Evaluation of the Wastewater Treatment Efficiency in Removal of Microbial Contaminants

The processes involved in the treatment of wastewater can be inconsistent in regards to efficiency, releasing unsafe levels of microbial contaminants into surrounding receiving water bodies. Exposure to these contaminants may lead to various health effects, especially gastrointestinal illnesses. Our study was based on determining this efficiency in a wastewater treatment plant by investigating the occurrence of Fecal Indicator Bacteria (FIB), specifically total coliform (TC) and Escherichia coli, throughout the waste water treatment process. Samples were obtained from five points including the influent, secondary treatment, UV disinfection, upstream from the treatment plant, and the receiving downstream river. The samples were taken once a month for 12 months. Rapid USEPA approved method (Defined Substrate Technology by Colilert®) was utilized in analyzing the serial diluted water samples. The results showed that E. coli in the effluent 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). There was a significant correlation between TC and E. coli (R2 = 0.928, p = 0.008) as TC showed to have the highest concentration among all FIB. Our results indicated the better removal of microbial contaminants at the UV disinfection stage than any other stage. Further study in our lab involves the application of molecular methods to detect the antibiotic resistance gene occurrence in the samples and the receiving water body; this will help in estimating the potential health risks upon exposure to the water.