| In recent years, with the determination of the national sewage treatment and people’s increased awareness of environmental protection, particularly The Action Plan for Water Pollution Prevention and Control(ten measures for water treatment) was enacted, and it makes a number of sewage treatment plants have been built to face the problem how to make treatment effect better. The primary treatment effects have been very good, CODCr removal is very mature, but sewage treatment plants are facing new requirements, that are the further removal of nitrogen and phosphorus. And the attention of water treatment has been extended to small towns, the treatment of small towns’ wastewater gradually becomes the research direction. Under this condition, the research of A/O land treatment system under the plow layer has been promotioned very well in small towns, which also faces with the problem of further removal of nitrogen and phosphorus. How to improve the efficiency of nitrogen removal efficiency under the premise of the other pollutant removed and in the most economical and reasonable way has become an important issue.At present, there are many methods to remove nitrogen from wastewater, which are very important in water treatment and denitrification, but there are still many ways to explore the biological nitrogen removal process, which include adding some metal elements to the reactor to promote the growth of microorganisms and improve their activity. This experiment method is to add Fe(OH)3 to the reactor to improve the activity of microorganism, diversity, community structure and so on, then improves the denitrification effect. Some scholars have applied this method to the activated sludge process, and have carried out a series of research and experiments, but the research on the biofilm system is still less.The biofilm treatment is the core of A/O land treatment system under the plow layer, it is the major material for sewage purification. The removal rate of CODCr is high and stable, but there are other water quality indexneed to improve. In this case, the study for further optimization of nitrogen removal efficiency of A/O was studied by using this system, and used the sewage discharged by the school life area to do the experiment about conventional water quality and microbial activity in autumn and winter. The optimal amount of iron was determined by analysising the biological system dentrification effect and water quality purification effect.Then the method of macro genomic sequence were used to analyse the microbial diversity.The conclusions of this study are as follows:(1) In autumn and winter, the removal rates of CODCr,ammonia nitrogen, total nitrogen were higher than the traditional biofilm, and the best and most stable treatment effect of the composite iron enzymatic biofilm was the 6% iron concent of the biofilm, compared with the traditional biofilm, CODCr removal rate increased 9.9%, 11.3%, ammonia nitrogen removal rate increased 14.8%, 22.1%, and the rate of total nitrogen removal rate increased 30.2%, 33.7%, respectively; In autumn and winter, the DHA and the ETS activities were higher than the traditional biofilm, and the highest was 6% iron concent of the biofilm, compared with the traditional biofilm, the DHA increased 57.1%, 38.7%, respectively,and the ETS activity increased 42.9%, 57.9%.(2) In winter, the effect of denitrification and water quality purification in different biofilm systems was better than that in autumn, but the effect was significantly enhanced when iron added. Thus, at low temperature, the composite iron enzymatic biofilm has good ability of resisting low temperature and better water purification.(3) From the macro genomic detection, it indicated that, there were big differences of microbial community, species abundance, community structure and dominant bacteria in the 6% iron concent of the biofilm and the traditional biofilm in autumn and winter. In the two seasons, 6% iron concent of the biofilm’s species distribution were uniform, and community diversity were higher. In the two seasons, 6% iron concent of the biofilm had individual or high content denitrification microorganism.These explain that the addition of composite iron changed the community structure of the biofilm microorganism, enhanced the activities and speeded up the microbial metabolism of some denitrification bacteria, which makes 6% iron concent of the biofilm has higher and more stable nitrogen removal efficiency.(4) The two biofilm samples’ species abundance difference in winter were more than those in autumn. It tells that the addition of composite iron is more beneficial at low temperature.This study was combinated with the A/O land treatment system under the plow layer, indicating that composite iron enzymatic biofilm system has good nitrogen removal ability and better stability. From the macro and micro perspectives,the study expounds the effect of the composite iron enzymatic biofilm on biological denitrification and microbial diversity, Lay the theoretical foundation for the application in other biofilm denitrification systems. |
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