Implementation of a constructed wetland for the sustainable treatment of water in shrimp farming activities, Mekong delta, Vietnam

In the Mekong delta, inland-based shrimp breeding is a profitable activity requiring significant inflow of high quality freshwater. In turn, discharge of substantial loads of poor quality effluents causes salinization and eutrophication of adjacent water bodies and favors the advent of disease outbreaks. Therefore, development of aquaculture systems targeting water treatment and reuse has become the cornerstone for long-term sustainability. The project focused on the implementation of a continuous water recirculation and filtration system for the removal of nitrogen and phosphorus compounds, organic matter and bacterial pathogens in shrimp culture basins. For this purpose, a multi-stages constructed wetland (CW) was designed, which included successive phases for passive filtration, denitrification and UV disinfection. This CW had a 21 L practical volume and was connected to a 400 L shrimp culture tank, with a constant flow rate of 0.016 m3/h (HLR = 1.54 m/d and HRT = 1.31 h). As a result, denitrification was highly effective, with the complete removal of nitrite and ca. 78% reduction in nitrate throughout the 45 days of the experiment. Ammonia and phosphorus concentrations were kept constant (23 and 0.017 mg/L respectively). Dissolved organic matter, reaching 379 mg/L within the CW influent, was reduced to 90.5 mg/L (76% reduction) in the effluent. Vibrio sp., (potential shrimp pathogens), were fully removed and a 4 Log reduction of total aerobic bacteria was attained. In conclusion, the CW developed so far demonstrated high efficacy in water treatment, opening the door to real size, sustainable water-cleaning systems in shrimp aquaculture.