A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1992

The feasibility of anaerobic treatment for low strength domestic wastewater was investigated using a semi-pilot scale UASB reactor of 126 l volume and 4 m height. This experiment was a continuation of the previous experiment conducted by Lalit Agrawal and H. Harada. The domestic digested sludge was used as seeding. The results reveals that an anaerobic treatment such as UASB is effective in treating domestic wastewater and is able to maintain a large amount active microorganism and effective removal of TSS. The duration of the present experiment was about 7 months. About 92% .COD reduction can be achieved under ambient temperature with a HRT of 3 hr and organic loading of 4 kg-COD/m3 - d. The average methane production was 141 Nl/kg-COD removed. This process also gave a high removal efficiency of COD(about 90 %) for lower strength of 300 mg-COD/L According· to the results obtained, the anaerobic treatment of domestic wastewater appears to be an attractive proposition for tropical countries. A morphology of sludge was examined by Scanning Electron Microscopy and Transmission Electron Microscopy. The granular sludge contained diverse groups of microorganisms whereas rod- type Methanothrix-like cells prevailed inside the granules.