The City of Snohomish’s Wastewater Treatment Plant is a dual-powered, multi-cellular, aerated lagoon system employing Submerged Fixed-Film Media in order to achieve the necessary quality of water for discharge into the Snohomish River.
Snohomish is a city in Snohomish County, in Washington state, located along the north bank of the Snohomish River near where Washington Wastewater Treatment Plant discharges water.
The plant’s primary tasks are:
• Remove suspended solids and degrade biodegradable organics
• Reduce ammonia nitrogen
• Eliminate pathogenic microorganisms from the wastewater
The process of ammonia nitrogen removal, called nitrification / denitrification, results in a loss in alkalinity passing through the plant.
Because the incoming wastewater to the Snohomish treatment plant is typically very low in alkalinity, an alkaline additive is needed in order to maintain an alkalinity and final pH above their allowed discharge permit.
With guidance from the engineering firm, magnesium hydroxide was sourced from a regional chemical supplier. Soon after the system was operational, they ran into mixing issues in their bulk storage tank, while also encountering plugging issues in their metering pumps and feed lines. Requests for support from the supplier were not met with a helpful response, putting them at risk at risk of:
Damaging the health and activity of their aerobic microorganism population.
Being out of compliance with their NPDES permit.
IER visited the Snohomish Wastewater Treatment Plant and offered to help sort out the chemical storage and feed issues, while performing an on-line comparison of the magnesium hydroxide in use and ALKA-Mag+, IER’s innovative and proprietary (Mg(OH)2) slurry.
With both products (magnesium hydroxide in use and ALKA-Mag+) being slurry products, with a propensity to settle in low-flow or stagnant lines and cause plugging, John shared with the staff that the feed system would need to be completely revamped into a much simpler, more direct feed approach.
In essence, he helped the staff to realize that for reliable feed of a slurry product, the simplest approach is the best approach, leaving no places for the slurry to hide, or to be held stagnant for long periods of time.
IER’s installation expert, John Strong, worked closely with the Snohomish staff to assess the problems. The bulk storage tank mixer needed to be re-set in order to optimize dispersion of the slurry in the tank.
In addition, the existing metering and feed system was extremely complex, with multiple lines and redundant valving. While this type of feed system works well for a purely aqueous product, the multiple lines were an opportunity for the magnesium hydroxide slurry in use to settle and plug.
John also noticed that the feed line from the storage tank to the pump was too large, resulting in too slow of a flow velocity when pumping the magnesium hydroxide slurry.
After agreeing on an alternative storage and feed system plan, John made multiple trips to work on-site with the Snohomish staff. In order to maintain the necessary pH and alkalinity control while making changes to their bulk storage and feed system, IER provided the plant with a temporary 1,000-gallon agitated storage tank filled with ALKA-Mag+ product.
This allowed John and the Snohomish team to take their time to modify everything correctly so that when they switched back to the bulk system it ran smoothly right from the start.
This also allowed the Snohomish staff to observe the performance of ALKA-Mag+ versus what they had been using, finding that there was no difference in feed rate for overall pH and alkalinity performance, which is consistent with both products being 60% concentrates.
“The most obvious difference was that the initial supplier was unwilling or unable to provide assistance, while IER was both willing and able.
By demonstrating our technical credibility in the storage and handling of a slurried product, and willingness to spend multiple days on-site to make sure that their chemical storage and feed system was reliable and robust, the City of Snohomish converted to IER and to our supply of ALKA-Mag+ magnesium hydroxide.”
– John Strong, IER Technical Service Manager
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