SE--Structures and Environment 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 1·6 d. The secondary reactors were operated with hydraulic retention times of 0·8, 1·6, and 3·2 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 1·6 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 mgl-1 (COD=80 mg l-1) and 36 mg l-(COD=112 mg l-1), respectively. To examine the enhanced stability provided by the sequential reactor approach, the dual-reactor system was overloaded at 3·5 times the normal COD concentration (8000 mg l-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.