Heat production profiles from batch aerobic thermophilic processing of high strength swine waste

Abstract

AbstractThe literature reports several cases where biological wastewater solids or swine wastes have been aerobically oxidized at thermophilic temperatures. Although the heat generated is reported, little information is given about the heat production profiles with time and average values reported for the overall runs. These studies have also generally been in the medium‐to‐low concentration ranges for swine processes. This paper reports on work done in a laboratory batch reactor with the objectives of generating the actual heat release time profiles in higher strength swine wastes (6 to nearly 10% total solids). Significant amounts of heat were generated, and the amounts generated were determined by two methods [total solids removal calorimetry and chemical oxygen demand (COD) removal] with good agreement. Linear models were constructed showing that the biological heat production is strongly related to the specific air flow rates through the reactors and the interaction between air flow rate and solids or COD concentrations. At 55° C, nitrification was not detected and the nitrogen in the waste was converted to ammonia, which subsequently strips into the exhaust air. In some cases, ammonia was recovered with acid absorbers. In the 2.0‐L reactor with 1.2 L of reaction mixture, energy production rates ranged from 0.7 to 2.43 W and COD removal ranged from 28.5 to 62.7% with a common residence time of 6 days. © 2005 American Institute of Chemical Engineers Environ Prog, 2005