Study On Nitrifying/Denitrifying Capacity And Microbial Diversity Of Polluted River Water With Constructed Wetland System

In this paper， the nitrifying/denitrifying capacity and diversity ofmicroorganisms were studied in horizontal subsurface flow constructed wetland（HFCW） and vertical subsurface flow constructed wetland （VFCW） to treat pollutedriver. Many different operational modes were set in test and the main content could bedevided into three parts:（1） The influence of the change of water level and inflowconcentration on the nitrifying, denitrifying capacity of microorganisms;（2） Theinfluence of padding in constructed wetlands （CWs） on the nitrifying and denitrifyingcapacity of microorganisms;（3）Biological species and distribution of microorganismsin CWs’ system were analysed and microbial diversities were invested usingPCR-DGGE protocols in molecular biology. The main conclusions as follows:（1） In the VFCW+HFCW system with slag padding， the nitrifying capacity ofmicroorganisms in VFCW decreased with the increase of the padding depth whenpollutant inflow concentration was same and water level was different in VFCW （thewater level respective was60cm and45cm）. The nitrifying capacity decreased from0.296mg·kg^-1·h^-1to0.109mg·kg^-1·h^-1on high water level condition and from0.486mg·kg^-1·h^-1to0.045mg·kg^-1·h^-1on low water level condition. The nitrifying capacityof microorganisms in HFCW decreased with the increase of the padding depth anddescended with flow process. It’s obvious that the denitrifying capacity ofmicroorganisms were different with the change of water level in VFCW. Thereduction of water level make the denitrifying capacity to decline of middle and deeppacking layer in VFCW+HFCW system， that illustrated that high water level makefor the growth of denitrifying bacteria.（2） Under the conditions of the combination of VFCW+HFCW filled with slags，when controlling the VFCW water level at45cm unchanged， and changing theinfluent ammonia nitrogen and nitrate concentration， the capacity of microbialnitrification and denitrification in the wetland system are significant changed. Theincreased NH₄⁺-N concentration of the influent improved the nitrification capacity，with the average raise of0.195mg·kg^-1·h^-1， and promoted the reproduction ofnitrifying bacteria; At the same time the decreased NO₃^--N concentration in the fluentimproved the denitrification capacity, with the average of0.189mg·kg^-1·h^-1increasing to1.007mg·kg^-1·h^-1.（3） In the zeolite padding HFCW+VFCW system with full pool level， thenitrifying capacity enhanced with the decrease of NH₄⁺-N inflow concentration in firstlevel HFCW， and it increased from0.020mg·kg^-1·h^-1to1.542mg·kg^-1·h^-1. Thenitrifying capacity decreased from0.138mg·kg^-1·h^-1to0.067mg·kg^-1·h^-1when theconcentration of available NH₄⁺-N declined and the growth of nitrifying bacteria wasrestricted in second level VFCW. The influence of the reduction of NH₄⁺-N inflowconcentration on denitrifying capacity wasnot obvious， that showed it is not directrelation between NH₄⁺-N concentration and the number and distribution ofdenitrifying bacteria.（4） In the slag padding HFCW+VFCW system with full pool level， thenitrifying capacity of middle padding layer was higher that low layer in slag HFCWwhen NH₄⁺-N inflow concentration was about8mg·L^-1. But at same condition ofNH₄⁺-N inflow concentration， the law of nitrifying capacity in zeolite HFCW wasadverse. The nitrifying capacity of middle padding layer in slag VFCW was just1/2of it in zeolite VFCW. The denitrifying capacity in slag and zeolite CWs was closeand varied from1.35to1.61mg·kg^-1·h^-1. When NH₄⁺-N inflow concentration wasabout3.2mg·L^-1， the nitrifying capacity of middle padding layer in slag and zeoliteHFCW were little difference but all of the nitrifying capacity of low padding layer inslag HFCW were lower than0.04mg·kg^-1·h^-1. the nitrifying capacity of slag VFCWwas higher that zeolite VFCW. The denitrifying capacity of slag and zeolite CWswere close and maintained at1.40¹.60mg·kg^-1·h^-1. The results showed that thedifference of padding would have an affect on nitrifying capacity but have littleinfluence on denitrifying capacity.（5） The diversity of microorganisms in zeolite CWs was analysed usingPCR-DGGE protocols in molecular biology. Many DGGE separation stripesillustrated that there were many kinds of microorganism in CWs. In the slag paddingHFCW+VFCW system with full pool level, when NH₄⁺-N inflow concentration wasabout8mg·L^-1, the dominant bacteria in HFCW were Alphaproteobacteria,Betaproteobacteria and Gammaproteobacteria, and the dominant bacteria in VFCWwere Alphaproteobacteria, Bacillus and Actinobacterium. When NH₄⁺-N inflowconcentration was about3.2mg·L^-1, the dominant bacteria in HFCW wereProteobacteria and Nitrospirae, and the dominant bacteria in VFCW were Bacillus,Actinobacterium, Proteobacteria and Gemmatimonas.