Evaluating the performance of the wastewater treatment plant in intensive whiteleg shrimp (Litopenaeus vannamei) brackishwater pond aquaculture

Intensive technology of whiteleg shrimp (Litopenaeus vannamei) aquaculture generates wastewater that, if not properly managed, can adversely affect the long-term viability of brackishwater pond aquaculture and threaten environmental sustainability. This study evaluates the performance of wastewater treatment plant (WWTP) associated with this intensive whiteleg shrimp aquaculture. Wastewater samples were collected from various locations: the reservoir, grow-out pond, WWTP inlet, WWTP, WWTP outlet, and the sea, at four stages of shrimp growth (15, 45, 75, and 105 days of culture (DOC)). Key variables analyzed included temperature, salinity, pH, dissolved oxygen (DO), ammonia (NH3), nitrate (NO3), nitrite (NO2), phosphate (PO4), total organic matter (TOM), biochemical oxygen demand 5-day (BOD5), and total suspended solids (TSS). Data from the WWTP inlet and outlet were used to assess removal efficiency (RE) and calculate compliance index (CI) values for evaluating WWTP performance. The Storage and Retrieval (Storet) system was used to evaluate the wastewater quality status. The results indicated that the WWTP utilized constructed wetlands with a hydrological design that included both surface and subsurface flow. On the culture of 105 DOC, the concentrations of NH3, NO3, and PO4 at the WWTP outlet surpassed the threshold for marine and brackishwater aquatic life. However, the levels of pH, DO, NO2, TOM, BOD5, and TSS were within the acceptable range for marine and brackishwater aquatic life. The WWTP covered 9.51% of the total pond area, with a wastewater residence time of 0.76 days (18 h). It was effective in reducing TSS concentration (RE 60.05%) and demonstrated moderate effectiveness in lowering concentrations of NO3 (RE 58.71%), NO2 (RE 51.48%), PO4 (RE 49.85%), and BOD5 (RE 41.15%). The WWTP significantly reduced levels of NO2, TOM, BOD5, and TSS while raising the pH, achieving a compliance rating (CI < 1.00). Initially, the wastewater quality at the WWTP inlet was classified as class D (poor or heavily polluted), but changed to class C (moderate or moderately polluted) by 75 and 105 DOC. However, NH3, NO3, and PO4 levels still exceeded acceptable limits for shrimp aquaculture. Overall, WWTP is successful in enhancing the quality of wastewater from intensive whiteleg shrimp brackishwater pond aquaculture. However, it has shown limited effectiveness in improving the levels of specific pollutants like NH3, NO3, and PO4. To improve the system’s efficiency, it is suggested to expand the WWTP area to 3.22 ha, increase the residence time to a minimal of 2 days, and add an aeration and equalization ponds to the system.