Studies On Pollution Characteristics Of Nitrogen And Phosphorus In Recirculating Ponds Aquaculture System

Recirculating ponds aquaculture system is a new ecological ponds aquaculture guided by the idea of cyclic economy.In order to explore the pollution characteristics of nitrogen and phosphorus in recirculating ponds aquaculture system,a nine-month investigation was conducted into six typical recirculating ponds aquaculture systems.The survey included:the structure and size of the major functional area,species and stocking density,feeding mode,the composition of bait and the frequency of feeding,the breeding cycle,the water quality,etc.On the basis of finding out the current situation of the typical recirculating ponds aquaculture system,the research was conducted in three parts:evaluation of the water quality indicators, dynamic analysis of the critical water quality indicators, calculation of nitrogen and phosphrosus pollution load.The results showed:(1)Some recirculating ponds aquaculture systems were not in normal operation,the water quality of the water treatment unit was worse than the water quality of the ponds.The main problems included:the cycle numbers of water was not enough in the system, the water treatment unit was badly managed, the water treatment unit was communicated with the outside water system,etc.(2) The water quality of the shrimps-crabs ponds was good. In the shrimps-crabs ponds, the average concentrations of ammonia nitrogen, total nitrogen and total phosphorus satisfied the primary standard value of Water Quality Standards of Aquaculture Discharge in Taihu Lake Watershed (DB32/T1705-2001) (NH3-N?1.5mg/L,TN?2.0mg/L,TP?0.3mg/L). The water quality of the fish ponds was poor.In the fish ponds, the average concentrations of total nitrogen satisfied the inferior V standard value of Environmental Quality Standards For Surface Water (GB 3838-2002) (TN>2.0mg/L)and did't satisfy the primary standard value of Water Quality Standards of Aquaculture Discharge in Taihu Lake Watershed(TN?2.0mg/L). The water quality of the shrimps-crabs ponds was better than the water quality of the fish ponds.(3)In the water of the poods,the degree of nitrogen pollution was higher than the degree of phosphorus pollution.The concentration of nitrogen pollution was the significant factor that restricted the optimization of the water quality of aquaculture ponds. (4)The nitrogen and phosphrosus pollution load of fish farming was higher than The nitrogen and phosphrosus pollution load of shrimp-crab farming.Fish farming was more suitable as the extension goal of recirculating ponds aquaculture system.Considering the actual operation of recirculating ponds aquaculture system and learning from the experience of the researchs and the engineering projects,some measures were recommend in technology and management,technology measures including:arrange aquaculture area and decontamination area reasonbly,build recirculating ponds aquaculture system based on geographical conditions,choose artificial wetlands correctly,increase water purification technology,promote industrial recirculating aquaculture,etc;management measures including:guarantee rate of water exchange,strengthen aeration,ensure the maintenance and management of the water treatment unit,arrange species and stocking density reasonbly,improve the feed composition and feeding mode,etc.The measures could provide a reference for the project implementation and construction of recirculating ponds aquaculture system in the future.