Design And Application Research Of Modular Constructed Wetlands

Constructed wetlands have been applied to treat and recycle pond aquaculture tail water recently.The pond aquaculture tail water was reused in the fishpond after been treated by the constructed wetlands which formed an integrated constructed wetlands-fishpond circulation aquaculture system.This kind of integrated circulation aquaculture system.has been regarded as the one of the green culture modes in China In this study,a new combined modular constructed wetland was constructed and was combined with aquaculture pond to form a pond recirculating aquaculture system.The treatment efficiency of the new modular constructed wetland on pond aquaculture tail water,the optimal operation parameter of the new modular constructed wetland,the regulation effect on the water quality in the fishpond,and the constructed wetland-fishpond area ratio were calculated.The main research results are as follows:The new combined modular constructed wetland was composed of pretreatment basin,water inlet area,the upward flow wetlandⅠarea,catchment area,the upward flow wetlandⅡarea and outlet area Geomembrane is laid at the bottom and on both sides of the whole wetland for seepage prevention.Shale ceramsite is used as the wetland substrate,with a particle size of 0.5～1 cm and a porosity of 0.42.The pond aquaculture tail water is pumped through an inlet lifting pump into the inlet area and precipitated by inclined plate.After pretreatment,the upper clear water flows into the inlet area through the overflow port,and the silt deposited in the inlet area is processed regularly.The water then flowed in the water inlet area,the upward flow wetlandⅠarea,catchment area,the upward flow wetlandⅡarea successively and flow back into the fishpond.Disinfect equipment could be installed in the outlet and disinfect the water before returning into the fishpond.The optimal operating hydraulic retention time of the combined wetland was studied.The effects of different hydraulic retention time on the water treatment capacity of combined wetland were discussed.The results showed that when the hydraulic retention time was 5 h,the system with consideration of time effective principle had a better purification efficiency and a larger water treatment capacity,and the removal rates of TN,TP,and COD_Crcould reach 46.07%,51.25%,and 51.6%,respectively.The results showed that the removal rates of TN,TP,COD_Crand Chla from the pond aquaculture tail water were 33.07%～51.55%,40.12%～72.58%,32.04%～56.98%and 38.40%～78.40%respectively.The TAN,NO₂^--N and COD_Crwere more effectively removed in the upward flow wetlandⅠ,NO₃^--N,TP and PO₄^3--P were more effectively removed in the upward flow wetlandⅡ,whereas TN were both effectively treaed in the upward flow wetlandⅠarea and upward flow wetlandⅡ.At the later stage of the experiment,the combined wetland could effectively regulate the physical and chemical indexes of aquaculture pond water quality,and the concentrations of nitrogen,phosphorus and COD_Crwere significantly lower in the test pond than the control pond.During the experiment time Arundo donax and Canna indica grew well and the plant coverage rate,plant height and root length increased gradually.The contribution of plants absorption of nitrogen and phosphorus nutrients to the total removal were studied.The results showed that the contribution of Canna indica on nitrogen and phosphorus removal were only 7.89%and 5.40%,and the contribution of Arundo donax on nitrogen and phosphorus removal were only 5.13%and 1.00%,respectively.Canna indica had a higher contribution on nitrogen and phosphorus removal thanArundo donax indicating a better absorptive capacity.In addition,the aboveground part of both plants had a higher contribution on N and P removal than the underground part,.The dynamic process of biofilm formation in wetland was studied,and the results showed that:API ZYM（API）assay was used to evaluate the fingerprint of extracellular enzyme in the plant root and substrate in the wetland to identify the microbial metabolism activity and microbial functional diversity in relation to biofilm development processes in the start-up phase.Of the 19 enzymes examined,15enzymes（indicators of phosphorus,nitrogen and carbon acquisition）showed evidence of activity in the plant roots,rhizosphere substrate and non-rhizosphere substrate suggesting that the extant heterotrophic microbial communities in the wetland were able to decompose a wide spectrum of organic compounds although in the start-up phase.The number of active enzymes（N）,the synthetic enzyme index（SEI）,and Shannon,s diversity index（H’）significantly increased in the start-up phase,and approximately 60 days were required to reach consistent for biofilm development in the surface of plant roots and rhizosphere surface of plant roots and rhizosphere substrate while 80 days is not enough for the growth of biofilm in the surface of the non-rhizosphere substrate.The N,SEI and H’in the plant roots and rhizosphere substrate while there was no distinct differences between the plant roots and rhizosphere substrate.The results of this study provided a new configuration in aquaculture systems in areas where water resources are limited to treat effluents from the intensive fishpond and reveal the process of biofilm development in the constructed wetland in the start-up phase.