Case Study – TIN Removal for Mount Vernon, WA

THE CHALLENGE:

Mount Vernon, WA

Planning for future permit effluent limits always carries the risk of significant capital costs. With the recent Puget Sound Nutrient Permit nitrogen limits becoming more stringent, the City of Mount Vernon, WA WWTP needed to explore cost-effective options to achieve Total Inorganic Nitrogen (TIN) removal at their facility. The plant had recently finished a 38.5-million-dollar upgrade to reduce combined sewer overflows (CSOs), and the proposed TIN permit would require the facility to spend millions more in upgrades, or de-rate the plant capacity. The existing MLE process was suited for removing nitrogen, but not doing so year-round, and not at plant design flows. Their challenge was this: achieve stable nitrification and denitrification without spending millions of dollars on new concrete tanks.

WHY THE MOB PROCESS WAS CHOSEN:

Nuvoda’s MOB Process was installed at the Mount Vernon WWTP on a trial basis to increase nitrification, as the plant already had denitrification capacity. After establishing the biofilms, complete nitrification was achieved and sustained throughout the winter despite the low water temperatures and denitrification followed, resulting in the lowest effluent Total Inorganic Nitrogen concentrations observed to date. The MOB Process offered low installation costs, ease of incorporation into the existing facility, and no concrete for extra treatment volume.

WHAT WAS ACHIEVED:

• Sustained Nitrification During Winter Season Temperatures
• Historically Low Effluent TIN
• Installed Without Facility Down-Time
• Less Susceptibility to Variable Loadings