Evaluation of two-stage anaerobic sequencing batch reactor systems for animal wastewater treatment

Anaerobic treatment of screened swine and dairy manure was studied in the l aboratory with two-stage anaerobic sequencing batch reactor (ASBR) systems. The effects of anaerobic treatment on odor control in subsequent manure st orage units were evaluated. One thermophilic (55 degrees) mesophilic (35 de greesC) system (II) was evaluated against one mesophilic (35 degreesC) meso philic (35 degreesC) system (I) at a system hydraulic retention time (HRT) of six days and four volatile solid (VS) loading rates (1, 2, 3, 4 g/L/day) . Generally: anaerobic digestion under all the test conditions resulted in higher solids reduction in swine manure than in dairy manure. The thermophi lic-mesophilic system had a better performance in treating dairy and swine manure with 6 to 15% more VS removal than the mesophilic-mesophilic system. The headspace gas analysis results using manure storage jars showed that b oth systems were effective in reducing the generation of odorous sulfur gas es during storage. The untreated dairy and swine manure exhibited strong of fensive odors with high hydrogen sulfide (H2S) and mercaptan concentrations detected in the headspaces of storage jars. The anaerobically treated manu re, however, showed minimal residual odors while in many cases, H2S and mer captans were not detectable. With the consideration of its better capabilit y for destructing fecal bacteria in animal manure, the thermophilic-mesophi lic ASBR system is more advantageous than the mesophilic-mesophilic ASBR sy stem for treating animal manure. However the higher energy requirement for heating the reactors in the former system needs to be considered when selec ting thermophilic vs. mesophilic anaerobic digestion systems.