Operating Characteristics And Microbiological Study On Biological Aerated Filter For Contaminated River Water Treatment

In this paper, in order to overcome some shortcomings of treatment of contaminated river, the representative Xiaoqing River, which is badly contaminated in Jinan City, China, was chosen as the paradigmatic research area. A biological aerated filter (BAF) reactor combined with the chemical phosphorus removal technique was employed to treat the contaminated river water aiming at wastewater purification and recycle. The operational characteristics and the effect of operational factors, microbiological characteristics, treatment kinetic model and postpositive chemical phosphorus removal technique were studied in detail.Continuous start-up and microbial domestication experimental results indicated that the BAF system had an excellent performance for start and microbial domestication. The system needed about 15 days to achieve the stabilized organic removal efficiency above 75%, while the nitrification ability began to do its work after 30 days since the start-up.It was demonstrated that hydraulic loading, the ratio of gas and water and media depth had great effect on pollutant removal efficiency. For the removal of organic substances and ammonia, under hydraulic loading of 1.2 m³/(m²Â·h) and ratio of gas and water of 3:1, highest removal efficiency of COD and NH3-N were achieved. The COD and NH3-N concentration in effluent is under 50 mg/L and 10 mg/L, respectively, and the removal efficiency of COD and NH₃-N could be above 80% both. BAF had steady removal ability for suspended solids (SS), which was less influenced by the hydraulic loading and ratio of gas and water, and the turbidity of effluent is less than 5 NTU. BAF system had excellent recoverability after a period of intermission. At low temperature, the NH₃-N removal was influenced, but the COD could still fulfill the set removal goal. The removal of suspended solid received little influence and the turbidity of effluent remained very low.Microbiological study revealed that active biomass in BAF was greatly affected by the concentration of substrate. More biomass was obtained near the inlet where the concentration of organic substances is high than that near the outlet with less organic substances. Microbial activity and biomass has no positive correlation. Owing to the limit of substrate diffusion, the microbial activity may decrease with the increase of biomass. Most organic substances were removed in the bottom 40cm of the biofilter near the inlet, where microbial activity and biomass was comparatively high. Microbial activity and biomass decrease with the flow in general, but nitrification bacteria began to accumulate by playing an increasingly significant role in the nitrification of NH3-N.Kinetic model of organics removal based on plug flow and Monod model was established in this paper, and the model coefficients were determined according to the results of experiment. The results indicated that the kinetic model could be described as first order reaction. In this research, as the characteristics of influent and media were specific, the coefficient K is the function of hydraulic loading. The kinetic model revealed the treatment mechanism of BAR and was instructive for engineering design and prediction of treatment efficiency.Postpositive coagulating phosphorus removal technology was used to remove excessive phosphorus. Polymeric ferric sulphate (PFS) is the ideal coagulant, and when the dosage of PFS was 35 mg/L, the removal efficiencies of total phosphorus (TP) and phosphate were 86% and 91%, respectively. The concentration of TP and phosphate in effluent were 0.38 mg/L and 0.20 mg/L, respectively. At the same time of phosphorus removal, the COD and SS could be further removed, and the COD concentration and turbidity in effluent were as less as 44mg/L and 1.1 NTU, respectively.