Conference Agenda

A major interceptor with 7MGD flow in Pierce County’s Chambers Creek Water Resource Recovery Facility (CCWRRF) collection system has historically been plagued by microbially induced corrosion (MIC) and odor problems, with gas phase hydrogen sulfide concentrations as high as 200ppm. The rate of concrete corrosion as measured by weight loss was 8-9 % annually based on a concrete coupon study.

The CCWRRF was expanded to provide biological nutrient removal in anticipation of nitrogen nutrient limit from the state, which in turn led to the requirement for industrial users to reduce nitrogen nutrient loadings. A wastewater characterization study revealed that an industrial user discharges a high-strength waste stream with an ammonia concentration as high as 2000 ppm and is a major contributor of ammonia loading to the interceptor. Armed with the knowledge that nitrate compound addition is one of the best solutions to control MIC, CCWRRF decided on a creative approach for nutrient removal by this industry. Instead of complete nitrogen nutrient removal through the full cycle of nitrification and denitrification, the industry is asked to nitrify only, generating a waste stream with nitrate concentration as high as 2000ppm which is discharged to the collection system. This strategy has been proven to be very successful and is mutually beneficial to CCWRRF and the industrial user: MIC and odor in this interceptor have largely been controlled, as evidenced by liquid phase sulfide concentration at less than 0.2ppm and gas phase hydrogen sulfide reduction by 90%, without incurring the significant cost of nitrate salt addition by CCWRRF; and the industrial user achieved significant costing savings by not having to add supplemental organic carbon to achieve denitrification.

EPA promulgated aluminum aquatic life criteria in 2021 for Oregon based on the 2018 nationally recommended criteria. Aluminum is traditionally measured in environmental samples as total and dissolved aluminum, and criteria were based on total aluminum. However, the method to measure total aluminum uses a very low pH digestion which aggressively dissolves aluminum bound in clays and other mineral forms. This overestimates the amount of aluminum that is bioavailable and potentially toxic to aquatic life. Using total aluminum would assess more water bodies as impaired than would be accurate, and the listing could require TMDLs to be developed. For NPDES permittees using alum, this could result in unnecessarily restrictive aluminum limits which may impact the ability of WRRFs to use alum to meet phosphorus limits. Therefore, in implementation efforts, EPA recognized a new analytical method (Rodriguez et al. 2019) that measures bioavailable aluminum and allowed its use for river measurements.

Clean Water Services (CWS) is committed to studying analytical methods that best measure the potential toxicity of aluminum. The CWS Water Quality Lab began using the bioavailable aluminum method in 2019 and analyzed total, bioavailable, and dissolved aluminum in concurrent effluent and river samples from the Tualatin River. Results consistently show that a low fraction of the total aluminum is bioavailable to aquatic life in the Tualatin River, with an average of 7% bioavailable. Bioavailable aluminum concentrations were always less than the instantaneous water quality criteria calculated from the water quality standard, while 50% of total aluminum concentrations were greater than the criteria. Data also demonstrated that aluminum from CWS WRRFs that use alum is almost entirely bioavailable, highlighting the importance of reducing tertiary alum and the implementation of alternative methods of phosphorus removal. CWS has collaborated with Oregon DEQ to monitor total, dissolved and bioavailable aluminum in a broader range of rivers. CWS plans to continue bioavailable aluminum monitoring efforts and collaboration with Oregon DEQ in support of this method. ASTM publication, as well as 40 CFR approval, are important next steps in wider acceptance of the method by EPA in future aluminum criteria updates.