Nutrient removal in wetlands during intermittent artificial aeration

In a pilot-scale study, the contribution of intermittent artificial aeration to nitrogen and phosphorus removal in three (i.e., aeration in the middle of the substrate, aeration at the bottom of the substrate, nonaerated substrate) subsurface vertical-flow constructed wetlands planted with Typha latifolia L. (cattail) was tested with eutrophic river water in Tianjin (China). In contrast with the nonaerated wetland, aeration enhanced ammonia-nitrogen, total nitrogen, soluble reactive phosphorus, and total phosphorus removal: 10.1, 4.7, 10.2, and 8.8% for aeration in the middle, and 25.1, 10.0, 7.7, and 7.4% for aeration at the bottom of the substrate, respectively. Analysis of above-ground plant biomass indicated that intermittent aeration restrains the increase in biomass, but stimulates assimilation of nitrogen and phosphorus into stems and leaves. Additional total nitrogen removal of 116 kg N/ha and 126 kg N/ha by harvested above-ground T latifolia biomass for intermittent artificial aeration in the middle and at the bottom of the wetland substrate, respectively, was observed. Outflow water quality of aerated subsurface vertical-flow wetlands was better than the one in the nonaerated wetlands during the whole period of the test run. Artificial aeration improved nitrogen and phosphorus removal, especially during the very hot month of August.