Estimation of Graywater Constituent Removal Rates in Outdoor Free-Water-Surface Wetland in Temperate Climate

Although constructed wetlands have become an accepted technology for the treatment of graywater for nonpotable reuse, little guidance is available on the design and sizing of wetlands specifically for graywater treatment. A common practice for sizing constructed wetlands is to apply the first order plug flow $k\text{-}{C}^{*}$ model. The objective of this work was to estimate $k$ and $C^{*}$ parameters in a free-water-surface wetland processing graywater during summer, fall, and winter months for five-day biochemical oxygen demand (${\mathrm{BOD}}_5$), total nitrogen (TN), and ammonia. Mass removal rates were consistently higher during summer months than winter months. Estimated values for $k$ were higher in summer than winter for ${\mathrm{BOD}}_5$ ($15.9\mathrm{m}{\mathrm{year}}^{-1}$ compared to $2.5\mathrm{m}{\mathrm{year}}^{-1}$) and TN ($16.4\mathrm{m}{\mathrm{year}}^{-1}$ compared to $5.5\mathrm{m}{\mathrm{year}}^{-1}$). Additionally, estimates of $k$ for ${\mathrm{BOD}}_5$ removal during all seasons was lower for graywater than typically observed for domestic and livestock wastewaters. The parameter ($k$ and $C^{*}$) estimates provided here can be applied to appropriately size free water surfaces intended for the treatment of graywater, and $k$ values should be modified based on the season of interest.