Purification of Tail Water from Large-scale Aquaculture by Ecological Ditch-Root Channel Wetland System
[Objective]The capacity of a drainage ditch modified as a root channel wetland(ecological ditch)to purify aquaculture tail water was analysed in order to provide a scientific reference for circular aquaculture and pollution reduction in areas of large-scale aquaculture.[Methods]The study site was Koujia Lake Park,in Helan County,Ningxia Hui Autonomous Region,with an aquaculture area exceeding 500 hectares.We constructed experimental root channel wetlands on both sides of an original farmland drainage ditch to improve the purification capacity of the ditch.To evaluate the purification effect of this ecological ditch system on the tail water from large-scale aquaculture,we collected water samples in the ecological ditch in 2022 and 2023.[Results]In 2022,at the onset of its operation,the ecological ditch effectively purified phosphate,nitrite,and ammonia nitrogen in the aquaculture tail water,with the purification rate being 97.15％,96.00％,and 59.65％,respectively.In 2023,the ecological ditch effectively purified the aquaculture tail water on a daily basis.The maximum purification rate for phosphate,nitrite,and ammonia nitrogen was 87.70％,72.89％,and 83.15％,respectively.The concentration of ammonia nitrogen at the purification end of the system was less than 0.5 mg/L,reaching the Class Ⅱ standard of the'Surface Water Environmental Quality Standard'(GB3838-2002).After shortening the purification distance by half,the ecological ditch still had a good purification effect on the aquaculture tail water,with no significant increase in the nutrient concentration at the ditch outlet(p＜0.05).[Conclusion]The construction of a root channel wetland around the drainage ditch could effectively purify the tail water generated in the daily aquaculture operations across a large-scale aquaculture area,and achieve water recycling.
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