Municipal Wastewater Treatment Using Two-stage Biological Aerated Filter

Biological Aerated Filter (BAF) is a recently developed process which is used for the advanced wastewater treatment. A major characteristic of BAF reactors is the use of granular media which integrated solids separation as well as secondary or tertiary biological treatment in one unit. It has the function of filtration, adsorption and biodegradation, etc. The practical operation proves that it has advantages of less land occupied, high treatment efficiency, higher capacity for absorbing shockload, no requirement for secondary settling tanks and the quality of effluent reaches the standard.In order to investigate the two-stage BAF (up-flow&down-flow) process, a series of experiments had been carried out on a bench-scale with a synthetic effluent containing organic carbon and ammonium nitrogen as substrates. The aim of this work was to verify experimentally the suitability of two-stage BAF and ascertain the relationship between removal efficiency and performance of reactor.In order to quicken the culturing process of biofilm, the biofilter was inoculated with activated sludge from the MBR reactor in Tianjin University. After one week from start-up, steady-state was reached and the removal percent for COD was 67.8%.The experimental results show that the performance of two-stage BAF for sewage treatment is excellent. Under the hydraulic rate of 2.8m/h, the average removal percent for COD,BOD5,NH3-N and turbidity is 82.62%,90%,70% and 90% respectively, the average effluent concentration of COD,BOD5,NH3-N and turbidity is 33.2mg/L,10 mg/L,10 mg/L and 1NTU.The objective of the experiments is to study the influence of temperature,pH,ratio of gas to liguid,influent hydraulic loading and volumetric loading. The correlativity between performance and filter medium height had been studied too. The results show: for hydraulic loading 2.8m/h, the removal efficiency of COD and SS have positive correlation with the height of filter medium. Up to 60~70% of COD was removed in the up-flow BAF.The relationship between the removal of COD and backwashing was also determined.