Purification Performance Of Odorous-black Water And It's Microbial Mechanisms In Integrated Constructed Wetland

With the rapid development of economy and urbanization,environmental deterioration described as an increasingly perilous situation.The malodorous black river is common in many areas of China,in particular,seriously restricts the construction of ecologically-civilized city.Although the effect of physical and chemical methods such as artificial aeration,sediment dredging and enhanced flocculation is obvious in river harnessing,there are still various problems with those methods,such as high economic input,secondary pollution and short-term effect,et al.Therefore,how to rehabilitate malodorous black river more economically and effectively and maintain their good ecological functions has become a key issue for the construction of eco-civilization.Based on the characteristics of malodorous black river and the screening of suitable plants,a pilot-scale integrated constructed wetland system?HVHCW?was designed and constructed to investigate the effect of hydraulic retention time?HRT?,wetland construction matrix and seasonal changes in temperature et al on removal efficiency of pollutants by HVHCW.Meanwhile,microbial community changes were analyzed by high-throughput sequencing techniques of bacterial 16 S r DNA gene,and the pollutant removal in flora-microbe-matrix combination mechanism was illuminated.On the basis of the pilot studies,the HVHCW engineering application research is further developed,and extended on the comprehensive performance evaluation of the HVHCW system with network Analytic Hierarchy Process?ANP?.Traditional subsurface flow constructed wetlands are easy to plug,and it has limited efficiency on removal of organic matter such as nitrogen and phosphorus.In order to address the problem,two groups of parallel HVHCW pilot systems consist of micro-aerobic hydrolysis,downflow-upflow constructed wetland and horizontal subsurface flow constructed wetland units were designed and constructed filled with lava and gravel respectively.The constructed wetland was planted with Myriophyllum,Canna and Cyperus as purifying plant.The research indicated that when the hydraulic retention time?HRT?was 2d,the two HVHCW systems both have an effective removal performance for the mild odorous black water.For severe odorous black water and when the HRT was 3d,in lava HVHCW system,the average removal efficiency of TSS,BOD₅,COD,TN,NH₄⁺-N and TP were 89.39%,90.63%,72.02%,67.61%,72.11%and 93.75%,respectively.Accordi ng to GB18918-2002,all the data reach the standard A of the first class for“Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant”;in gravel HVHCW system,all the indices also reached the standard A of the first class except the removal of NH₄⁺-N.The concentration of Dissolved Oxygen?DO?in effluent was positively correlated with the removal efficiency of BOD₅,COD,TN and NH₄⁺-N.It was found that the Micro-aerobic hydrolysis unit significantly reduced the Total Suspended Solids?TSS?in the influent,accounting for more than 60%of the total removal rate.Micro-aerobic hydrolysis unit could significantly reduce the risk of plugging wetland,ensuring the long-term stable operation of the system.In order to further improve the efficiency of HVHCW,the effects of HRT,matrix,season and temperature on the removal of pollutants were analyzed.The results showed that all the effluent concentration of DO,TSS,BOD₅,COD,TN,NH₄⁺-N and TP in the system increased more or less during HRT stage from 4d to 1d,but the TSS removal rate still maintained above 50%in micro-aerobic hydrolysis unit.Due to the different content of mineral elements such as Al,Fe,Ca and Mg,the adsorption capacities of phosphorus on lava and gravel were 756.1 and 256.9 mg kg^-1,respectively.Moreover,TP removal in the lava and gravel systems was 97.30%and 91.70%,respectively.Seasonal variation by temperature change on the HVHCW had a greater influence on the removal efficiency of pollutants.For the lava HVHCW system,at the lowest temperature month in winter?11.9??,the removal rates of BOD₅,COD,TN,NH₄⁺-N and TP decreased by 12.07%,10.75%,13.30%,17.90%and 5.96%respectively compared with the with the highest temperature months in summer?29.1??.In order to further understand the mechanism of the pollutants degradation in HVHCW system,the bacterial 16 S r DNA gene was analyzed by high-throughput sequencing technology.The results showed that in HVHCW system,Proteobacteria was the most abundant,accounting for about 42.04%of the total number of bacteria;Betaproteobacteria subclasses was dominant,accounting for about 63.15%of the Proteobacteria.Thiobacillus and Bacillus were the dominant species,accounted for about 11.91%and 5.32%,respectively.Microbial diversity indices were significantly different at different depths of wetland systems.The analysis indicated that the Shannon index and BOD₅,COD,TN and NH₄⁺-N removal rate were significantly correlated.In HVHCW system,abundance of denitrifying bacteria was higher than Ammonia Oxidizing Bacteria?AOB?and Nitrite Oxidizes Bacteria?NOB?.A positive correlation was also found between the abundance of major denitrifying bacteria and relative removal rate of TN in corresponding treatment units.The analysis of the denitrification mechanism in HVHCW system showed that NO₂-N was accumulated in each unit;the Nitrite Accumulation Rate?NAR?was related to the p H value,DO,temperature,Free Ammonia?FA?,and the abundance of AOB and NOB.It was speculated that the removal of nitrogen in the system was achieved by the combination of the complete nitrification and denitrification pathway and short-cut nitrification-denitrification pathway.Based on the successful pilot study of the HVHCW technology,a demonstration treatment of malodorous black river was established in Nanning,and project processing capacity was 225⁶95 m³ d^-1.The engineering operation results of the HVHCW demonstration project showed that average removal of TSS,COD,TN,NH₄⁺-N,TP of polluted river water were 88.67%,63.79%,50.72%,71.78%and80.85%,respectively.Moreover,the outlet water quality was better than Standard B of the first class in "Discharge standard of pollutants for municipal wastewater treatment plant"?GB18918-2002?.The evaluation of HVHCW based on the ANP comprehensive evaluation system showed that the constructed wetlands system had a very good performance in malodorous black river pollutant purification and ecological restoration with promising benefits in economy,environment and management.