Solid Waste & Recycling

Feature

De-Bagging

A number of curbside-collection programs in Canada use blue recycling bags to collect recyclables. There has been a lot of debate about these bag collection systems that has focused on the operating a...


A number of curbside-collection programs in Canada use blue recycling bags to collect recyclables. There has been a lot of debate about these bag collection systems that has focused on the operating and capital costs associated with mechanical de-bagging of recyclables.

In an attempt to debunk some of the myths surrounding de-bagging systems, in February 2003, Clorox Company of Canada Ltd. contracted Entec Consulting Ltd. of Pickering, Ontario to assess the incremental cost of mechanically breaking and removing these plastic recycling bags at two different Canadian materials recovery facilities (MRFs). The study focussed on MRFs that utilize mechanical bag breakers as an initial sorting step — one in Edmonton, Alberta and one in Northumberland County, Ontario.

The productivity of removing blue bag film plastic from a sorting line is a function of a number of variables, including:

the quantity of incoming bags that break open either in the collection vehicle or on the tipping floor;

the success of the bag breaker in separating the recyclables from the film;

the configuration of the sorting station (height, conveyor width, etc.);

the operating throughput of the MRF (tonnes/operating hour);

the ergonomics involved in depositing the film once removed from the conveyor (side chute, vacuum chute above the conveyor, etc.); and,

the motivation of the individual sorters themselves.

Edmonton MRF

In 1999 the City of Edmonton initiated a blue bag curbside-collection program. This system now services approximately 150,000 curbside-eligible households and 113,000 multi-family households. Materials collected include: corrugated cardboard, boxboard, newsprint, magazines, fine paper, junk mail, paper bags, envelopes, paper egg cartons, paperback and hard cover books; polycoat gable top cartons and aseptic containers; aluminum and steel cans; empty aerosol cans; plastics (#1 to #5); and, glass bottles and jars. (A deposit-refund system exists in Alberta for all beverage containers, however containers that do enter the curbside system are processed and marketed).

Recyclables are collected by a variety of city and private contractor collection vehicles and then delivered to the city’s MRF at the Edmonton Waste Management Centre. The city contracts the operation of the city-owned MRF to Canadian Waste Services (CWS).

In 2002, the MRF processing system was upgraded to incorporate new screening systems to improve productivity and reduce staff requirements. The total MRF throughput in 2002 was 30,558 tonnes (residential = 29,418 tonnes).

The specific process is as follows:

incoming blue-bag recyclables are unloaded onto the floor and stockpiled by a front-end loader;

material is fed into in-floor conveyor hopper and up an inclined conveyor to the presort area;

there is considerable breakage of bags in the collection vehicles and on the floor;

sorters remove OCC and contaminants (non-recyclables, wire and other materials that may cause a problem with the disc screens) from the presort conveyor;

all material is then top-fed into a single bag breaker (Mayfran’s BRT Schlitz-O-Matic), the majority of which are broken upon leaving the breaker;

staff at the film conveyor sort blue film plastic out from other material on conveyor where it is air-conveyed to a bin at floor level that removes plastic grocery bags and other film;

all material is then directed to a Machinex disc screen in Fibre Line #1, which receives “overs” from the top paper screen; and,

in Fibre Line # 2, sorters remove remaining blue-bag film, grocery film and other contaminants.

Northumberland MRF

Northumberland County is a largely rural area on the north shore of Lake Ontario. In 1996, to accommodate the need for a more advanced diversion program and to reduce collection costs, Northumberland decided to adopt a two-stream wet-dry collection system. Residents are required to source separate household refuse into one of two streams, one being dry recyclable wastes and the other being wet organic wastes. Of the 33,141 households in the county, 31,796 are served by curbside collection (primarily single family and small multi-family dwellings in buildings containing five or fewer units).

A key component of Northumberland’s waste management master plan was a MRF designed to separate, process and market co-mingled dry waste and recyclable material. All dry waste is collected curbside by a private contractor and delivered to the MRF. In addition, some dry waste in rural areas is delivered by residents to depots and transferred to the MRF.

Materials collected in the recycling program include: corrugated cardboard, boxboard, newsprint, magazines, fine paper, junk mail, paper bags, envelopes, paper egg cartons, paper cups, paperback and hard cover books, telephone directories; glass bottles and jars; aluminum and steel cans; foil; empty aerosol cans; all plastics; polycoat gable top cartons and aseptic containers; and, textiles.

The county contracted the design, construction and operation of the MRF to Miller Waste Systems and the MRF began operating in 1996. After an initial period of contractor operation, the County took over and now continues that role. In 2002, there was a total throughput of 14,879 tonnes (residential = 11,204 tonnes).

The process at this MRF includes:

incoming blue-bag recyclables are unloaded onto the floor and stockpiled by front-end loader;

material is fed into in-floor conveyor hopper and up an inclined conveyor to the presort area;

there is some breaking of bags in the collection vehicles and on the floor;

blue-bag removal;

recyclables are manually de-bagged at the conveyor where possible;

excess bags are pulled from the conveyor and deposited down a chute from the pre-sort area to a return conveyor that directs these bags to a floor level bag breaker (top-fed BHS model BB60) situated beside the in-feed hopper;

material is mechanically de-bagged in the breaker and re-deposited onto the in-floor conveyor for transport back to the presort cabin; and,

the majority of the bags are broken on leaving the breaker.

The sorters remove OCC, ONP and contaminants.

Conclusions

The estimated cost to break and remove blue recycling bags at the MRF operations investigated was $8.03/tonne in Edmonton versus $6.19/tonne in Northumberland for an average of $7.11/tonne.

The study reveals that the Northumberland sorters have a higher film sorting productivity than the Edmonton sorters. This may be due to a number of the factors, but it’s difficult to assess the extent to which the bag breaker influences the productivity. Indeed, both breakers appear to do an acceptable job of breaking the bags, but the sorters in Edmonton clearly needed to do more work to free recyclables from the film plastic.

Each MRF has a different process design for bag breaking and removal. All recyclables flow through the bag breaker in Edmonton, whereas sorters in Northumberland manually de-bag recyclables and only return excess bags to the bag breaker. In this case, the bag breaker may be more efficient since it is dealing with smaller flow of only bagged material.

When designing a recycling program, it’s important to look at the entire system holistically and examine the collection system as well as the processing of the recycled commodities. Bag-based recycling systems have allowed municipalities to capitalize on collection efficiencies, due to higher collection productivity than container-based systems and the ability to utilize conventional collection equipment.

This study sheds some light on another component of the recycling equation, the processing of the recycled commodities and the incremental cost of debagging recyclables collected in bags. Using a holistic approach to analyze the total recycling system and analyzing both the collection and processing system in their entirety will allow for more accurate decision-making. (Also see “Technology Solves Contamination Concerns in the June/July 2002 edition.)

Productivity of Sorters / De-Baggers

Estimated Annual Cost for Blue Bag Removal at Edmonton MRF

Annual MRF Tonnes Processed (2002) = 30,558

Operating: Cost/tonne

Sorters (equivalent of 12 MRF staff dedicated to blue bag removal) – 12 sorters, 9.5 hrs/day, 250 days/yr. @ approx. $8/hr = $228,000

Maintenance – 16 hrs/week x 12 months @ $18/hr = $3,456

Welding rods – $200 x 12 months = $2,400

Power consumption = $2,140

Sub Total = $235,996 / $7.72

Capital:

Estimated capital costs (April 1999) = $72,000

Interest rate = 5%

Anticipated life (yrs) = 10

Amortized annual cost = $9,324 / $0.31

Total Annual Cost = $245,320 / $8.03

Estimated Annual Cost for Blue Bag Removal at Northumberland MRF

Annual MRF Tonnes Processed (2002) = 11,204 (residential line only)

Operating: Cost/tonne

Sorters (equivalent of 2 MRF staff dedicated to blue bag removal) – 2 sorters, 7.58 hrs/day, 250 days/yr. @ approx. $12/hr = $45,480

Maintenance – cleaning 30 min./day x 250 @ $17/hr = $2,125 – maintenance 30 min./day x 250 @ $17/hr = $221

Power consumption (estimated) = $2,000

Sub Total = $49,826 / $4.45

Capital:

1999 capital costs (breaker, hopper, return feed conveyor) = $130,000

Interest rate = 5%

Anticipated life (yrs) = 10

Amortized annual cost = $16,836 / $1.74

Total Annual Cost = $57,720 / $6.19

Bob Graham is president of Entec Recycling Inc., based in Pickering, Ontario. E-mail Bob at entec@sympatico.ca


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