Evaluation Of Water Quality Renovation By Advanced Soil-Based Wastewater Treatment Systems.

25% of US households utilize onsite wastewater treatment systems (OWTS) for wastewater management.  Advanced technologies were designed to overcome the inadequate wastewater treatment by conventional OWTS in critical shallow water table areas, such as coastal zones, in order to protect ground water quality.  In addition to the septic tank and soil drainfield that comprise a conventional OWTS, advanced systems claim improved water renovation with the addition of sand filtration, timed dosing controls, and shallow placement of the infiltrative zone.  We determined water quality renovation functions under current water table and temperature conditions, in anticipation of an experiment to measure OWTS response to a climate change scenario of 30-cm increase in water table elevation and 4^◦C temperature increase. Replicate (n=3) intact soil mesocosms were used to evaluate the effectiveness of drainfields with a conventional wastewater delivery (pipe-and-stone) compared to two types of pressurized, shallow narrow drainfields.  Results under steady state conditions indicate complete removal of fecal coliform bacteria, phosphorus and BOD by all soil-based systems.  By contrast, removal of total nitrogen inputs was 16% in conventional and 11% for both advanced drainfields.  Effluent waters maintained a steady state pH between 3.2 – 3.7 for all technologies.  Average DO readings were 2.9mg/L for conventional drainfield effluent and 4.6mg/L for advanced, showing the expected oxygen uptake with shallow placement of the infiltrative zone.  The conventional OWTS is outperforming the advanced with respect to nitrogen removal, but renovating wastewater equivalently for all other contaminants of concern.  The results of this study are expected to facilitate development of future OWTS regulation and planning guidelines, particularly in coastal zones and in the face of a changing climate.