Abstract
On-site wastewater treatment systems (OWTS) work by first storing the wastewater in a septic tank before releasing it to soils for treatment that is generally effective and sustainable. However, it is not clear how the abundance of E. coli changes during its passage through the tank. In this study, which was conducted under the UGA young Scholar Program in summer of 2010, we examined the change in wastewater quality parameters during the passage of the wastewater through the tank and after its release into soil. We collected wastewater samples at the inlet and outlet of an experimental septic tank in addition to obtaining water samples from lysimeters below trenches where the drainpipes were buried. We report that E. coli concentration was higher by 100-fold in the septic tank effluent than influent wastewater samples, indicating the growth of E. coli inside the tank under typical Georgian summer weather. This is contrary to the assumption that E. coli cells do not grow outside their host and suggests that the microbial load of the wastewater is potentially enhanced during its storage in the tank. Electrical conductivity, pH and nitrogen were similar between the influent and effluent wastewater samples. E. coli and total coliform concentrations were mainly below detection in lysimeter samples, indicating the effectiveness of the soil in treating the wastewater.
Highlights
More than a quarter of US households employ on-site wastewater systems (OWTS) to treat and dispose wastewater [1]
The wastewater and water samples in this study were collected from an experimental on-site wastewater treatment system (OWTS) that was installed at the Westbrook Farm of the University of Georgia, Griffin Campus in 2008 [19]
The study reports the growth of E. coli in wastewater inside a septic tank under typical summer weather in Georgia, USA
Summary
More than a quarter of US households employ on-site wastewater systems (OWTS) to treat and dispose wastewater [1]. In Georgia, the percent use of OWTS is higher than the national average at about 37%. These systems, known as septic systems, are commonly designed to accumulate the waste in a two-chamber tank where solids settle while the wastewater flows to a distribution box that is connected to one or more perforated drainpipes that distribute wastewater to the soil. The drainpipes are commonly installed in trenches and surrounded by a supporting material such as gravel or polystyrene to prevent clogging. OWTS must, be installed in suitable soils that can accomplish the treatment processes properly [3,4,5]
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