| In order to meet the increasingly rising standards of domestic sewage treatment plants, it is a prerequisite to improve the technologies and equipment of wastewater treatment plants.The aeration biological filters have excellent potential application in sewage treatment field. For the drawbacks of the traditional aeration biological filters, a new type of filter was developed, namely, the gradient flow biological aeration filter(for simplify: GBAF).GBAF is feasible to realize the effect of plug flow from lower to upper and to achieve mixed flow in lower and upper respectively by using the structure of thin middle, coarse upper and lower. Therefore, compared with the traditional BAF, it is more conducive to remove organic matter. Furthermore, combined with the wastewater treatment principle of A/O, the lower and upper perform denitrification and nitrification, respectively, which is beneficial for nitrogen and phosphorus removal.The GBAF body was designed. Then, several factors, such as biofilm formation and startup of GBAF, the biofacies observation in the filter were investigated. And the influence parameters such as flow regime, hydraulic loading, gas water ratio, temperature, pH and etc., were optimized. Lastly, the best effect parameters were determined.GBAF body is mainly composed of organic glass, with a total height of 900 mm, and the volume is designed for 21 L with irregular shape.GBAF applied the method to form membrane successfully by undergoing a whole process, which is from inoculating sludge to sludge and stuffy aeration to intermittent flow biofilm cultivating. The CODCr and NH3-N removal rate can reach 82% and 84% after 20 days, respectively, which can be regarded as the cultivating biofilm is accomplished.Accompanied by dissolved oxygen and the flow direction in the GBAF reactor,there are different kinds of microorganism of biological membrane such as nematodes, amoeba, epistylis plicatilis, carchesium batoligetiense, paramecium, which shown obvious trends of species variation.In the experiment of optimizing parameters, it was found that the GBAF flow keeps a kind of favourable flow form between totally mixed flow and plug flow. The removal of CODCr and NH3-N become bad by increasing the hydraulic loading when the hydraulic loading changed from 0.14 m3/(m2·h) to 0.52 m3/(m2·h). However, TP removal rate gradually increased along with the hydraulic loading increasing when the hydraulic loading changed from 0.14 m3/(m2·h) to 0.43 m3/(m2·h). It is also beneficial to increase the gas water ratio for CODCr, NH3-N and TP removal in the operating condition of gas water ratio in 1:1 ~12:1. The best result of CODCr removal can be obtained when the water temperature reach 25℃, the average removal rate of 89.7% can be reached. Meanwhile, the optimal temperature range for denitrification is 25℃~30℃, while the water temperature had little effect on TP removal. The best pH ranges for removing CODCr, NH3-N and TP are 6.5~8.5, 7.0~8.5, 6.0~7.0, respectively.The optimal operation parameters of GBAF can be determined, that were water flow of 9 L/h, hydraulic loading of 0.43 m3/(m2·h), gas water ratio of 8:1, water temperature at 30℃, pH at 8.5. The results shown that the average removal rate of CODCr, NH3-N and TP can reach 92.4%, 98.1% and 67.7% under the optimum technological conditions, respectively. |
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