Effects of purification of recirculating water in over-winter aquaculture in brackish wastewater constructed wetland

To develop constructed wetland in the application of aquaculture, the purification effect and overwinter cultural performance of obscure puffer (Takifugu obscurus) in the recirculating over-winter aquaculture combined with integrated brackish wastewater (from 7.6‰ to 9.9‰ of salinity) constructed wetland were investigated. The results showed that the average survival rates of young fish of obscure puffer was (76.94±13.87)% after 166 d overwinter culture, and the feed conversion coefficient (FCC) was 5.49±1.77. The water temperature of the system was above the lowest survival temperature of the obscure puffer without heating. The total nitrogen removed rate of the system was 30.5%, the total ammonia nitrogen was 69.6%, nitrite nitrogen was 96.1%, nitrate nitrogen was 9.7%, total phosphorous was 18.4%, chemical oxygen demand was 38.8%, total suspended solids was 79.7%, from the overwinter aquaculture wastewater under a hydraulic loading rate of 0.679 m/d. Various water quality parameters in the culture tanks were deemed suitable for obscure puffer overwinter culture. The removal rates of total nitrogen and nitrate nitrogen in overwinter were significantly lower than that in summer, however, there was no obviously difference between winter and summer in the removal rates of the other parameters. Mass removal rates were increased with the increase of mass loadings in the range of the investigated mass loading. The actual ratio of wetland area (Aw) to culture tank area (At) was 1.26, and the estimated optimal ratio Aw/At was 0.36-0.97. Thereby, cultural densities of obscure puffer did not reach the maximum in the recirculating overwinter aquaculture system. Consequently, the wetlands exhibited flexibility and reliability in consistently removing the main pollutants from obscure puffer recirculating overwinter aquaculture system. The study showed that the recirculating aquaculture system could be developed in overwinter aquaculture.