COMPARISON OF STARTUP PERFORMANCE OF 4 ANAEROBIC REACTORS FOR THE TREATMENT OF HIGH-STRENGTH WASTE-WATER

An experimental study was carried out to compare the startup performan ce of four equal-volume anaerobic reactors of different design operate d in parallel at 37-degrees-C. The four reactors, namely, (a) upflow a naerobic sludge blanket (UASB), (b) hybrid of UASB and anaerobic filte r, (c) fluidized bed and (d) expanded bed, were seeded with sludge fro m the anaerobic digester of a local municipal wastewater treatment pla nt and tested with synthetic wastewater comprising milk and sucrose wi th balanced nutrients and trace metals. The volumetric COD loading was increased gradually from the initial 0.5-1 g L-1 d-1 to 20 g L-1 d-1 after 70 days. During this startup period, the COD levels in wastewate r were gradually increased from the initial 500-1000 mg L-1 to 6500 mg L-1, whereas the hydraulic retention time (HRT) was reduced from 24-4 8 h to 8 h. After the acclimation, the four reactors were tested at th e loading rate of about 20 g L-1 d-1, but at three different levels of COD (6000, 4000, 2600 mg L-1) and HRT (8, 5.7, 3 h). The percentage o f COD removal from wastewater in an anaerobic reactor appeared to be m ainly dependent on the volumetric COD loading rate, and relatively ins ensitive to the COD level in wastewater and the HRT. At the COD loadin g rate of about 20 g L-1 d-1, COD reduction was about 95% for the UASB and the hybrid reactors, but was about 80% for the fluidized bed and expanded bed reactors.