Biosolids from wastewater treatment plants at Metro Vancouver are put to use just about everywhere nearby.

From cover material at landfills, to fertilizer on grasslands and hay fields, to land reclamation at copper and molybdenum mines, to soil for city parks and recreation areas, biosolids from MV’s wastewater treatment plants go to beneficial uses.

“It’s a different mindset,” says Laurie Ford, program manager for Utilities Residuals Management at MV, which serves the British Columbia city of Vancouver and its surroundings — a total population of 2.4 million. “It’s always been our intention to use the material beneficially. More recently, we have worked with our upstream project teams to design systems that produce high-quality end products.”

The utility’s website calls the approach integrated resource recovery: “It’s a new way of thinking about waste — as a valuable resource and not just something that must be disposed of.”

The biosolids program dovetails nicely with MV’s efforts to lead the way in municipal sustainability. It’s also cost-effective. “Because of where we are, landfill space that will accept biosolids is nonexistent,” Ford says. “Our after-dewatering costs for reuse can run between $50 and $120 a metric ton. That is actually cheaper than shipping the material to the nearest landfill that will accept biosolids, which is in Alberta, 900 kilometers [560 miles] away.”

Road to reuse

The 494 million liter per day (130 mgd) Annacis Island Treatment Plant is the largest secondary plant among five treatment facilities serving the 23 municipal members of MV. Eighty percent of the biosolids headed for reuse are processed there.

Raw influent enters the plant from a trunk line operated by MV and fed by local sewers owned by the member municipalities. After bar screening and grit removal, the wastewater settles in 13 primary sedimentation tanks. Secondary treatment consists of four trickling filters filled with plastic media, followed by aeration basins. The water then flows to secondary clarifiers before disinfection with sodium hypochlorite and dechlorination with sodium bisulfite. The Fraser River receives the effluent.

Influent and effluent pumps are EBARA. Treatment processes are controlled by a distributed control system from ABB Automation. A rotary auger press (Parkson Corp.) screens the primary solids, and a dissolved air flotation unit (Evoqua Water Technologies) thickens the waste activated sludge. A small amount of solids originating at MV’s Northwest Langley Plant (12.2 million liters per day/3 mgd) is added to the flow.

Primary and waste activated sludge are mixed and digested anaerobically at thermophilic temperatures (55 degrees C/130 degrees F). Polymer conditions the digested solids, which are dewatered in centrifuges (Alfa Laval Ashbrook Simon-Hartley). Piston pumps (Schwing Bioset) move the biosolids to hoppers before transport to application sites. The process at Annacis Island produces 40,000 to 45,000 metric tons (44,000 to 50,000 tons) of dewatered biosolids per year. The cake, at 26 to 30 percent solids, meets British Columbia Class A standards.

MV uses similar processes for smaller amounts of biosolids at the 70 million liter per day (18 mgd) Lulu Island and the 90 million liter per day (23 mgd) Lion’s Gate treatment plants. Both use mesophilic digestion to produce Class B biosolids, used on grasslands and farm fields.

MV tests its biosolids regularly for metals, pathogens and vector attraction. The agency follows rigorous source control standards that improve biosolids quality by limiting contaminants entering the wastewater. For example, through the Sewer Use Bylaw, MV works with dentists to reduce mercury from amalgams, and with photo imaging operations to limit silver.

Finding uses

A Utilities Residuals Management team of project coordinators, environmental technicians and engineers manages the biosolids from the loading zone to the final destination. Finding sites is a constant challenge. “We’re always looking for new beneficial use sites,” Ford says. Because Greater Vancouver practices source separation of food and yard wastes, compost is abundant in the area. A surplus of organic material and nutrients in a small geographic area makes it difficult at times to find places to reuse MV’s biosolids.

That’s why a recent project with the Regional District of North Okanagan was important. MV sent 3,700 metric tons (4,000 tons) of dewatered biosolids to the district’s Vernon Recycling and Disposal Facility, about 440 kilometers (273 miles) northeast of Vancouver, where it was mixed with sand, yard waste compost and mineral soil. The finished material was used as topsoil cover for about 8 hectares (20 acres) of the Pottery Road Landfill, which the district is closing.

The Vernon facility served as the mixing site to limit odor issues: There are no homes nearby. The Pottery Road application site is in the middle of a residential area. Loaders and backhoes mixed the material at two part biosolids, three parts compost, one part mineral soil and two parts sand. After coarse mixing, the material was mixed a second time to create a finer product.

Spreading was completed over the winter. The topsoil covering is 150 mm (6 inches) thick, over 300 mm (12 inches) of clay and 700 mm (28 inches) of fill. The site was planted with grass in May. The community plans to use the site for recreation. “Metro Vancouver is easy to work with,” says Nicole Kohnert, manager of regional engineering services with the district. “They are experienced in biosolids reuse and have a good rapport with the environmental ministry here.”  

Reclaiming mines

The Pottery Road Landfill is one of several MV beneficial reuse sites. The dewatered cake, containing nitrogen and phosphorus, provides an organic boost to soils. In 2014, about 10,000 metric tons (11,000 tons) of the material was spread on grasslands where cattle graze.

In this application, nothing is mixed with the biosolids. The material is broadcast onto the fields, where the soil naturally assimilates it through degradation and rainfall. “We’ve been delivering biosolids for agricultural purposes for over 15 years,” Ford says. “It’s very effective in establishing good soil on nutrient-deficient lands.”

MV has been delivering biosolids to copper and molybdenum mines for reclamation for even longer — more than 20 years. Canada’s Surface Mining and Reclamation Act of 1975 promotes reclamation through its abandoned mine program. MV’s biosolids are mixed with the mine’s overburden — material removed during surface mining — or directly applied and mixed with mine tailings and waste rock. “The biosolids add nutrients and organic matter to the material which generally has little organic and nutrient content,” Ford says.

In another arrangement, MV has a soil manufacturing contract that calls for 10,000 metric tons (11,000 tons) of biosolids a year to be used for landscaping projects at parks and other MV properties. Because of the long distances to many reuse sites, MV is always on the lookout for ways to cut costs. The organization uses contractors who haul loads into the city and normally would be returning empty. That works especially well with the utility’s mining customers, who truck ore into Vancouver, then fill up with biosolids for the return trip. “That way, we save on fuel costs as well as greenhouse gas emissions,” Ford says.

Continuing challenges

The MV team has contracts into coming years for agricultural and mining reuse projects. “You want to have all your biosolids committed, but things can change with little notice, and you need to be able to react quickly,” Ford says. “With mines, reclamation is not always their first priority. If the price of copper goes up or down, that can change the demand for biosolids and can make planning difficult. We face a constantly moving target. Where do we send our biosolids, and what is the nature of the places we are sending the material to?”

Since 1990, MV has delivered hundreds of thousands of tonnes of biosolids to dozens of beneficial reuse sites. That record earned the utility the 2010 Award of Excellence from the Northwest Biosolids Management Association. Sites have included the Vancouver International Airport, the Sea to Sky highway between Vancouver and Whistler, numerous landfills and mine reclamation sites, gravel pits, rangelands, city parks and silviculture projects.

With experience like that, it’s a good bet that Ford and her team will continue to find places for MV’s biosolids: “We’re old hands at this.”