| Due to the salinity effect and the complexity of the main components of pollutants in wastewater from the marine aquaculture farms, it is not feasible to adopt the current technologies and techniques either oriented for general freshwater aquaculture or domestic sewage system It is urgent for both marine aquaculture iarmers and local community to develop cost-effective and high-efficient wastewater treatment technologies and easy-management system, in order to support the sustainable development ofboth marine aquaculture and marine ecosystem.In this study, two different types of wastewater treatment systems, i.e., artificial wetland technology (AWT) and multi-soil-layering system (MSL), were adopted to test the feasibility and capacity of wastewater treatment for marine aquaculture by comparing the removal efficiency on COD, turbidity, total phosphorus (TP), total nitrogen (TN), ammonia and nitrate. In order to make a technical comparisons on removal capacity and relative feasibility at farm-scale operation, we also set up two hydraulic loadings lor the tests of MSL system, i.e.. MSLl-400L/(m2·d) and MSL2-600L/(m2·d), while four types of vegetation lor AWT system, including spartina anglica, reed bulrush and cattail as well as no plant for control. The main conclusions are as follows:1.The field survey found that the current typical marine aquaculture generated a serious pollution to local water ecosystem. Relative to fresh seawater, concentrations of COD, turbidity, TP, TN, ammonium and nitrate in wastewater discharged from marine aquaculture farmers were found as234mg/L,110NTU,13.1mg/L,0.70mg/L,10.2mg/L, and2.61mg/L, respectively, during a typical breeding cycle. Coefficient of water pollution are ranked as29.3,20.0,16.4,20.9,22.6, and5.7correspondingly. The discharge intensities of COD, turbidity, TP, TN, ammonium and nitrate were found as5195,295,16,220, and138kg per ton of shrimp yield, while these pollution fluxes reached as3.8×10-2,2.1×10-3,1.2×10-4,1.6×10-3,and1.0×10-3kg/m2·d, respectively. 2.There were remarkable removal capacities of COD, turbidity, TP, TN, ammonium and nitrate for MSL operation, however these capacities were depended to levels of hydraulic loading. By comparison, the average removal rates of these six parameters for MSL2were found as81%,81%,68%,41%,43%, and54%, respectively, which are7%,6%,9%,5%,5%, and9%lower than those of for MSL1. It indicates that the ability of low hydraulic loading is better than that of high hydraulic loading for removal capacity of marine aquaculture pollutants.3. There were relatively high removal capacities of COD, turbidity, TP, TN, ammonium and nitrate for AWT operation, and these removal capacities were relatively higher in the plant-covered AWT than no plant AWT. Among the different types of vegetation treatments, the average removal rates of COD, turbidity, TP, TN, ammonium and nitrate were found as65%,46%,31%,31%,30%, and36%, respectively, for spartina anglica AWT;58%,40%,21%,25%,22%, and30%, respectively for Reed AWT;51%,33%,17%,20%,19%, and28%, respectively, for Cattail AWT;45%,27%,12%,19%,15%, and20%. respectively, for no plant AWT. By comparison, the average mean removal rates of COD, turbidity, TP, TN. ammonium and nitrate under treatment of spartina anglica AWT were19%,19%.19%12%.15%, and16%higher than these of AWT without plants. This indicates that the ability to remove pollutants is ranked in order of spartina anglica wetland> reed\vetland> cattail wetland> wetland without plants.4.The ability of the removals of COD, turbidity, TP, TN, ammonium and nitrate for MSL groups are better than the groups of AWT. and the average removal rates for these parameters for MSL1were found16%,35%,37%,10%,12%, and18%higher than these of spartina AWT which was found as the highest removal efficiency among the four types of artificial wetland system. As a whole, the ability to remove pollutants from high to low in order is ranked as MSL1> MSL2> spartina anglica AWT> reed AWT> cattail AWT> wetland without plants. The removal efficiencies of COD, turbidity, TP, TN, ammonium and nitrate in MSL1are found as26g/m2·d,7NTU,0.07g/m2·d,0.61g/m2·d,0.61g/m2·d, and0.24g/m2·d, respectively, while21g/m2·d,4NTU,0.03g/m2·d,0.45g/m2·d,0.42g/m2·d, and0.16g/m2·d, respectively, in the spartina anglica AWT. |
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