Development Of Ecological Filter And The Study Of Its Purification Effect Of Low Concentration Wastewater

In this study, a reactor named ecological filter low concentration wastewater treatment was developed on the basis of vertical flow constructed wetland and biological aerated filter(BAF), which was made up of down-flow chamber and up-flow chamber, with the function of aeration and backwashing. Influence factors and removal efficiency under different operating conditions were investigated in this paper, and the recommended optimal operating conditions were obtained. And then, the purification efficiency of low concentration domestic sewage and the transformation of pollutants along the reactor were investigated under those optimal operating conditions, in order to analyze the removal mechanism of contaminants in ecological filter. This treatment system was applied to water quality improvement of the Zhaojia creek in Chongqing, and the good effect achieved would be of great significance for its application in low concentration wastewater treatment. The main conclusions of this study include:① Hydraulic loading affect the removal efficiency of ecological filter. When the hydraulic loading is too small, the corresponding residence time would be long, which results in the formation of anoxia or anaerobic conditions in the reactor, and then affect the removal efficiency of the system; However, when the hydraulic loading is too large, the removal efficiency would decline with the strong erosion action to the matrix. The optimal hydraulic loading was about 1.55 m3/(m2·d) for this pilot test.② C/N ratio of influent has a great impact on COD and nitrogen removal efficiency, but the influence on the total phosphorus removal is not significant. When C/N ratio is 10, the COD removal efficiency is above 85%, which is higher than those of C/N ratio is 5 and 20. Total nitrogen, nitrate and nitrite nitrogen removal efficiency increases with the carbon and nitrogen ratio increased, while ammonia removal, on the other hand, decreases with the carbon and nitrogen ratio increased. Optimal C/N ratio is 10, it does not influence the removal of ammonia nitrogen, at the same time, nitrate nitrogen, nitrite nitrogen and total nitrogen removal efficiency is also high, basically maintained at above 60%.③ The issue of poor nitrogen removal in ecological filter system can be solved by aeration. The results showed that contaminants removal efficiency were maximized when the gas-water ratio was maintained at about 6, it is the optimal gas-water ratio in this pilot test.④ Ecological filter system had a good treatment efficiency of low concentration wastewater. Under the conditions of hydraulic loading of 1.5m3/(m2·d), C/N ratio of 10, gas-water ratio of 6, and HRT of 2 d, the average effluent concentrations of COD、NH4+-N、TN and TP were 26.02mg/L、1.22 mg/L、8.62 mg/L and 1.27 mg/L, with average removal rates of 90.70%、93.10%、52.90% and 79.07% respectively.⑤ Compared with the filter with no plant, the average removal rates of COD、NH4+-N、TN and TP were improved about 13.03%、25.30%、14.80% and 2.32% in ecological filter. The presence of plants had a positive impact on the removal of organic matter and nitrogen, but had little impact on the removal of phosphorus. Ecological filter also has a strong capacity of resisting impact load, which has a stable effluent quality under different conditions of organic pollution load.⑥ On the whole, the concentration of pollutants in ecological filter diminishing along the ladder. It plays the dominant role of organics and phosphorus removal in the down-flow chamber, the COD and TP removal of which account for more than 80% of the total removal of the ecological filter. The removal of organics mainly depends on the adsorption and degradation of the biofilm which attached to matrix and plant roots; the removal of phosphorus mainly relies on the filtration, adsorption and interception of the filler. Nitrification and denitrification occur simultaneously in ecological filter, nitrification plays the dominant role in down-flow chamber and denitrification plays the dominant role in up-flow chamber. Ammonia concentration increased in the transition area of down-flow chamber and up-flow chamber, which may be due to the transfer downward and decomposition release of particulate organic nitrogen. The concentration and removal efficiency of nitrogen result from the overprinted performance of plants adsorption, microbes assimilation, nitrification and denitrification and the decomp osition release of particulate organic nitrogen.⑦ In this study, based on the analysis of water quality and pollution load of Zhajia creek, a set of water quality protection technology was proposed with the main processing of ecological filter. The water quality of Zhaojia creek can reach better than class IV of surface water quality standard substantially with the treatment process.