Waste

What is Waste?

In the natural world, there is no such thing as waste. Nature efficiently recycles materials through a very complex ecological process. Our industrial processes have not yet been developed to this level of efficiency or complexity. However, there are many new and exciting developments which reduce the environmental, social and financial costs of waste treatment and disposal. In the words of Dr. Amory Lovins of The Rocky Mountains Institute:

"Now the reason it is extremely profitable to wring out waste... is that there is so much waste, and quite an astonishing amount... Indeed in the American economy, (and I think the Australian is not very different in this regard), the material that we extract from the planet, that we mobilise for economic purposes, and process and move around and ultimately dispose of, totals about 20 times your body weight per person per day... So worldwide this resource flow is in the order of a half-trillion tonnes per year. And what happens to it? Well, only about 1% of it ends up in durable goods, the rest is wasted first; the system is about 99% waste. That’s a business opportunity" (ABC, 2001).

According to the New and Emerging Renewable Energy Technologies in New Zealand, published by EECA (Energy Efficiency and Conservation Authority) and the Centre for Advanced Engineering in 1996; the meaning of the term “waste” can be changed over time:

“Waste is the result of industrial societies organised as open systems operating in a predatory mode with respect to their environment. The word "waste", through Old French g(u)ast, comes from the Latin vastus which originally meant an uninhabited and uncultivated expanse of land (as in the English vast), that nowadays we call wilderness or, more ideologically, the environment. By extension the word meant land that had been rendered uncultivated and uninhabited or sparsely populated as a result of war, or predatory use, which we now call environmental degradation. By further extension, in the eighteenth century, the word waste took as well the meaning of a superfluous and lavish abundance of something and, a century later, the meaning of worthless surplus material (such as the extra sheets of good but now worthless paper left after a printing run). It is only in comparatively recent times, essentially towards the beginning of the industrial revolution, that the word came to mean the useless products of any industrial process from which no further economic value can be generated and that therefore must be rejected somewhere in a waste land, a tip, a dump, or nowadays a sanitary landfill.”

The Need for Energy from Waste in a Sustainable Energy System

As the population of the world increases, the management of industrial and municipal waste grows from being an environmental problem for local government authorities, to an issue of national and global importance. In Australia alone, over 14 million tonnes per year of domestic and commercial solid waste is deposited in landfill sites, thus giving Australians the notorious honour of being one of the world’s highest waste producers at almost 1 tonne per person per day. Concern over the short and long term management of landfill sites, particularly the establishment of new sites, as well the cost of waste disposal, has led to the development of technologies that convert waste into energy or useful by-products. Today's consumer society cannot continue forever. We must make better use of Earth's limited resources, using them sparingly and wisely so as to create as little disposable waste as possible. Even after waste minimisation has been implemented, the residual products that society produces should be either recycled, reused or used as a source of energy. In these roles the waste becomes a resource.

Waste Streams as a Resource

Organic waste is an energy carrying product that is playing an increasingly important role in renewable energy systems. Wastes suitable for energy extraction consist largely of organically derived material or "biomass", usually arising from domestic household refuse. When this rubbish is dumped in landfills, the biomass component is naturally converted by bacteria to methane that can be collected and used as landfill gas.

Waste produced by the domestic, industrial and commercial sectors of the community can be broadly classified into two streams: Solid Wastes and Liquid Wastes. This Portal file examines the potential for energy generation from both streams. In addition, gaseous by-products of industries associated with the extraction and refining of fossil fuels are also used to produce energy, yielding both financial and environmental benefits. Heat, another by-product of many industrial processes, can also represent a pollutant when released into the environment, such as when river water is used for cooling. In some instances there is the potential for some of this heat to be captured and "recycled" to increase process efficiency, or it may be profitably used for local heating needs, or even converted into electricity for on-site use, such as in fertiliser manufacturing plants.

Figure 1 An automatic grab transfers the municipal solid waste (MSW) from the reception bin on to a conveyor that feeds the combustion plant.

Anaerobic digestion of wastes stored in tanks is another method of using bacteria to convert organic wastes to methane, usually termed biogas, which has been used in sewage treatment plants for many decades, usually to produce electricity for use on-site. Combustion of solid waste is perhaps the most efficient way to convert the energy stored in it into useful heat. Incineration techniques have become more effective and the resulting emissions of hazardous substances to the atmosphere are far better controlled than they were in the 1980s. In Sweden, for example, the amount of waste delivered to incineration plants has doubled since the 1980’s, whereas the energy extraction has increased four-fold whilst stringent clean air regulations are being met.

“Solid” wastes include:

forest and wood processing residues;
agricultural crop residues; and
municipal solid wastes (MSW), which is domestic refuse, commercial wastes and industrial wastes, such as pallets, paper, cardboard and plastics.

“Liquid” wastes include:

sewage sludge and effluent;
animal wastes;
food processing residues; and
industrial effluents.

“Gaseous” wastes include:

methane from coal mining and oil refining:
industrial waste gases.

1. Solid Wastes

Solid wastes are primarily deposited in landfill sites. In Australia, approximately 20% of all solid waste is deposited in open dumps, usually servicing small towns. Recycling, incineration and waste-to-energy systems are increasing in popularity, particularly in the major population centres. Recycling programs exist in most urban local government areas, particularly for paper, aluminium, steel cans, glass, plastics and some hazardous materials, such as batteries (lead acid) and hydrocarbon products. These have gradually reduced the amount of solid waste going to landfill sites.

Solid wastes are classified according to the Australian Draft National Solid Waste Classification System, developed by the Cooperative Research Centre for Waste Management and Pollution Control in 1993. Under this classification system, solid wastes are categorised as Municipal Solid Waste, Commercial and Industrial Waste or Building and Demolition Waste.

Municipal Solid Waste
Municipal solid waste (MSW) is domestic rubbish collected through local government refuse programs, including bulk verge collection.

Figure 2 Domestic wheelie bins and a recycling box, ready for collection (courtesy of ABC).

MSW is only, at best, a transient resource, and a poor one at that since waste products are negative value products that cost more and more to return safely to the environment or to reuse in some way. The key issue is its high entropy (the traditional definition of entropy is that it refers to changes in the status quo of the system and is a measure of "molecular disorder" and the amount of wasted energy in a dynamical energy transformation from one state or form to another) (Wikipedia, 2007). Large costs are incurred in reordering the waste material to make something valuable out of it, often also requiring high energy inputs.

MSW is not an energy resource per se but is the end stage of many very complex and ever changing production and consumption processes. It “contains nothing in particular and a bit of everything in general!” As part of the transition towards more sustainable forms of social life, the processing of MSW is essentially and inherently a fractionation and refining process generating, hopefully, a range of commercial co-products, of which energy, in the form of heat, gas, oil, or power, is only a small component.

Figure 3 Typical components of Municipal Solid Waste in an urban location (courtesy of Golder Associates (1999), “Waste Profile Study of Victorian Landfills”).

Commercial and Industrial Waste
Commercial and industrial waste is bulk rubbish collected through local government or private contractors, usually in large bins, which can be loaded onto trucks. This category also includes manure from farms, crop residues and other ‘green’ wastes from agricultural and forestry processes.

Food and fibre processing industries produce many types of residues and by-products that can also be used as biomass energy sources. These waste materials are generated from all sectors of the industry, including meat processing and rendering, wool scouring, pulp and paper making, fish processing, fruit canning, confectionery, and vegetable processing. Only a small proportion of these wastes are converted to energy due to the high capital cost of plant (such as biogas digesters), lack of financial incentives, and the poor attitudes of many companies towards their environmental obligations. In New Zealand, with a population of 3.8 million people, it has been estimated that the wastes from the food and fibre export industry equate to the domestic waste from a population of 100 million. Higher landfill charges and stricter environmental regulations would encourage greater use of these wastes for energy purposes.

Solid food and fibre wastes include peelings and scraps from fruit and vegetables; outer leaves and off-cuts; food that does not meet quality control standards; unsold produce at markets and supermarkets; pulp and fibre from sugar and starch extraction; returned food scraps in restaurants; filter sludges and coffee grounds. These wastes are usually disposed in landfill dumps with the food company paying for their disposal so that there is increasing interest in “waste-to-energy” solutions as the conversion technologies improve and the value for the green energy increases.

Building and Demolition Waste
Building and demolition waste is bulk rubbish collected by private contractors in large format ‘skip’ bins from construction / demolition sites and usually disposed of in landfills or burnt in the open air.

2. Liquid Wastes

Liquid by-products of effluents of industrial processes and sewage treatment usually have a high water content, hence the use of the term "wastewater" to describe these products. In Western Australia alone, with a population of 1.9 million, the Water Corporation treats and disposes of more than 96,000 million litres of wastewater each year through its network of 89 treatment plants. Much of Western Australia’s commercial and industrial wastewater is also treated through Water Corporation facilities.

Liquid waste streams are generated by such activities as washing meat, fruit and vegetables; blanching fruit and vegetables; pre-cooking meats, poultry and fish; wool scouring; dairy whey; grease traps; other cleaning and processing operations; spent brewery wastes and wine making. These effluents contain sugars, starches and other dissolved organic matter, but in a relatively dilute form.

The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of these waste-to-energy conversion routes already exist. Often there remains a final stillage (or dilute effluent) disposal problem to be overcome. Tertiary treatment can improve the stillage quality sufficiently for consent to be granted for discharging it into nearby waterways. Alternatively there is growing interest in land treatment by irrigating the effluent onto growing crops. There are health concerns from applying sewage, farm and some industrial effluents to edible crops or even to pastures grazed by meat or milking livestock. A solution is to link the land treatment of effluent with the growing of energy crops, thus removing the material from the food chain.

Figure 4 Pathways for Wastewater. In-house treatment, sewage treatment plants (STP) and septic tanks are sources of greenhouse gas emissions. (Source: AGO).

A small component of the total wastewater produced is treated and disposed on site, via septic tanks . Like solid wastes, wastewater including sewage, is sourced from domestic buildings, commercial buildings or industrial processing plants. Unlike solid wastes, liquid wastes, where practical, are recycled in house (such as the use of grey water for irrigation), and are usually treated and disposed of without further recycling of the liquid component. Some energy is recovered from the wastewater in sewage treatment plants as biogas.

Liquid waste in the form of recycled frying oils collected from restaurants and other olefinic wastes, such as low-grade beef tallow, may also be used to produce diesel fuel, called biodiesel. Biodiesel is largely produced from crops such as rapeseed and canola, but this production may be supplemented with triglyceride wastes.

3. Gaseous Wastes

Industrial processes associated with the fossil fuel industry frequently produce by-product gases, which were once considered waste products. For example, the light fraction of hydrocarbons produced as a by-product of refining oil at the BP Kwinana refinery, once flared as a waste product, is now used to generate power for the refinery via gas turbines.

Methane is often released to the environment during the extraction of coal. This coal seam methane can present a serious safety threat, and must be extracted from the mine shaft. There can be considerable commercial benefits in using it for local power generation, and consequently methane is increasingly viewed as a resource by the coal and petroleum industry. New South Wales is leading Australia in its use of coal seam methane.

Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Applications & System Design - Renewable energy application information and system designs.

RISE System Displays - Case studies and information on installed renewable energy systems & performance data.

Waste to Energy Technologies - RISE Information Portal

Waste to Energy – a Guide for Local Authorities

Environmental Solutions

The Veggie Van: From the Fryer to the Fuel Tank

CADDET Biomass and Waste Technical Brochures

Rocky Mountain Institute

CLP Envirogas

The Septic Information Website: Inspecting, Designing and Maintaining Residential Septic Systems.

WA Water Corporation

Future Energy Solutions

Sustainable Development International

Energy Products of Idaho : Gasifiers and fluidised bed systems for waste to energy systems.

National Biofuels Program - US Department of Energy

Peter Brotherhood Ltd : Engineering a new environment

Lahmeyer International Consulting services for energy, water resources and hydropower, transportation and project management

Alternative fuels data center - US Department of energy

Juniper Waste-Energy Technology

Juniper: Pyrolysis and Gasification of Waste A Worldwide Technology and Business Review

Toshiba PKA Pyrolysis and Gasification Process

EnerTech Waste Conversion and Energy Technology

Your Home Technical Manual - Waste Minimisation - Australian Greenhouse Office

References

ABC 2001, “Natural Capitalism” (Online).

Australian Greenhouse Office 1998, "Methane capture and use: waste management workbook" (Online).

Australian Greenhouse Office 1998, "Greenhouse Challenge: Waste " (Online).

Wikipedia 2007, "Entropy " (Online).

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