Solid Waste & Recycling

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Single Stream vs. Two Stream: Round 3

While a number of larger municipalities have moved to single-stream recycling -- most recently Halton Region -- the success of these programs has been mixed. Smaller programs are still undecided on whether or not single stream is advantageous....


While a number of larger municipalities have moved to single-stream recycling — most recently Halton Region — the success of these programs has been mixed. Smaller programs are still undecided on whether or not single stream is advantageous. Key issues to consider with such programs include:

• Concerns from end markets over product quality, particularly from the fibre end-markets;

• Increased residue quantities that must be managed in the Material Recovery Facility (MRF); and

• Labour costs, and thus overall processing costs in excess of expectations.

Current net recycling costs

It can be difficult to compare program costs across municipalities considering the variances in materials collected and, more importantly, the demographics of each of the programs. For the purposes of the review herein, the three largest single stream programs (Programs 1 to 3) and the three largest two stream programs (Programs 4 to 6) were chosen to try to minimize the variances.

Outlined in Table 1 are the costs for the three single-stream programs in 2003 and in 2008. In 2003, Programs 1 to 3 were two-stream. 2008 represents the third full year of single stream operation. Table 2 presents the costs for the three two-stream programs over the same period.

Comparing the 2008 results shows that two-stream programs have a $27.82 lower net cost per tonne. On a cost per household basis, the net cost of two-stream programs is $6.44 lower.

A number of things should be noted when comparing the results. First, two of the large single-stream programs receive a fibre premium for their materials. Across the three programs (only two of which receive a fibre premium), the premium equates to approximately $6 to $7 per tonne (i.e., comparing programs on an equal revenue stream basis, the two-stream programs would be $6 to $7 per tonne lower than indicated).

Secondly, there are economies of scale associated with recyclables processing. With the larger facilities (greater than 60,000-65,000 tpy) processing typically occurs over more than one shift per day which means that capital costs are monetized over two shifts and more tonnes, thereby lowering the capital cost per tonne, thereby lowering overall operating costs for the larger facilities. Monetizing capital over two shifts reduces capital costs by $5 and $8.50 per tonne. However, part of this savings is offset by higher maintenance costs. This is estimated at an incremental $2.50 to $3.50 per tonne.

It could also be argued that the population density of the three largest programs gives them a collection cost advantage. However, as there are many factors that go into this argument, it was left out of the evaluation.

Adding up these additional costs and the potential savings, the result suggests that two-stream programs in Ontario on an equal basis would have a large cost advantage over single-stream programs (Table 3).

Accounting for the differences in the programs, two-stream programs show an even larger savings per tonne of between approximately $35.30 and $40.80 (or from 23 per cent to 26 per cent) when compared to single-stream programs.

Impact on diversion from single stream

Typically, all municipalities report an increase in the quantity of material arriving at the MRF as a result of moving to single stream. However, the increase may not be solely due to the single-stream collection system; rather, it may be attributable to a combination of factors such as increased promotion, bag limits, user pay, etc. Overall, there is no clear evidence that the implementation of single-stream recycling itself is the main basis for increased diversion rates.

Quantity diverted in Ontario

With single-stream recycling, the total quantity of materials arriving at the MRF does indeed in most instances increase. However, after accounting for increase in residues, the total quantity diverted may or may not increase. Currently there are limited data to specifically state that single-stream recycling will result in increased diversion.

The three major municipalities in the province that employ single-stream recycling saw the quantity of recyclables managed increase by approximately seven per cent per household between 2003 and 2007 (Table 4). Over the same period, municipalities employing a two-stream system increased their recovery rates by the same seven per cent (Table 5). However, the total quantity of material collected per household was about 5.6 per cent higher in two-stream municipalities than under a single-stream program.

One of the large single-stream programs has a large percentage of its population in multi-family dwellings, which would account somewhat for the lower recovery rate. One would expect recovery rates for programs 1 to 3 to have somewhat higher recovery rates as a result of the number of large daily newspapers not typically found in the same quantities in the smaller two-stream programs. This is a critical factor considering recovery rates for newspapers on average exceed 90 per cent for most Ontario municipalities.

Comparing the data in Tables 4 and 5 suggest that there is no benefit from moving from two-stream collection to single-stream collection with respect to the quantity of material that could be diverted from disposal.

Optical sorting for fibres

Metro Waste Paper Recovery’s Scarborough facility installed optical sorting on its fibre line in hopes that it would improve the quality of the ONP being sent to end markets and reduce the sorting staff requirements, thereby improving the viability of single-stream recycling. In pre-installation material audits, prohibitives and outthrows in the ONP bale were approximately 13 per cent; this is typical of most single-stream plants. Unfortunately the efficiency of the optical sorting units for fibres is not high enough to improve the quality of the ONP. In fact, the facility has had to extend its sorting lines for ONP and add more sorters to help maintain the marketability of the ONP.

Based on investigations in Metro’s facility, it was determined that there was no cost-benefit associated with installing optical sorting for ONP cleanup.

As this is the first installation of its kind in North America managing such a mix of materials, it’s not possible to draw definitive conclusions about its effectiveness. With the increasing residue rates of the inbound material resulting from a move to closed carts, the optical sorting machine has to sort more prohibitives and residues. However, the throughput rate through the optical sorting machines has been decreased to help account for the change in composition. Overall, ONP product quality has not significantly improved. Therefore, the concerns of the ONP mills have yet been addressed. Downgrades are still a concern with resulting decreases in revenue.

The above comments come with a caveat: Unfortunately in today’s economic climate however, even two-stream programs are having some difficulty meeting ONP market specifications thanks to the quantity of boxboard in the fibre mix. In other words, cleaning up ONP is an issue for all facilities, irrespective of the collection approach.

Conclusions

With the collection of recyclables tending to move back to weekly from biweekly as municipalities continue to decrease garbage collection services and recyclables volumes continue to increase, alternating week collection system with fibres in the first week and containers in the second provides collection costs similar to single-stream collection, i.e., the cost advantage of single stream recyclables collection is lost. Therefore, to compete, processing single-stream recyclables has to become more cost effective. As the equipment for separating the materials, particularly fibres from containers, is still not perfe
cted, single-stream collection just exacerbates the problem of trying to make consistently high quality materials to meet end market specifications.

Making matters worse for Ontario programs is that they collect and process many more materials than are typically managed in US-based programs (e.g., tubs and lids, polystyrene, polycoat, aseptics, plastic film, PET trays, etc.) meaning our programs need the mechanical and optical sorting equipment to do even more.

Discussions with manufacturers suggest that in a typical single-stream MRF the efficiency of the front-end processing, separating the fibres from containers, is only about 80-85 per cent. In other words, 15-20 per cent of the fibres end up on the containers line and 15-20 per cent of the containers end up on the fibre line. This results in additional requirements for screening and/or sorting staff to clean up and sort the materials to meet end-market specifications. This carries a high cost; higher than doing two sorts at the curb or, better yet, having residents do the two sorts.

Advances in optical sorting technologies for containers can result in fewer sorting staff and lower overall processing costs, although two stream MRFs can also benefit from optical sorting for containers to reduce costs. As separation and fibres optical sorting equipment continue to develop, it may take another generation — or two — of equipment before single-stream recycling becomes truly cost competitive.

In summary, with increased processing costs exceeding collection savings in most instances (and zero under alternating week collection), overall, single-stream recycling does not show the cost advantage that was originally anticipated. As well, the expected increases in capture rate are also not apparent. Overall, two-stream recycling is more cost effective — and the gap appears to be widening!

Daniel Lantz, M.Sc., MBA, MCIWM is Director, Environmental and Engineering Services for Metro Waste Paper Recovery in Toronto, Ontario. Contact Dan at dlantz@metrowaste.com


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