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

Thesis (M.Eng.) - Asian Institute of Technology, 1993

A biological aerated filter combines bacterial degradation of pollutant by fixed biomass with physical filtration in a single reactor. An organic removal process has been operated on an experimental basis at a pilot plant over five months at the AIT - Environmental Engineering Division Laboratory. The wastewater feed was modified AIT domestic wastewater. The process consists of a granular media bed, particularly of polystyrene (thus, named biostyr process) with a specific gravity of approximately 0.06. The cylindial reactor was 4 m high and 0.2 m diameter. Headloss measurement was studied as a function of wastewater temperature, velocity and time. Experiments were conducted at 30°C, 38°C, 45°C and 55°C with velocities of 2 m/h, 4 m/h, 6 m/h and 8 m/h respectively. At 38°C, filtration time range was 5.5-10 hours and over 84% of the soluble COD was removed at all velocities investigated. At 30°C, 75.8- 89.4% COD removal was noticed, 89.4% COD removal with the exception of 6 m/h velocity and 8.5 hour filtration time. At 45 °C, 77.1-87.9% of soluble COD was removed, in which 87.9% COD removal could be obtained at 2 m/h velocity with a filtration time of 40 hours. A decreasing gradient of biomass from bottom to top of the reactor was observed. 2- 5.8% of purified water was consumed for backwashing operation. The optimal suspended solids removal occurred at 30°C with 6 m/h velocity. At lower temperature, maximum suspended solid removal could be obtained. The results indicated that effluent SS could be less than 30 mg/L, that is secondary treatment effluent standard in Thailand.