Investigation Of Efficiency For Removal Of Ammonia-nitrogen By Biological Aerated Filter From Low Temperature And Micropolluted Raw Water

At present,China has been a country with extremely scarce of drinking water resources.Protecting the quality and conservation of water resources,especially the fresh water,has been an urgent problem to be deal with.Nowadays,the water environment has been polluted seriously.Ammonia nitrogen,which mainly comes from farmland drainage of fertilizers or coking wastewater and other industrial wastewater,is a major pollutant in fresh water pollution.According to a large numbers of water quality monitoring,it could be found that ammonia nitrogen pollution in china gets the character of universality,specificity and orderliness.Universality is performed in that three kinds of drinking water resources,river,lake and groundwater,are contaminated at different levels across the country.Specificity is appeared that the ammonia nitrogen pollution has different concentrations thresholds when area and drinking water type changed.Orderliness is reflected in that these numerous water sources get a lighter ammonia nitrogen pollution concentration in high temperature period in June and July,while it has a high pollution when the temperature becomes low in December and January.At present,coagulation,sedimentation,chlorine and disinfection,the current conventional water treatment process,which has 15% removal of ammonia nitrogen pollution,is adopter in most of waterworks in China.However,when the temperature gets low at 3-5? in the north area,ammonia nitrogen pollution in the water is more difficult to be removed.In this paper,the Songhua River water in the low temperature period was been used as treatment object,and monolayer aeration biofilter and zeolite-suspended filler double layer biological aerated filter and the biological zeolite were conducted to solve the ammonia nitrogen removal problem at low temperature.The removal characteristics of ammonia nitrogen at different temperature with single and double aeration biological filter were studied systematically.The differences in the structure of the microorganisms grown on the filler at different temperatures and the differences in biodiversity were analyzed.Firstly,natural hanging membrane method was adopted when the single-layer biological aerated filter got started.Ammonium chloride was added to the water to ensure sufficient nitrogen source to keep the growth of nitrifying bacteria.1# zeolite filter got hanging film at 6-8?.2# and 3# zeolite filter adopted hanging film temperature at room temperature.The three single-layer BAF were successfully coated in 10 days,and the removal rate of ammonia nitrogen was above 90%,among them 2# zeolite filter got the highest removal rate.Then,the ambient temperature was reduced to 4 ?,which found that low temperature have significant impact on the single-layer BAF.1# reactor maintained high biological nitrification due to the low temperature hanging membrane.In addition,1# reactor got a better adaption ability than the other two because the adsorption and ion exchange capacity of zeolite got to ammonia nitrogen.Even so 1# reactor has a removal of 51.71% at low temperature.Besides,nitrite nitrogen was accumulated to influence the ammonia nitrogen removal rate.Single-layer BAF could buffer ammonia nitrogen load at short time when ammonia nitrogen concentration increase.And then,the phenomenon of negative removal of zeolite desorption may occur.Further,the removal ability of ammonia nitrogen dealing with zeolite suspension double-BAF was investigated at low temperature.Artificial inoculation biofilm hanging and natural hanging at a low temperature were conducted by combination.The removal rate achieved 60% after the reactor started 6 days.The average removal rate was 61.30%.The removal rate had a rough drop after the second start,which caused by microbial dormancy and filter biofilm covered too thick.Two points of intake and water cleaning was conducted to remove old biofilm and then the bacteria liquid boring exposed to increase the biomass.The visible removal rate increased after 22 days conducting at 4?.The removal rate could reach 77% and the ammonia nitrogen concentration could achieve under 0.5mg/L which meet the water standards.It could be found that biological aerated filter has better low-temperature ammonia removal efficiency than monolayer,and the nitrification is enhanced with the running time.In order to study the effect of zeolite adsorption on the removal efficiency of ammonia nitrogen in the biological aerated filter furtherly,the adsorption capacity of zeolite before and after the coating was conducted at 5? and 25?.At the same time,the ammonia concentration,Environmental temperature impact experiment was carried out with elution bacteria.The adsorption capacity of the modified zeolite to ammonia nitrogen at room temperature or under low temperature were higher than that before modification.The biofilm covered by the zeolite after the membrane is not considered for biological nitrification,which affects the adsorption of ammonia nitrogen,resulting in a decrease in its adsorption capacity.At the low temperature of 5 ?,the initial removal rate of ammonia nitrogen was the highest when the initial concentration of ammonia was 4mg/L.At 4mg/L,the other conditions were the same,and the temperature was the factor that affected the whole process and speed of nitrification.In the range of 5-25 ?,with the increase of temperature,the higher the biological activity,the higher the degree of ammonia nitrogen in the degradation water.At this point,the temperature was no longer a limiting factor for ammonia removal.Through analyzing the diversity statistics index and the differences of single and double layers of BAF in different stage,it could be found that long-term low temperature domestication of the community will cause the occurrence and differentiation of bacteria.Horizontal comparison,the diversity and abundance of bacteria would increase as the run time goes,and the higher the stability of biological filler system would be.By analyzing the community composition of single and double layer BAF,there exist two common nitrifying bacteria,Nitrospira and Candidatus_Nitrootoga.It is speculated that Nitrospira and Candidatus_Nitrotoga can maintain their ammoxidation in low temperature environments.From the biological community composition of the double-layer biological aerated filter,we could see that,the microbial composition of the double-layer biological aerated filter after biological stuffing exposed to the bacteria solution was higher than before.The relative abundance of the functional bacteria Nitrospira was higher.Combined with the effect of ammonia nitrogen removal,the effect of bacteria liquid on the rapid start of biological aerated filter in low temperature environment has important research significance and engineering application value.