Impacts Of Hanging Patterns Of Flexible Biofilm Carriers And Their Interaction With Aquatic Plants On Water Purification

Flexible biofilm carrier is usually hanged under structures（e.g.ecological floating bed）as the filler to provide surface for microbial growth.Previous studies have reported the effects of carrier type and hanging dencity on water purification.In order to enhance the efficiency of water purification,this paper changed the hanging patterns（e.g.spiral hanging pattern）of the carrier based on the optimization of the flexible carrier to increase the population of microorganisms for water purification.Moreover,the effect of aquatic plant roots on the population and community structure of microorganisms attached to the surface of the carrier is an important factor in controling the efficiency of water purification.Therefore,this paper have studied the impacts of hanging patterns of the flexible carrier and its interaction with aquatic plants（Iris pseudacorus L）on water purification,to investigate characteristics of the changes of biomass and its community structure on the carrier,and to explore the purification mechanism.The major findings of this paper are as follows:（1）Seven flexible biofilm carriers which are currently sold on the market and widely used were selected for the experiment of microbial attachement on the carriers in urban water.The results showed that the biomass per unit mass/volume/length on a three-dimensional elastic flexible carrier was the highest,and was 1.8-3.0,1.9-4.3and 4.0-6.9 times of the other six flexible carriers,respectively.The three-dimensional flexible carrier had also advantages in terms of price and delivery.Therefore,this carrier was selected for subsequent experiments.（2）The influence of different hanging patterns on the water purification by the flexible biofilm carrier was studied under high and low pollution loadings.The results showed that the removal efficiencies of total phosphorus,total nitrogen,ammonia nitrogen and COD_Cr by the carrier in spiral hanging pattern group（L）were higher than that in conventional hanging pattern group（C）（p<0.05）under both high and low pollution loadings.Their respective increment in group L was 19.4%-30.0%,19.2%-35.7%,18.3%-24.0%and 12.0%-15.3%as compared to group C.The results of biomass on the carrier and its microbial community structure showed that the spiral hanging pattern could significantly improve the oxygen environment and increase the carrier biomass and then enhanced the population of microorganisms related to nitrogen and phosphorus transformation.Meanwhile the water purification effect was consistent with the population of microorganisms related to nitrogen and phosphorus transformation.（3）The effect of interaction between flexible biofilm carriers（i.e.,group L and group C）and Iris pseudacorus L（Z）on water purification was studied.The results showed that the removal efficiencies of total phosphorus,total nitrogen,ammonia nitrogen and COD_Cr in all groups were in the order of ZL>ZC>L>C,except for ammonia nitrogen in group L and group C（the difference was not significant）.In addition,the increment in the removal efficiency of ammonia nitrogen by Iris pseudacorus L（33.4%）was significantly higher in group L than in group C（22.4%）.According to the data of carrier biomass and microbial community structure,the number of microorganisms related to nitrogen and phosphorus conversion can be further increased by root system of Iris pseudacorus L releasing oxygen and nutrients,which is consistent with the water purification effect.Because plant assimilation contributed little to the increase of total nitrogen and phosphorus removal rate（not more than 3%）.Therefore,Iris pseudacorus L can improve the water purification effect mainly by increasing the number of microorganisms related to nitrogen and phosphorus transformation on the carrier,and further improve the ammonia nitrogen removal efficiency by synergistic action with spiral hanging pattern carrier.