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, 1990

Multi Stage Reversing Flow Bioreactor (MRB) uses new biological interaction among sulfur bacteria for organic substrate removal under biological environments different from aerobic and anaerobic. The biological interaction between sulfate reducing bacteria and sulfide oxidising bacteria is responsible for COD and SS removal from wastewater. An experimental study to determine mechanism and operating conditions of MRB was carried out. Batch experiment and microscopic observations were taken to support the mechanism of MRB. Performance of MRB under three different hydraulic conditions was studied and effect of organic loading and wastewater recycle was also studied. Organic substrate removal was due to aerobic metabolism in aeration vessels and due to sulfur metabolism in biological vessels. Only about 1% of total COD removal was due to methanogenesis in biological vessels and assimilation of sulfur microorganisms was the main mechanism responsible for COD removal . Yield coefficient of MRB process was found to vary between 0.1-0 .2. At flow rate of 0.78 l/min (upflow velocity 73 m/day) 85-90 % of COD removal efficiency was achieved and effluent SS was between 15-20 mg/l. At flow rate of 1.17 l/min (upflow velocity 109 m/day) , without recycle 70-80 % of COD removal efficiency was obtained and SS was between 30-40 mg/l. However with recycling of wastewater 84- 88 % of COD removal efficiency was achieved even at a flow rate of 1.17 l / min.