New Performance-Based Passive Septic Tank Underground Drainfield for Nutrient and Pathogen Removal Using Sorption Media

Removal of nutrients and pathogens in wastewater effluents is very important for the sustainability of the aquatic ecosystem and environment. On-site sewage treatment and disposal systems commonly referred as septic systems are one of the major sources of nutrients and pathogens in groundwater systems. Drainfields in septic tank systems are normally located in permeable, unsaturated natural soil or imported fill material so that wastewater can infiltrate and percolate through the underlying soil to the groundwater for final disposal. In the past, removal of nutrients in these conventional drainfields was too low to meet the water quality requirements. This article presents a new passive underground drainfield of innovative design with soil amendments (sorption media) for nutrient and pathogen removal in a field-scaled septic tank system. This new system, which is filled with green sorption media consisting of recycled materials mixed with naturally occurring materials, was fully tested in both Phases I and II periods in late 2008 and early 2009, respectively. The new drainfield system with soil amendments was designed to furnish aerobic and anoxic environments, which were fully demonstrated to support final nitrification and denitrification in our pilot study. In this embodiment, the green sorption material mixture includes *68% fine sand, *25% tire crumbs, and *7% sawdust by volume. Overall, >70.21% and 81.79% of total nitrogen and total phosphorus were removed, respectively. Removal efficiency of 5-day carbonaceous biochemical oxygen demand and ammonia was also >80%. Removal efficiency of Escherichia coli was 99.93%. Such a new biofiltration system may be integrated with any type of on-site sewage treatment and disposal systems to effectively remove nutrients and pathogens. The technology will make a significant contribution to the development of sustainable rural areas.