An Experimental Study On Nitrogen And Phosphorous Removal Of The Hybrid Activated Sludge And Biofilm System

There are different sludge age requirements between nitrification germs and polyphosphate-accumulating bacterium in activated sludge. Biofilm process benefited bacteria with longer generation time. According to the features of the activated sludge and the biofim, hybrid activated sludge and biofilm system is designed with biofilm mediums are put in the activated sludge reactor. In comparison with SBR, the optimal operating mode is determined, experiments of nitrogen and phosphorus removal are carried out on the carbon nitrogen ratio and sludge retention time, kinetic parameters are analyzed, the mechanism of biological nitrogen and phosphorus removal is explained, and microbial community structure is analyzed.The influent COD concentration are 400-800mg/L, influent NH3-N concentration is 50mg/L, influent TP concentration is 8mg/L.The effects of nitrogen and phosphorus are analyzed in extend anaerobic time,extend aerobic time,extend anoxia time between Hybrid and SBR, and optimal operating model is determined:anaerobic 120min/aerobic 240min/anoxia 60min.Influence of carbon nitrogen ratio(influent COD concentration is 400 mg/L,600 mg/L,800mg/L) on the nitrogen and phosphorus removal is investigated. Tests show that C/N=16 is the best condition for nitrogen and phosphorus removal in SBR and Hybrid. In three C/N conditions, NH3-N removal efficiency are all over 93% between SBR and Hybrid, C/N has less effect on NH3-N removal. When C/N increase from 8 to 16, TN removal rate increase from 65% to 79% and TP removal rate increase from 42% to 93% in SBR, TN removal rate increase from 73% to 86% and TP removal rate increase from 32% to 93% in Hybrid. The removal nitrogen of simultaneous nitrification and denitrification account for 18.5% of total removal nitrogen when COD=400mg/L, and the removal nitrogen increase from 1.49mg/L to 5.9mg/L with COD concentration increase from 400mg/L to 800mg/L in aerobic phase. The denitrification is obvious in aerobic phase.Contrast experiments are carried out with C/N=16 and with 5d,10d,20d in SRT. Tests show that C/N=16 and SRT=10d is best condition, and it can solve sludge age contradiction between nitrification germs and polyphosphate-accumulating bacterium to some extent. The attached biofilm of Hybrid have relative independent SRT, they isolate microorganisms which have different generation time. In Hybrid, the TP removal rate is 96%, TN removal rate is 89%, NH3-N removal rate is 96%. The results show that the increase of SRT would promote the nitrification rate and denitrification rate. In SBR, the average transition rate of nitrification rate is 57.2%, however is 26.8% in Hybrid. The Hybrid adaptation to the change of SRT is stronger than SBR. The suspended sludge plays a main role to the nitrification, suspended sludge against the attracted sludge is 1.66.The attracted sludge plays a main role to the denitrification and dephosphorization, attracted sludge against suspended sludge is 2.19 about denitrification, is 3.5 about phosphorus release, is 3.76 about phosphorus uptake.The dynamic changes of community structure are monitored in SBR and Hybrid by PCR-DGGE under different C/N. Tests show that denitrifying phosphorus removal bacteria Dechloromonas sp. is founded in SBR under the condition of C/N=16 and SRT=20d.The Hybrid biofilm diversity index is highest, up to 3.30,and similarity index is lowest, at 43.3%.The Hybrid reach the optimal nitrogen and phosphorous removal effectiveness under this condition, and nutrient removal microbe Uncultured BacteroidetesFJ828150 is founded and nitrifying bacteria Uncultured Nitrospira sp. is dominated. There have arisen many bacteria in Hybrid which did not in SBR, such as COD removal bacteria Uncultured Saprospiraceae, denitrifer Ferribacterium sp.,Uncultured Saprospiraceae,Flavobacterium sp. and Ignatzschineria sp. easy to grow in biofilm. All these facts suggest Hybrid have advantages in COD removal and denitrification.The dynamic changes of community structure are monitored in SBR and Hybrid by PCR-DGGE under different SRT. Tests show that phosphorus removal bacteria Runella and denitrifying phosphorus removal bacteria Thauera sp. are founded in Hybrid under the condition of SRT=10d and C/N=16, which make the phosphorus removal rate reach 96%.There are kinds of denitrifer, such as Uncultured Sphingobacteriales,Uncultured BacteroidetesFJ828150,Uncultured Rhodocyclaceae,Ferribacterium sp.,Uncultured Nitrospira sp. These bacteria help to solve sludge age contradiction between nitrification germs and polyphosphate-accumulating bacterium. This similarity index is lowest under three conditions, at 43.3%, this show that the microbial population differences between suspended sludge and attached sludge improve nitrogen and phosphorous removal effect.