Nitrate Effects on the Anaerobic Sequencing Batch Reactor Treating Swine Wastes

Abstract

The Anaerobic Sequencing Batch Reactor (ASBR) is a new technology that is able to efficiently treat swine waste. This technology was developed by Dr. Richard R. Dague and coworkers at Iowa State University. Previous studies with swine waste have shown that the ASBR system can achieve higher volatile solids destruction and methane yields when compared with other systems treating swine waste. The ASBR has been incorporated into a scheme that would allow for the recycling of treated flush/wastewater from confinement facilities. This scheme includes an aerobic unit which would be used to “freshen up” the waste by converting sulfides and ammonia to both sulfates and nitrates. This recycled waste would be high in nitrates which could possibly inhibit methanogenesis in the ASBR through denitrification. To study the effects of denitrification in the ASBR being fed swine waste two 12-L lab-scale ASBR reactors were constructed for this study. Both of the reactors were fed swine waste at a 3 g VS/L/day loading rate and had a 4 day hydraulic retention time. One of the reactors was operated as a control while the other reactor was fed nitrate concentrations of 20, 40, 80, 160, 180, 240, 320, 480, and 720 mg/L as N. Performance data collected included chemical 23oxidation demand (COD) removal, volatile fatty acid concentrations, nitrogen production, ammonia concentrations, nitrate and nitrite concentrations, methane production, and oxidation reduction potentials. Denitriflcaton was observed to occur within 3 hours of introduction of nitrate. Nitrate readings taken at the end of each cycle showed virtually no nitrate in the effluent indicating complete denitrification. Also, COD removals showed no adverse effect from the introduction of nitrate.