Coliforms removal by an integrated activated sludge-maturation pond system

Aims: This study assesses the removal of fecal indicators (i.e., total coliforms, fecal coliforms) in a full-scale activated sludge and maturation pond system with primary screening facility that is operating in center of Iran. Materials and Methods: A total of 54 grab samples for microbiological test were collected from the inlet and outlet of activated sludge (AS) and maturation pond (MP) during the winter and summer 2010 (3 sample per month in 3 locations). Collected samples were sent to laboratory and were analyzed for total coliformbacteria (TCB) and fecal coliform bacteria (FCB) according to Standard Methods. Results: The results of this study show that the maximum TCB removal in AS (92.2%) and MP (99.2%) were occurred in summer. Also, for FCB, the highest removal rate (99.7%) was recorded during the summer. The mean winter TCB numbers for AS and MP effluents were 2.7 × 10 ⁷ and 2.3 × 10 ⁶ (MPN per 100 ml), respectively. However, the effluent still contained a significant number of coliforms, which was greater than the permissible limit for unrestricted irrigation as prescribed by Iranian and WHO guidelines. Conclusion: Removal efficiencies of fecal indicator bacteria were maximum during summer and minimum during winter. Statistical analysis indicated that TCB and FCB removal in MP is significantly affected by ambient temperature, whereas there was weak correlation between ambient temperature and coliform removal in AS system.