Baffle and fixed media effects on coliform removal and bacterial die-off rate coefficient in waste stabilization ponds (a case study in Ahvaz)

Background: The use of waste stabilization ponds is one of the cheapest wastewater treatment processes. This study evaluated the effects of baffles and fixed media on coliform removal in facultative lagoons. Methods: In this study, the settled wastewater from four pond systems of the city of Ahvaz was used as input. Each system was composed of two ponds that were connected to each other serially. Three of them were equipped with two, three, and four baffles. Packages of fixed media were installed in the first baffled pond equal to the number of baffles. During a 12-month sampling period from March 2016 to February 2017, the capability of each system to remove coliform with different detention times was studied. Results: The control system with no baffle and no media reduced the coliform index by an average of 67% in a detention time of 6 to 12 days. Increasing the baffles and fixed media in the ponds improved the coliform removal efficiency; systems with two, three, and four baffles achieved coliform removal in the amounts of 77%, 81%, and 83%, respectively. The coliform die-off coefficients (Kb) were higher in the attached growth systems than in the control system. The coefficients were determined to be 0.21, 0.26, 0.29, and 0.31 d-1 for the second ponds of the control, two-, three-, and four-baffle systems, respectively. Conclusion: This method can be used to upgrade the existing waste stabilization pond and to design new ponds with at least two baffles in the facultative lagoons.