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Effect of Temperature Control on the Composting Process¹

ABSTRACT

Aeration is a method for controlling temperature in composting of organic materials so that microbial activity can be optimized. To determine the conditions for optimum composting, two studies were conducted using a self-heating laboratory composter in which aeration at two constant rates was evaluated and aeration at constant rate vs. aeration in response to temperature was evaluated. A mixture of raw, limed sewage sludge and woodchips (v/v, 1:1.8) was composted and CO₂-C and wet and dry weight losses were recorded. Numbers of thermophilic bacteria, fungi, and actinomycete were determined in the mixture before and after composting. Comparison of composting at rapid constant aeration rates of 900 and 1800 m³ h^–1 Mg^–1 indicated no difference in losses of CO₂-C, NH₃-N and moisture in composting runs of 12 and 14 d. Single peak temperatures between 60 and 68°C were recorded. In comparing constant aeration with that of temperature response, twice as much moisture was lost and 2.5 times as much CO₂-C evolved from the latter where temperatures were not allowed to exceed 55°C. Because both dry weight and N losses were increased similarly in the temperature response system, the final total N content of the compost was near that of the compost resulting from the constant aeration system. The total number of thermophilic microorganisms was greater in the final compost from the temperature response study, but more significantly, the population of fungi was substantially larger than in the compost from the constant aeration study. Control of composting by adjusting aeration in response to temperature as opposed to composting by constant aeration resulted in a drier, more stabilized compost for agricultural or horticultural use.

Key Words: fungi • carbon dioxide • moisture • nitrogen

¹ Contribution from Soil-Microbial Systems Laboratory, Agricultural Environmental Quality Inst., USDA-ARS, Beltsville, MD 20705.

² Microbiologist, USDA-ARS, and research associate-chemist, Maryland Environmental Service, Annapolis, MD 21401.

Received for publication July 30, 1984.