Anaerobic Decomposition of Swine Manure and Ammonia Generation in a Deep Pit

Abstract

This article reports a laboratory study of swine manure decomposition in a deep pit. Distributions of solids, organic matter, pH, and ammonia in fresh swine manure after 12 h settling in a 1.2 m column were characterized, and solids reduction and ammonia generation rate during 28 d anaerobic decomposition were determined by using the manure initially having 1.8% and 3.3% total solids content (TS). In the settled manure, the pH became lower toward the bottom of the pit where manure solids and organic matter became concentrated, and the pH of bottom manure layer was 0.5 and 0.9 unit lower than the pH of top manure layer for the manure initially having 1.8% and 3.3% TS, respectively. Ammonia distribution in the manure was relatively uniform. The manure started to decompose rapidly after excretion from pigs. During the 28 d decomposition period, the solids contents of bottom manure layers were reduced linearly with time, and ammonia increased logrithmically with time. Higher temperature resulted in higher solids reduction and ammonia generation rate in the manure. The TS of bottom layer manure was reduced by 15% at 20C and 27% at 30C by the end of the 28 d period. The determination methods and prediction equations for ammonia generation rates in discrete layers of decomposing manure are presented.