Physical management and interpretation of an environmentally controlled composting ecosystem

Abstract

Compost for mushroom cultivation was prepared in an environmentally controlled composting(ECC) system of 10 t maximum loading. Early in processing, ventilation was manually controlled to provide aerobic conditions. When the desired compost temperatures were reached, control through temperature feedback was used. Physical uniformity of processing conditions was achieved by recirculating large volumes of air within the reactor. Heat production was found to peak early in the composting process, reaching a maximum of about 8-9 W/kg initial wet (67-71%) substrate. When compost temperatures were allowed to rise to 63�C, maximum heat production occurred at 55-63�C. Total heat production per initial wet weight averaged 1.23 MJ/kg (range 0.92-1.51 MJ/kg), or 5.11 MJ/kg (range 4.04-7.57 MJ/kg) when measured per initial volatile dry matter. Heat evolution averaged 18.3 MJ/kg decomposed (range 15.4-22.0 MJ/kg). Oxygen usage followed a pattern similar to that of heat production reaching a maximum in the 55-63�C range. Peak O2 usage was about 9 x 10-7 kg O2/kg composts, or in volume terms, 2.9 x 10-6 m3 Air/kg comp0st.s. During temperature feedback control, O2 levels were maintained at about 19%. The enclosed ECC system permitted mass balance data to be collected for various components. Trials demonstrated that temperature and O2 could be closely controlled, resulting in-good compost uniformity.