AC25 Benefits of Hydrocyclones for WRRF Performance: Better Settling, Improved Nitrification… and Reduced E. coli?!

CWEA Members: $35.00
Non-Members $45.00

The aerobic granular sludge activated sludge process using batch reactors has received attention for the potential it offers to intensify activated sludge. Intensification allows WRRFs to improve effluent quality with a smaller footprint. Alternate technologies like hydrocyclones have become commercially available, which help to retain faster settling particles while the slower-settling particles are wasted out of the system. This type of technology can be more easily incorporated into plug flow reactors. At some plug flow facilities that have both hydrocyclones and unaerated high food-to-microorganism (F/M) selector zones, a relatively high fraction of the activated sludge can become granules producing a “densified sludge”.

In 2020, the City of Wichita installed a four-cyclone skid (180 gpm of return activated sludge [RAS]) on one of six nitrifying activated sludge trains at the Plant 2 WRRF (rated 54 million gallons per day [mgd]). The benefits to settleability through reductions in the sludge volume index (SVI) of the mixed liquor and improved water clarity in the test basin was observed. The SVI in the main basins averaged 120 mL/g compared to 91 mL/g in the hydrocyclone pilot basin. The City has started sampling E. coli in its secondary effluent prior to ultraviolet (UV) disinfection. Initial sampling has indicated about a 0.5-log reduction in E. coli counts in the hydrocyclone train compared to the non-cyclone trains.

Current biological nutrient removal (BNR) improvements project at the Plant 2 will incorporate a full-scale hydrocyclone system. This presentation will present the design criteria and layout of the new hydrocyclone facility and BNR facilities, a 5-stage Bardenpho process with high F/M selector zones and 19 cyclones for sludge wasting. Design considerations for the ancillary support facilities will also be presented, including a cyclone feed sludge (RAS) pumping, discharge of the cyclone underflow into the selector zones of the BNR process, and overflow as waste activated sludge (WAS).

With many utilities in California facing addition of nutrient limits in their discharge permit, the approach provided in this presentation will help these utilities save capital dollars on their improvement projects.
Learning Objectives:
Upon completion, participants will have a good understanding of densified sludge and the benefits it provides for wastewater plant operations.
Upon completion, participants will learn the key elements to consider when designing a full-scale hydrocyclone based system to provide densification in a plug flow reactor.
Upon completion, participants will learn about the latest research associated with hydrocylones, which indicates that they can potentially reduce disinfection dose at WRRFs, in addition to process benefits .