the compost after it has been created.