Location: Marlborough, Massachusetts
Project Type: Municipal Wastewater Treatment - Phosphorus Removal
Completion Date: January 2012
Average: 15,700 m3/day (4.15 MGD)
Peak: 43,990 m3/day (11.62 MGD)
- 0.07 mg/L Total Phosphorus
Project Background & Challenges
Lagoons—particularly the newer aerated lagoons—are effective at removing cBOD5 and Total Suspended Solids, but they struggle to remove ammonia and nutrients, including nitrogen and phosphorus. Unfortunately for Ontario’s ecosystem, wastewater rich in phosphorus has long been known to cause destructive algae blooms on the Great Lakes.
So when lagoons can’t keep up, small communities have traditionally found themselves facing a big bill to abandon the existing infrastructure and build a new mechanical wastewater treatment plant. That’s what the community of Sundridge, Ontario thought. Nestled on the northern shore of Bernard Lake, just south of North Bay, Sundridge was concerned about its lagoon discharging as effluent containing up to 8 mg/L of phosphorus into the Lake Huron watershed, not to mention ammonia and fecal coliform.
But they don’t worry about that anymore, thanks to some Nexom ingenuity.
The Nexom Answer
Removing phosphorus from lagoons is typically a matter of binding it to another element (e.g. alum) to create a phosphate floc, then settling or straining those flocs out of the water. The challenge, then, is optimizing the timing of each stage to minimize the alum usage.
At Sundridge, the engineers at Nexom came up with an innovative phosphorus removal solution. They installed the two-tank infini-D system, where the first tank rapidly mixes the alum and wastewater, followed by a second tank that mixes more slowly, allowing the new aluminum phosphates to flocculate.
The matter of filtering the floc out is yet another challenge. The centrepiece of the Sundridge system is the infini-D Zero-Downtime Cloth Disk Filter. Individual disc filter cartridges can be easily and cost-effectively exchanged or cleaned without taking the system offline. In Sundridge, where they targeted an effluent phosphorus level of 0.27 mg/L, the engineers chose to place the disk filter after the lagoons and the Nexom SAGR so the majority of the phosphate flocs could settle out well in advance, improving the phosphorus-removal performance and further saving operating costs on the disk filters.
Upgraded System Performance
With 18 months of data under its belt, covering more than 75 discrete samples, the Sundridge plant has seen influent phosphorus as high as 8.3 mg/L, but it has yet to produce one effluent result over 0.1 mg/L, with more than two-thirds of those measurements not registering a detectable level of phosphorus at all (anything below 0.03 mg/L registered as undetectable on the test).
In fact, the whole lagoon upgrade is performing impressively. By baffling the existing lagoon, Sundridge now has an anoxic cell for nitrate removal and phosphate settling, followed by three aerated cells for cBOD5 and TSS removal. The addition of the SAGR allows for full nitrification of the wastewater’s ammonia, working around northern Ontario’s low wastewater alkalinity levels by dosing the influent with soda ash and recycling some of the SAGR effluent back to the lagoons. In addition, the SAGR reduces effluent coliform levels, so a subsequent disinfection stage was deemed unnecessary.