Conference Agenda

Clean Water Services (CWS) is a wastewater, stormwater, and watershed management utility serving the populous of Washington County, Oregon USA through implementation of a watershed based NPDES permit. CWS operates 4 water resource recovery facilities (WRRF) with biological nutrient removal (BNR) activated sludge configurations to achieve phosphorus and ammonia nitrogen removal to low levels.

The Rock Creek WRRF is comprised of East and West trains configured in an anaerobic-anoxic-aerobic (A2O) process. On the East side there are 4 activated sludge basins (AB 4-7) that exist as pairs of identical basins. AB 4 and 5 are single pass basins tending towards complete mix reactors. AB 6 and 7 are three-pass plug-flow style basins with three swing zones for denitrification. All basins receive an independently controlled dose of volatile fatty acids (VFA) from primary sludge fermentation to effect enhanced biological phosphorus removal (Bio-P). Differences exist between AB 4-5, and AB 6-7 in the ability to step feed primary effluent to different zones within the basin. The basins are operated as discrete units with independent and isolated biomass in each basin.

Nitrification and Bio-P are sensitive processes prone to upset conditions, particularly during the colder months. To increase the resiliency and reliability of the basins to perform this biology, CWS has installed a Cross-Basin Activated Sludge Seeding system (C-BASS). This system is capable of diverting a portion of the return activated sludge (RAS) from one basin to another. The plant is required to nitrify year-round to varying levels depending on receiving stream flow, so one basin is kept in a fully nitrifying condition. C-BASS is used to rapidly establish nitrification in other basins as permit limits change. The facility faces VFA limitations even with primary sludge fermentation. One or two basins may be heavily dosed with VFA for robust Bio-P, and C-BASS used to get the benefit of residual phosphorus uptake in the other basins. Waste activated sludge (WAS) remains an independent system and can be managed to retain biomass during C-BASS.

C-BASS is a simple and effective system that many facilities could install in-house to improve resiliency and expand process control options.

Aerobic Granular Sludge (AGS) technology operates on an optimized batch cycle structure that creates the proper conditions to develop and maintain granules: large, dense microbial aggregates displaying as particles greater than 200 microns in diameter that perform biological nutrient removal and display exemplary settleability relative to conventional activated sludge (CAS). The layered microbial community of these granules enables simultaneous nitrification/denitrification and enhanced biological phosphorus removal to occur within the granular biomass. This technology therefore eliminates the need for clarifiers, carrier media, and return sludge pumping stations, as well as selectors or separate compartments for plants looking to achieve BNR. The enhanced settling properties allow the system to operate at a high MLSS in excess of 8 g/L without a loss in aeration efficiency due to the granular nature of the sludge. The AGS process can therefore provide a significant reduction in footprint requirements and energy demand compared to a conventional technology.

The AGS process has been implemented successfully for nearly years with over 100 plants either in operation or under construction globally. Introduced to the North American market in 2017, there are now over 10 plants operating or under construction in the United States. This session will present case studies of plants that selected the technology to prepare sites for future regulatory demands, population increases, and climate resiliency.