Environmental impacts of farm-scale composting practices

Because of its agronomic benefits, farm-scale composting is an efficient means of recycling agricultural waste. Composting process is an aerobic degradation of fresh organic matter in mature compost. Nevertheless, according to the literature, composting may induce some environmental problems. The environmental impacts of composting will be described, along with an assessment of farm-scale composting practices which play a major role in pollution. The main environmental components potentially affected by composting pollution are air and water. Various gases released by composting, such as NH3, CH4 and N2O, can impact air quality and are therefore studied because they all have environmental impacts and can be controlled by composting management. The effect on water quality can be evaluated by considering loss of NO3-, NH4+, organic compounds and PO43-. Technical evaluation criteria for the impact of farm-scale composting on the air are determined from the physical and chemical characteristics of the raw materials, the use of additives, the turning method and frequency and the duration of the composting operations. Regarding water, the weather conditions at the beginning of the composting operation, the location of the heap, the protection against rain, the water addition during the process, the use of covers and the recovery of leaching and runoff water are also taken into account. The two main practices which control the air and water pollution from composting are: the choice of the raw material which influences gas emissions and the choice of composting location which have an high effect on losses by leaching and runoff.