Purification efficiency in an “in-pond raceway recirculating(IPRS)-shrimp-crab” tandem system aquaculture model
XIE Huiliang1,2, XU Gangchun1,2, WANG Yuyu2, XU Pao2*
1.College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China; 2.Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi 214081, China
Abstract: Temperature (T), pH, dissolved oxygen (DO)level, transparency (SD), contents of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen chemical oxygen demand (CODMn), and chlorophyll a and density, biomass and diversity index of phytoplankton and zooplankton were determined in a series of circulating aquaculture system with four functional areas (circulating fish, shrimp and crab culture, sewage collection area, wetland with aquatic plants and outlet of the shrimp and crab) including the front of the in-pond raceway system (IPRS), for 4 months to evaluate the purification efficiency of “in-pond raceway system(IPRS) -shrimp-crab” tandem recirculating aquaculture model. The results showed that the descending order of nutrient level was ranged as sewage collection area > outlet of the shrimp and crab > the front of the flume > constructed wetland. There were significant differences in contents of TN, in the front of the flume, in contents of TN, and CODMn in the sewage collection area, SD, TN, TP, in the constructed wetland and the outlet of the shrimp and crab between May and July (P<0.05), without significant difference between July and August(P>0.05), indicating that the levels of nutrients were increased to some extent with the increase in temperature, and that the index of nutrient tended to stabilize with the operation of the system. The density and biomass of phytoplankton and zooplankton were shown to be decreased rapidly in the aquaculture water passing through the purification zone, indicating that the decrease in nutrient level led to restraint the growth and reproduction of phytoplankton and zooplankton. However, there was an overall rising trend of Shannon-Weaver diversity index (H′), Pielou evenness index (J), and richness index (D) in phytoplankton and zooplankton over time, showing a gradually improved community structure and the more and more stable water environment in the system, which was more conducive to strengthening the self-purification ability of water quality. The average removal rate was 8.22% in TN, 33.41% in TP, 18.44% in 20.98% in CODMn and 30.41% in Chl-a in the circulation system, in which most of the culture water was in a state of slight eutrophication. It is concluded that the breeding model was characterized by purification effect on nutrients and gradually stable and increase in purification capacity in the whole system over time. The removal efficiency still needs to be further enhanced. The whole recycling process has reached the goal of “zero emission” of aquaculture influent water, and its successful application can provide certain scientific basis for the development of ecological intensive aquaculture.
2021, Vol. 36 
