Investigation of various gases, pH and redox potential in mushroom composting Phase I stacks

Abstract

Investigations of hydrogen sulfide and ammonia concentrations, pH and redox potential were carried out within Phase I mushroom composting stacks in conjunction with measurements of temperature and oxygen concentrations. Gypsum-derived sulfate supported significant microbial activity by sulfate-reducing bacteria in anaerobic core areas. Ammonia concentrations up to 800 ppm were strongly associated with pH values up to 8.8 in aerobic stack areas. Anaerobic areas had pH values of 5-7, with little or no ammonia. Redox potential generally agreed with oxygenation history, with stacks exhibiting reducing conditions overall and with potential rising with compost maturity. Anomalously negative redox potentials in aerobic, outer stack areas were associated with actinomycete colonisation. Physical factors such as temperature, oxygen availability and water potential, which determine microbial and chemical activity in stacks, are distributed very unevenly, both spatially and temporally.