DFE2008 Disposal of non-recyclables

This page is part of the Design for the Environment course

Waste management systems have evolved from the simple transportation of waste out of residential settlements to recently introduced more complex processes like plasma arc incineration. Only after the 1960s municipal waste management started to improve. Shifting from a purely economic stand-point while planning waste treatment technologies, municipalities started to evaluate the environmental impacts of their choices. This change was brought about by the large environmental damage caused by landfills which could not be overlooked. Some improvements involved the installation of base liner systems in landfills to collect leachate, the development of flue gas scrubbing technology for MSWI (municipal solid waste incinerators), etc. For the first time the aspect of using waste as a resource to make energy was taken into consideration.

Over the past few years, waste management strategies have been greatly supplemented by product related regulation. For example, regulations on packaging, end-of-life treatments and electrical equipment have made the producer responsible for the entire life cycle of the products. Therefore, forecasting the consequences of waste management strategies (environmental, economic and social) has become a highly sophisticated task. The proper disposal of non-recyclable substances is vital to the environment as well as the society. Environmental protection has aroused world wide concern since the end of the 1990s. Political authorities have amended their environmental protection norms and industrial producers are re-designing their manufacturing plants to avoid, collect, sort and recycle waste. Consumers have become selective in choosing environmentally friendly products.

This report will study the waste management strategies based on the statistics for the City of Toronto. Recently, the City has been firmly focused on diverting waste sent to Michigan landfills to a method that takes environmental, societal and economic aspects into consideration. This is in lieu of the Toronto-Michigan Contract expiring at the end of 2010. The alternatives evaluated were landfilling of waste in Michigan, incineration, and plasma arc gasification and vitrification.

A landfill in Hawaii with exposed liner for containment of leachate.

Project Information

Section 1 Group 15

S. Dhamija (Saguna)
D. Campbell(Dan_Campbell)
H. Panesar (harpreet)
S. Shalchian (shervin.shalchian)

Background

The process steps of the baseline alternative(landfill) and the two diversion alternatives (incineration and plasma arc gasification) are detailed in this section. Since the process of landfilling waste is simply tipping it into the constructed landfill, the steps of construction are described. For incineration and plasma arc gasification however, steps describing the process by which waste is treated.

Landfill

The steps to construct a landfill are: :

• Scientific Research about location of the site, geology, underground water level, location of the bodies of the water such as river and the density of the waste.
• Clearing the landfill site of all ground cover.
• Excavation of the ground (the volume of the excavation depends on the results of the first step).
• Construction of the berm all around the landfill site.
• Construction of the liner and leachate management system.
• Construction of High Density Polyethylene (HDPE) which avoids leachate to escape into the environment from the landfill.
• Installation of the leachate and methane extraction pipe.
• Installation of the leachate tank for each landfill cell.
• Installation of power plant generator and flaring system (for generating electricity) or compressor station (for selling methane itself).

Incineration

An Incineration facility processes waste in the following steps:

• Waste is dumped into a waste pit by dump trucks
• An overhead crane picks up the garbage from the waste pit into a hopper which feeds a moving grate that passes through the incinerator furnace
• The waste is set on fire by using 10 to 12 GJ of fuel
• 70% of waste sludge is evaporated
• An additional 1 GJ of fuel is used to reduce the production of hazardous compounds such as organochlorines
• Waste is transformed into solid ash and recycled for further application
• Energy is extracted from the toxic fumes produced by generating steam in a boiler
  • Steam is used to turn a turbine to generate electricity
• Toxic gases pass through an electrostatic precipitator to allow the dust to settle
• The toxic fumes then go through flue gas and other cleaning systems before being released into the atmosphere through smoke stacks

Plasma Arc Gasification and Vitrification

A plasma arc facility processes waste in the following steps:

• Waste is received and weighed inside a containment building
• Large pieces of scrap metal and hazardous waste are separated from the waste stream
• Waste is shredded into small pieces and fed on a conveyor into a gasification vessel
• Process waste heat from the latter plasma arc conversion phase is used to gasify waste.
  • Gas is fed into a plasma arc conversion vessel, where a plasma torch breaks the gas stream down at an elemental level, converting it to an energy rich synthesis gas.
  • Fly ash is liquefied in a separate plasma vessel (vitrification process) and is cooled into a glasslike solid called slag.
• Synthesis gas is purified to separate toxic constituents
• Purified synthesis gas is used to fuel a reciprocating engine generator set.
• Excess process heat from the reciprocating engine and plasma arc vessels power a steam turbine to generate additional electricity

Highlights and Recommendations

Functional Analysis
Functionally, landfills and incinerators can both be scaled to handle the city of Toronto's waste requirement of 3,825 tons per day . Plasma arc gasification is currently in its preliminary testing stages and most data is based on research scaling estimates. The only plasma arc gasification facility in Canada is run by the Plasco Energy Group based in Ottawa. It is operating at one tenth its maximum capacity of 100 tonnes per day. Thus it would not be unreasonable to doubt the functionality of scaling the plasma arc gasification model run in Ottawa to meet the city of Toronto's requirements. To assess plasma arc gasification as a viable alternative, it is assumed that such scaling is in fact possible.

Streamlined Lifecycle Assessment (SLCA)

The process implementation stage and the primary process operation stage contribute most to the environmental impacts of all the alternatives. The streamlined life cycle assessment (SLCA) demonstrates that incineration has the least impact in the area of material use, energy use, solid waste and gaseous waste. This is because of its relative ease of implementation as compared to landfill where the ecology of the existing land has to be destroyed before construction . Plasma arc gasification's advanced technology is also difficult to implement as compared to incineration. However, in the primary process operation stage, plasma arc gasification proves to be most environmentally friendly due to its maximum energy production and marketable solid outputs. Although plasma arc gasification has a definite advantage during the primary process operation stage, its drawbacks during its implementation cannot be ignored.

Cost Analysis

The most feasible solution to disposal of Toronto’s non-recyclable waste is landfill. Currently, Toronto pays Michigan $33 per tonne of waste tipped in the Carleton landfill. This cost will decrease further if Toronto's waste is locally landfilled. If an incineration plant is constructed to handle Toronto’s waste, it will cost $80 per tonne of waste whereas, if a plasma arc gasification plant is built it will cost $55 per tonne of waste. The highest contributor to the cost of incineration is the purchase of air purification equipment as well as the maintenance and operational costs.

Economic Input-Output Life Cycle Analysis (EIOLCA)

Incineration contributes heavily to the emissions of sulfur dioxide (SO₂), carbon monoxide (CO) and gases that cause an increased global warming potential (GWP). Plasma arc gasification also impact the environment with the large about of lead(Pb) emissions. To further explore the impacts of incineration and plasma arc incineration, an in-depth process analysis was carried out. Landfill was not included as a part of this analysis due to the lack of published information on its life long emissions. The results from this analysis proves plasma arc gasification to be a much cleaner process as compared to incineration. However, comparing landfill and plasma arc gasification EIO-LCA tables, it can be seen that process implementation for a landfill releases lower levels of criteria air contaminants.

Societal Analysis
Societal analysis plays a major role in the successful completion of any project. It is clear that all three waste disposal processes cause people living in the vicinity discomfort at different levels but plasma arc incineration seems to have the least resistance from the public. Public is less aware of plasma arc incineration’s new technology and this avoids pre-conceived notions about its negative impacts as in the case of landfills and incineration plants. This leads to the belief that plasma arc incineration technology might face lesser public opposition and hence be easier to implement. It is common belief that landfills are considered to be a waste of arable land. The use of incinerators is controversial because of issues such as emissions of gaseous pollutants including small quantities of heavy metals. Incineration and landfills can gain public acceptance only if the concentration of low volatile organic compounds can be guaranteed.

Details

Functional Analysis

To be a feasible solution for handling the City of Toronto's municipal solid waste stream, each alternative must be able to satisfy the following functional requirements:

• Capacity to handle Toronto's large mass of waste now (currently ~700000 tonnes per year), and in the future considering population growth.
• Minimal impact on human health and the environment.
• Economically viable in terms of both capital investment, and operating costs.
• Reliability.
• Acceptability to society (including traffic density, noise, aesthetic concerns, odours, etc.).

Both landfilling and incineration are well proven technologies that are known to be able to meet Toronto's capacity and reliability requirements. Plasma arc gasification and vitrification has primarily been implemented in limited scale plants. Plasco Energy Group's facility in Ottawa is currently the only plasma arc facility in Canada intended for processing municipal solid waste. It is only a demonstration plant at the moment, designed for a capacity of 100 tonnes per day(~5% of Toronto's requirement), but currently holds approval for only 85 tonnes per day, and to date has only processed 10 tonnes per day. It is currently operating under a special regulation, providing exemption from full Environmental Assessment Act requirements for a two year trial period. As such, it is still only in a beta testing stage, so there is considerable uncertainty regarding it's feasibility. While other plasma arc plants have been constructed in other locations around the world, they have generally proved costly, and unsuccessful as net generators of electricity. The Plasco facility does however incorporate some proprietary technological advances, which are claimed to significantly improve performance relative to existing facilities. For the purposes of this assessment, it is assumed that the technology is capable of achieving the performance claimed by Plasco Energy Group.

Other functional requirements are assessed in the relevant sections of this article.

Streamlined Lifecycle Analysis (LCA)

Background Information

The environment impacts of a product through out of its life cycle are qualitatively estimated by using the Environmental Life Cycle Assessment (LCA) method. Although the life cycle assessment method gives a precise description of the environment impacts of the product, it is not feasible because of the time it requires and the amount of data that needs to be gathered. A method that can be used to solve the problems mentioned above is Streamlined Life Cycle Assessment (SLCA). This method allows companies to identify and evaluate the environmental impacts of their products and compare different alternatives.

The results from the SLCA differ by a small score count. This is because this analysis deals with scores that are highly subjective and arbitrary. Thus, these scores are relatively the same for all three alternatives. Therefore, the SLCA is not an efficient tool to compare these three alternatives. The economic input-output life cycle assessment and cost analysis was performed to compare the three alternatives.

Spittelau incineration plant in Vienna.

Incineration versus Landfill

The life stages of the three alternatives is divided into five steps. The process implementation step is studied to compare the difference between incineration and landfill.

Once the site survey is carried out, the process of construction starts by clearing the land from any plants and excavating the land. In some cases existing industrial buildings are used for the incineration process however this is not always a possibility and in some cases the building needs to be constructed. Keeping in mind that using the existing buildings will result in less heavy machinery use, less emissions and more cost effective, it is a greener option.

The Hiroshima City Naka Incineration plant in Japan handles approximately 14000 tonnes/day of non-recyclable waste is chosen to be compared with the Michigan Landfill site . The Michigan Landfill site covers an area of 500acers which is 145 times bigger in comparison with the incineration process building in Japan that covers an area of 3.44288221 acres . The depth that is excavated in order to build the incineration process building and the landfill site is assumed to be equal since the area of the landfill site is much greater than the building area of the incinerator. With the knowledge that a landfill site covers 145 times more land than an incineration process building, more heavy machinery is used to excavate the land. Although constructing the incineration process building requires energy, one needs to consider the fact that the landfill site requires construction work such as PVC layering of the walls and installation of the methane and leachate extraction system. To conclude, it is certain that the construction of a landfill uses more energy than that of an incineration process building.

Plasma Arc Gasification versus Landfill

Although the secondary process operation of plasma arc gasification(the energy generation process)has a large volume of gaseous emissions; it still performs well in comparison to the alternatives, especially when considering offsets due to the large amount of electricity generated. The plasma arc gasification technology ensures that all gaseous emissions released to the environment are minimized and cleaned . In landfills, methane is produced when the organic waste starts to decompose and methane is 23 times more potent than the other greenhouse gasses such as carbon dioxide .

Every year 40-60 Mt of methane is released to the environment from landfills all around the world. The methane emissions are generated from landfills that have inappropriate methane extraction systems or from older sites . Although landfill gas collection captures almost all gasses in the system, some of the methane manages to escape. High Density Polyethylene Pipe (HDPE) which is joined by heat fusion is used in order to minimize the escape of methane into the environment. HDPE is a strong material that can survive under high pressure of methane gas and it is resistive to corrosion and chemical reactions in the environment .

Therefore, the mass of methane produced and released into the atmosphere by landfills has a greater effect on global warming than the carbon dioxide released in the energy generation stage for plasma arc gasification process.

Cost Analysis

The cost analysis is a crucial portion since it is the basis to conducting an Economic Input-Output Life Cycle Assessment (EIOLCA). This is because the values inputted into the EIOLCA are those obtained from the cost analysis. These values can be divided into two separate costs. Direct costs are those expenses that are directly related to the plant or landfill site. Indirect costs are expenses that are related to any other network other than the plant or landfill site (i.e. social costs, health care costs etc.). Negative costs are those that generate profit for the company (i.e. selling energy). Costs within direct costs are divided into three sections: Capital Costs which are fixed costs, Operational Costs which are costs depended on the life of the plant or site and Refurbishment, Recycling and Disposal Costs which are costs needed once the plant or plant’s major components have completed their service.

Incineration vs. Landfill

The constructing, operation, maintenance and other direct costs are about four times greater for an incineration plant than a landfill site. Such a difference is created due to the technology required to run an incineration plant. Because of the pressure build-up from anti-incineration groups, incinerator plants are forced to purchase and maintain a state-of-the-art air filtering system . This is seen from the air purification equipment and the commercial machinery repair and maintenance costs. Thus it is because of the opposition created from such groups that has increased the large difference in direct costs, this is seen from the table above as excluding the two sectors mentioned would result in a similar amount of direct costs.

Even though landfills do release more furans and dioxins , the health risks caused by incinerator plants emit a greater amount of sulphur oxides which causes asthma and other respiratory illnesses . Thus, using an incinerator uses a bigger portion of the overall healthcare budget than using a landfill site to dispose the non-recyclable waste.

However, an incinerator plant generates a larger profit than a landfill site. This is mainly because a greater amount of energy is released by burning the waste rather than letting it settle in one spot collecting the methane is emits. Furthermore, a landfill will collect only about 30% of the total methane produced . However, when comparing to a conventional power plant, incineration is seen as an inefficient way of producing electricity . Despite the greater profit made by an incinerator plant, a landfill site will cost about four times less over a ten year due to its relative inexpensive direct and indirect costs.

Plasma Arc Gasification (PAG) vs. Landfill

A plasma arc gasification plant generates about three times the amount of direct costs than a landfill site. This is due to the advanced technology being used for a plasma arc gasification plant. The manufacturing of such equipment can be expensive and with beta testing and research in progress, direct costs are increased by a substantial amount.

A plasma arc gasification plant also uses a major portion of the overall health care budget. This is due to the greater amount of SO₂ released. Note that even though an EIOLCA refers back to the cost analysis, this specific indirect cost is dependant on the EIOLCA as it presents the gaseous fumes released and thus gives an estimate on how big of a roll each alternative respectively plays on respiratory illnesses. Because this is a comparative analysis, this figure is used to show which alternative has a bigger impact on healthcare costs in money value.

A great advantage of implementing a plasma arc gasification process is the profit it makes from selling generated power. Even though a large portion of the budget is contributed towards the high end technology used for PAG, the income compensates a major portion of its expenses. It is because of this large income that presents PAG as a better solution than incineration according to this analysis. Nonetheless, the total cost for a plasma arc gasification plant is about three to four times that of a landfill site.

EIOLCA

The majority of environmental impacts for the disposal methods explored occur during their use phases. These impacts cannot be tracked well using EIOLCA methods. As such, a hybrid EIOLCA method was employed to compare disposal methods, supplementing available EIOLCA data with data for direct emissions occurring during the use phase. EIOLCA data was found for implementation and disposal costs for each type of facility, and for economic activity during usage phases.

Landfill

Before a landfill is constructed, the suitability of a location is evaluated through studies of local geology, transportation costs, and societal factors. Environmental impacts are incurred for these studies primarily through power generation for offices. Land must then be cleared and landscaped before a liner is installed to contain leachate. Machinery for moving and compacting waste in the landfill is then purchased. As waste is added in layers it is covered with soil, and once capacity for a section is reached, wells for landfill gas and leachate are installed. Landfill gas recovery and power generation equipment is then installed. Trucking waste to the Carleton Farms landfill in Michigan creates significant air emissions. Direct air emissions from a landfill are primarily methane and carbon dioxide, the proportion of which varies depending on the efficiency of landfill gas recovery.

Incineration

An incineration plant requires a large capital investment in process equipment, including material handling equipment, incineration vessels, flue gas scrubbers, and power generation equipment. When the plant is operating, fossil fuels are used to sustain combustion of waste, with larger amounts necessary for waste with low energy content or high moisture content. Throughout the life of a plant, periodic maintenance must also be performed. Decommissioning costs include demolition, recovery of scrap metals and disposal of residual solid wastes.

Plasma Arc Gasification and Vitrification

A plasma arc plant involves an even greater capital investment than incineration for assets of a similar nature. During the operating phase, no external energy input other than the waste itself is required to sustain operation. Some periodic maintenance must be performed on process equipment however. Decommissioning costs similar to incineration are also incurred at the end of plant life. Throughout the life of the plant numerous valuable by-products are sold, including aggregate from slag, and sulphur for fertilizer production.

Direct Process Emissions

In the case of incineration and plasma arc gasification, direct process emission data were obtained for facilities considered representative of each process. Unfortunately, for landfilling only a limited amount of data was found, as much of landfill releases are fugitive emissions which are not as easily tracked as point source emissions. Data for air contaminants was converted to units of mass per tonne of MSW processed. It was found that use phase emissions greatly outweighed emissions during other life cycle phases. In the case of plasma arc gasification, GHG emissions during the use phase accounted for 98-99% of all GHG emissions. Heavy metal emissions for both incineration and plasma arc gasification were found to be significant. Although directly comparable quantitative data for landfills was not found, it was determined that while Pb and Cd air emissions are insignificant in landfills, Hg emissions are significant owing to there lower vapour pressure, yet rarely tracked and highly variable.

All three alternatives considered generate electricity. Landfill gas capture can generate about 0.3 MWH per tonne solid waste over the life of a landfill, while incineration produces about 0.6 MWH per tonne, and plasma gasification produces a net gain of about 1.15 MWH per tonne of waste processed. For this analysis, it was assumed that the electricity produced would otherwise be generated at Nanticoke Generating Station (a coal fired power plant) for the purpose of calculating offset credits. While electricity in Ontario is generated from a variety of sources, a detailed analysis of power generation was beyond the scope of this assessment. By providing data for gross emissions with no offset credits, and for offsets based on 100% coal fired power, both the worst and best case scenarios are covered.

Societal Analysis

Societal issues are one of the most sensitive and most weighed factors when deciding which process to implement for the disposal of non-recyclables. This is because public acceptance is important when politicians decide which process to implement for the disposal of non-recyclables . However, since each alternative vary in the amount of land used, noise pollution, emitted toxins and the effects of aesthetics, the extent to how sensitive this analysis is varies for each alternative. Note that because certain aspects are controversial, some sources portray aspects that are a matter of opinion rather than facts.

Landfills

One of the greatest societal concerns regarding landfills is related to residential areas that are three to five miles away. Those living three to five miles away from a landfill face diseases, such as congenital abnormalities , due to air and water contamination . As a result, politicians are using micro-organism technologies to reduce the toxins and odour being released . Noise pollution is another issue when considering this alternative as almost 60db of noise comes from the transport trucks . This is a major residential effect as the large number of trucks can cause loss of hearing and disruptions to the community.

Incineration

Societal concerns relating to incinerators include noise pollution and mainly the amount of dioxins and furans released. Note however, although depletion of land is a factor, it does not weigh as heavily as the other previously mentioned issues for incinerator plants. Incineration is the most sensitive and controversial alternatives since there are a lot of protest against it from groups such as Friends of the Earth and the Global Anti-Incineration Alliance. Such groups claim that incinerators are the number one source of dioxins and furans and harmful toxins are released from the solid waste when being burned . The controversial aspect of this issue is that the definition of an incinerator can be skewed by such groups. Thus this statistic can include those incinerators that do not take air pollution into account such as a cigarette or an internal combustion engine. Pro-incineration groups, on the other hand, will present theories such a bonfire emits more dioxins and furans than an incinerator plant . Another source of pressure is created from the Not In My Back Yard (NIMBY) movement which minimizes the amount of land allowed for incineration facilities . Noise pollution is another societal issue because it concerns those working in the incineration plant. Hearing loss is a concern as almost 85 db of noise is generated from the incinerator furnace and boilers . However, it should be noted that facilities which generated a lot noise now install wall insulation along with new building design structures that may reduce noise .

Plasma Arc Gasification

Because of this new technology, not much is said about its societal impact as it is not widely practiced and is still in research phase . However, those issues that are mentioned are not as significant when comparing to other alternatives analyzed. Because of the small size, a great advantage over the other alternatives is that it does not require using a lot of land. To reduce odour, low pressure is kept within the waste pit. Furthermore, the plasma arc gasification plant owned by the Plasco Energy Group claim that since minimal oxygen is used for the process, the amount of emissions is small. However, groups such as the Global Alliance for Incineration Alternatives will argue that such facts are simply not true .

See also

• Design for the Environment