Nicholas P. Cheremisinoff. Handbook of Solid Waste Management and Waste Minimization Technologies

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resources benefits the environment while it improves the economy. This chapter

explores some of the issues that require consideration in establishing viable

markets and managing large-scale resource recovery schemes.

INDUSTRY VERSUS CONSUMER MARKETS

There are many success stories and examples where a business-to-business

relationship flourishes on the reliability of one party's waste being an essential

raw material to another. The strength and reliability of these relationships

reinforce the fundamental issues for postconsumer recycling efforts. Between the

two industrial parties, the quantity, quality and price of the waste/raw materials

can be readily assessed and controlled. Security of resource for the user can be

satisfactorily provided by the waste generator. Operational strategies can be

efficiently designed and implemented for the advantage of both parties. For the

supplier, a waste becomes a resource, and for the user, a more cost-effective or

alternative raw material supply provides an opportunity or a commercial

advantage. Such relationships and forms of recycling essentially focus on waste

minimization or a logical extension of the concept of clean production.

However, post-consumers pose the challenge of resource security, which can

have an impact on resistance for recycled products to re-enter a second life-cycle

market.

Resistance to wide-scale recycle markets stems from economic concerns. For

example, since industry made the product, they should be prepared to take it

back. Communities will readily collect any material for which there is a viable

market. But it costs money to collect and forward, and hence communities should

receive at least this amount as a fair return for their effort in collecting it for

generators.

Industry can afford to pay a fair price for the materials because they can always

pass on the costs to the consumer. Industry's view of the issues generally are that

cheap and reliable sources of raw materials are always welcome. Clearly, the

supply must be regular in quantity and quality and at a price that demonstrates an

advantage over virgin or more traditional supplies. However, if the combined

cost of collecting and sorting materials is more than a market will offer, the

whole enterprise should be discontinued, or the collecting and sorting processes

need to be made more efficient, or the quality should be tailored to attract a

commensurate price.

To ensure optimum use of specialist equipment to process secondary resources,

an often-adopted strategy for industry is undercapitalisation. If, say, marketing

research showed that about 200,000 tons a year of a particular reclaimed

resource was potentially available, a plant could be commissioned with a capacity

of 100,000 or 150,000 tons a year. The effect of this strategy is to ensure that

the selected plant will always run to capacity on the available supply and that the

surplus material will tend to keep the price down and the quality up.

REVIEWING THE TECHNOLOGY OPTIONS

Waste-to-Energy by Combustion (WTE)

Incineration of wastes can be considered a landfill pretreatment if volume

reduction and detoxification is the primary aim. In the context of resource

recovery, waste-to-energy involves the addition of power generation equipment

to combustion for the recovery of process heat. The main products of

incineration are carbon dioxide, water, ash residue, and heat energy.

Unfortunately, by-products having environmental importance are also generated,

such as sulfur, nitrogen, and chlorinated compounds including dioxins and some

heavy metal compounds of lead, mercury, and cadmium.

Combustion equipment must be designed around the Three Ts of combustion:

time,

temperature, and turbulence in the presence of oxygen. Systems without

these factors in their design usually experience operating and maintenance

problems as well as posing environmental hazards. The better a system is at

controlling these factors, the lower the environmental impact. Time is usually

accounted for by the volume allowed for the combustion chamber. It must be

large enough to retain the gas flow for sufficient time to allow complete

combustion of the fuel and volatile gases. Temperature is a critical

consideration. Organic matter usually oxidizes at a relatively low temperature

(600° to 700

C) and usually has enough calorific value for combustion. A few

refractory organics need a much higher temperature to achieve full

decomposition. Other organic wastes have such a high moisture content that they

require a subsidiary fuel for combustion. These moist green wastes are probably

more valuable as composts. The higher the temperature, the greater the assurance

of complete combustion — and the higher the maintenance and running costs of a

facility and often the lower the reliability. For other than the extremes of organic

matter, temperatures between 850

C and 950

C are enough for the safe and

efficient combustion of organics. Turbulence of the gas flows is necessary to

promote mixing of the hot products of combustion and the oxidizing substance,

air. Turbulence can be achieved by duct design or by the injection of a substance

into the hot gas flow. The conversion of water to steam in a hot gas flow creates

good turbulent flow conditions.

Industrial incinerators are integrated systems of raw waste handling and storage

equipment, combustion chambers, energy and by-product recovery operations,

exhaust-gas cleaning facilities, and effluent and solids discharge control devices.

Refuse-Derived Fuels

The concept of treating waste products to obtain a cheap, transportable and

storable fuel has been around for several decades. In most countries, the quantity

of waste products increases during spring, summer, and autumn and reaches a

low point in winter. Researchers have always aimed to transform or treat these

wastes so they could be stored, transported, and used as a fuel during winter.

Waste-to-energy plants often supply district heat in Europe and demand is highest

in winter when the availability of normal waste fuel is at its lowest point.

It is technically possible to transform normal waste into pellets or briquettes with

increased calorific value and greater bulk density for transport. Refuse-derived

fuels (RDF) can be used by themselves but more often they are mixed with

another solid fuel such as coal in steam or hot-water generating plants. One form

of RDF being used comes from the increase in the number of material recovery

facilities (MRFs). One stream from these facilities normally contains

contaminated dry combustible matter, an ideal fuel for waste-to-energy plants.

Some industries which incorporate fuel-burning equipment can be used for niche

burning. The displacement of normal fuel by RDF is a true waste-to-energy

application. Blast furnaces, hot-melt cupolas, and cement kilns are some of the

industrial plants using waste fuel. Industry will usually use an alternative fuel

only when it is offered at a price premium to compensate for inconvenience.

Contaminated petroleum products and plastics are used as fuel in cement kilns

only when the price of waste disposal is high and the cost of normal fuel is

appreciable.

The choice of adopting waste-to-energy rather than landfill disposal is seldom

based only on energy or landfill costs. Even if landfill operators in one region

were forced to adopt more stringent standards that exist elsewhere, landfill would

still be cheaper than incineration unless landfill costs included a large transport

component. It is often cheaper to carry waste over 200 to 400 km to a landfill

than to burn it in most of the world.

A combination of factors is leading many entities to adopt waste-to-energy plants:

• Consistent production or availability of a waste product

• Consistent need for high-grade and low-grade energy

• A desire to maintain control over waste products

• A desire to minimize the environmental impacts of a waste product

Modern plants pose little danger of adverse health effects to their neighborhood.

The evidence is that the emissions from a well-operated incineration plant

complying with the stringent air quality standards are most unlikely to cause any

health effects. However, environmental impacts of incineration plants should go

beyond health considerations. Other factors include:

• Visual intrusion

• Odor and noise

• Vehicle movement

• Socioeconomic effects

Parts of the waste stream can have potential energy recovered only before or

after a period of landfill. Where a reliable end user of the energy is available,

the recovery of energy by combustion must be a legitimate option. Much

opposition to combustion comes from the potential of waste-to-energy plants to

mindlessly consume materials that should have been recycled, reused, composted

or put to some higher value use. This view has the potential to deny the valuable

role of incineration to recover energy that might otherwise be lost.

Biofermentation

Biofermentation is the in-vessel fermentation of the organic parts of waste

streams to produce methane (for power generation) and simultaneously stabilize

putrescible wastes. This process is receiving renewed interest as a method of

pretreating and stabilizing putrescible or organic wastes to recover methane. The

residues can then be aerobically composted. The energy recovered is hoped to be

enough to run the overall plant. As a volume-reduction technique, only about 7

to 10% of the material in the waste stream will be affected by biodegradation

without a prior hydrolysis process to convert the ligno-cellulosic material into

fermentable sugars.

Hydrolysis

Hydrolysis converts the cellulose content of ligno-cellulosic wastes (paper and

wood) into fermentable sugars so that methane or ethanol can be produced as

alternative fuels. The traditional method is for a high temperature and pressure

process, in the presence of acid, to break down the cellulose materials. More

recently, enzyme hydrolysis (which is basically the industrialization of the natural

processes of degradation from the forest floor) and steam explosion hydrolysis

have been receiving significant development interest. However, all hydrolysis

processes are sensitive to continuity of feedstock in quality and quantity, which

make them unsuitable for mixed wastes and more suitable for agricultural

residues such as sawdust, straw, or specially grown crops.

Pyrolysis

Pyrolysis is the process of heating waste materials in the absence of oxygen to

produce volatile gases, fuel oils and inert charred residues. It is sensitive to

reliability and quality of feedstock if valuable products are to be produced.

INTEGRATED RESOURCE RECOVERY

One approach that is being considered as a model for large-scale resource

recovery and reuse on an economical scale is based on the concept of an eco-

industrial park (EIP). This is a community of manufacturing and service

businesses seeking enhanced environmental and economic performance through

collaboration in managing environmental and resource issues including energy,

water, and materials. By working together, the community of businesses seeks a

collective benefit that is greater than the sum of the individual benefits each

company would realize if it optimized its individual performance only. The goal

of an EIP is to improve the economic performance of the participating companies

while minimizing their environmental impact. Components of this approach

include new or retrofitted design of park infrastructure and plants; pollution

prevention; energy efficiency; and inter-company partnering.

Figure 16 illustrates the basic scheme for an integrated resource recovery system

as a whole, with all community sources feeding discards into an eco-industrial

park anchored by a resource recovery facility. Finance, communications,

education, and government agencies support the development of the system.

Within the manufacturing sector an industrial ecosystem generates by-product

flows between plants as well as into the resource recovery facility and eco-park.

The collection and aggregation of smaller quantities of by-products not useful in

plant-to-plant flows enables a higher level of overall recovery.

The resource recovery facility itself includes

dropoff,

sorting, and sales

operations which serve collectors, community members, and industries. It can

operate at both wholesale and retail levels in both intake and sales functions. The

eco-industrial park includes processors of discards, manufacturers, and crafts

people using the outputs of processors, and other environmental businesses.

Service businesses in the EIP can serve clients in the community as well as firms

in the park.

A resource-recovery-focused industry includes reuse, recycling, remanufacturing

and composting, as well as the marketing and end use of reclaimed discarded

materials. As a vertical industry it involves a wide range of business activities

including collection, sorting, and processing of industrial and biological

materials; repair, refurbishing, or dismantling of equipment; and wholesale or

retail sales. The unifying concept is that discarded materials, goods, and by-

products are turned into salable materials and products. Businesses and

communities benefit through a reduction in disposal costs, creating new revenues,

and by opening new sources of materials and goods. The environment benefits

from reduction in demands on limited natural, virgin resources and on the

capacity of the environment to accommodate solid waste and pollution.

Figure 16. Conceptualized view of an eco-industrial park.

An investment recovery company could be a valuable coordinator of the logistics

of materials acquisition, movement, and recycling/reuse by the diverse network

SERVICE & COMMERCIAL SECTORS

MANUFACTURING

UTILITIES

HOUSEHOLDS

FARMS

CONSTRUCTION

& DEMOLITION

COLLECTOR

RESOURCE

RECOVERY

FACILITY

SERVICES

PROCESSOR

MANUF. 1

MANUF. 2

ECO-INDUSTRIAL

PARK

of companies involved. It could also manage the resource recovery facility that

serves as the entry point for discard resources in the EIP.

The major streams of materials and goods coming through resource recovery

companies (and direct connections with other industrial sources in the region)

would define the initial set of companies to recruit or develop for the EIP. These

would include: manufacturers using recycled feedstocks; remanufacturers of

capital or consumer equipment; companies with major supply requirements that

could be filled by the outputs of other tenants or plants in the area; and users of

reclaimed materials and energy by-products or agriculture and aquaculture firms

if there is by-product energy or water available to the site.

Another group of prospective tenants would be those with a broader

environmental mission, including manufacturers of renewable energy and energy

efficiency equipment; companies pioneering the use of bio-materials; firms

providing services and products for sustainable agriculture industry; and

industrial ecology and other environmental consultants.

An eco-industrial park offers a combination of economic development and

environmental benefits. The resource recovery foundation for an EIP increases

the local economic value of these returns, which include:

• Expansion of existing firms and creation of new local businesses

• Job development at a broad range of skill levels and with a good pay

range

• Utilization of industrial energy and materials by-products now wasted

• Recovery of economic value of many materials and products households

now send as solid waste to landfills

• Utilization of restaurant, agricultural and food processing discards

• An attractive, ecologically designed and landscaped industrial complex

• High environmental standards for the park tenants and the park

management

A SHORT REVIEW

The composition of MSW is broad and contains both organic and inorganic

components. Some portion of MSW may be considered hazardous and pose

potential threats to public health. Waste management strategies that have proven

to be cost effective in industrial settings heavily favor prevention technologies.

However, the identical approaches at the municipal level have not always proven

effective. On the hierarchy of waste management practices, resource recovery

and recycling and waste-to-energy are more readily adaptable to MSW

management. The selection of specific technologies that are relied upon in many

cases for several decades depends on the technical feasibility of the options

considered in relationship to local waste profiles, and requires the application of

life-cycle costing tools to evaluate the risks of investments.

Electricity can be produced by burning MSW as a fuel. MSW power plants, also

called waste-to-energy (WTE) plants, are designed to dispose of MSW and to

produce electricity as a by-product of the incinerator operation. The term MSW

describes the stream of solid waste generated by households and apartments,

commercial establishments, industries, and institutions. MSW consists of

everyday items such as product packaging, grass clippings, furniture, clothing,

bottles, food scraps, newspapers, appliances, paint, and batteries. It does not

include medical, commercial, and industrial hazardous or radioactive wastes,

which must be treated separately.

MSW is managed by a combination of disposal in landfill sites, recycling, and

incineration. MSW incinerators often produce electricity in WTE plants. EPA

estimates that in 1998 17% of the nation's MSW was burned and generated

electricity, 55% was disposed in landfills, and 28% was recovered for reuse. In

the United States there are currently two main WTE facility designs. Mass Burn

is the most common waste-to-energy technology, in which MSW is combusted

directly in much the same way as fossil fuels are used in other direct combustion

technologies. Burning MSW converts water to steam to drive a turbine connected

to an electricity generator.

There are several types of mass-burn combustion systems. They include

refractory, modular, and waterwall furnaces. Waterwall technology is the most

widely used and is similar to the furnaces used at coal-burning power plants. In

all three systems, untreated MSW is incinerated and the heat that is recovered is

converted to steam. The steam can then be passed through a turbine to generate

electricity and low-temperature heat suitable for space heating. The technology

for producing electricity from high temperature steam and usable heat as a by-

product is called cogeneration or combined heat and power (CHP). The

application of this technology results in more efficient use of fuel. Incineration of

MSW generally results in a volume reduction of between 80 and 90%, which

therefore achieves the environmental benefit of reducing landfill space

requirements.

Refuse-derived fuel (RDF) facilities process the MSW prior to direct combustion.

The level of precombustion processing varies among facilities, but generally

involves shredding of the MSW and removal of metals and other bulky items.

The shredded MSW is then used as fuel in the same manner as at mass-burn

plants.

Facilities that handle more than 100 tons per day use a continuous feed

arrangement. An overhead crane moves the refuse into the furnace. The furnace

walls are composed of water-filled tubes, called waterwalls; they absorb heat

released during combustion and create steam. A refuse stoker moves and agitates

the waste, allowing it to burn thoroughly. Air is forced in above and below the

stoker to cool the stoker and provide oxygen. Combustion gases rise from the

fuel bed into the upper furnace and flow through the boiler and superheater

sections to produce steam. A variation of the mass-fired unit has a furnace

without waterwalls. The heat is transferred through a waste heat boiler where the

energy is absorbed to create steam. Another mass-burning unit is the rotary kiln,

a large steel cylinder supported by rollers. The kiln is sloped and revolves

several times a minute. The rotating motion helps to remove moisture from the

refuse before it is burned. This process is suitable for waste water sludge and

refuse with a high moisture content.

The advantages of mass-fired waterwall systems are that no processing of waste

is required, other than removing large objects to prevent jams. Waterwall

systems can handle up to 1000 tons per day and have been used for more than 30

years in Europe, Japan and the United States. The disadvantages are that precise

control of the combustion process can be difficult. Refuse glass and clay may

cause excessive slagging when melted.

RDF preparation separates different waste into combustible and noncombustible

materials. Once separated, the more homogenous combustibles can be burned in

a furnace dedicated to the fuel or co-fired with coal or another fuel. RDF

preparation separates recyclable secondary materials. Materials such as glass and

metals can be sold. Fuel prepared from refuse can be formed into cubes;

briquettes, or cylinders called densified RDF (dRDF). This fuel can then be used

in more traditional furnaces. Processing RDF into dRDF creates a fuel that is

more easily transported and handled. dRDF, being closer in physical and

combustional characteristics to coal, can be burned with or instead of coal.

Biomass RDF has been successfully applied in parts of Europe with several

unique designs.

Reverse-burn gasification is a method of incineration that emits a combustible

exhaust gas that can be burned rather than treated. In reverse-burn gasification,

wastes are destroyed by conversion to a combustible gas and a dry, inert

carbonaceous solid. The process produces nonhazardous water and inorganic

salts as by-products. The process has been successful in laboratory-scale

operation, although the long-term efficient use of this system is in question.

Burning MSW can generate energy while reducing the volume of waste by up to

90%,

which is a major environmental benefit. Ash disposal and the air-polluting

emissions from plant combustion operations are the primary environmental

impact control issues. MSW contains a diverse mix of waste materials; some are

benign, but a portion are highly toxic. Effective environmental management of

MSW plants aims to exclude toxics from the MSW-fuel and to control air

pollution emissions from the WTE plants. Toxic materials include trace metals

such as lead, cadmium and mercury, and trace organics, such as dioxins and

furans. Such toxics pose an environmental problem if they are released into the

air with plant emissions or if they are dispersed in the soil and allowed to migrate

into ground water supplies and work their way into the food chain. The control

of such toxics and air pollution are key features of environmental regulations

governing MSW fueled electric generation. Burning MSW in WTE plants

produces comparatively high carbon dioxide emissions, a contributor to global

climate change. The net climate-change impact of these emissions is lessened

because a major component of trash is wood, paper, and food wastes that would

decompose if not burned. If left to decompose in a solid waste landfill, the

material produces methane, which is a major greenhouse gas. Also, WTE plants

generate comparatively high rates of nitrogen oxide emissions. The on-site land

use impacts are generally equal to those of coal- or oil-fueled plants.

Composting is a form of recycling and is the only technique discussed that may

be viewed as approaching P2. The benefits of using compost include:

• Soil enrichment

o Adds organic bulk and humus to regenerate poor soils

o Helps suppress plant diseases and pests

o Increases soil nutrient content and water retention in both clay

and sandy soils

o Restores soil structure after reduction of natural soil microbes

by chemical fertilizer

o Reduces or eliminates the need for fertilizer

o Combats specific soil, water, and air problems

• Pollution remediation

o Absorbs odors and degrades volatile organic compounds

o Binds heavy metals and prevents them from migrating to water

resources or being absorbed by plants

o Degrades, and in some cases, completely eliminates wood

preservatives, petroleum products, pesticides, and both

chlorinated and nonchlorinated hydrocarbons in contaminated

soils

• Pollution prevention

o Avoids methane production and leachate formation in landfills

by diverting organics for composting

o Prevents pollutants in stormwater runoff from reaching water

resources