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

Thesis (M.Eng.) - Asian Institute of Technology, 1996

Feasibility of a 21.5-L bench scale upflow anaerobic sludge blanket (UASB) reactor at ambient temperature was investigated for the anaerobic treatment of starch industry wastewater. The reactor was seeded with sludge obtained from anaerobic pond treating the starch wastewater. The reactor startup lasted for about 6 weeks. The neutralized feed was initially diluted to about 2,000 - 3,000 mg/Land was fed at organic loading rate (OLR) upto 8 kg CODf/mr3/d. Low upflow velocities upto 0.24 m/hr were maintained and no recirculation was employed upto 25 days to initiate the wash out of lighter fraction of seed sludge. The feed concentration and OLR were increased in steps as soon as COD conversion was higher than 80%. By the end of the startup period, VF A concentration in effluent was less than 500 mg/L while gas production rate of 100 Lid was obtained. After successful startup, undiluted supernatant wastewater with COD concentration of 12,000 - 24,000 mg/L was fed into the reactor at OLR of 10 - 16 kg CODrlmr3 /d. The upflow velocity was increased upto 0.5 m/hr to facilitate effective mixing of sludge granules while recirculation ratio was maintained at 4: 1. COD conversion efficiencies more than 95% and gas productivity of 5-8 m3/mr3.d were obtained during the steady state operation. About 83 . 6% of COD removed was converted into methane. The VSS/TSS of sludge increased from 0.42 at the beginning reactor startup to 0.86 towards the end, while specific methanogenic activity improved from 0.03 at the beginning of reactor startup to 0.7 kgCH4-COD/kgVSS/d towards the end of the study.