performance evaluation and efficiency enhancement of water purification system in a semi-recirculated aquaculture system (ras)

In this study, the status and efficiency of the wastewater treatment system of a semi-recirculated aquaculture system (ras) in firoozkooh county were investigated. information regarding aquaculture systems in the region was obtained with the guidance of the experts at the agriculture organization in firoozkooh county. during visits to the recommended aquaculture systems, namrud aquaculture was selected. to evaluate the effect of water pollutants on fish, national standards 8726 and 7961 were employed to determine water quality parameters and to guide sampling and sample protection. water quality parameters were assessed at four stations to determine the extent of pollution. the results indicated that ammonia (nh3), nitrite (no2), and nitrate (no3) were the main issues in this aquaculture system. rainbow trout (oncorhynchus mykiss) exposed to ammonia levels exceeding the limits set by national standard 8726 displayed behavioral changes, including altered swimming speed, total distance traveled, average direction change, and increased average distance from a central point. the second aeration tower was found to be ineffective in releasing dissolved gases due to its inappropriate design, including the spacing between floors and lack of proper atmospheric connection. it is recommended to redesign the second aeration tower, elevate the second entrance pond, and adjust the return flow to the grit chamber to reduce suspended particles and improve the water quality parameters of the effluent.