Evaluating the Efficiency of Aerated Lagoon System regarding the Removal of Indicator Bacteria from Municipal Wastewater

Introduction: Treatment of municipal wastewater is essential to remove bacteria. This study is designed to evaluate the efficacy of a wastewater treatment plant (WWTP) for the removal of bacteria and using for irrigation or discharge in the Caspian Sea according to the World Health Organization (WHO) regulations. Materials and Methods: A total of 105 samples were collected from 7 stations, including the inlet and the outlet of the WWTP in Bandargaz City (Iran), the intersection point of wastewater effluent with Caspian Sea (Gorgan Bay), and a radius of 200 meters in three directions east, west, and north of the intersection point of wastewater in Gorgan Bay. The multiple-tube fermentation technique was used to enumerate bacteria, and results were expressed as the Most Probable Number (MPN) per 100 ml. Results: Bacteriological analysis exhibited that the concentration of total coliform, fecal coliform, fecal streptococci, and Clostridium perfringens were 1.38 ×1010, 5.57 × 107, 5.53 × 109, 1.26 × 109 in inlet, and 1.38 × 1010 , 5.57 × 107, 5.53 × 109 , 1.26 × 109 in outlet of WWTP, respectively. Conclusion: The aeration lagoon has a low performance in bacteria population removal, which may be due to the climate condition of this region (few sunny days and many cloudy and rainy days). This effluent was not generally acceptable for discharge in the environment and reuse. Therefore, it is essential to modify the disinfection process to keep the concentration of bacteria under control. Additionally, continuous monitoring is necessary to control the quality of wastewater  before discharge into the environment or reuse.