Effects of different temperature regimes on microbial activity and biomass in composting municipal sewage sludge

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Abstract
Municipal sewage sludge was composted under two different temperature regimes. The temperatures within the composting piles were regulated using a temperature feedback system controlling aeration fans which blew air up through the piles. Each composting run lasted about 2.5 weeks. In one part of the composting pile, the mean temperatures were kept below about 58 °C, while in the other part the mean temperatures reached 84 °C. Two experimental composting runs of this type were performed. In both cases the major treatment effect was the highly significant differences in microbial activity ([14C]acetate incorporation into lipids) per gram of compost or per unit of microbial biomass, with the low-temperature part of the piles having the greatest activity. Microbial biomass (measured as lipid phosphate) was greater in the low-temperature part of the pile by day 10 of the second composting run. The pH of the low-temperature piles also tended to increase more rapidly than that of the high-temperature piles. These results confirm other work in which increased rates of CO2 production were detected in materials composting at lower temperatures. It is suggested that the efficiency of batch composting processes is greatest at moderate temperatures (not exceeding about 55 °C), since higher temperatures greatly inhibit the growth and metabolism of the micro-biota.

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