Nitrogen removal from domestic wastewater using the marshland upwelling system

Malfunctioning or nonexistent wastewater treatment systems are one of the primary causes of water quality degradation in coastal areas. The marshland upwelling system (MUS) was developed as a low-cost, low-maintenance on-site treatment alternative for coastal dwellings, in which wastewater is injected into the saline subsoil and pushed toward the surface by buoyancy forces. Four injection regimes, characterized by flow rate (L/min), duration (min), and frequency (h), were evaluated for a MUS located in Moss Point, Mississippi, from June 2001 to June 2002 to determine the system's ability to remove nitrogen from wastewaters generated from recreational facilities. Nitrogen data were collected from a cluster of monitoring wells surrounding the injection well. The injection regime of 2.8 L/min (30 min/3 h) resulted in the best removal efficiency. Total kjeldahl nitrogen (TKN) and total ammonia nitrogen (TAN) were reduced from an influent average of 168 and 160 to 2.4 and 1.5 mg-N/L, respectively. Vector distance-based removal coefficients were estimated to be 0.88 and 0.84 m−1 for TKN and TAN, respectively. Subsequently, 3.2 and 3.1 vector meters were required to reduce TKN and TAN to 10 mg-N/L. The probabilities of the system effluent to exceed 10 mg-N/L were estimated to be 3% for TKN and 0% for TAN, respectively. Bench-scale laboratory studies indicated the potential for further treatment in the upper zone of the MUS system due to increases in redox potential caused by the Juncus roemerianus’ rhizosphere, which provided a nitrification zone.