Occurrence of Microbiological Contaminants in a Watershed Impacted by a Wastewater Treatment Plant

Exposure to contamination of environmental waters may cause various adverse health outcomes such as gastrointestinal and respiratory illnesses, skin, ear, eye, and neurological infections. Treated sewage is usually released to the environment upon disinfection by either chlorine or UV. One major public health concern is release of antibiotic resistant bacteria (ARB) after the treatment process. The ARBs in the environment can cause dramatic changes in the ecosystem, often leading to more adverse impacts on human health upon exposure. In the study, we examined the presence of fecal indicator bacteria (FIB); total coliform, fecal coliform and Escherichia coli throughout the wastewater treatment process. Samples were taken once a month from November 2013 to October 2014 from five different sampling points (influent, secondary treatment, UV disinfection, upstream river and down-stream). Serial diluted water samples were analyzed for total coliform (TC) and E. coli by using a rapid US EPA approved method (Defined Substrate Technology by Colilert(R)). The results showed that E. coli in the influent was 2.51 X 106 CFU/100ml and decreased to 1.34 X 104 CFU/100ml after secondary treatment, followed by 1.34 X 101 CFU/100ml after UV disinfection. Mean log removal of E. coli post-UV disinfection was 5.5±0.46. The lowest reduction was detected in January (4.8) and the greatest reduction was detected in April (6.1). Among all fecal indicator bacteria, TC had the highest concentrations. The relation between TC and E. coli was significant (R2=0.928, p=0.008). Our results showed that UV disinfection applied in this setting provided better pathogen removal than other WWTP that used chlorine disinfection in other studies. WWTP effluents created a dilution effect on river; indicating that the effluents had lower bacteria concentrations than the stream. Ongoing investigation by using molecular methods to detect the antibiotic resistance gene occurrence in this area is expected to help understand the impact of wastewater effluents on the environmental water quality