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The construction of Highway 416 has meant many things to many people and for the people of North Grenville, Ont. it has driven rapid growth.
While that growth is welcomed in terms of the vibrancy it brings to the community, it also puts a strain on infrastructure, case in point, the local wastewater treatment facility.
The issue, as Karen Dunlop, North Grenville’s director public works explains, is that the The Kemptville Water Pollution Control Plant (WPCP), a conventional activated sludge (CAS) plant with tertiary treatment needs to double its capacity by 2022.
"It sounds like it’s a way off but of course it isn’t," she said. "And we can’t really expand the footprint because we’re right beside a creek and an operating forest station on the other we really don’t want to eat up the land if we can avoid it."
Building a new treatment facility isn’t economically feasible. In the meantime, the municipality is about to commission an engineering study to look at options, a continuation of a process started with an Environmental Assessment completion in 2010.
The most recent completed phase involved funding from the Ontario Ministry of the Environment’s Showcasing Water Innovation to field test an innovative water treatment system using biomagnetics.
It turns out that BioMag, is a Siemens Water Technology, can do part of the job required. Still, designed as a cost effective alternative to Membrane Bioreactor (MBR) and conventional filtering, based on a process using magnetite, a common naturally occurring iron oxide, it did prove in its first Canadian installation that it works.
In the BioMag process, magnetite becomes a ballast in "a patented activated sludge and flocculation process of the mixed liquor which to improves sludge settleability," according to background reports from North Grenville.
"The BioMag technology is relatively new in wastewater treatment applications and focuses specifically on the secondary treatment components of an activated sludge wastewater treatment plant."
There is no installation in Canada but there are several examples in the United States and it works by because the "increased specific gravity of the biological floc when embedded with magnetite improves its settle-ability, allowing the secondary clarifiers to operate at higher loading rates and mix suspended solids (MLSS) concentrations while maintaining adequate settling and thickening."
What’s also attractive about the process is that the magnetite, having magnetic properties of course, can be easily recovered and reused using a shear mill and rotating drums with fixed magnets.
A test facility was installed at the Kemptville plant to see if it could produce results in a real world setting and, perhaps, help resolve the expansion issue. The XCG Consultants, an environmental engineering firm, was retained to oversee the program which ran for 10 weeks in the summer of 2013.
The results, as Melody Johnson, the engineer running the program reports, were completely as projected.
"It was for secondary treatment for bio microorganisms," she said.
"The magnetite in the ballast makes the flock heavy and it settles a lot faster which means more microbes are in the system which allows for treatment of a higher flow."
In retrospect it worked well, she said, and could assist North Grenville in finding a path to doubling their capacity. XCG estimated it would cost about $3 million to convert two of the existing trains to a BioMag process which is about 75 per cent of expanding using Conventional Activated Sludge (CAS).
However, in and of itself, it’s not a one shot solution unfortunately, said Dunlop.
"It proved it could improve the secondary water treatment as per the design specs but unfortunately there are four other treatment trains within the plant it can’t help," said Dunlop. "Our plant has seen a lot growth and we’re tightening up in other areas but we haven’t been able to increase our capacity. Right now, we’re still looking at options."
The current plant is rated at 4,510 m3/d and with a peak flow of 11,370 m3/d and the methods of treatment include screening, grit removal, primary clarification, biological treatment, secondary clarification, flocculation, filtration, and ultraviolet (UV) disinfection. Sludge management is provided by waste activated sludge co-thickening in the primary clarifiers and anaerobic digestion of the co-thickened sludge.
While it runs about half its daily average rate, historic peak flows have breached the upper capacity so there is some urgency already.
The 2010 EA recommended an influent equalization facility but it too would require an increase in footprint. XCG suggested using the BioMag made by Evoqua, to be retro-fitted at the bioreactors and secondary clarifiers.
As XCG noted in its report, BioMag could double the secondary treatment train ADF to 9,000 m3/d but there are still issues.
"It’s the other trains, primary, aeration, tertiary and UV and they have a capacity they can handle and so there are other bottlenecks," Dunlop said.
"We’re to look at other options. Maybe BioMag is part of it, maybe it isn’t at this point."
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