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The primary role of a dirty materials recovery facility(MRF) is to recover resources that would otherwise belandfilled, so these materials can then be used in the

manufacture of new products. After the recoverable recyclablematerials have been removed, the remaining ‘dirty organics’an be converted to compost, so they, too, are not being sento a landfill.

Te goal of these facilities is to process everything that is col-ected, in hopes that nothing collected is hauled directly to landfill;nd, that only the residue from a processing or composting facilitys landfilled. We know, from experience, that it is not likely thatll residents and businesses will separate their discarded materialsrecisely the way we want them to, in the way that will maximizeecovery. As long as we collect and dispose of garbage, we wille sending some recoverable resources to landfills; and, we wille sending some methane-generating organic materials to theseisposal sites.

Generator responsibilityLooking at a dirty MRF, several questions need to be posed at the

utset, including how much sorting is required to make a munici-

pality’s current diversion program work? How many categoriesof materials does a program want residents and businesses to sort?How many containers, per household or business, are needed tostore the number of categories of materials? How many trucks,

with how many compartments, are needed to collect all of thesecategories of materials? And, how much time, per stop, is requiredfor the driver to load the truck with more categories of materials?

The collection systemTe collection system cost is based on the number of trucks anddrivers required to provide the required services; the total numberof loads collected; the number of loads per truck, per day; thenumber of miles driven; the locations of the processing facilitiesand whether the various facilities are at the same or separate loca-tions. Te cost of collection can be reduced by designing a systemthat requires fewer trucks, with fewer drivers, plus burns less fueland produces fewer greenhouse gas emissions.

Collection strategiesIn 2010, many municipal collection programs recover materials

Reprinted from

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from residents in three streams: Recy-clables, plant trimmings and garbage(e.g., a mix of wet compostable materialsand dry trash). Te recyclables and planttrimmings are processed to recover valu-

able resources, and the garbage is sent to alandfill.One alternative is to collect the same

three streams, but, instead of sending thegarbage directly to landfill, it would besent to a dirty MRF to be processed, whereadditional recyclables and compostables

would be recovered. It is easy to imaginethat over half of the garbage could berecovered.

Another alternative is to collect threestreams, but with a focus on collecting allorganics (e.g., combined plant trimmings,food scraps, soiled paper and other com-postables) as one stream, clean recyclablesas a second stream, and trash (materials for

which there is no feasible, cost-effectivemarket) as a third stream.

A wet-dry collection system, whereclean recyclables are the primary categoryand everything else (plant trimmings andgarbage) is collected as mixed organics, hasbeen implemented in three small commu-nities in the San Francisco Bay Area. Teclean recyclables are processed in a clean

MRF and the mixed materials are hauledto a mixed-waste composting facility.

An alternative to the basic wet-dry sys-tem is to collect clean compostables as theprimary sort (instead of clean recyclables)and everything else as the secondary sort.Te clean compostables would be hauledto a composting facility, to be made into ahigh-quality compost, and the mixed drymaterials would be hauled to a dirty MRFto be sorted to recover recyclable materi-als. Only a small amount of residuals from

each facility would need to be landfilled.

Commercial collectionTe commercial collection system can bedesigned to mirror the residential collectionprogram alternative selected; in either two

or three streams. Te role of the processingfacility is to resort what is collected com-mingled, as the materials have to be separatedinto marketable commodities, so that theycan be used to manufacture new products.

And, processing facilities can use either high-tech or low-tech sorting lines to achieve this.

High-tech facilities are equipped withhigh-volume sorting installations, gener-ally rated at about 20 tons per hour (Figure1). Low-tech facilities, designed to processmaterials at a lower rate, have less expensiveequipment and typically require the use ofmore manual labor to process the materialhandled. A high-tech facility is not necessaryto process a wide range of collected materials.Conversely, low-tech facilities provide smallercommunities the opportunity to collect morematerials, since the equipment is lower costand requires less maintenance.

Low-tech facilities are also able to usethe physical characteristics of the materialsto be sorted, in order to assist in the process.

As noted in “Softening the Blow,” found inthe August 2008 issue of Resource Recycling ,

one concept for a low-impact sorter wasdescribed, which separates glass from otherrecyclables before much of the glass is brokenduring the handling process. Tis sorter usesrubber conveyor belts and gravity to separateflat items (e.g., newspaper, film plastics, flat-tened cans, etc.) from round materials (e.g.,bottles, cans, wadded paper, flower pots, etc.)and an air classifier (blower fan) to separateheavy and lightweight materials. And, mostof the glass bottles remain whole, so they canbe color sorted.

Again, the purpose of processing is to

sort the recovered materials to the level ofquality necessary to meet manufacturerspecifications for making new productsfrom them, not just to move what is col-

lected through the processing facility andoff to a market. Tis means that almost allpaper loads are shipped sans plastics, glassor metal in the load, that almost all plasticsloads are shipped devoid of paper, glass andmetal, and so on and so on.

Organics processing All collected organics should be processed.Tere are two primary forms of process-ing in use: Aerobic composting, whichproduces compost and sequesters carbon,and anaerobic digestion. Anaerobic diges-tion can either be with liquid (wet) or withalmost no free liquid (dry). Te primaryproducts of aerobic composting are com-post, water and carbon dioxide (CO

2).

Te primary products of anaero-bic composting are digestate, CO

2and

methane. If the anaerobic process hap-pens in a landfill, a significant percentageof the methane generated is released intothe atmosphere. If the anaerobic digestionoccurs in a sealed vessel, the methane can

be recovered. Clean organics can easilybe composted in either of the processesdescribed above. Mixed organics requireextensive pre-processing and post-pro-cessing to make a marketable product (seeMarketing compost sidebar).

The SMaRT StationTe SMaR Station is the materials recov-ery and refuse transfer facility in Californiashared by the cities of Mountain View

(30-percent use), Palo Alto (20-percent

Figure 1 | High-tech facility installation

Source: City of Sunnyvale, Public Works, 2010

Marketing compost• Clean organics make high-

quality compost that can beused with food crops and inbackyard gardens

• Dirty organics make asecond-label qualitycompost that is best used forroadways, orchards and non-

food crops. It is likely that, ifall the organics in municipalsolid waste were composted,the potential uses for themixed waste compost willalways exceed the supply.

1. Receiving hopper -3 yard, 60°,variablespeed feeder

2. Elevating conveyor,variable speed feeder

3. Low impact sorting belt, variablespeed, adjustable inclined conveyor

8. Blower and machinery7. Glass sorting station

5. Light fraction roundtake-away conveyor

4. Flats/paper take-awayconveyor

6. Heavy fraction roundtake-away conveyor

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rechargeable and automotive batteries; used

motor oil and oil filters; and medical sharpsand lancets.

MRF challengesand benefitsLike with any facility or process, there arechallenges and benefits to the use of a dirtyMRF. Challenges typically encountered bysuch facilities include:

• Worker safety, compensation standards• Contract concepts

– Operator incentives for creativediversion

– Maintenance versus repair versusreplacement

– Fixed annual payment or per-toncharge

• Tree-city issues – Finding common denominators – Fair, transparent dealings (e.g.,budget, annual audit)

One of the bigger issues, though, faced

Chart 1 | Composition of source-separatedrecyclables processed


Tin cans, 2%

Tin cans,

2%

Plastics, 6%

Plastics,

6%Newspaper, 34%

Newspaper,

34%

Mixed paper, 31%

Mixed paper, 31%

Cardboard, 4%

Cardboard,

4%

Glass, 22%

Glass, 22%

Aluminum, 1%

Aluminum, 1%

se) and Sunnyvale (50-percentse). Te City of Sunnyvalewns and manages this ventureor the partner cities. Since itsnception in 1993, this coop-rative venture has proven to besmart decision.

Te SMaR Partnershiprovides:• Te sharing of resources to

reduce operational costs ofsolid waste management

• Cost-efficient waste andrecycling opportunities forresidents and businesses

• A facility to assist in meet-ing state mandates for

waste reduction

Te facility was originally con-eived to process only commer-ial waste, since the memberommunities already had

mature residential recycling programs inlace; but, the first facility operator wantedo try to recover additional materials fromhe residential wastes still being landfilled,o it became a dirty MRF.

Materials ReceivedTe cities collect residential and commer-ial source-separated recyclables, as well aslean plant trimmings, including:

• Yard trimmings from Mountain View

and Sunnyvale (Palo Alto processes itssource-separated recyclables and planttrimmings at other facilities)

• Single-family and multi-familyrecyclables from Mountain View andSunnyvale

• Commercial recyclables, includingSunnyvale’s cardboard routes andMountain View’s mixed commercialrecyclables collections.

Measuring programsuccessThe measures of success of thefuture resource management systemare resource recovery rates, theelimination of methane release tothe atmosphere, and an overallreduction in greenhouse gasemissions from waste managementactivities. So, dirty MRFs will playan important role in processingmaterials that have not beenproperly sorted by generators.

Te curbside recyclables processing system

was installed in 2001 and enables theSMaR Station to accommodate process-ing of source-separated materials from thepartner cities’ curbside recycling programs(Chart 1). Te system uses mechanicalseparation and an air classifier to sort glassand ferrous cans from mixed containers,

while other containers are sorted by hand.Te system also includes a horizontal balerthat is capable of baling paper, plastics andcans.

Wood and yard waste recovered for

recycling are further processed througha grinder at SMaR. Ground wood ismarketed to wood-fuel power plants andground green waste is sent off-site forcomposting. Composted plant trim-mings are made available to residents andcity crews for use in landscaping projects.

With respect to refuse, the municipalsolid waste received from the three citiesis conveyed through a series of mechanicaland manual sort processes to recover mate-rials for recycling. Te remainder is hauledin transfer trucks to the Kirby CanyonLandfill, located in south San Jose.

Further, the SMaR Station servesas a convenient place for the public torecycle additional materials not commonlyaccepted in curbside recycling programs.In addition to being a California Certi-fied Redemption Center, where the publicmay redeem beverage containers for cash,the station also serves as a universal publicrecycling center, providing an opportu-nity for residents of the partner cities todrop-off a myriad of products, including

fluorescent bulbs and tubes; household,

What’s hauled toa dirty MRF?

• A typical dirty MRF will receiveand process:

• Municipal solid waste fromthe residential and commercialsectors

• Construction and demolitiondebris, which many facilities willhand sort on the tipping floor

• Self-hauled refuse

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by officials oversee-ing these facilitiesincludes commu-nicating the “dirtyMRF” concept tothe public, while en-couraging continuedsource separation.

Conversely, thebenefits of utilizinga dirty MRF includeincreased total diver-sion and recyclingrevenue; the plantacts as a safety net forrecyclables that slippast source-separa-tion services; and, theuse of a dirty MRFallows for removal ofhazardous waste priorto residuals beingshipped to a landfill.

Dirty MRFs are an important elementin an overall resource management system.In fact, for some communities, the dirtyMRF may be a key role player for thosemunicipalities looking to achieve zero

waste.

More information on the SMaR Sta-

tion, including a link to a video of the

operation of the City of Sunnyvale’s wastemanagement system, can be found at www.recycling.insunnyvale.com.

Richard Gertman is principal of theCascadia Consulting Group. He can becontacted at (408) 249-0691 or [email protected]. Mark Bowers is

the solid waste program manager for the

City of Sunnyvale, California. He can becontacted at [email protected].

Reprinted with permission from ResourceRecycling , P.O. Box 42270, Portland, OR97242-0270; (503) 233-1305, (503) 233-1356 (fax); www.resource-recycling.com.

Chart 2 | Composition of materials recovered fromgarbage


Concrete/inerts, 39%

Concrete/

inerts, 39%Scrap steel, 19%

Scrap steel, 19%

Aluminum, glass, plastic, 14%

Aluminum,

glass, plastic,

14%

Wood, 13%

Wood, 13%

Mixed paper, 12%

Mixed paper,

12%

Cardboard, 3%

Cardboard, 3%

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Gert Man 0810 Rr