Research On Water Characteristics Simulation And Function Of Biofilm Purifying Water In Large-scale Raw Water Distribution Systems

Chinese economy is developing,the thought of saving water is receding,water resource unequally distributes and the city water resource is polluted,which results in a shortage of water in some districts,limits the development of industry and agriculture.The long distance delivery water has become an effective measure to solve water shortage,the imbalance of water distribution and the contradiction of the water supply and demand,which is widely applied in all the world.So far,the research focus of the long distance delivery water project are the choice of locations and pipe materials,pipe line and hydraulic distribution security and so on.It is scarce about water quality,pipeline biofilm microbial ecology and the effect of pipeline biofilm on water quality.In this paper,three large-scale distribution systems operational conditions were surveyed and water quality change was monitored.Results showed that Xijiang water distribution distance was the longest and pipe diameter was the widest.Dongjiang water distribution distance was the shortest,the concentration of ammonia nitrogen was higher and the concentration of dissolved oxygen(DO)was lower.The amount of heterotrophic bacteria(HPC)firstly increased and then reduced and the amount of Coliform gradually reduced along water delivery.The concentration of ammonia nitrogen,organic matters and dissolved oxygen decrease,which reflected the role of biofilm purifying water.By calculating hydraulics conditions and comparing the water quality between real distribution water system and simulation system,simulation system composed of eight Biofilm annual reactors(BAR)could appropriately simulate real distribution water system and the eighth BAR simulator flow state was close to real distribution pipeline.The removal quantity of ammonia nitrogen as an important inspection index,Beijiang simulation system matured on 210 days,Xijiang and Dongjiang simulation system matured on 180 days.At the moment,nitrification was the strongest.The removal quantity of ammonia nitrogen were respective 0.31mg/L,0.25mg/L and 0.84 mg/L.In Xijiang simulation system,the relation between the concentration of ammonia nitrogen and retention time was investigated and ammonia nitrogen kinetic model was built,which could forecast ammonia nitrogen change along distribution.Using 454-pyrosequencing technology,we analyzed biofilm microbial community structures in three distribution water systems.The results suggested that water quality and retention time influenced biofilm microbial community structures.Proteobacteria,Bacteriodetes,Firmicutes and Nitrospirae were common and Proteobacteria was dominant.Acinetobacter,Enterobacter,Pseudomonas and Nitrospira were common and Pseudomonas was dominant.Nitrospira abundance increased with ammonia nitrogen concentration rising.The effect of dissolved oxygen and oxidizers concentration on the efficiency of biofilm purifying water was studied.Results indicated that higher DO concentration could increase the removal quantity of ammonia nitrogen.When DO concentration rose from 0.8 mg/L to 4.9 mg/L,the removal quantity of ammonia nitrogen increased from 0.08 mg/L to 0.53 mg/L.But DO concentration rose from 4.9 mg/L to 7.1 mg/L,the removal quantity of ammonia nitrogen increased from 0.53 mg/L to 0.59 mg/L.The soluble quantity of total iron reduced,which reduced from 0.96 mg/L to 0.39 mg/L.The 454-pyrosequencing technology was employed to study biofilm microbial community under different oxygen concentration.Nitrifying bacteria amount rose with increasing DO concentration.When DO concentration rose from 0.8 mg/L to 7.1 mg/L,the relative abundance of Nitrospiraceae and Nitrosomonadaceae rose from 0.08% to 7.83% and from 0.25% to 6.62%,respectively.In addition,the effect of oxidizers concentration on biofilm purifying water efficiency was made.It was found that the removal quantity of ammonia nitrogen increased from 0.57 mg/L to 0.68 mg/L.But oxidizers concentration exceeded 4 mg/L,ammonia nitrogen was not removed.Results demonstrated that low concentration oxidizers did not influence the efficiency of biofilm purifying water.To investigate the correlation of Nitrospirae richness and ammonia nitrogen concentration and compared the change of microbial quantity in biofilm and raw water.The correlation coefficient of Nitrospirae richness and ammonia nitrogen concentration was higher.But,the change of microbial quantity in biofilm and raw water was uncorrelated.So,we concluded that biofilm was not a major factor to deteriorate water and reduce the biological safety.