Session 21A: Facility Operations - Livestream
8:00am - 8:45am
Exploring an Alternative Alkalinity Source - Full Scale MBR Pilot Using Ultra-Fine Calcium Carbonate
1Jacobs, United States of America; 2Columbia River Carbonates, Woodland, WA; 3Heimburger & Company, Blaine, WA; , ,
Jacobs and Columbia River Carbonates worked closely together in 2020 to trial alternative RAS alkalinity and pH control at the 8.0 MGD Spokane County Regional Water Reclamation Facility (SCRWRF) operating in Spokane, WA. Jacobs has had responsibility for operating this facility for Spokane County since its start-up in 2011. Currently, the SCRWRF uses nearly 100% of its Class A reclaimed water for Spokane River streamflow augmentation. The remaining amount is used for process water and irrigation of the facility site. This membrane bioreactor (MBR) facility uses state-of-the-art membrane technology and is designed to meet or exceed Washington State Department of Ecology permitted limits for contaminants in discharged effluent.
In June 2020 Jacobs and Columbia River Carbonates began a full-scale pilot replacing the 25% active sodium hydroxide with MicronaTM Aquacal 70, a 70% active micronized calcium carbonate aqueous slurry, for alkalinity and pH control of mixed liquor in the MBR. At this facility, phosphorous removal from wastewater is achieved by addition of ferric chloride in 1st and 2nd stage treatment. This trial of Aquacal 70 continued for 90 days while closely monitoring wastewater quality and membrane permeability while maintaining standard operating conditions.
Results from the Aquacal 70 operating period that began in late June and continued until the end of September 2020 were found to a) fully replace NaOH in mixed liquor with a significantly lower volume (and operating cost) requirement, b) decrease variability of alkalinity and pH in MBR mixed liquor, c) have no negative impact on membrane functionality during or after the trial d) decrease the requirement for 25% sodium hydroxide added for final effluent pH control, and e) increase solids content of sludge and cake to waste from anaerobic digestion. These will be fully documented and presented.
Additionally, extensive use of a similar product at municipal and industrial wastewater treatment plants in Western Europe – and particularly in Germany, Austria, and Switzerland, built confidence in the trial and use of Aquacal 70 by Jacobs at the SCRWRF.
8:45am - 9:30am
Septage: Regional Water Quality and Practical Considerations in Managing and Treating High-strength Wastes
HDR, United States of America;
In Washington State, there are nearly 950,000 individual on-site wastewater disposal systems, primarily septic tanks connected to drain fields. Recommended practice is for the septic tank contents to be removed for disposal every 3 to 4 years. Historically, septage collected from septic tanks has been treated in publically-owned treatment works (POTWs). This presentation will address septage characteristics, water quality objectives, vehicle management, and in-plant handling of septage.
A large number of septic systems exist in the Puget Sound basin in western Washington. On-site sewage system management areas have been formed in basins with critical water quality considerations to ensure the proper management of septic systems to protect water resources. Septage treatment in municipal treatment plants is therefore consistent with regional water quality objectives.
However, there are also drivers away from septage receiving at POTWs. Due to declining water quality in Puget Sound, nutrient loading caps will soon be implemented, and nitrogen limits will follow. An individual utility could chose to restrict septage receiving to meet near-term nutrient discharge loading caps, contrary to regional water objectives. Also, microorganisms in biological nutrient removal systems are sensitive to heavy metals which are typically prevalent in septage. Future restrictions on septage receiving may be necessary to protect biological nutrient removal processes.
Septic tank effluent pump (STEP) collection systems have become common in some areas. The disadvantages and disadvantages to a utility of accommodating STEP systems will be discussed.
The final part of the presentation will review practical considerations for managing vehicles on treatment plant sites and designing septage receiving facilities at municipal wastewater treatment facilities. At many facilities, septage is introduced into influent wastewater, but other facilities have had success with feeding septage into solids handling processes. Alternate methods of introducing the septage into the treatment process will be discussed and examples presented.
9:30am - 10:15am
Return Activated Sludge Rate Impacts to Biological Phosphorus Removal
1T-O Engineers; 2University of Idaho;
Biological phosphorus removal (BPR) is necessary to realize sustainable recovery of phosphorus from wastewater. In achieving BPR, perhaps the most accepted characteristic of a successful process is the necessary cycling of a mixed microbial consortium through anaerobic and aerobic conditions. Key to the anaerobic state is the absence of nitrate. However, most BPR facilities, which commonly achieve nitrification and operate with pre-anoxic denitrification, have moderate to significant levels of nitrate within their return activated sludge (RAS). It has been suggested that nitrate can be reduced by slowing the RAS rate such that organisms within the secondary clarifier can perform denitrification, thereby reducing the concentration of nitrate within the RAS. Even though RAS is the backbone of all activated sludge treatment, there appears to be little research on the impacts of RAS rate on overall system performance, as well as BPR specifically. There is also limited understanding on the specific impact of nitrate loading on the BPR system and the anaerobic capacity for nitrate. To investigate these topics further, a full-scale water resource recovery facility (WRRF) performing BPR was monitored before and after RAS rate changes to assess and evaluate impacts to the BPR process. Denitrification was assessed in the secondary clarifier, and key anaerobic BPR metabolisms were evaluated. Correlations noticed within the full-scale system were investigated further with batch tests and process modeling software. Data indicates that even low nitrate loads can have a significant impact on the BPR system but may not lead to a noticeable change in effluent phosphorus concentrations until a failure-inducing nitrate load is reached. The findings from this research will help guide WRRF operators to make informed decisions related to adjusting RAS rate to enhance and maintain BPR. Results will also lead to more stable operation and application of BPR.