Alternative Waste Treatment Technologies
This article deals with two viable and modern technologies for treating residual waste with far less environmental impact than engineered landfills as proposed by LDC for the Municipality of Alleyn and Cawood. The two technologies are incineration and plasma gasification.
We have often heard of large incinerators where the waste is burned and the hot gases given off are used to generate electricity. Over 250 of such Waste to Electricity facilities have been installed in Europe and Asia since1995. Sweden alone has 29 plants incinerating 47 percent of all household waste and generating a total of 9.3 terrawatt hours of energy. The amount of landfilled household waste is now less than 10 percent of the total household waste – no need for mammoth landfill sites in Sweden. Incineration has been improved so much that dioxin emissions from all 29 Swedish incineration plants amount to a total of only 0.7 grams compared to 100 grams from 18 plants 15 years ago. Incineration has been amply demonstrated to be a safe and environmentally friendly method of dealing with garbage. Unlike vented landfills which generate methane ( a greenhouse gas which over 100 years has 23 times the potential for global warming than carbon dioxide) incineration does not emit methane.
For small municipalities there is not normally enough garbage to install a large incinerator with an accompanying electricity generator. However, as advanced by Robert Wilson at the May 23, 2006 meeting of the mayors of the MRC of Pontiac, there is a potential local solution to waste management which would be under the control of the municipalities. This is an incinerator technology available from a Canadian firm (Eco Waste Solutions) willing to establish manufacturing in a Quebec location e.g. Shawville, if the municipalities in the Outaouais were to opt for this technology. The modern incineration plants made by this company have three stages. In the first stage municipal waste is loaded into a burning chamber where it is ignited using a fuel such as diesel or propane or natural gas. This starts the burning process even though municipal waste may have high moisture content. After about four hours the burner in the primary chamber turns off automatically because from that point on the waste is largely self-fueling and burning continues at temperature from 650-850 °C. As the burn takes place, the gases generated pass through into a richly oxygenated secondary chamber and are destroyed in this “afterburner” at a temperature in excess of 1000 °C, where only a 2 second retention time is needed to cleanse the gases. In the final stage, a scrubber removes solid content from the remaining gases. The air emissions from the Eco Waste incinerators have been verified by the Environment Canada –Industry Canada initiative delivered by ETV Canada Inc. to meet the tightened requirements issued by the Ontario Ministry of the Environment in 2004.
The incinerators come in sizes able to handle from 500 lbs to 10 tons of waste per day. A 4 ton per day unit would handle the requirements for Shawville, or a logical grouping of 3 or 4 small towns. 15-17 units could replace 50 trench landfills in the Outaouais scheduled for 2008 closure (commitment to these numbers could trigger manufacturing in Shawville). A 4 ton unit would be housed in a building of approximately 75 feet x 75 feet, with space for trucks to enter and dump their garbage and for hauling out of the ash generated - which contains nothing hazardous to leach into the water supply. The ash is only about 5% of the volume fed into the incinerator, obviating the need for a mammoth landfill site. A 4 ton unit would cost about $1.3 million shared among 3-4 municipalities, plus a building of the suitable size, and could be delivered within 4 months from order placement. Operating cost is approximately $100 per ton which is essentially the fuel cost – this is equivalent to the cost one municipality in the Outaouais is now paying for trucking to get its garbage to Lachute. One operator is needed to unload ashes from the previous burn, load the garbage and attend the equipment for the first four hours, then the system operates automatically until the burn is complete and the system cools down.
The second alternative is one that would suit the complete Outaouais including the City of Gatineau. This is plasma gasification, a technology which uses a plasma torch to treat the waste in an oxygen starved environment. The plasma torch typically reaches up to 8000 °C in its center and the garbage sees typically 3-4000 °C. At these temperatures the waste is pyrolysed into its constituent elements such as Hydrogen, Oxygen, Carbon, Nitrogen, etc. Prior to exit the elements are reformed into a synthetic gas (syngas) rich in CO and H2 with high energy content. The materials that are not converted to syngas (metal, glass, rock and concrete) are vitrified to produce an inert slag. For one ton of garbage there is typically 50 lbs of slag, which can be sold to be crushed and used as an aggregate in concrete and asphalt. The syngas can be used to produce steam to generate electricity and is cleaned as it is cooled down so that there are minimal emissions into the air. The plasma gasification process produces no dioxins or furans and other potential pollutants are tiny fractions of the regulations for incinerators. There are plasma gasification units operating in various parts of the world to handle hazardous waste.
Handling municipal waste using this technology is relatively new – various experimental facilities exist but these are of small size (including two in Quebec). A 75 ton per day unit is being installed on a 4 acre site at the Trail Road landfill site in Ottawa to prove the technology. The unit will generate 5 MW of electricity and use only 1 MW for its own operation – the rest will be sold. Note that the company carrying out this project, Plasco Energy Group, is building the plant at its own cost, and will operate it – the city has only to provide the space and guarantee the contracted supply of garbage, and pay approximately $60.00 per ton for treatment. For the future Plasco is offering municipalities the same model, which means no capital cost risk for the municipalities. A 200 tons per day unit is the optimum (corresponding to the garbage generated in the whole of the Outaouais), and depending on the price negotiated for the electricity, Plasco will enter into an agreement for 20 years for a price to treat garbage of between $50 and $60 per ton. With this business model and a technology far superior to anything else available for treating residual waste, to me it is a no-brainer to hold out for this approach if we want a single solution for the whole of the Outaouais. A complete plant could be delivered in 18 months, and could put Quebec on the map as being the most advanced in the world in residual waste treatment. The technology particularly likes fuels rich in carbon such as plastic containers (which while currently collected in recycling programs 60% of the plastic ends up in landfill sites) and automobile tires, since these allow control of the gasification process.
Both alternatives presented above would eliminate the hazards of a large landfill site where threats to the environment and the water supply would be around for hundreds of years. They would also be acceptable to tourists allowing development of eco tourism thereby increasing the revenue to all municipalities in the MRC of Pontiac.
R.E. Thomas, Ph.D. P.Eng