Composting

Composting is the process of using certain bacteria to break down organic material-food scraps, bones, vegetable and fruit peels, and many paper products-into usable components. In natural environments, bacteria turn dead animals and plants into basic organic material which is then deposited into the soil. In large-scale municipal projects, a certain combination of carbon, nitrogen, water-and, depending on the process, air-is necessary to promote decomposition at the highest possible rate.

Using waste from the recently introduced green bins, organic material is screened for large, non-organic objects, and the remaining usable material is blended into a pulp. Any remaining metal or plastic particles still present can be easily filtered out. The organic liquid mixture then undergoes ‘anaerobic digestion’ (anaerobic indicating the bacteria does not need oxygen to function). After 15 days, the end products are biogas-comprised mostly of methane and carbon dioxide-and an organic solid material. To be useful for agriculture and gardening, this organic solid material must be further treated at outdoor, aerobic composting facilities with a supply of oxygen.

Composting can potentially divert 70 per cent of the total domestic garbage produced in Toronto toward sustainable processes. The biogas by-products are a concern, since carbon dioxide and methane are greenhouse gases that contribute to global warming. Biogas can be cleaned up and used for heating or electricity production, although at a considerably higher cost than natural gas.

-Dan Rios

Incineration

Decades ago, incinerators were simply massive burning units where everything and anything in municipal trash was left to burn, often with toxic by-products like dioxins. Present-day incinerators, dubbed “energy-from-waste” (EfW) plants, have sorters to remove metals, glass and inorganic waste such as drywall and bricks. The high temperature produced by the burning is used to generate steam to power turbines that produce electricity or heat, which can be fed into Toronto’s power grid.

Incineration produces compact waste materials (ash) for landfills. Mercury, lead, cadmium, copper, and zinc may be released as solid ash content, but new techniques have helped reduce the amount of toxic materials through more careful sorting procedures, lower burning temperature to minimize dioxin release, and “scrubbers” that prevent the release of acid gases into the atmosphere. A 75 per cent volume reduction of space is estimated for incinerated garbage over garbage that is merely buried.

Despite a number of EfW plants nearby, Toronto does not currently use any EfW technology on its waste. Environmentally-friendly Sweden has seen good results from their 29 EfW plants. They report drastic drops in both dioxin and toxic metal release, but incineration technology has not yet managed to reduce these to zero. Incineration of 47 per cent of all household waste in Sweden generates two per cent of the country’s total energy supply.

-Mandy Lo

Gasification

The chemical process of gasification is almost something out of science fiction: it can vapourize our garbage out of existence while generating fuel. Gasification involves burning solid waste to generate a fuel gas known as “syngas.” This consists mostly of carbon monoxide and hydrogen, and has about a third of the energy capacity of natural gas when burned. Syngas is a popular ‘green’ gas that can be used much like natural gas for a variety of applications like transportation or electrical generation.

Like incineration, gasification is essentially a burning process, though it recovers more energy through syngas than EfW plants, potentially generating enough electric power to meet the needs of 15 to 20 million people. Depending on the type of waste used, gasification proponents argue that little to no carbon, sulfur, or nitrogen-based emissions are released. Further, any solid by-products can be re-constituted into useable building material.

However, these claims have created a misplaced optimism. Because of the relative novelty of gasification, the short-term studies conducted do not thoroughly examine the process. They also use the ‘ideal’ garbage-clean homogenous waste-as feedstock for tests. Gasification, like incineration, requires the removal of metals and other inert substance that do not have the ability to react. Simply feeding all our waste into a gasification system will not work.

Implementing a viable gasification system comes at a steep cost, in addition to the complexity involved in building the structure to have it. Gasification does release various metals and chemicals, including highly toxic dioxins and furans.

-Nira Datta

Plasma Gasification

Garbage will always be unwanted, but advancements in waste-processing technology means that not every banana peel or plastic wrapper will end up on the funeral pyre of incineration. Plasma gasification is one such technology.

Plasma is neither a solid, liquid, or gas, but a state of matter all its own. It is created by passing an electric charge through a gas until some of its atoms become ionized and lose their electrons. The plasma is the resulting mosaic of ions, electrons and neutral atoms, and is one of the hottest heat sources available, with a temperature of about 20,000 degrees Celsius.

In an oxygen-starved environment, plasma can break down almost any waste you feed it (except nuclear waste) into simple gases like hydrogen, carbon dioxide, and water vapour. Anything that can’t be converted to a gas is melted down into a harmless slag, often only 0.4 per cent of the original volume of waste input.

The procedure produces almost no emissions and completely breaks down toxic waste compounds. The slag can be reused for road construction and the gases, once cleared of contaminants, can be used as fuel to power the plasma facility itself as well as feed power into a city’s grid. When the gases are used as fuel for electricity generation, the emissions released are similar to those of natural gas.

Because of the enormous expense and equipment necessary to run a plasma gasification plant, only a select few cities have turned theory into reality. Come March 2007, Ottawa will begin a trial to examine the efficacy of a small-scale plasma plant.

-Jen Bates

Landfills

Unsustainable, bulky, and temporary by nature, dumps-open pits of garbage not engineered to be isolated from the environment-are the oldest form of garbage disposal. As recently as the early 1980s, sanitary landfills have taken over as the dump of choice. They have clay or synthetic liners that isolate the waste from the air, groundwater, and the environment in general.

Among the many dangers of landfills is the production of greenhouse gases, 50 per cent of which are methane. However, gases can be captured and managed in modern landfills for conversion into a useful energy source. Though the process releases carbon dioxide, which still contributes to greenhouse emissions, its global warming potential is less than one twentieth that of methane, giving it a relatively lower environmental impact. Captured methane, used as a direct energy source, will conserve other non-renewable energy sources such as fossil fuels.

In 1999, approximately 20 million cubic meters of methane were collected in Canada to be converted or used directly, and this reduced greenhouse emissions by the same amount as taking 1.5 million cars off the road. This quantity of methane contains enough energy to heat 160,000 homes, though the process may not always be feasible because of the cost of collection and conversion.

The latest developments in landfill techniques involve “sustainable landfills.” These include sequential anaerobic and aerobic reactors, “biofiltration” of methane using special bacteria, and moisture distribution throughout the landfill cell.

-Mayce Al-Sukhni