The New & Emerging Technologies Policies & Practices Advisory Group has completed its mandate and is no longer active. The following information is provided for archival purposes.

Technologies
This section presents an overview of new and emerging technologies for solid waste management. The development of new and emerging technologies has been driven by the need to find alternatives to landfilling and mass-burn incineration. The City of Toronto is evaluating the potential to apply new and emerging technologies to manage up to 40% of the City's solid waste stream that cannot be diverted through other means (see Figure 1). This remaining 40% of the solid waste stream is referred to as residual waste.

The objective of this section is to describe the fundamental processes upon which most current technologies are based and not to provide a comprehensive listing of technologies. This section also introduces the concept of a waste management system and describes the components of a system that includes a new and emerging technology for residual waste processing.

New and emerging technologies includes a group of processes collectively referred to as advanced thermal treatment technologies (ATT). These technologies are of particular interest because of their relatively advanced stage of development, their ability to derive energy from residual waste and their generally low levels of emissions. ATT technologies are based on the following thermal processes:

• gasification;
  
• pyrolysis;
  
• plasma gasification; and,
  
• depolymerization.
  

A brief description of each process is provided in the following paragraphs.

Gasification

The process of gasification is the thermal degradation of organic compounds, or otherwise referred to as carbonaceous materials, at high temperatures (900 - 1400 °C) in a low oxygen atmosphere, to produce a combustible gas, referred to as syngas, and an inert, possibly vitrified, solid residue.
As defined by the Gasification Technologies Council (GTC):

• A process technology that is designed and operated for the purpose of producing synthesis gas (a commodity which can be used to produce fuels, chemicals, intermediate products or power) through the chemical conversion of carbonaceous materials.
  

• A process that converts carbonaceous materials through a process involving partial oxidation of the feedstock in a reducing atmosphere in the presence of steam at temperatures sufficient to convert the feedstock to synthesis gas; to convert inorganic matter in the feedstock (when the feedstock is a solid or semi-solid) to a glassy solid material known as vitreous frit or slag; and to convert halogens into the corresponding acid halides.
  

• A process that incorporates a modern, high temperature pressurized gasifier (which produces a raw synthesis gas) with auxiliary gas and water treatment systems to produce a refined product synthesis gas.

Pyrolysis

Pyrolysis is the thermal decomposition of organic materials at temperatures in excess of 200^oC in the complete absence of air. The end product of pyrolysis is a mixture of solids (char), liquids (oxygenated oils), and a combustible gas, or syngas, comprised of methane, carbon monoxide, and carbon dioxide, with proportions determined by operating temperature, pressure, oxygen content, and other conditions. Metals, ceramics and other inert materials are not affected by the process.

Plasma Discharge Technology/Plasma Gasification

Plasma discharge uses extremely high temperatures in an oxygen-starved environment to completely decompose input waste material into very simple molecules in a process similar to pyrolysis. Products include combustible gas and a vitrified solid residue.

The heat source is a plasma discharge torch, a device that produces a very high temperature plasma gas. Plasma is an electrically neutral, highly ionized gas composed of ions, electrons, and neutral particles. It is a phase of matter distinct from solids, liquids, and normal gases. Plasma is very common and is found in the sun, fire, fluorescent and neon lights. A plasma gas is the hottest, sustainable heat source available and results in a temperature profile of between 3,000 and 8,000 degrees Celsius.

Depolymerization

Depolymerization processes use high-energy microwaves in a nitrogen atmosphere to decompose organic material. The waste absorbs microwave energy increasing the internal energy of the organic material to a level where chemical decomposition occurs on a molecular level. The nitrogen blanket forms an inert, oxygen free environment to prevent combustion. Temperatures in the chamber range between 150 to 350 degrees Celsius. At these temperatures, metal, ceramics and glass are not chemically affected.

An ATT or other new and emerging technology for residual waste processing would be a component of a waste management system designed to collect, handle and process residual wastes and to manage all resulting products and residues. The components of a simple residual waste management system are presented in Figure 2.

Of particular interest when evaluating ATT or other new and emerging technologies is the degree of pre-processing required to convert the residual waste into a suitable feed material. Residual waste, as collected, is not suitable for most ATT technologies because of its varying composition and size of some of its constituent materials. Residual waste may also contain materials that are undesirable because they either contribute to the quantity of solid residue, jeopardize the process or cannot be captured by the emission control systems.

Typically pre-processing involves the physical operations of separation or sorting, shredding or grinding, blending with other materials, drying and possibly pelletization or a similar reformation process. The purpose of pre-processing is to produce a feed material with consistent physical characteristics (size, shape, moisture content) and chemical properties (energy content). A consistent input material will minimize process upset conditions and will improve overall performance. Pre-processing operations are also designed to produce a material that can be safely handled, transported and stored, thereby allowing for separation of pre-processing and processing operations.

Environmental control technologies must also be considered in this process. Any new and emerging technology that is considered will need auxiliary equipment for the control of any emissions or effluent resulting from the process. These technologies will be put in place to comply with existing environmental regulations. These systems could include bag filters for the removal of particulate matter removal, scrubbers for the removal of impurities from air stacks, odour control system, and effluent pre-processing.

Figure 1. Application of New & Emerging Technologies for Solid Waste Management Services

Figure 2. Simple Residual Waste Management System