A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

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

After studying various alternatives for the treatment of mungbeans starch wastewater, two stage treatment i . e anaerobic fol lowed by aerobic, was se lected . As a first stage, anaerobic pond, fixed bed reactor and up-flow anaerobic s ludge blanket (UASB) were studied. Activated s ludge process (ASP) and Aerated Lagoon fol lowed by High Rate Algae Pond (HRAP) were employed as second stage treatment. After studying the ex isting treatment system (pond system) at the factory, to establis h the effectiveness of anaerobic pond treatment, it was determined that the first anaerobic pond reduced the3 COD - m from 2000-6000 mg/l to about 700-900 mg/l at a loading of 0.35 kg COD/(m .d}. Lab-scal e reactors were operated at the factory. Anaerobic reactors were able to reduce the COD - m to less than 200 mg/l (average) and COD - f to less than 70 mg/l (average) irrespective of tye influent COD( of upto 6000 mg/I). In one day HRT and at a loading 4 kg COD/(m .d), the effluent has a very low level of volatile fatty acids, less than 10 mg/l. The effluent SS was about 100-200 mg/I. The gas has a CH~ content of about 75 3. Activity tests on the s ludge s how a specifi c methanogemc activity of 0.12 g CHcCOD/(g MLSS.d) at 37°c. In case of aerobic treatment of effluent of first anaerobic pond, optimum cond itions for ASP were F/M loading of 0.4 kg COD/(kg MLSS.d) and HRT of 0.9d. About 95 3 of COD - m & f was removed. The effluent COD - m&f and SS was 60, 40 and 40 mg/I (average ) respectively. The s ludge has SVI between 80 to 90 ml/g. The aerated lagoon, although heavily loaded, 0.4 kg COD/m3.d}, showed very high COD removal with an effluent COD - f of lower t han 70 mg/l (average). The effluent was high in SS at 200-300 mg/ 1 under steady state conditions. Algae production in the HRAP after the aerated l agoon was low about 100 mg/l due to low carbon and nitrogen source in the aerated lagoon effluent and was therefore not considered feasible. The experimental results obtained strongly indicates technical feasibility for t he higher-tech anaerobic-aerobic treatment for this type of wastewater.