Research On The Treatment Of Low Concentration Domestic Sewage By The Biofilter Filled With Limonite

At present,most of the urban sewage treatment is disposed by activated sludge process in China.The main processes are traditional activated sludge process,oxidation ditch method,A²/O and so on.Although all technologies are effective in water pollution control,there are many problems such as large investment and residual sludge disposal.Biofilter,as a biological treatment technology,has the advantages of stable operation,long sludge age and so on.In this paper,limonite was used as the filler of the biofilter.The influences of the start-up of the biological filter,different C/N ratios,and HRT conditions on the treatment of real domestic sewage and simulated low-concentration domestic sewage were examined.Through analysis of the microbial community of the biofilter,the relationship between pollutants removal and microbial community has been preliminarily studied.The experimental results were listed as follows:?1?In the start-up stage,results showed that the limonite group achieved stable stage8 days earlier than the control group,which shortened nearly one fifth of the start-up time.And the removal rate of COD and ammonia nitrogen increased by 2%and 4%respectively.?2?During the stage of treatment simulating domestic sewage,when the C/N ratio was 8,the best removal effect of COD and TN by the biological filter could be achieved.The removal rate of limonite group increased by 4.6%and 4.3%respectively more than that of the control group.When the HRT was greater than 12 h,the removal rate of COD?TN and TP gradually increased with the shortening of HRT,and the better HRT was 12 h.At that moment the average removal rate of TP of limonite group was 57%higher than that of control group,which demonstrated that limonite is more suitable for the filler.?3?In the treatment of the actual sewage stage,the better condition of HRT for removal of ammonia nitrogen was 20 h,and COD,TN and TP was 16 h.At that moment the removal rate of NH₄⁺-N was not significantly lower than that of 20 h.Based on the processing cost,the better HRT of biofilter for treating domestic sewage was 16h,which has a good removal effect on COD and phosphorus,and their average concentration in the effluent was 32.6 mg/L and 0.32 mg/L,respectively,which met the first grade A emission standard of urban domestic sewage.?4?Microbial analysis results showed that the bacteria in the three layers of biofilter were no difference at the phylum level.At genus level,the dominant bacterium in the lower layer was nitrobacteria,and its relative abundance was 18.5%.The predominant bacterium of middle layer was denitrifying bacteria,and its relative abundance was17.9%.Iron reducing bacteria mainly existed in the middle and upper filler.Methanosaeta was the dominant species in archaea microorganism,and its relative abundance was 20%,23%and 12.21%in the upper,middle and lower strata,respectively.