Shrimp pond effluent: pollution problems and treatment by constructed wetlands

Abstract

An intensive shrimp culture in Thailand has rapidly expanded especially along the coast during the last decade. Excessive feed basically given during the culture causes water and sediment in the pond to contain organic matter and nutrients in high concentration. After harvesting, discharging sediment is prohibited; however, pond water is mostly discharged directly to natural water resources without any effective treatment. The nutrient load discharged from shrimp ponds can form significant source of nutrients causing pollution and eutrophication in littoral areas of Thailand. The possibility of a subsurface-flow constructed wetlands application for treating shrimp pond effluent containing high salinity was studied. An experimental-scaled model planted with Acrostchum aureum (mangrove fern) in gravel was studied by comparison with one containing only gravel. The results showed that models can reduce suspended solids, biochemical oxygen demands, total organic carbon, totel nitrogen (T-N) and total phosphorous (T-P) up to 84%, 91%, 46%, 48% and 31%, respectively. Higher removal efficiencies for TOC, T-N and T-P of the planted model compared with the gravel model were clearly found.