Searching for alternatives to land-applied sewage sludge
Municipalities are trying many things across the country, none as cheap as land application
By Frances Anderson - Found in Ontario Farmer Vol. 44 No. 18
Burlington – Politicians need to be aware there are beneficial uses of sewage sludge beyond applying it to agricultural land, says Michael Payne, an environmental management specialist with OMAFRA.
“You’ll get a municipality that gets frustrated with the land application program, or a council that’s not supportive, and the next thing you know, they’re landfilling,” said Payne, who recently co-chaired a conference on alternative options for biosolids.
Power from people
The state of Connecticut has never allowed land application of biosolids, so that’s one reason the Town of Stamford has a plan to use human waste to generate electricity. Another reason for power generation is that Stamford residents already pay 18 cents a kilowatt hour for electricity and the price is rising.
Jeanette Brown, an engineer, and the executive director of the Stamford Water Pollution Control Authority, explained how sewage sludge from its “sewered population of 110,000” will be dried and pelletized. The pellets will power an electrical generator through a process called gasification. Heat from the engine will help dry more solids, and most of the 2MW electricity generated will be used to keep the plant going.
Ash left over from the process is about a tenth of the volume of the original solids, and has “beneficial use as a fertilizer,” though it can also be used in making tiles and concrete, Brown said.
Stamford is using gasification, as opposed to anaerobic digestion, to create gas because there’s more thermal energy released in “undigested” solids.
Installing an anaerobic digester would also have a higher capital cost, higher maintenance costs, and would leave more solids behind.
Testing has confirmed the Stamford project is technically feasible and they have selected a supplier. The challenge, now that natural gas prices have dropped, is funding, though the entire project will pay for itself over time, Brown said.
“Look at what’s happening in the Gulf of Mexico,” said Brown. “We can make every waste water treatment plant energy self-sufficient and we need to demonstrate this.”
The closest Ontario comes right now to energy generation from waste is incineration. The Lakeview Waste Water Treatment Plant on Lake Ontario, operated by the Ontario Clean Water Agency, is currently the largest incinerator of municipal sewage in the world. It has the capacity to dry 118 million gallons of sewage a day, and incinerates 400 tonnes of dry sludge for the communities of Mississauga, Caledon and Brampton, in the Region of Peel.
Manager William Fernandes, said the plant has cut its natural gas consumption by 75 per cent – and reduced odour – by changing from cold wind box fluid beds, to hot wind box technology. Heat from the incineration process is recycled, but it doesn’t produce electricity – yet.
Fernandes said energy generation wasn’t feasible when Peel’s waste management master plan was developed, but “it might be a natural progression” when the plan, begun in 2003, is complete.
Incineration also generates ash. Fernandes said he’s give it away from brickmaking and concrete, but the tradesmen want to be paid to take it, so it’s currently being stored on site. The 105-acre site has enough space for ash storage for the next 25 years.
Land rehabilitation
Mark Teshima, of Sylvis Environmental explained how his company is using biosolids from the City of Vancouver to rehabilitate Canada’s largest sand and gravel mine, in Sechelt, B.C. The site is 250 hectares and Sylvis worked with the B.C. Ministry of the Environment to establish regulations that allow it to apply up to 50 dry tonnes of biosolids per hectare and then plant trees.
It has been working there for 10 years, and the first trees planted are now being harvested – ironically, for fibre to make toilet paper.
Agricultural application is not an option unless you truck the biosolids 400 miles away, because “the (Fraser) Valley is already nutrient-rich,” Teshima said. The open pit mine at Sechelt is large enough that using it for biosolids is “a sustainable long-term management option.”
Ontario certainly has lots of pits and quarries where biosolids could be used – about 6,000 active ones and, in southern Ontario, another 4,000 to 5,000 abandoned ones. These tend to be smaller, one to two acres, said Maria Vanden Heuvel, a policy advisor to the Ministry of Natural Resources.
MNR, which regulates the pit and quarries under the Aggregate Resources Act, has “limited experience with biosolids applied to aggregate sites, to our knowledge,” said Vanden Heuvel, though, she added, “a handful” have been used for pulp and paper waste.
Quarries go deep, often below the water table, so typically become ponds. Pits are more likely to be suitable for rehabilitation with biosolids, although the side slops may be too steep for agricultural applications. However, Vanden Heuvel suggested, the biggest obstacles to using biosolids are likely to be “public perception” and regulations limiting the kind and quality of off-site material that can be introduced.
Nevertheless, Vanden Heuvel said the door is open for industry to propose a pilot project that would test the use of biosolids for rehabilitation. There is even an Aggregate Resources Trust, with a mandate to do research on management, including rehabilitation, that could fund such research, she noted.
Allan Mumby, of EPCOR Water Services In. in Edmonton, and Dave Nussey, of Belle River Waste Water Treatment Plant, Ontario both explained how they are composting sewage sludge in those municipalities.
EPCOR markets its compost to Edmonton’s parks department, as well as landscapers and developers, but compost from Belle River is applied to agricultural land under a Certificate of Approval from the Ministry of Environment.
Elaine Collis, the biosolids management co-ordinator for the Regional Municipality of Durham outlined its “unconventional” agricultural application for biosolids. It has been working with Terratec Environmental and Dutchmaster Nurseries Ltd., since 2007, to apply biosolids from three waste water treatment plants, to ornamental trees on one of seven licenced sites, comprising 600 acres.
The tree nursery is not bound by the traditional cropping schedule, and the process has had good public acceptance. “There is notice to the neighbours, and the municipality. We have site signage, and signage on trucks and trailers,” she said. There have inquiries, but not complaints.
The nursery saves approximately $240 an acre in fertilizer costs over the five-year application cycle and the municipality benefits by diverting the sludge from incineration, said Collis.
At the end of the day, however, Larry Davis, a director of the Ontario Federation of Agriculture from Burford, told Ontario Farmer that none of the alternatives appeared to be as viable – from a cost perspective – as land application of biosolids.
Davis, who grows corn, soybeans and hay, on sandy loam soil uses biosolids to build up the organic matter in his land, at no cost.
Human waste is typically five per cent nitrogen, two per cent phosphorus, and calcium, with a lot of micronutrients like zinc, copper and molybdenum.
“It might be worse $50 an acre in fertilizer value,” Davis estimated, “but the value is really in the organic matter.” He’s not concerned about the accumulation of metals in his soil, because, he said, “after 30 years of research,” there’s no increase in metals if the sludge is applied properly.
