Study On Baffled Biological Filter (BBAF) For Municipal Sewage Treatment

With advantages of footprint space saving, low operation fees and convenient management, biological aerated filter (BAF) is appropriate to the status of our country. Its shortcomings include harsh restriction for suspended solid in influent, low phosphorus removal efficiency, high water-head loss and the height of lifting sewage. To improve existing BAF for better use in practice, a new kind of BAF, named Baffled BAF (BBAF), was developed in this paper. The study covered the hydrodynamic behavior of BBAF reactor; start-up of filter, performance of treating municipal sewage, effect of operational parameter on treating efficiency. The result of trial indicated that hydrodynamic behavior in each stage of BBAF tended to be completely mixed flow, while for whole reactor it tended to be plug flow. The start-up process was gradual and continuous lasting 18 days. The removal efficiency of COD, BOD and SS was 88.4%, 90.3%, and 95% respectively. The removal of ammonia had greatly to do with the media size in BBAF. With part of media changed for the smaller, the average efficiency of NH3-N removal rise up to 71.22% from 56.77%. Removal efficiency of TN was also enhanced to 40.81% from 35.1%. The mechanism of filtration in BBAF played a main role on phosphorus removal. The operation time was about 7~8 days. Stages of BBAF were backwashed separately depending on the status of each stage. As biomass and species in BBAF distributed spatiotemporally, dominant bacteria for each stage was distinctive. Through testing the factors on BBAF performance, it is found that the reactor could operate satisfactorily when the ratio of anaerobic to aerobic was 2︰6 and the ratio of air to water was 10︰1. Under this condition, not only the biodegradability of influent was improved, but also the removal efficiency of organic pollutants and NH3-N. The removal efficiency of COD and BOD5 changed little with enhancement of hydraulic loading, which whereas had the negative effect on removal efficiency of TP, NH3-N and TN and leaded to the increase of SS concentration in effluent. The appropriate hydraulic loading was 17.4m3/ (m2·d). Though enhancing volume loading of COD would make the concentration of COD and SS in effluent higher slightly, the removal efficiency of COD and SS was almost not weakened. However, the removal efficiency of NH3-N would descend sharply. The fluctuation of SS volume loading scarcely effected on the removal efficiency of SS. The main function of first four stages of filter was for organic pollutants removal and the aim of following stages was for nitrification and denitrification. SS concentration along the filtration length represented the big capability of pollution-receiving and the characteristic of hard-block in BBAF. According to the test data, the degradation model of BBAF for organic pollutants ( SCODcr ) was as follow:...