Evaluation of Nutrient Removal Capabilities of the Marshland Upwelling System: An Onsite Treatment Alternative for Coastal Dwellings

The problems encountered with coastal onsite wastewater treatment systems are quickly becoming a national issue. Discharge of poorly treated sewage from malfunctioning onsite systems is responsible for diminishing water quality, fishery losses, and threats to ecological and human health. Coastal limitations created by the saturated soils, sporadic dwelling use, and high treatment system maintenance have inhibited septic and mechanical systems from functioning properly. In response to the need for alternative onsite treatment systems, environmental engineers from Louisiana State University and biologists from Nicholls State University developed the Marshland Upwelling System (MUS).The MUS has been listed as the top onsite wastewater treatment alternative in Louisiana. Over the past ten years, Marshland Upwelling Systems have been installed at three separate project sites: Port Fourchon, Louisiana; Moss Point, Mississippi; and Bayou Segnette, Louisiana. The current project site, Bayou Segnette, is included on EPA's 303(d) list of impaired water bodies with faulty septic systems as the main input of non-point source pollution.The MUS uses a combination of the existing sand/soil matrix and saline groundwater of the native marshes to create an “upflow filter” capable of removing organic matter, fecal pathogens, and nutrients. The upward flow is generated when wastewater is pumped down an injection well, introducing a freshwater plume into the nonpotable saline groundwater. The density difference between the fresh wastewater and saline groundwater forces the freshwater plume upwards through the sand/soil matrix. A longer filter distance is created when the buoyancy forces are exceeded by the native groundwater flow velocities, thus inducing lateral and longitudinal dispersion. Treated wastewater is ultimately discharged to the surface of the marsh.The specific objective of this research is to evaluate the nutrient (nitrogen and phosphorus) removal capabilities of the MUS. Since nutrient removal efficiencies are not available for the Port Fourchon system a comparison of the removal capabilities will be made using only the data collected from the Moss Point and Bayou Segnette sites. Moss Point nutrient removal efficiencies were modeled using a first-order removal reaction. The mean influent phosphorus as total phosphorus, concentration for the Moss Point system was found to be 14.1 mg-P/L with a corresponding removal rate constant of 0.9 m−1. Nitrogen, as TKN and TAN, mean influent concentrations were found to be 120 and 86 mg-N/L with corresponding removal rate constants of 0.7 m−1 and 0.6 m−1, respectively. Nutrient removal efficiencies for the Bayou Segnette system are currently being evaluated and modeled using a first-order removal reaction.