A New Approach to Evaluating the Performance of a High-Rate IFAS Treatment System

The Council Bluffs Water Pollution Control Plant (WPCP) added a high-rate, integrated, fixedfilm, activated sludge (IFAS) process in 2007 to increase the organic removal capacity of their conventional trickling filter plant. Plant staff uses an innovative approach to estimate the fixed biomass on the IFAS media through strategically placed miniature textile-media coupons. These coupons were used to evaluate the performance of the high-rate IFAS system at design conditions during cold-weather operation in 2009. Results showed that the system could operate within permit limits at design conditions; however, the effluent quality was less than predicted target values. Results also showed that the average IFAS media biomass loading was only 40% of the manufacturer's design value. Additional testing is needed to evaluate options for improving effluent quality at design conditions such as increased mixed liquor, increased solids retention time (SRT) or even increased hydraulic retention time (HRT).