Phosphate removal from urban stormwater runoff using Canna lily and Cyperus alternifolius-based bioretention system

Rainfall is considered to be the purest form of water; however, it gets contaminated as it sweeps along suspended impurities from the atmosphere, and it traverses its path through different land uses. Hence, an effective water-sensitive urban design (WSUD) is required to treat this low-strength urban stormwater runoff to minimise water loss and to improve its quality, lest it should cause eutrophication in receiving water bodies. The current study was undertaken to explore the performance of Canna lily and Cyperus alternifolius-based constructed wetland (CW) towards the removal of phosphate from the stormwater runoff. Total phosphate removal efficiency varied from 77.5% (winter) to 82.6% (spring) to 90.3% (summer) for Canna lily based-CW; while it varied from 62.3% (winter) to 74.2% (spring) to 84.1% (summer) for Cyperus alternifolius based-CW. The phosphate removal efficiency improved with a rise in ambient temperature through the changing seasons. The increase in biomass of both the plants, and accumulation of phosphate in different plant tissue suggested that the plants should be harvested periodically and nutrients be exported for use as fodder, manure, and for thatching. Therefore, an effective design standard and code of practice is required to be developed for WSUD in India. It will help in making future studies more effective in combination with other WSUD techniques for improved pollutant removal efficiency from real stormwater runoff.