Study On Purification Of Aquaculture Tail Water In Taihu Lake Basin By Floating Island With Emergent Plants

Taihu Lake Basin is located in the center of Yangtze River Delta in China,and plays an important strategic role in China’s economic development and ecological construction.With the vigorous development of aquaculture in Taihu Lake Basin,the problem of tail water pollution is becoming more and more serious,which poses a serious threat to the water ecological environment in Taihu Lake Basin.With the release of"Taihu Lake Basin Pond Aquaculture Water Discharge Standard"in 2017,how to treat aquaculture tail water safely,efficiently and at low cost has become an urgent problem to be solved.Artificial floating island,as an ecological sewage remediation technology,has been increasingly applied to practical ecological remediation projects in recent years.Artificial floating island uses soilless aquatic plants to be carried on floating carriers and placed in ponds,rivers,lakes or other waters.Through the absorption capacity of floating island plants and the synergistic effect of plant-microorganism,nutrients in water are absorbed,and finally the purpose of purifying polluted water is achieved.The emergent plants have strong adaptability,strong purification ability,easy management and harvesting,as well as ornamental landscape,and have more advantages in the selection of floating island plants.This study is based on the ecological reconstruction project of Zhangyadang East Fish Pond in xinying village,Bachang Street,Wujiang District,Jiangsu Province.Three emergent plants,Canna indica L.,Acorus calamus L.and Lythrum salicaria L.,were selected as test plants,and the purification effects of the three plants and their combinations on aquaculture tail water were compared and analyzed.The results showed that Canna indica L.had the strongest TN removal ability in floating islands with an average removal rate of 66.05%.Lythrum salicaria L.has the strongest TP removal ability,with an average removal rate of 65.52%.The average removal rate of NO₃-N by Acorus calamus L is 73.25%.The average removal rate of NH₄⁺-N by Canna indica L.was 51.30%.In order to further improve the purification ability of floating islands,based on the removal rate of artificial floating islands planted by single plants,three kinds of plant combination floating islands were constructed,respectively Canna indica L.+Lythrum salicaria L.,Canna indica L.+Acorus calamus L.,Canna indica L.+Acorus calamus L.+Lythrum salicaria L..The experimental results show that the improvement of water quality indexes of floating island with plant combination is higher than that of floating island with single plant cultivation.The removal rate of TP by Canna indica L.+Lythrum salicaria L.is 73.33%.The removal rate of n and COD by Canna indica L.+Acorus calamus L.is 84.41%and 61.61%,respectively.In order to explore the purification upper limit of artificial floating island to aquaculture tail water,Plant-filler composite floating island was constructed by hanging combined packing under artificial floating island.The results showed that the removal rates of TN,TP,NO₃-N,NH₄⁺-N and COD increased by 5.16%～8.92%,7.26%～16.81%,2.59%～6.37%,1.13%～19.04%,respectively,compared with those of the floating islands without packing.The purification speed of plant-filler composite artificial floating island is faster.Considering the effluent quality of floating island after 5 days and 31 days of operation,and the adaptability of plants under long-term operation conditions,Canna indica L.+Acorus calamus L+filler was finally selected as the optimal configuration of artificial floating island in the tail water purification project of xinying village aquaculture in Baguan Street,Wujiang District.The removal rate of P can be further improved by adjusting the plant ratio,adding physical facilities such as biological ropes and brushes,or increasing the coverage rate of artificial floating islands in oxidation ponds and ecological ponds.