Utilizing a settling pond-based constructed wetland for the treatment of shrimp aquaculture wastewater – From laboratory to field scale: A case study in Ben Tre Province, Vietnam

Abstract

The shrimp aquaculture industry, while bringing high economic benefits, simultaneously presents many environmental challenges for many countries, including Vietnam. Our survey results regarding shrimp farming management in 30 representative rural households within Ben Tre province have revealed that 96.7% of wastewater does not meet the allowable standards. Although approximately 76.66% of which is crudely treated by settling ponds, the percentage of substandard wastewater is reduced only to 70%. Unfortunately, >93% of the wastewater is discharged directly into the environment. Faced with that situation, a proposed wastewater treatment option suitable for the rural areas is to utilize settling ponds and indigenous reeds (P.australis and P.vallatoria) to build constructed wetlands (CW). A lab-scale CW was designed to mimic a settling pond on the surveyed farm, which was scaled down to a ratio of 1:500, aiming to validate the efficacy of the CW approach. Accordingly, the P.vallatoria-planted CW with a density of 25 roots/m2 effectively treats the wastewater to meet the permissible standard within 4 weeks. The removal efficiencies of organics, nutrients, heavy metals, and total coliform could reach up to 80, 85, 91, and 41%, respectively. Upon transitioning to the field scale, these efficiencies increased up to 13.09, 18.79, 29.47, and 5%, respectively. More importantly, the treatment time could be shortened to 3 and 2 weeks, respectively, when the wastewater is diluted 1.5 and 3 times, thereby serving as a foundation to upgrade the current farming model from intensive to super-intensive.