Study On Characteristic And Effect Of Charcoal Stuffing In Biological Aerated Filter

To prevent water pollution and alleviate water crisis, the development of advanced wastewater treatment processes with high effective, low consumption and investment saving, will have the vital practical significance to the districts which need pollution treatment urgently in a long time. Meanwhile, it is an eternal subject in water treatment. With the development of new material and improvement of the matched technology, biofilm method which is simultaneously invented with active sludge method obtains the fast development. As a typical process of biofilm method, the biological aerated filter (BAF) takes a good function in carbonaceous removal, liquid-solid separation and nitrification, expanding its application scope. It was firstly used as an advanced treatment in the urban sewage, and then served as the urban sewage second-level process, industrial wastewater process, as well as tap water pretreatment process.The development of the stuffing in the BAF is its core technology. At present, although wide - used light - weight haydite stuffing overcomes many shortcomings of traditional padding, development of new kinds of stuffings is still an important aspect of BAF in the application of BAF. By using new kinds of adsorptive stuffing, the removals of nitrogen, phosphorous and natural organic matters might be greatly strengthened by BAFs. And BAFs will take a more effective function in advanced treatment of sewage and tap water treatment. The activated carbon has great pore structure, huge specific surface area and perfect adsorption characteristics, which is regarded as one kind of most popular stuffing in the water treatment. But the high price restricts its wide application. Finding inexpensive material substitution for activated carbon is still a hot topic at present. Contrastly, the price of charcoal is low. Charcoal has attractived people's much attention in recent years. This research's cooperation company, based on the introduction of overseas technology, has developed a biological contact oxidation process called modified charcoal sewage treatment and the advanced purification technology, which gets some good effects in the treatment of domestic sewage, remediation of lake water, protection of river environmental and so on. The quality of effluent water is up to level IV specified in the Surface water Environment quality Standard GB 3838-2002. However, some problems are significant, for example: fussy structural units in this technology need to be optimized, some limitations need to be improved when used to treat urban sewage, the imported phosphorus and nitrogen removal material is costly, additionally, whether the modified charcoal is suitable to our country's sewage quality also needs to be further studied.In this paper, combining the merits of BAF and modified charcoal process, charcoal was applied as a light - weight stuffing of biological filter to treat municipal sewage. The performance of three lab-scale biological filters was monitored to compare the characteristics and effect of charcoal with that of haydite and modified charcoal as stuffing. The main content of the study is: research on fast stable startup mode of charcoal biofilter; discussion the removal rules of COD,SS,NH₄⁺-N,TN and TP, the influence of pH value, aeration intensity, loading rate and temperature on removal efficiency, optimizing the running parameters; adoptting scanning electron microscope (SEM) and the microscope observation to study structure of stuffing and biofilm, biofacies constitution; removal efficiency of natural organic matters by charcoal biofilter, and research the substrate removal kinetics of reactors, evaluation of dynamic parameters, and discussion the mechanism of denitrogen removal.The research indicated that it was efficient and feasible to treat wastewater by charcoal biological aerated filter. It can be proved as following.(1) Inoculated biofilm formation with merely aeration was benefit for initial removal efficiency of pollutants. Increasing the dissolved oxygen (DO) concentration can shorten the total time of biofilm formation. In the initial time of biofilm formation, three kinds of stuffing can adsorb ammonia nitrogen (NH₄⁺-N) . The chitason modified charcoal stuffing was not adaptive to growth of autotroph nitrobacteria, which effect the NH₄⁺-N removal. Charcoal's surface characteristic and pore structure was more adaptive to growth of autotroph nitrobacteria than that of haydite, and so the effect of charcoal filter was better than that of haydite.(2) By changing some parameters, such as the hydraulic loading, DO concentration, NH₄⁺-N concentration and temperature, we investigated the removal of phosphorous and nitrogen. The removal performance of the charcoal biological filter was superior to that by haydite. Under the condition of certain stuffing height, the optimum parameters by charcoal biological filter were: hydraulic retention time 6 h, DO concentration 2-3 mg/L and the backwashing period 2-3 d.(3) The scanning electron microscope (SEM) and the microscope observation indicated that various types of organism existed on the surface of charcoal. The pore structure of charcoal was more benefit to the protozoon, rotifer and nematode's growth and reproduction than those on haydite.(4) The GC-MS examination indicated that the more efficient removal of natural organic matters by the charcoal than that by the haydite. It provided that the charcoal biofilter was an advanced technology for the treatment of tailwater from sewage treatment plant.(5) The substrates removal kinetics of reactors has been studied. On the basis of Monod equation, the half experiential formula of the reactor was established, viz.ln(S/S_i) = -1.024^(T-15) k^*A/(QS_i)ⁿH. The influence of temperature and the organic loadingon reactor velocity constant was taken into account. It showed the concentration of COD and NH₄⁺-N, which changed with the height of stuffing. The formula can model the degradation process of substrate and can be used in engineering design and running control.