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ABSTRACT
Soil treatment of wastewater has the potential to achieve high purification efficiency, yet the understanding and predictability of purification with respect to removal of viruses and other pathogens is limited. Research has been completed to quantify the removal of virus and bacteria through the use of microbial surrogates and conservative tracers during controlled experiments with three-dimensional pilot-scale soil treatment systems in the laboratory and during the testing of full-scale systems under field conditions. The surrogates and tracers employed included two viruses (MS-2 and PRD-1 bacteriophages), one bacterium (ice-nucleating active Pseudomonas), and one conservative tracer (bromide ion). Efforts have also been made to determine the relationship between viruses and fecal coliform bacteria in soil samples below the wastewater infiltrative surface, and the correlation between Escherichia coli concentrations measured in percolating soil solution as compared with those estimated from analyses of soil solids. The results suggest episodic breakthrough of virus and bacteria during soil treatment of wastewater and a 2 to 3 log (99-99.9%) removal of virus and near complete removal of fecal coliform bacteria during unsaturated flow through 60 to 90 cm of sandy medium. Results also suggest that the fate of fecal coliform bacteria may be indicative of that of viruses in soil media near the infiltrative surface receiving wastewater effluent. Concentrations of fecal coliform in percolating soil solution may be conservatively estimated from analysis of extracted soil solids.
Abbreviations: BT^sub 10^, time to 10% breakthrough; BT^sub 50^, time to 50% breakthrough; cfu, colony forming units; INA, ice-nucleating active; pfu, plaque forming unit; STE, septic tank effluent; TOC, total organic carbon.
MORE THAN 25% of the U.S. population and 37% of all new development is served by on-site and small-scale wastewater systems. Wastewater treatment for these on-site and small-community applications commonly relies on infiltration and percolation of septic tank effluent through soil to achieve purification before recharge to ground water (Crites and Tchobanoglous, 1998; USEPA, 1997; Jenssen and Siegrist, 1990). These porous media-based systems (wastewater soil absorption systems) are widely used due to their high purification performance resulting from the complex interactions of hydraulic and purification processes (Siegrist et al., 2001; McCray et al., 2000; Ausland, 1998; Schwagger and Boiler, 1997). However, in many settings, there is an increasing awareness and concern...