Waste Treatment

Waste to Energy (WTE)

The energy content of waste products can be harnessed directly by using them as a direct combustion fuel, or indirectly by processing them into another type of fuel. Thermal treatment ranges from using waste as a fuel source for cooking or heating and the use of the heating to fuel for boilers to generate steam and electricity in a turbine.

WTE is the process of creating energy in the form of electricity or heat from the combustion of waste source. WTE is a form of energy recovery. Most WTE processes produce electricity directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or other synthetic fuels.

There are a number of other new and emerging technologies that are able to produce energy from waste and other fuels without direct combustion. Many of these technologies have the potential to produce more electric power from the same amount of fuel than would be possible by direct combustion. This is mainly due to the separation of ash from the converted fuel, thereby allowing higher combustion temperatures in e.g. boilers, gas turbines, internal combustion engines, fuel cells.

MSW

Municipal solid waste (MSW), - more commonly known as trash or garbage - consists of everyday items we use and then throw away, such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances, paint, and batteries. This comes from our homes, schools, hospitals, and businesses.

Health Care Waste (HCW)

Medical (biomedical) wastes or HCW pose numerous potential health and safety hazards. In addition to their infectious and toxic characteristics, the highly variable and inconsistent nature of medical waste streams has increased public concern about storage, treatment, transportation, and ultimate disposal. In recent years, techniques have been developed to reduce human exposure to the toxic and infectious components of medical wastes. The most commonly used techniques include internal segregation, containment, incineration, and gasification. Other common techniques include grinding, shredding, and disinfection, e.g., autoclaving and chemical treatment followed by landfilling. Of all the available technologies for medical waste treatment and disposal, plasma gasification has been found to be the most effective method overall for destroying infectious and toxic material, volume reduction, and weight reduction in the medical waste stream. Plasma gasification destroys the broadest variety of medical waste constituents and can recover energy from the medical waste stream. Gasification also is an appropriate alternative to burial of human pathological remains.

Treatment Technologies: Comparison

	Incineration	Autoclave	Microwave	Chemical disinfection	Thermal gasification
Investment/operating cost	High	Moderate	High	Low	Moderate
Suitability of the waste	Not for radioactive	All except Pathological	All except cytotoxic, radioactive	Liquid waste	All
Ease of operation	No	Yes	Yes	Yes	No
Waste volume reduction	80 %	Less	Significant	-	95 %
Odor problem	Yes	Slight	Slight	Slight	No
Environmental friendly	No	Yes	Yes	No	Yes

Landfill

Waste is normally collected and deposit in a municipal landfill. Disposing of waste in a landfill involves burying the waste, and this remains a common practice in most countries. In the developed world the average person produces approximately 1 kg per day.

Over time, solid waste begins to decompose biologically shortly after being buried in landfills and, through the anaerobic decomposition process, generates landfill gas (LFG). Landfill gas, comprised primarily of methane (CH₄) and carbon dioxide (CO₂), would contribute to the formation of smog or global warming, cause odours, and even pose safety and health hazards if not properly controlled. Landfill gas is combustible and can be used as an energy source.

Older, poorly designed or poorly managed landfills can create a number of adverse environmental impacts such as wind-blown litter, attraction of vermin, and generation of liquid leachate. Another common byproduct of landfills is gas (mostly composed of methane and carbon dioxide), which is produced as organic waste breaks down anaerobically. This gas can create odour problems, kill surface vegetation, and is a greenhouse gas.

Design characteristics of a modern landfill include methods to contain leachate such as clay or plastic lining material. Deposited waste is normally compacted to increase its density and stability, and covered to prevent attracting vermin. Many landfills also have landfill gas extraction systems installed to extract the landfill gas. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity.

RDF

Refuse-derived fuel (RDF) or solid recovered fuel (SRF) is a fuel produced by shredding, sorting and drying of Municipal Solid Waste (MSW). RDF consists largely of combustible components of municipal waste such as biodegradable waste. Recycling of MSW is almost always economic. The rest is called RDF and processing facilities are normally located near a source of MSW. RDF is a homogenous mass and suitable for using in a gasification unit. Today RDF is combusted or incinerated giving large amounts of ash and pollution. This problem will be neutralized by gasification.

The production of RDF may involve some but not all of the following steps:

• Preliminary separation
• Size screening
• Magnetic separation
• Coarse shredding
• Refining separation
• Compacting
• Torrefication

The finished RDF product may be stored for some time and have many different uses, like raw material for firewood, combustion and gasification. We have found that some 50 % of most MSW can be recycled on the open market, giving a very short return on investment. The remainder (RDF) is highly valuable as energy source for production of power or heat. The return on investment for a complete system for most of our clients is below 5 years.

Case studies on RDF.