Purification Effect And Optimization Techniques Of Composite Constructed Wetland

In recent years, aquaculture has developed rapidly. As one of themain models of freshwater culture, pond culture is faced with more andmore problems. With the continuous improvement of production scale,increasing stocking density of fish, a large amount of feeding and moreand more pollutants by metabolism of fish led to more endogenouscontamination in the pond. Meanwhile, the deterioration of exogenousenvironment of water had caused frequent occurrence of fish disease,which created enormous loss to aquaculture. Thus, it was important toimprove water quality for aquaculture. In order to alleviate theseproblems, many water treatment techniques have been applied toaquaculture. Traditional treatment included physical sterilization,chemical drug treatment and microbiological control, etc. Although thesemethods improved the water quality in some extent, drugs’ andchemical reagents’ residues would make other contamination. As anefficient, environmentally friendly water treatment technology,constructed wetlands have been applied the treatment of aquaculturewater. Composite constructed wetlands combining different types of wetlands, can make up the lack of different types of wetlands in order toachieve better water purification effects.The aim of the present study was to establish a regulation anddemonstration model in Yangtze River Delta region for controlling waterquality of pond culture region, and promoting sustainable development ofpond culture. we had built a ecological aquaculture model as the theme ofpurifying water by composite constructed wetland. Compositeconstructed wetlands consist of upward vertical flow constructed wetlandand downward vertical flow constructed wetland. Water from the culturepond was purified by composite constructed wetland and flowed back tothe culture pond, which achieved the aim of aquaculture water recyclingand wastewater zero emissions.Before the running of composite constructed wetlands, annual waterquality of water source, impounding reservoir and culture pond wasmonitored. The water samples in these three regions were obtained in theend of each month from December of2012to October of2013. Themajor indexes including temperature(T), pH, dissolved oxygen(DO),transparency(SD), total phosphorus(TP), total nitrogen(TN), ammoniumnitrogen(NH3-N), nitrite nitrogen(NO-2-N), permanganate index(CODMn)and chlorophyll a(Chla) were determined. The results showed that thedifferences were not significant for SD and NH3-N of water source, butsignificant differences existed among the other indexes in different levels, and the water quality sort was that summer＞autumn＞spring＞winter;significant differences existed among the whole indexes of impoundingreservoir in different levels, the water quality sort was that autumn＞winter＞spring＞summer; the differences were not significant for pH,DO, SD, CODMnand Chla of culture pond, but significant differencesexisted among the other indexes in different levels, the water quality sortwas that autumn＞spring＞summer＞winter. Water in culture system wasall eutrophicated, inside, water in culture pond was hyper eutrophicated.In conclusion, water of the culture system needed to be purified as thewater quality was bad that the level was Ⅳ-Ⅴ class mostly(GB3838-2002).During the running of composite constructed wetland, water qualityof influent and effluent was monitored as five times. The major indexesmonitored were same to above. The results showed that the averageremoval rates of TP, TN, NH3-N, NO-2-N, CODMnand Chla were24.8%,40.4%,27.1%,57.0%,4.7%,71.1%. The level of effluent quality wasbetter than influent, and except late August, the rest effluent quality levelwere Ⅲ class(GB3838-2002), meeting the needs of aquaculture water.eutrophication of influent and effluent were evaluated by usingcomprehensive nutrition state index(T I(∑)), and it showed that T I(∑)of effluent was lower than influent indicating eutrophication was lower.Above all, composite constructed wetland was effective to purify culture water.Composite constructed was optimized in the early andlate operation. In the early operation, Iris pseudacorus of poor growthwere replaced by Pontederia cordata which growed well, overflow portswere set on the side wall of constructed wetland; in the late operation,sedimentation tank was transformed.