Evaluating Full-Scale Impacts of Densified Activated Sludge on Disinfection Efficacy: A Look at WRF 5274

Presentation Description: Water resource recovery facilities (WRRFs) are faced with more stringent nutrient limits, population growth, limited footprint for process upgrades and increasing financial pressures. In addition, many utilities are trying to find the optimum way to spend the precious financial resources they have while meeting permit limits and, in many cases increasing treatment capacity. Densified activated sludge (DAS) systems have emerged as a cost-effective means to increase the capacity of conventional activated sludge (CAS) processes at WRRFs, while improving nutrient removal, all with a relatively low capital cost. Despite numerous studies exploring the advantages of DAS compared to CAS systems, DAS impacts on microbial communities and the performance of disinfection technologies are unknown. The Water Research Foundation has funded a tailored collaboration project (WRF 5274) investigating how DAS systems impact disinfection processes at WRRFs. WRF 5274 has three main tasks: (1) implementing a sampling and analysis program at Metro Water Recovery (Denver, CO), EPCOR (Edmonton, Alberta) and Johnson County Wastewater (Kansas) to compare the E. coli concentrations in the secondary effluent between full-scale CAS and DAS systems; (2) comparing the disinfection efficacy between DAS and CAS of four disinfectants (UV, Chlorine, Peracetic Acid and Performic Acid) by performing four disinfection dose response experiments at Metro Water Recovery’s Robert W. Hite Treatment Facility; and (3) developing disinfection efficacy models based upon the disinfection dose response experimental results to quantify the differences between CAS and DAS disinfected effluents. WRF 5274 is half way through its project schedule and has compiled a sizeable database of results from the three utilities, has performed two of the four disinfection dose response experiments, and has performed statistical analyses of all the results to date. All the sampling and testing will be completed by the end of the first quarter of 2026.
This presentation will layout the need for this research, the technical approach utilized on the project, present results from the CAS versus DAS data collection and disinfection dose response testing, and insights into what water quality and or process conditions are likely leading to these results.