The Characteristics Of The Integrated Biological Aerated Filter With Multi-layer Filter

For many prolems exist in the actual engineering applications of biological aerated filter (BAF) with single filter, this subject was supported by the water pollution control technology integrated research and engineering demonstration of Dongjiang high-speed urbanization tributary area, leading under the major science and technology projects of national water pollution control and management (2012Z-X07206-002), a novel integrated multi-layer filter BAF was built, and the multi-layer filter composed of volcanic rock, coal ash and polypropylene ethylene foam filter beads was divided into anoxic layers and aerobic layer. The start-up characteristics, process operation parameters were investigated, as well as the variation of different pollutants, bio mass and TF (TTC-dehydrogenase) with the height of multi-layer filter. Comparative analysis of multi-layer filter BAF and a single filter BAF was made for the treatment of urban sewage.The start-up test showed that bio film formation was completed after28days using compound inoculation. Due to aeration uneven of perforated aeration tube, biofilm was serious off. After improvement, the restart-up period was only15d using two-phase compound inoculation. When the temperature varied from12℃to25℃, the reflux ratio was1:1, the gas to liquid ratio was3～5, hydraulic retention time was26～78min, the removal efficiencies of COD, SS, NH3-N and TN were about70%,87%,97%and51%, respectively.This paper systematically studied the influence of process parameters such as thydraulic loading, air-water ratio and reflux ratio for the sewage treatment efficiencies, determined the optimal operational parameters for the BAF were: hydraulic loading was1.7～2.2m3/m2·h, air-water ratio was3:1, reflux ratio was1:1. Under the condition of the optimum process parameters, the removal efficiencies of COD, SS, NH3-N and TN were about71%,84%,91%and53%, respectively.The variation of pollutants along the height of multi-layer filter showed that COD was mainly removed in the volcanic rock-anoxia and ceramsite-aerobic layer I, COD removal efficiency in the two sections of the filter layer accounted for64.45%and33.89%of the total COD removal efficiency; NH3-N and SS was mainly removed in the ceramsite-aerobic layer I and polypropylene ethylene foam filter beads aerobic Ⅱ. The variation of biomass and TF along the height of multi-layer filter showed that biomass and TF rised gradually along the volcanic rock-anoxia, increased and then decreased in the ceramsite-aerobic layer I, the difference was that biomass decreased gradually in aerobic Ⅱ, but TTC increased slightly after the first drop. Over-all, bio film and TTC in aerobic layer I more than that of anoxic zone and aerobic layer Ⅱ.Comparison study for the treatment efficiencies of the multi-layer filter BAF, coal ash BAF and volcanic rocks BAF found the average removal efficiencies of SS by the multi-layer filter BAF was the best. The removal efficiencies of NH3-N and TN by the multi-layer filter BAF and volcanic BAF were almost the same, both of which were higher than those of the coal ash BAF. The COD removal efficiencies by three BAFs were close.