Nutrient removal in vertical subsurface flow constructed wetlands treating eutrophic river water

Abstract

Four planted (Typha latifolia L.) pilot-scale vertical subsurface flow constructed wetlands were constructed to purify the eutrophic water of the Jinhe River in Tianjin (China) and to determine the feasibility of constructing a full-scale system in the future. The effects of intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on the nutrient removal potential were also evaluated. During the entire running period, supplementary aeration enhanced the chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus first order mean removal constants by 0.28 m/d, 3.05 m/d, 0.92 m/d, 0.74 m/d and 0.60 m/d, respectively, but reduced the nitrate-nitrogen removal constant by 1.72 m/d in contrast to non-aerated wetlands. A significantly positive contribution of PHPB to nutrient removal was obtained. The combination of artificial aeration and PHPB resulted in the augmentation of the first order mean removal constants by 0.29 m/d, 3.12 m/d, 1.15 m/d, 0.65 m/d and 0.54 m/d for chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus, respectively. Findings from a brief cost-benefit analysis suggest that both artificial aeration and the presence of PHPB would result in enhanced nutrient removal that is cost efficient for future projects, particularly if electricity costs are low.