Effect of temperature on bacterial species diversity in thermophilic solid-waste composting

Abstract

Continuously thermophilic composting was examined with a 4.5-liter reactor placed in an incubator maintained at representative temperatures. Feed was a mixture of dried table scraps and shredded newspaper wetted to 55% moisture. One run at 49°C (run A) employed a 1:4 feed-to-compost ratio, while the other runs used a 10:1 ratio and were incubated at 50, 55, 60, or 65°C. Due to self-heating, internal temperatures of the composting mass were 0 to 7° C hotter than the incubator. Two full-scale composting plants (at Altoona, Pa., and Leicester, England) were also examined. Plate counts per gram (dry weight) on Trypticase soy broth (BBL Microbiology Systems) with 2% agar ranged from 0.7 x 109 to 5.3 x 109 for laboratory composting and 0.02 x 109 to 7.4 x 109 for field composting. Fifteen taxa were isolated, including 10 of genus Bacillus, which dominated all samples except that from run A. Species diversity decreased markedly in laboratory composting at 60°C and above, but was similar for the three runs incubated at 49, 50, and 55°C. The maximum desirable composting temperature based on species diversity is thus 60°C, the same as that previously recommended based on measures of the rate of decomposition.