McDowell Creek Achieves Plant-Wide BNR Process Visibility

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McDowell Creek Achieves Plant-Wide BNR Process Visibility

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Overview

In 2022, the McDowell Creek Water Resource Recovery Facility (WRRF) sought to update ChemScan equipment serving the plant since 2007. Two ChemScan sequencers were installed to monitor the plant’s five-stage BNR process, testing for nitrite, nitrate, ammonia and phosphorous from primary clarifier influent through tertiary filter effluent.

Challenge

The McDowell Creek Water Resource Recovery Facility, part of Charlotte Water, expanded from a permitted capacity of 6 MGD to 12 MGD in 2007. The expansion prompted the plant to invest in ChemScan analyzers for online and continuous process measurements. Fifteen years later, McDowell Creek was ready to replace its reliable analyzers with two new ChemScan Sample Sequencers, developed specifically for plant-wide monitoring of nutrient removal processes.

“Specifically for this plant, my permitted effluent limits are very stringent,” says Daniel Matias, Plant Supervisor. “So, the earlier I can detect an issue, the quicker I can resolve it. We need the predictability of catching it before it’s too late.”

McDowell uses a combination of methods to monitor the process and verify the accuracy of measurements. In addition to the ChemScan units, phosphorous analyzers at the first and final stages of the process run continuously to provide additional points of reference. A wet lab ammonia analyzer at the start of the treatment process also contributes measurements. Additionally, plant operators take process control samples during each shift, to monitor changes throughout the treatment process over a 24-hour period.

“We always have redundancy in place, just in case,” says Matias.

Still, plant staff have responsibilities beyond process control sampling and would be overwhelmed if required to conduct multiple process control sampling events during each shift. While operators conduct sampling events as frequently as possible, this still leaves an eight-hour interval between manual sampling. Even with the phosphorous and ammonia analyzers, McDowell Creek wanted the ability to keep tabs on the entire process at more frequent intervals.

“If you don’t have that capability,” says Matias, “you might waste eight hours before you realize there’s an issue.”

Plant-wide monitoring 24/7 allows McDowell to treat analyzer and grab sample data as confirmation of process trends, rather than relying on them as guides for process adjustments.

Solution

While the 2007 ChemScan analyzers satisfied this requirement, the new ChemScan Sample Sequencers expand the plant’s ability to correct issues that come up in between grab samples. The sequencers provide measurements of each of the plant’s seven sample locations every 55 minutes. One sequencer monitors the BNR basins, while the second takes samples from primary clarifier influent through tertiary filter effluent.

“We get a snapshot of our whole biological treatment process,” says Matias. “I can see all the trends. And as I’m watching as the day goes on, I can kind of predict trends because of the frequency of the measurements. I can see issues arising. It’s like I have somebody down there doing process consistently every 55 minutes.”

In addition to an overview of the process, the sequencers give Matias the ability to customize the sampling order. The sequencer will pull samples consecutively from each zone in the usual influent-to-effluent direction, but Matias can also set it to sample from each zone in reverse.

“The new installation lets us test where we want, at the time we want to test,” he says.

If process adjustments are needed, Matias can also set the sequencer to take samples of select locations repeatedly. “For example, if I think there might be a phosphorous issue, it’s usually at the last three sample locations,” says Matias. “So, I can change the sequence and test just the back half. I can set it to test just zones five through seven and update data every 10 minutes instead of every 55. It’s super easy and quick to do that.”

Integrating equipment into the plant’s infrastructure so the sequencer could provide a full-plant view of the BNR process was critical to the installation’s longevity and benefit to McDowell.

Usually, ChemScan products are connected to multiple submersible pumps that bring samples up from the different zones of the treatment basins and through the analyzer system. But this design was less effective for McDowell’s infrastructure, which features large vertical mixers and a single main sample pump connected to seven actuators, one for each sample location.

“The submersible pumps just didn’t fit how we mix in our zones,” says Matias.

In-Situ Vice President of Process Analysis Scott Kahle helped design a custom installation for McDowell Creek’s facility. Kahle and In-Situ engineers programmed the sequencer to control McDowell’s sample zone actuators, manipulating sample control valves to draw samples from each of the treatment basins’ seven zone locations through one main pump.

As an added benefit, having all seven sample locations flow through a centralized pump makes maintenance much easier on McDowell operators, who don’t have to travel to each basin or zone to clean the equipment. “Instead of maintenance in every single zone, it’s all located in one 15- by 15-foot area,” says Matias. “And it’s in a controlled environment, out of the elements. That also helps with the maintenance aspect.”

Results

The new sequencers have allowed McDowell to be even more...

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