Aquaculture has become one of the major sources of lake eutrophication, due to the lack of direct and efficient technologies for pollution control and remediation. This study proposes a novel ecological dam (Eco-dam) system, which consists of biofilter floating beds and plant floating beds that form an enclosure (the test zone) around the breeding area that allows lake water to pass through. A pilot-scale test was conducted to test pollution control and in situ bioremediation during breeding of Chinese mitten crab (Eriocheir sinensis) in Yangcheng Lake, China. The results showed slight improvement of water quality in the test zone compared with the breeding zone. The biofilm that formed on the biofilter played a major role in removal of organic pollutants and nitrogen (0.609 kg COD/(m2·d), 0.512 kg NH4+-N/(m2·d), 0.482 kg NO2−-N/(m2·d), and 0.112 kg NO3−-N/(m2·d)). Both proteins and volatile suspended solids (VSS) in the Eco-dam biofilm decreased from the water surface towards the lake bottom, especially below 0.5 m depth. The average ratio of VSS to suspended solids in the biofilm was 0.337 ± 0.025 g/g. Analysis with the Illumina MiSeq System confirmed the presence of a diverse microbe population in the biofilm, performing organic carbon removal and nitrification and denitrification, with limited photosynthesis near the lake surface and methane oxidation near the lake bottom.
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