Tackling Tough Wastes

A new MBR plant in Port Rowan successfully handles a high-strength mixture of regular influent, septage, portable toilet waste and landfill leachate.
Tackling Tough Wastes
Operator Kyle Van Paemel in the laboratory (digital scale from Ohaus).

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Talk about a tough assignment. In Port Rowan, Ontario, a greenfield treatment plant equipped with the latest technology takes on high-strength wastewater loaded with septage, hauled wastes and landfill leachate and discharges to an environmentally sensitive waterway.

But the Port Rowan Wastewater Treatment Facility is cutting it, according to Bob Fields, manager of the Environmental Services Division for Norfolk County and a licensed water and wastewater operator. "We're starting to meet our limits," he says. "We've been adjusting the blending of the wastes, trying to find the sweet spot. We've had a bit of an issue with phosphorus and other constituents from our hauled wastes, but we're getting that under control."

Port Rowan, a small community on the north shore of Lake Erie, thrives on tourism and fishing. For years, the community was served by a small facultative lagoon system that was under capacity and struggled to meet its permit levels.

With the internationally designated Long Point Biosphere just downstream of the plant's discharge point, environmentalists and government regulators brought pressure on the county to install more effective technology for the Port Rowan facility. Or, as project manager David Evans of the firm R.V. Anderson said in a news report about the official opening of the plant, "It became pretty obvious with the sensitivity of the area that we were going to have to do the best technology application."

The technology includes SCADA-driven blending of the various waste streams, preliminary and primary treatment, and a membrane bioreactor (MBR) system.

Mixed wastewater

Raw sewage from the community of Port Rowan passes through a pump station equipped with flow equalization and then into the preliminary treatment area, where it is screened in two mechanically cleaned Mahr bar screens (Headworks).

Hauled waste from portable toilets, septic tanks and holding tanks comes in through a dual receiving station in the headworks building — it can handle more than one truck at a time if necessary. This wastewater passes through a 6 mm coarse screen (also Headworks). Leachate from the area landfill, free of rags, flows directly into the wet well, which contains three chambers, one for each waste stream.

The blend of these wastes is a key to successful treatment. "We're tweaking the blend all the time, basically using a trial-and-error method," Fields says. "Depending on the quality of the raw sewage, we can add more or less leachate."

The design capacity of the hauled waste pumps is 20 percent of the raw sewage flow; the leachate pump capacity is 10 percent of the raw sewage flow. The blend is monitored and controlled by the plant's SCADA system (Hollen Controls).

In the headworks building, a cyclone-type grit remover (ENV Treatment Systems) takes out sand and debris and pumps it to a classifier. The effluent moves on to a pair of rectangular primary clarifiers. After settling, it passes through a 1 mm fine-mesh filter before the biological tank in the MBR system, or can be diverted back to the 580,000-gallon equalization tank next to the facility. "The equalization reservoir gives us a cushion against high flows or mechanical breakdowns," Fields says.

Fouling prevention

The fine screen protects against fouling in the membrane portion of the Zenon MBR (GE Water & Process Technologies). The MBR includes a biological treatment tank containing two parallel anoxic/oxic trains.

The anoxic zone is a "swing zone" that can function in the oxic mode during peak load conditions. The oxic (or aerobic) zone contains fine-bubble membrane diffusers (SSI Aeration Systems). Positive-displacement blowers are from Aerzen Canada, and Flygt (Xylem) provided the submersible pumps and mixers.

Two separate membrane trains are available, each with two ZW 500d cassettes, for a total of four cassettes. Each cassette contains 38 hollow-fiber membrane modules. Normally, the primary effluent is split into the two trains and enters the anoxic tank, then flows under a baffle to the oxic zone. In low-flow conditions, only one train is in operation.

Membrane maintenance includes chemical cleaning with sodium hypochlorite and recovery cleaning with citric acid. Syntec Process Equipment supplied the process valves. The mixed liquor from the aeration tanks then overflows into the MBR tanks, and the sludge from MBR system is recirculated to the anoxic tanks. The excess sludge is wasted and co-settled with primary sludge before final treatment.

Handling solids

The treated wastewater can be disinfected with chlorine and dechlorinated, but since startup in the spring of 2012, the coliform count has been so low that this step hasn't been activated. The staff can also add alum for phosphorus removal and sodium hydroxide for pH adjustment through multipoint injection systems. Metcon Sales and Engineering supplied the chemical metering pumps.

A single-stage aerobic digester processes the primary and waste activated sludge solids, and pumps (Weir Minerals) deliver the treated material to an on-site biosolids storage tank. Sludge and scum collectors are from C & M Environmental Technologies.

The facility has about 160,000 gallons of storage capacity, good for about a year. Norfolk County uses a third-party contractor to deliver the biosolids to area farms. "Liquid application is typically the preference of the large agricultural community up here," says Fields. "The nutrients like nitrogen and phosphorus are in demand from ginseng farms in the area once the crop has been harvested."

The plant has an odor-control system. Operating at negative pressure, two wood chip biofilter units pull gases from the headworks and digestion areas and strip off odor-generating compounds. These areas are covered to prevent odorous releases. The plant operates with one full-time operator on site, with backup available if necessary. Veolia Water North America has the operational contract for the county.

Adapting to change

Moving from a lagoon to an MBR is quite a jump, and Fields credits membrane manufacturer GE with helping the county get familiar with the technology. "They were an integral part of the whole process," says Fields. "We selected our membrane vendor before the actual design of the plant. We were able to use their engineers and designers to help. They played a major role and continue to be a great resource for us."

The countywide SCADA master plan also helped. The plant SCADA system is based on the master plan and ensures that data-handling conflicts are avoided. "We developed our own standards, and it's paying off," Fields says.

Still, the facility represents a large investment for this small community. The project cost about $11 million (Canadian), of which $3.9 million came from the federal government. "It's fairly expensive to operate," Fields says. "Our energy costs are high, but then we're treating a high-strength waste."

The economic and environmental impacts of the plant make it worthwhile. The grand opening was attended by more than 100 officials and featured poster boards by all vendors. Norfolk County councilors Betty Chanyi and Don Edwards — representing Federal Member of Parliament Diane Finley — stressed the economic benefits. Chanyi noted, "the plant provides an opportunity for residential and business expansion." Edwards called the facility another successful step toward economic recovery.

Help for the environment

The local environment may be an even bigger beneficiary. The plant discharges to Dedrick Creek, which flows into Lake Erie just a few miles upstream of Long Point, a 20-mile sand spit that juts into the lake and features one of Canada's most fragile ecosystems. In 1986, the United Nations Education, Scientific and Cultural Organization (UNESCO) recognized the area as a prime example of a Great Lakes coastal ecosystem and designated it as a biosphere, only the third such area in Canada.

The land is a unique blend of habitats — beaches, dunes, meadows, woodlands, marshes, ponds and streams — and is a world-renowned refuge and stopover for migrating birds in the fall and spring. "We received a lot of scrutiny when it came to the environmental assessment for the facility," says Fields. "It's a very sensitive receiving stream, experiencing low seasonal flows. Birders, environmentalists and others were behind the move to upgrade this facility."

Fields says the goal was to build a facility that could meet very stringent criteria. Although the plant has been operating for less than a year, the performance data makes it obvious that Port Rowan is meeting the challenge.


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