Fundamentals of the static granular bed reactor

Abstract

The static granular bed reactor (SGBR) has been shown to be a highly efficient anaerobic system. High organic removal, low effluent suspended solids (TSS), and high methane content in the off gas were consistently obtained with all SGBRs operated. Two SGBRs treating non-fat dry milk, or synthetic wastewater, were operated continuously for more than four years at hydraulic retention times (HRTs) ranging from 36 h to 4 h, equivalent to over three solids retention time (SRT) periods. During the four years, effluent chemical oxygen demand (COD) concentrations were less than 50 mg/L and TSS concentrations were less than 30 mg/L under most conditions. Because of the exceptional performance when the SGBR treated synthetic wastewater, the performance was examined under more stressful operating situations. SGBR performance was evaluated while treating wastewater with high sulfate concentrations, during HRT transitions, and at fractional bed volumes. In stressed circumstances, the SGBR continued to operate efficiently. The addition of sulfate had little effect on the SGBR system, and the overall COD removal was greater than 90% and effluent TSS concentrations were less than 70 mg/L. During HRT transition, the SGBR was relatively unaffected immediately after the HRT was changed from 36 h to 5 h. A slight decrease in COD and TSS removal was observed during the first 12 hours after the HRT change, but operation returned to greater than 90% COD removal in about 24 hours. The SRT of the SGBR appears to be relatively unaffected by changes in HRT. The SGBR also showed outstanding organic removal when operated at a fraction of the design bed volume. Four SGBRs were operated at 25%, 50%, 75%, and 100% of the