| Biological aerated filter (BAF) has been widely used in recent years in municipal wastewater treatment for its advantages of high treatment efficiency and low landuse. However, traditional BAF has strict requirements to influent SS and is easily blocked up, which limits its efficiency of organic pollutant removal. To overcome these limitations, modifications were performed in this study on the traditional BAF based on the pollutant removal principles of BAF and an integrated biological filter (IBF) was developed by combining aerobic process and anoxic process in one single treatment facility. And a pilot scale experiment was designed to study the characteristics of IBAF in municipal wastewater treatment. A kind of enzyme-enhanced bio-filling, which is a paten product developed by Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, P.R.China is used in this experiment. Diameters of the filling ranges between 10 and 15mm, bulk density is 1.56 g/cm3 and porosity is 0.506. With high strength and large number of micro-holes for micro-organism, this kind of bio-filling is suitable for the formation of spatial net structure of micro-organism and growth of bio-film. In this experiment, start-up is performed under continuous inflow condition .On the ninth day, metazoan organisms such as eelworm, bell worm and rotifer can be observed under optical microscope in the situation of 10h HRT, indicating that the microorganisms have played a leading role in pollutant degradation. With biomass increase, COD values of effluent decrease gradually and two weeks later, a great amount of metazoan organisms can be observed, and COD values of effluent are in a steady range of 40~60mg/L. Now it is considered that start-up period is over. In the loading operation period, 9 groups of experiments are designed in this study by controlling HRT and aeration intensity and test data in each operational group are analysed respectively. The results show that, with the increase of HRT, COD value of effluent decreases gradually and the removal rate increases gradually. When HRT are 4h and 10h,COD removal rates are 71.3%and 94.6% respectively, proved that HRT is an important factor influencing the reactor performance. Meanwhile, the results indicate that removal rate of organics is faster in the anoxic layer than that in the aerobic layer under the same HRT. Analysis of ammonia nitrogen removal rate shows that removal efficiency of ammonia nitrogen is relatively low in the first part of the reactor, even when HRT is 10h, the removal rate of ammonia nitrogen is only 32%. It is perhaps because that the first part of the reactor hasn't the suitable environment for the growth of autotrophic nitrifiers. By comparing the nitrification function of the two-section reactor, it found that in the first section, though the nitrification efficiency is not satisfactory, the high organic removal efficiency can lower the organic concentration of the second section and produce beneficial condition for the growth of nitrifiers in the second section. By this way, the nitrification bacteria can be the dominant bacteria and improve nitrification efficiency of the reactor. When HRTs of first section and second section are 8h and 3h repectively,the removal rate of ammonia nitrogen is over 75%. By summaring the organics removal dynamics, a model of organic removal is achieved, which is as follows: 237 q0.9895HSe Soe?= . The absolute error between estimate value and test value of effluent is no higher than 8.12mg/L, and the relative error is no higher than 18.5%, which indicates that the dynamics model can describe the real degradation mechanism and can reflect the real operation condition.
|
PDF Full Text Request