A dual-reactor anaerobic system for complete treatment of a food processing waste

Anaerobic technologies are commonly employed for the initial treatment of food processing wastewater; however, they are not typically considered capable of treating wastewater to meet final discharge requirements. To assess the potential of anaerobic technologies to meet discharge requirements, the performance of two dual-reactor high-rate anaerobic systems fed with confectionery wastewater was investigated. The primary reactors in the system were operated at constant hydraulic retention times of 1 times 6 d. The secondary reactors were operated with hydraulic retention times of 0 times 8, 1 times 6, and 3 times 2 d. The secondary reactors, which were both downflow anaerobic filters, achieved maximum chemical oxygen demand (COD) removal rates when operated at a hydraulic retention time of 1 times 6 d. The brick-filled downflow anaerobic filter and the plastic-ring-filled downflow anaerobic filter produced average effluent five-day biochemical oxygen demand concentrations of 26 mg l super(-1) (COD=80 mg l super(-1)) and 36 mg l super(-) (COD=112 mg l super(-1)), respectively. To examine the enhanced stability provided by the sequential reactor approach, the dual-reactor system was overloaded at 3 times 5 times the normal COD concentration (8000 mg l super(-1)) for an 8 h period. The secondary reactors were able to accommodate the increased organic loading emitted from the primary reactors, maintaining an overall removal efficiency of > 994%. The results suggest that full anaerobic treatment of readily degradable food waste streams may be realistic, and that a sequential reactor approach significantly enhances overall process stability.