Phosphorus Treatment Capability of Marshland Upwelling System under High Background Salinity Conditions

The marshland upwelling system (MUS) is an alternative onsite wastewater treatment system developed for coastal communities. The phosphorus treatment efficiency of the MUS operated under high background salinity conditions $(\sim 32\mathrm{ppt})$ was examined over the course of a one-year field study. Five individual studies were investigated by intermittently injecting wastewater at a depth of $3.8\mathrm{m}$ using flow rates/injection frequency regimes of $1.9\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , $5.5\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , $2.8\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , and $2.8\mathrm{L}∕\min$ $(15\min ∕\mathrm{h})$ . There were two studies conducted within the $2.8\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ flow regime: (1) with normal influent and (2) with high strength synthetic wastewater. Over the course of the study, no signs of phosphorus saturation were observed. The overall system efficiency for the entire study was estimated to be $>98\%$ . Removal rate coefficients ranged from 0.73– $1.25{\mathrm{m}}^{-1}$ and 0.66– $1.08{\mathrm{m}}^{-1}$ for total phosphorus and orthophosphate, respectively. Upon completion of the final $2.8\mathrm{L}∕\min$ $(15\min ∕\mathrm{h})$ study, it was determined that a travel distance of only $9.4\mathrm{m}$ would be needed to reduce influent concentrations below $0.1\mathrm{mg}\mathrm{P}∕\mathrm{L}$ .