Effects of Temperature on Methanogenesis in a Thermophilic (58°C) Anaerobic Digestor

S. H. ZINDER,* T. ANGUISH, AND S. C. CARDWELL
Department of Microbiology, Cornell University, Ithaca, New York 14853
Received 30 September 1983/Accepted 30 January 1984

The short-term effects of temperature on methanogenesis from acetate or CO2 in a thermophilic (58°C)
anaerobic digestor were studied by incubating digestor sludge at different temperatures with 14C-labeled
methane precursors (14CH3COO or 14CO2). During a period when Methanosarcina sp. was numerous in
the sludge, methanogenesis from acetate was optimal at 55 to 60°C and was completely inhibited at 65°C.

Methanosarcina culture isolated from the digestor grew optimally on acetate at 55 to 58°C and did not grow
or produce methane at 65°C. An accidental shift of digestor temperature from 58 to 64°C during this period
caused a sharp decrease in gas production and a large increase in acetate concentration within 24 h,
indicating that the aceticlastic methanogens in the digestor were the population most susceptible to this
temperature increase. During a later period when Methanothrix sp. was numerous in the digestor,
methanogenesis from 14CH3COO- was optimal at 65°C and completely inhibited at 75°C. A partially purified
Methanothrix enrichment culture derived from the digestor had a maximum growth temperature near 70°C.
Methanogenesis from 0CO2 in the sludge was optimal at 65°C and still proceeded at 75C. A C02-reducing
Methanobacterium sp. isolated from the digestor was capable of methanogenesis at 75°C. During the period
when Methanothix sp. was apparently dominant, sludge incubated for 24 h at 65°C produced more methane
than sludge incubated at 60°C, and no acetate accumulated at 65°C. Methanogenesis was severely inhibited
in sludge incubated at 70°C, but since neither acetate nor H2 accumulated, production of these methanogenic
substrates by fermentative bacteria was probably the most temperature-sensitive process. Thus, there
was a correlation between digestor performance at different temperatures and responses to temperature by
cultures of methanogens believed to play important roles in the digestor.