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 laboratory with two-stage anaerobic sequencing batch reactor (ASBR) systems. The effects of anaerobic treatment on odor control in subsequent manure storage units were evaluated. One thermophilic (55°C) mesophilic (35°C) system (II) was evaluated against one mesophilic (35°C) mesophilic (35°C) 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 thermophilic-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 both systems were effective in reducing the generation of odorous sulfur gases during storage. The untreated dairy and swine manure exhibited strong offensive odors with high hydrogen sulfide (H 2 S) and mercaptan concentrations detected in the headspaces of storage jars. The anaerobically treated manure, however, showed minimal residual odors while in many cases, H 2 S and mercaptans were not detectable. With the consideration of its better capability for destructing fecal bacteria in animal manure, the thermophilic-mesophilic ASBR system is more advantageous than the mesophilic-mesophilic ASBR system for treating animal manure. However, the higher energy requirement for heating the reactors in the former system needs to be considered when selecting thermophilic vs. mesophilic anaerobic digestion systems. Keywords. Anaerobic digestion, Anaerobic sequencing batch reactors, Odor control, Dairy, Swine, Manure.