Coliforms removal in two UASB + ASP based systems

Two full scale up-flow anaerobic sludge blanket (UASB) reactor with activated sludge process based STPs (43 Ml d⁻¹ and 100 Ml d⁻¹ capacities) purely for municipal wastewater having two different aeration systems (surface and diffused) were continuously evaluated for one year. Total coliforms (TC) and fecal coliforms (FC) were measured along with other performance monitoring parameters in raw sewage, UASB effluents, and in final effluents. The concentration of total and fecal coliforms ranged from 9.3 × 10⁶ to 1.2 × 10¹⁴ MPN/100 ml and 9.3 × 10⁶ to 2.4 × 10¹³ MPN/100 ml respectively in raw sewage. At both the plants, it was observed that finally treated effluent still contained significant number of total coliforms (5.71 × 10⁵ and 6.7 × 10⁵) and fecal coliforms (3.67 × 10⁵ and 2.2 × 10⁵) after overall removal of 99.9%, which is still greater than the permissible limit of 1000 MPN/100 ml and needs further treatment. Seasonal variation indicated the effective removal of coliforms in raw sewage was in summer. Fecal coliforms are highly correlated with phosphorous and total coliform concentrations.