Comparison of startup performance of four anaerobic reactors for the treatment of high-strength wastewater

Abstract

An experimental study was carried out to compare the startup performance of four equal-volume anaerobic reactors of different design operated in parallel at 37°C. The four reactors, namely, (a) upflow anaerobic sludge blanket (UASB), (b) hybrid of UASB and anaerobic filter, (c) fluidized bed and (d) expanded bed, were seeded with sludge from the anaerobic digester of a local municipal wastewater treatment plant and tested with synthetic wastewater comprising milk and sucrose with 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 wastewater 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 24–48 h to 8 h. After the acclimation, the four reactors were tested at the 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 of COD removal from wastewater in an anaerobic reactor appeared to be mainly dependent on the volumetric COD loading rate, and relatively insensitive to the COD level in wastewater and the HRT. At the COD loading 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.