Conference Agenda

WRFs using chemical disinfection with traditional means of control (e.g. flow pacing), typically overdose disinfectant by a factor of two. This overdosing can result in issues of excessive disinfectant cost, excessive quenching cost, disinfection byproduct formation, inconsistent performance, and inadequate public health protection. Advanced Dose Control (ADC) is a model-based disinfection control technology that seeks to account for the variables that impact disinfection performance (hydraulics, chemical background demand, and disinfection kinetics) and, regardless of process variability, to normalize disinfection outcomes while optimizing chemical dosages to avoid both over-dosing and under-dosing. Furthermore, in a complicated procurement environment, where disinfection chemical shortages and rising chemcical costs have become the norm, ADC provides a means by which to more tightly control chemical usage and for POTWs to hedge against supply volatility. ADC control technology has been included in the study matrix for WERF's most recently announced disinfection study, where bleach, PAA, and PFA will be compared under multiple control scenarios.

This presentation will highlight the foundations of the technology and present plant-scale pilot data, as well case studies from existing users demonstrating its performance vis-a-vis flow-pacing with both bleach, peracetic acid, and performic acid, and furthermore, will illustrate the implications of ADC's use at facilities using chemical disinfection, including significant cost savings (40%-50%), improved reliability, reduced discharge of residual disinfectant, reduction in dechlorination chemical, byproducts, and ultimately, reduced risk of permit violation.

Lake Stevens Sewer District (LSSD) and Columbia River Carbonates have worked closely since early 2022 to pilot improved RAS alkalinity and pH control at their Sunnyside WWTP operating in Lake Stevens, WA. This facility uses state-of-the-art membrane technology, designed to meet or exceed Washington State Department of Ecology permitted limits for contaminants in discharged effluent.

In January 2022, the two began replacement of 25% sodium hydroxide with MICRONA^TM AquaCal 70, a 70% solids micronized calcium carbonate aqueous slurry for alkalinity and pH control of mixed liquor at the 5 MGD MBR Sunnyside WWTP. While operating this pilot, wastewater quality and membrane permeability have been closely monitored while maintaining all standard operating conditions.

Results from the MICRONA^TM AquaCal 70 pilot for mixed liquor alkalinity and pH control and have been noted to a) decrease variability of alkalinity and pH in MBR mixed liquor, b) produce consistent pH control, allowing better conversion of ammonia to nitrates/nitrites and reduction to final effluent with a significant decrease in MBR mixed liquor alkali requirement, c) increased Suez membrane permeability and better operating conditions, d) decreased plant energy consumption, e) decreased overall alkalinity reagent chemical spend. These will be fully documented and presented.

LSSD also completed a 9-month pilot replacement trial of 25% sodium hydroxide added to MBR mixed liquor using 60% magnesium hydroxide from April through December 2021 and found improvement in some but not all operating and effluent quality parameters discussed above with respect to MICRONA^TM AquaCal 70.

Based on the 2021-2022 evaluations of magnesium hydroxide and calcium carbonate, LSSD is moving forward with converting from usage of 25% caustic soda to the continued use of 70% calcium carbonate aqueous slurry because of its cost-effective, non-hazardous and easy to handle qualities as a wastewater mixed liquor alkalinity and pH control product. Additionally, the selection of calcium carbonate aqueous slurry at the Jacobs run Spokane County Regional Water Reclamation Facility and Sunriver Utilities Co. build confidence in the use of CaCO₃ for required alkalinity and pH control during secondary stage aerobic biological treatment by LSSD.