Sequential Two-stage Anaerobic Treatment of Confectionery Wastewater

A bench-scale, two-reactor sequential anaerobic treatment system was tested for its ability to remove organic carbon from confectionery wastewater. The system consisted of an upflow anaerobic sludge blanket operated at 35°C followed by a downflow anaerobic filter operated at ambient temperature (∼ 25°C). The system had a total hydraulic retention time of 2·4 d. Reactor performance was characterized by monitoring chemical oxygen demand (COD), pH, volatile fatty acid concentration, alkalinity and biogas production and composition. An overall COD treatment efficiency of 98% was observed for the system, at an overall organic loading rate of 12·5 kg/m3/d (as COD). The upflow anaerobic sludge blanket worked extremely well at high organic loadings (COD added at 20 kg/m3/d). Effluent recycle enabled the upflow anaerobic sludge blanket to operate with influent COD concentrations up to 30 g/l. The downflow anaerobic filter maintained effluent COD concentrations below 400 mg/l, and effectively buffered fluctuations in the effluent of the upflow anaerobic sludge blanket reactor.