Abstract
In aquaculture, constructed wetland (CW) has recently attracted attention for use in effluent purification due to its low running costs, high efficiency and convenient operation,. However, less data are available regarding the long-term efficiency of farm-scale CW for cleaning effluents from inland freshwater fish farms. This study investigated the effectiveness of CW for the removal of nutrients, organic matter, phytoplankton, heavy metals and microbial contaminants in effluents from a blunt snout bream (Megalobrama amblycephala) farm during 2013–2018. In the study, we built a farm-scale vertical subsurface flow CW which connected with a fish pond, and its performance was evaluated during the later stage of fish farming. The results show that CW improved the water quality of the fish culture substantially. This system was effective in the removal of nutrients, with a removal rate of 21.43–47.19% for total phosphorus (TP), 17.66–53.54% for total nitrogen (TN), 32.85–53.36% for NH4+-N, 33.01–53.28% NH3-N, 30.32–56.01% for NO3−-N and 42.75–63.85% for NO2−-N. Meanwhile, the chlorophyll a (Chla) concentration was significantly reduced when the farming water flowed through the CW, with a 49.69–62.01% reduction during 2013–2018. However, the CW system only had a modest effect on the chemical oxygen demand (COD) in the aquaculture effluents. Furthermore, concentrations of copper (Cu) and lead (Pb) were reduced by 39.85% and 55.91%, respectively. A microbial contaminants test showed that the counts of total coliform (TC) and fecal coliform (FC) were reduced by 55.93% and 48.35%, respectively. In addition, the fish in the CW-connected pond showed better growth performance than those in the control pond. These results indicate that CW can effectively reduce the loads of nutrients, phytoplankton, metals, and microbial contaminants in effluents, and improve the water quality of fish ponds. Therefore, the application of CW in intensive fish culture systems may provide an advantageous alternative for achieving environmental sustainability.
Highlights
In recent years, rapidly growing aquaculture has provided an important source of animal protein nutrition, and the production of freshwater aquaculture is 30.1374 million tons in 2019 in China [1]
The fish in the constructed wetland (CW)-connected pond showed better growth performance than those in the control pond. These results indicate that CW can effectively reduce the loads of nutrients, phytoplankton, metals, and microbial contaminants in effluents, and improve the water quality of fish ponds
The phenomenon may be caused by the aerobic respiration of heterotrophic microorganisms in CW, which can effectively degrade the pollutants in aquaculture wastewater [16]
Summary
Rapidly growing aquaculture has provided an important source of animal protein nutrition, and the production of freshwater aquaculture is 30.1374 million tons in 2019 in China [1]. Inland pond culture is the major aquaculture model in China, having an area of 2,644,730 ha [1]. It is a well-known fact that the fish are fed heavy artificial diets in freshwater pond culture. Large amounts of un-utilized diet and produced excrement can cause the deterioration of the water quality [2]. Aquaculture effluent has become a serious public concern, because it is rich in solid matter, organics, and dissolved metabolites, which may cause eutrophication, silting, oxygen depletion, ammonia and sulfide toxicity in the aquatic environment [4]. The untreated effluent is likely discharged into rivers or lakes, affecting the quality of water source for drinking [5]. The remediation of effluent is required in aquaculture farms to ensure environmental responsibility and sustainability
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