The Study On The Performance For The Removal Of Nitrogen And Phosphorus From Wastewater With Low Carbon Source By Using A Composite Filter Bed With Iron Scurf And Zeolite As The Filter Media Materials

In order to further improve the quality of urban water environment,it is a research hotspot in the direction of water treatment to deeply remove nitrogen and phosphorus from secondary effluent of municipal wastewater treatment plant or micro-polluted urban lake water.However,due to the low carbon source characteristics of the above water bodies,the conventional nitrogen and phosphorus removal methods often requires a large amount of carbon source to reach anticipation effect.It will not only greatly cause a promotion of process operation,but also contrary to the current situation of advocating ’ resource conservation ’ and practicing ’ carbon peaking and carbon neutrality goals ’.Therefore,it is necessary to develop a new nitrogen and phosphorus removal technology for low carbon source wastewater without additional carbon source.Based on this,a cross-flow biofilter bed reactor based on the previous results of our research group was designed.This filter bed uses composite filter materials,including iron chips,zeolites,and iron-aluminum-magnesium composite oxides granule adsorbent(FCGA).In this study,the start-up of the reactor was first completed;then,the treatment effect of the reaction system on low carbon source wastewater was studied by conditional experiments.At the same time,the mechanism of nitrogen and phosphorus removal in the reaction system was explored by material characterization and microbial diversity analysis.Specifically as follows :(1)The filter bed was inoculated with sludge.The hydraulic load gradually increased from 10L/h to 30L/h after 37 days of start-up.When the hydraulic load reached 30L/h,the removal rates of CODMn,NO3--N,NH4+-N,TP and TN were 69.9 %,91.2 %,41.3 %,85.5 % and 52.7 %.(2)In this study,the ability of the filter bed to cope with the changes of water quality such as high NO3--N and low C/N ratio was explored by increasing the concentrations of NO3--N,NH4+-N and TP in the influent.The results showed that when the nitrate concentration in the influent increased from 4.60 mg/L to 8.70 mg/L,the reaction system could still maintain good NO3--N removal efficiency(removal rate was 88.6 %).When the influent C/N ratio decreased from 5 to 2.5,the reaction system could still maintain about 75.0 % of NO3--N.The above results show that the reaction system has a good ability to adapt to water quality changes.(3)In this study,by monitoring the changes of pollution indicators in the effluent of each filter section,it was found that the nitrogen and phosphorus removal process of the reaction system was mainly completed in the iron chip filter area.In order to reveal the mechanism of nitrogen and phosphorus removal in the reaction system,the surface microstructure and physicochemical characteristics of iron filings,zeolite and FCGA were investigated by characterization techniques,and the microbial community structure and functional bacteria distribution characteristics of each filter section were studied by biological sequencing technology.The results showed that the nitrogen and phosphorus removal in the reaction system was a ’ physicochemical-biochemical ’ synergistic process.The denitrification of NO3--N depends on the reduction reaction of Fe0 and the biochemical reaction of heterotrophic / autotrophic denitrifying bacteria.The removal of NH4+-N can be attributed to the ion exchange of zeolite,the coprecipitation of Mg2+ with NH4+ and PO43-,and the biochemical action of anammox bacteria and algae.The removal of TP mainly depends on the micro-flocculation of Fe3+,the coprecipitation of Fe3+ or Mg2+,the adsorption of FCGA and the biochemical phosphorus removal of PAOs and algae in the system.