m ANALYSIS I

Curbside Recycling: Energy & Environmental Considerations

Curbside recycling clearly reduces the amount of solid waste landfilled, but does it also save energy? A comprehensive study shows the greatest energy savings come from an integrated

waste system combining recycling, composfing, and waste-to-energy.

By Roger W. Powers

ne reason many, if not all, solid waste officials institute residential curbside recycling in their communities is to reduce the amount of waste

requiring landfill disposal. Whether it is precipitated by a state mandate, the clos- ing of a local landfill, or part of an inte- grated solid waste management plan, officials expect curbside recycling to help save landfill space, thereby extending its life, sometimes by many years. Plenty of evidence shows that curbside recycling does reduce the amount of solid wastes landfilled.

But as statewide and national debates over recycling grow more complex, more solid waste officials and pubic policy

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3,000

Mixed Waste Composting & Recycling (containers only) & Landfill k

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-6,000 ’ Pounds Disposed per ton of Waste Generated

Based on one ton of solid waste generated from single family households located in a metropolitan area. Yard trimmings generated and included; bulky items excluded. Source: Franklin Associates, Ltd.

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gure I Net energy requirements and solid waste landfilled for various waste management scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

nakers are asking: does recycling save mergy? They are also asking: what are

recycling’s environmental emissions, if any? These questions are especially important as they confront a tough bal- ancing act in assessing the costs and ben- efits of curbside recycling.

In fact, a few recent studies, including one commissioned by Keep America Beautiful, Inc. (KAB) discussed in this article, have shown that residentia! curb- side recycling does save energy, and it does reduce atmospheric and waterborne emissions. But to what degree? And, what does this mean for local solid waste planners? Although these issues can be considered national in scope, the petition-

ers-including public works officials and solid waste professionals from across the nation-seek information they might use to make decisions relating to their local solid waste management systems.

In response to these kinds of questions, Keep America Beautiful embarked on a comprehensive study of recycling, “The Role of Recycling in Integrated Solid Waste Management to the Year 2000.” One of the cbjectives of the stndy, con- ducted by Franklin & Associates and completed in fall of 1994, was to quantify the energy and environmental effects for the four main waste management options (recycling, composting, waste combus- tion with energy recovery, and landfill-

32 SOLID WASTE TECHNOLOGIES September/Ottober 1995

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ing) in various integrated combinations.

Parameters of the Research The energy and environmental emis-

sions in the KAB study were quantified using the life cycle inventory (LCI) methodology. The LCI technique quanti- fies results for a given product or system based upon certain established bound- aries, not from cradle-to-grave. For the KAB analysis, five steps in the MSW management process defined these boundaries:

1) Collection and transportation from point of waste generation to processing or

2) Processing of MSW and recy- clables;

3) Disposal of residuals from process- ing facilities; 4) Transportation of processed materi-

als to market; and 5 ) Increased use of secondary materi-

als (versus virgin materials) in the remanufacturing precess (the energy required to extract, transport, and process raw fuels into usable forms was account- ed for).

disposal;

Quantifying Energy Requirements . Eight soiid waste management scenar- ios were analyzed in the study. In each scenario, the energy requirements accounted for include not only the actual energy used in a specific waste handling system (e.g., energy used for collection vehicles and landfill equipment, recycling and compost processing, and transporting recovered materials to market), but also the energy required to extract, transport, and process raw materials or fuels into useable forms. For recycling analysis, this meant taking into account the energy required for the extraction of virgin or raw materials in the making of products and comparing it to the use of recyclable materials in remanufacturing in lieu of some virgin materials. For some waste management scenarios, for example, it

meant accounting for the energy value of the coal combusted at a power plant to produce electricity. Energy use at power plants, composting facilities and manu- facturing plants accounts for boiler effi- ciencies. Even “pre-combustion energy” is included, that is, the energy required to mine coal or the energy required to extract petroleum and process it into gasoline to fuel collection vehicles.

Energy credit represents the energy savings due to waste-to-energy combus- tion or use of recycled materials and the corresponding reduction in energy required for remanufacturing products. Tabulating the energy requirements and the energy credits provides a net energy requirement for each scenario.

Energy requirements have all been converted from original units (e.g., gal- lons, cubic feet, kilowatt-hours) to the thermal equivalent in British thermal units (Btu). As a reference, the average annual energy consumption for a residen- ~ a l h=nse.& is &Gut 100 pli!!i=n BtG.2

Quantifying Environmental Emissions Environmental emissions analyzed

were atmospheric emissions, waterborne wastes, solid wastes. The analysis accounts for discharges into the environ- ment after exiting emission control devices.

Some of the most commonly reported atmospheric emissions are: particulates, nitrogen oxides, hydrocarbons, sulfur oxides, and carbon monoxide. The major landfill gases, carbon dioxide and methane, are also accounted for in the analysis. Non-methane organic com- pounds (NMOCs) are left out of the inventory of landfill emissions because no reliable data exist for NNlOCs gener- ated per pound of MSW landfilled.

The waterborne wastes noted are pollu- tants still in the waste water stream after waste water treatment and represent dis- charges into receiving waters. Some of the most commonly reported waterborne

wastes are: biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, dissolved solids, oil and grease, sulfides, fluorides, phos- phates, and ammonia.

Solid wastes include not only land- filled MSW, but also residual wastes gen- erated during combustion, recyclables processing, or compost processing. Because this analysis is not an impact assessment, the composition of solid waste, including residues from various waste management options, are not dif- ferentiated.

Study limitations KAB’s research is limited to a quanti-

tative inventory of energy requirements and environmental emissions based on available data. This kind of analysis allows waste generators, handlers, and policy makers to begin to identify and understand the energy and environmental trade-offs associated with different waste

an environmental impact or human health impact or risk assessment. It in no way quantifies the risk to human health and/or the environment that may or may not result from materials emitted by certain processes. Further, the KAB study does not address broader energy and environ- mental issues of national or international significance, such as the effects on ecosystems or habitats of resource extrac- tion. More study would be necessary in order to fully explore those issues. Finally, while the study addresses many possible waste management options, the analysis only applies to residential curb- side recycling and does not include com- mercial recycling of any type.

rr,mzgerr,ent options. ThP zndysis is net

Recycling Saves Energy, But... The key results of the study are sum-

marized in Tables 1 and 2. Results are presented on the basis of one ton of resi- dential municipal solid waste (MSW) from singlc-family households. One ton

34 SOLID WASTE TECHNOLOGIES September/October 1995

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is approximately the amount of MSW generated in 10 months by a typical sin- gle-family household in a metropolitan area.

The study found that scenarios utiliz- ing composting and recycling generally reduce the amount of waste landfilled and show a net savings of energy. It also found that the more comprehensive the recovery system, the greater the energy savings. Thus, a system combining recy- cling, composting, and waste-to-energy produces the greatest net benefits. In such a system, waste-to-energy contributes the largest amount of energy to the equation.

The study also found landfilling and waste-to-energy projects have compara- tively low net expenditures of energy and environmental releases compared to the amounts required to get the products from raw materials through manufacturing and use. These overall conclusions are sup- ported by similar studies, including one published by the National Renewable Energy Laboratory in 1992.’

The KAB study also points out that there usually is a “negative” energy and environmental impact in the local com- munities where recyclables are collected curbside and processed, but that this neg-

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ative impact is typically more than com- pensated for in the remanukacturing plant. Indeed, most local solid waste planners view “energy” related to curbside recy- cling as an expenditure, primarily in col- lection, transportation and processing. Communities must allocate dollars to pay for fuel for the collection and transporta- tion vehicles, and power to run the pro- cessing plants. Also, the research sug- gests that communities may encounter more environmental emissions from increased truck traffic and industrial activity in the materials recovery facili- ties (MRF). Los Angeles, for instance, has doubled their trucks required to pick up curbside recyclables from 400 to 800, obviously impacting emissions.

The energy and environmental effects of curbside recycling occur both where the waste originates and at the remanu- facturing plant, sometimes hundreds of miles away. On the other hand, compost- ing and waste-to-energy facilities are generally located near where waste is generated, and therefore, the energy and environmental effects for these scenarios are realized locally or regionally.

Environmental Emissions Table 2 reports environmental emis-

sions in pounds of pollutants per ton of MSW generated. Emissions associated with the combustion of fuel for process or transportation energy are included in the analysis. To the extent that quantity data are available, non-fuel related emissions art: aibo iriciucied.

The KAB study found that residential curbside recycling generally reduces environmental emissions, principally from avoided emissions because of increased use of recyclable material in remanufacturing (versus manufacturing with virgin raw materials).

Any solid waste planner must proceed cautiously in using this generalization in assessing the impact of curbside recy- cling. Unlike energy and solid waste, which can be presented as a single value, such as Btu or pounds of waste, atmos- pheric and waterborne emissions cannot be added together and therefore must be considered individually for each scenario. No attempt has been made to quantify risk or impact associated with these emis- sions.

Of note is that for scenarios involving waste-to-energy, many emissions are avoided as well, because air emissions from waste-to-energy facilities are gener- ally iower than from power plant genera-

i

9

,$on of the same amount of electricity. Like othe; research, this study shows

that emissions increase and decrease with each scenario, but all of the changes are relatively small. These differences may vary with the design, operation and main- tenance of the equipment used in the sce- nario, as well as with the nature of the MSW being processed.

Scenario 1 : Landfilling Only For this scenario, where all municipal

solid waste is landfilled, the energy required for handling one ton of non- bulky single-family MSW is approxi- mately 0.5 million Btu, with no reduction in solid waste disposed (see Figure 1, on page 32). This represents less than one percent of the average annual consump- tion by a residential household.

In this scenario, no energy from land- fill gases is assumed. However, if energy is derived from landfill gases, it is esti- mated to be 150 kwh (or 1.6 million Btu) per ton of MSW landfilled.

Scenario 2: Waste-to-Energy In waste-to-energy facilities, over 90

percent of MSW processed undergoes energy recovery. These facilities typically generate between 500 and 600 kwh of electricity per ton of MSW combusted. About 10-15 percent of this electricity is used for intemal plant operations.

The net energy savings from combus- tion is about 4.7 million Btu per ton of non-bulky single-family MSW combust- ed. This represents about five percent of the annual energy consumption of a typi- cal household.

About 530 pounds of ash residue is generated for landfill disposal per ton of MSW combusted. However, under this scenario, the volume of MSW landfilled is reduced significantly, as the ash residue occupies only 1/10 the volume of MSW prior to combustion. There are three important considerations in the analysis of this scenario:

-The total energy savings may be understated because many waste-to-ener- gy facilities use magnets to recover fer- rous metal automatically from incoming waste and ash residue. Using the recov- ered ferrous metal saves energy in the steel making process.

-No recovery of recyclables or yard trimmings is assumed.

-It assumes there is no “bypass” waste (i.e., waste which bypasses the facility due to shutdowns). Bypass waste can be important because it can increase

the waste ultimately landfilled and thus reduce landfill space savings expected from using the WTE approach.

Scenarios 3 Yard Trimmings Composting In this scenario, yard trimmings are

curbside collected separately from MSW and composted at a windrow facility. The remaining non-bulky single-family MSW and compost residues are landfilled.

The net energy required for this sce- nario is 0.6 million Btu per ton of resi-

MSW landfilled is reduced by more than 30 percent (versus landfill disposal only).

Scenario 4: Base Case Curbside Recycling This scenario includes separate collec-

tion and recovery of traditional household recyclables-newspapers, glass, steel and aluminum beverage and food containers, PET soft drink bottles, and HDPE bottles.

The gross energy required for the activities in this scenario is 0.7 million Btu per ton of residential MSW generat- -

dential MSW generated-less than one percent of the average annual household energy consumption. Total residential

ed. This figure accounts for curbside col- lection of non-bulky recyclables and MSW from single-family households;

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sorting and preparing recyclables for mar- ket; transporting recyclables to market; and landfilling the remaining MSW and MRF residues. The energy requirements are higher if recyclables are collected through buy-back or drop-off sites. This seemingly counter-intuitive result is due to the increased use of fuel in collection vehicles and citizen vehicles to travel to drop-off and buy-back sites.

When recyclables are collected curb- side, approximately 3 gallons of diesel fuel are required for 1,000 pounds of recyclables collected. Drop-off sites require about 17 gallons of fuel per 1,000 pounds of recyclables collected and buy- back centers require about 6 gallons of fuel. These are national averages; actual fuel usage varies in each locality.

The net energy savings under this sce- nario are 3.3 million Btu per ton of resi- dential MSW generated. This represents 4 percent of the typical annual household energy consumption. Aluminum cans, newspapers and plastic account for over

90 percent of the energy savings. Using base case recycling reduces the

total MSW landfilled (including MRF residue) by 20 percent. The use of recov- ered materials in the remanufacturing process also leads to energy savings under this scenario. The most notable energy savings are associated with replacement of virgin raw material extraction with the processes of collect- ing, sorting and preparation, and shipping recovered materials to market. The differ- ent steps involved when manufacturing with recovered materials versus virgin raw materials result in different energy demands and environmental emissions. In general, this scenario found that the ener- gy requirements are less with recovered materials than with virgin raw materials.

Changes in industrial process waste due to increased use of recyclable materi- als in remanufacturing are not included in these calculations. Also, the energy sav- ings associated with increased recycling in this scenario are based on a mix of

materials normally Collected in a residena, tial curbside collection progr'am.

Scenarios 5: Curbside Recycling Plus Composting I

In this scenario, household recyclables under the base case scenario and yard trimmings are curbside collected sepa- rately. Gross energy requirements are over 0.7 million Btu per ton of residential MSW generated. Net energy savings are 3 .3 million Btu per ton of residential MSW generated, or about four percent of annual household energy requirements. Total residential MSW landfilled is reduced by over 50 percent.

Processing of recyclables at a MRF and windrow composting of yard trim- mings were taken into account in these calculations. Residue and the remaining non-bulky single-family MSW is collect- ed separately and transported to a landfill.

In each of the scenarios involving composting, researchers considered including a calculation for the displace-

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ment of some "virgin" soil amendment that would be used if yard waste or MSW compost were not available. However, this amount was not quantifiable. Instead, to account for the fact that compost added to soil potentially reduces the amount of tillage needed (or could be used as land- fill cover soil, the net energy require- ments associated with transporting com- post to market was assumed to be zero.

Scenario 6: Curbside Recycling + Composting + WTE

In this scenario, base case household recyclables and yard trimmings are curb- side collected separately. Recyclables are processed at a MRF and yard trimmings are windrow composted. Remaining non- bulky MSW is collected separately and combusted at a waste-to-energy facility. All residues are transported to a landfill for disposal.

Gross energy requirements for this sce- nario are 0.7 million Btu per ton of resi- dential MSW generated. Net energy sav- ings are 5.5 million Btu per ton of resi- dential MSW generated, primarily due to waste-to-energy combustion and the increased use of recovered material in the remanufacturing process. Because these calculations do not include magnetic recovery of metals, which some waste-to- energy facilities use, the net energy sav- ings may be somewhat understated. The inclusion of yard trimmings composting, recycling, and combustion results in a reduction of residential MSW ultimately !zndf;!!ed h ~ r Qn nprrpnt

J -" k'-'--"" Scenario 7: Mixed MSW Composting

This scenario assumes that all non- bulky single-family MSW is collected and composted in an in-vessel system with final curing in windrows. The com- post residues are transported to a landfill for disposal.

Total energy requirements are 3.7 mil- lion Btu per ton of residential MSW gen- erated, and includes the collection of MSW, in-vesseltwindrow composting, and disposal of residues. The energy requirements are higher for this scenario than for yard trimmings composting because of the energy required to power the in-vessel composting unit.

Accounting for compost residue, roral residential MSW landfilled is reduced by 65 percent.

Scenario 8: Recycling + Mixed MSW Composting

This scenario assumes non-bulky sin-

gle-family MSW ;Is collected and cow.- posted using in-vessel coinposting, and recyclable containers are recovered and recycled. Total energy requirements are reduced to 0.6 million Btu per ton of resi- dential MSW generated, accounting for energy savings through increased use of recovered materials in remanufacturing. Total residential MSW landfilled is reduced by over 70 percent.

Conclusion Compared to landfill only disposal, F-

KAB's research found that residential curbside recycling can reduce the amount of solid waste landfilled, can reduce atmospheric and waterborne emissions, and can produce net energy savings.

What does this mean for solid waste planning? KAB's research shows energy and environmental issues should be a consideration in local solid waste system decisions. The data can be useful, but they should not be considered alone. Instead they should be judged in the con- text of the costs, markets and infrastruc- ture when planning curbside recycling as part of long-term solid waste manage- ment systems. They must also be judged in consideration of the overall agreed upon goals of larger communities, includ- ing states, nations, or the world. The actu- al energy consumption and emissions reductions within operating systems may vary widely and are highly dependent on the mix of recyclable material.

It is clear, too, that individual waste

ing energy to saving energy. For instance, the three composting options all require a net energy expenditure to convert the material to a usable product. Landfill dis- posal requires relatively little energy. Use of energy can be avoided through waste- to-energy combustion and the use of recyclables in manufacturing.

Therefore, if landfill and energy sav- ings is a goal, an integrated approach to solid waste management yields the desired result. Use of energy can be avoided to the largest extent through waste-to-energy combustion, in addition to the energy savings realized through he use of recyclables in manufacturing. 4)

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minigement ~ p t i ~ n f T Z ~ U P frnm reniiir- 0- ------ - - - l - - A

Notes: 'SRI International for the National

Renewable Energy Laboratory, "Data Summary of MSW Management Alter- natives," August 1992, NREL/TP/ 431-4988.

*U.S. Energy Information Administration, Household Energy Consumption and Expen- ditures, 1990.

40 SOLID WASTE TECHNOLOGIES September/Ottober 1995