Mechanism Of Water Purification Of Polluted Lake Aquaculture Water By Eco-dam

Lake aquaculture is an important economic industry in China.However,if it is not well managed,water eutrophication may occur.At present,although numerous remediation technologies have been applied to treat lake eutrophication,direct and effective technologies for the control of pollutants from lake aquaculture are still missing.In this context,Eco-dam,an innovative integrated biological remediation technology,was proposed for the pollution control and ecological remediation of lake aquaculture.This research is funded by National Natural Science Foundation Council?No.51378305?.In the present study,first,to investigate the real control effect on aquaculture pollutants by Eco-dam,a pilot scale test of Eco-dam under simulated pollution control mode was established at a crab farm in Yangcheng Lake,and the water quality of studied area has been monitored for one year.Then,to study the water purification mechanism of biofilm attached on the biological fillers in Eco-dam,microbial activity tests and bacterial community structure analysis were conducted.Finally,for the mechanism of aquatic plant in Eco-dam,water spinach,a kind of economic plant,was selected to remove nitrogen and phosphorus in typical simulated aquaculture water under static state and dynamic state to study its absorption characteristics.The results indicated that:?1?Eco-dam showed some control effect on organic matter,nitrogen and phosphorus.COD_Cr,TN,NO₃^--N,NH₄⁺-N,TP,and DTP in the breeding area outside Eco-dam were lower than those in the polluted area by 3.2%,18.7%,4.4%,2.8%,28.6%,and 41.1%,respectively.?2?The biofilm grew on the biological fillers in lake water with low concentrations of nutrients,resulting in lower microbial activity than that of conventional activated sludge and biofilm biomass in wastewater treatment plant.But it still showed obvious microbial activity to clean the water around.The biofilm samples contained a ratio of VSS versus SS of about 0.54.The specific oxygen uptake rates of heterotrophic bacteria,ammonia oxidizing bacteria,and nitrite oxidizing bacteria in biofilm were7.3,19.9,and 6.1 mg O₂/gVSS·h,respectively.The specific ammonia oxidation rate was 0.34 mg NH₄⁺-N/gVSS·h.The specific nitrite oxidation rate was 0.15 mg NO₂^--N/gVSS·h,and the specific denitrification rate was 0.68 mg NO₃^--N/gVSS·h.?3?Complicated bacterial community structure was formed in the biofilm,and the most abundant bacteria at phylum level were Proteobacteria,Actinobacteria,Cyanobacteria,Firmicutes,Planctomycetes,Bacteroidetes and Nitrospirae.Meanwhile,various functional bacteria were found in the biofilm,such as ammonia oxidizing bacteria,nitrite oxidizing bacteria,sulfate reducing bacteria,denitrifying bacteria,heterotrophic bacteria,and steroid-degrading bacteria.?4?The removal effects of water spinach on nitrogen and phosphorus in simulated aquaculture water were positively coordinated with nitrogen and phosphorus concentrations under static conditions.The average removal efficiencies of nitrogen and phosphorus at low,medium,and high nutrient concentrations were 31.7%,68.4%,and 75.9%for TN,52.4%,74.8%,and 79.6%for NH₄⁺-N,40.8%,66.3%,and 78.2%for TP,and 48.0%,69.4%,and 80.5%for PO₄^3--P,respectively.However,under dynamic conditions,the removal effects were positively coordinated with hydraulic retention time.The average removal efficiencies of nitrogen and phosphorus at HRTs of 5 d,10 d,and 15 d were 6.1%,12.1%,and33.1%for TN,34.1%,57.9%,and 69.5%for NH₄⁺-N,8.0%,21.2%,and39.7%for TP,and 17.7%,23.5%,and 35.3%for PO₄^3--P??5?The NH₄⁺-N removal potentials of biofilm and aquatic plant in Eco-dam were estimated as 0.34 and 0.006 g NH₄⁺-N/m²·d,respectively,indicating that biofilm contributed more to the removal of NH₄⁺-N in aquaculture water than aquatic plant.However,the TP removal potential of aquatic plant was estimated as 0.67 mg TP/m²·d and aquatic plant contributed more to the removal of TP in aquaculture water than biofilm.