Wastewater Plume Dynamics and Bacteria Transport within the Marshland Upwelling System
The marshland upwelling system (MUS) serves as an alternative onsite method for the treatment of domestic wastewater derived from coastal communities. Previous studies on the MUS have focused on the efficacy of the system for the removal of fecal pathogens from settled and secondarily-treated wastewater sources. The objectives of this research were to: 1) characterize the extent of wastewater migration within the MUS, 2) evaluate the effectiveness of the MUS in removing fecal bacteria, 3) identify the mechanisms responsible for fecal coliform retention within the subsurface, and 4) describe the transport of fecal coliforms in a sand media based on the advection-dispersion equation.
Rhodamine Water Tracer (RWT) was selected for use in characterizing the migration of wastewater within the marsh subsurface. Its strong color and ease of detection in field scenarios enabled RWT to be an effective tracer for the identification of wastewater pathways within the MUS subsurface. However, the non-conservative nature of RWT (demonstrated in laboratory studies) prevented accurate quantification of wastewater retention times and subsequent average velocities within the system.
Intermittent injection of wastewater at a flowrate of 2.8 L/min and an injection frequency of 30 minutes every three hours demonstrated effective fecal coliform removal without sacrificing system integrity. At this flowrate, mean influent fecal coliform concentrations of 62,000 +/- 101,000 colonies per 100mL were reduced to 2.7 +/- 0.9 colonies per 100mL in the 1.5 m deep monitoring wells. Greatest removal of fecal bacteria was observed in the vicinity of the injection well where accumulation of injected solids and biofilm development were suspected to improve filtration.
Continuous input laboratory studies (simulating the injection phase of the MUS) were performed to quantify the level of bacterial retardation in a sand media. Bacterial retardation factors ranged from 2.59 to 3.56 with respect to the conservative wastewater solution. Higher clay content and greater biofilm development would likely result in higher bacterial retardation within the field MUS. Accurate mathematical description of bacterial transport within the MUS would require additional research focusing on the transport potential of bacteria during the resting phase of the system.
Advisor:Ronald F. Malone; Clint S. Willson; Kelly A. Rusch
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:civil and environmental engineering
Date of Publication:07/11/2002