Enhancement of Nitrogen and Phosphorus Removal in Pilot-Scale Vertical Subsurface Flow-Constructed Wetlands Using Polypropylene Pellets

Removal of nitrogen and phosphorus is known to be somewhat problematic in vertical subsurface flow (VSSF)constructed wetlands. In this pilot-scale study, two planted (Typha latifolia L. [cattail]) VSSF-constructed wetlands A (with polypropylene pellets) and B (without polypropylene pellets) and one unplanted control C (without polypropylene pellets) were designed to test the contribution of polypropylene pellets to nitrogen and phosphorus removal in eutrophic river water in Tianjin, China. The ranking order of nutrient removal for above tested wetlands was A B C. In contrast to wetland B, polypropylene pellets in wetland A enhanced the ammonia–nitrogen, total nitrogen, soluble reactive phosphorus, and total phosphorus removal: 13.38%, 8.90%, 9.29%, and 8.25%, respectively. Analysis of the aboveground biomass and nutrient content of the stems and leaves of the T. latifolia indicated that the polypropylene pellets restrained the increase in biomass, but stimulated assimilation of nitrogen and phosphorus into stems and leaves. Additional total nitrogen and phosphorus removal of approximately 29.38 gN/m2 and 13.47 gP/m2 by aboveground T. latifolia biomass with polypropylene pellets, respectively, was observed. Outflow water quality of wetland with polypropylene pellets was generally better than without polypropylene pellets during the whole period of the test run. Polypropylene pellets improved nitrogen and phosphorus removal, especially in August, when it apparently stimulated wetland microbial activity.