Much attention has been given recently to the transition of curbside recycling to single-stream, cart-based collection. Programs that take this step see dramatic increases in tonnage and participation, along with new operational efficiencies that improve the long-term economics of curbside service. But what about drop-off systems? Is it possible to achieve similar gains through conversion to single-stream collection? Work in the state of North Carolina indicates that the answer is yes.
The convenience center system
Staffed “convenience centers” are a common public infrastructure that is widely used by local governments in North Carolina to provide solid waste and recycling services mostly to rural citizens. Ninety-six counties out of the 100 in North Carolina operate a total of 692 staffed convenience centers. On average, counties in North Carolina operate about seven of these facilities, with some counties having as few as one and 24 counties having more than 10. Many of these centers evolved from unattended 8-yard “greenbox” sites in the 1980s to a now staffed system of facilities that mostly use roll-off containers.
Convenience centers typically offer a range of services beyond collection of garbage and traditional household recyclables, accepting materials such as oil, oil filters, white goods, textiles and electronics. The overall trend is for convenience centers to live up to their name and allow citizens to divert many different kinds of materials—one “super” convenience center in Orange County allows citizens to bring separated food waste for composting as well as plastic bags, used cooking oil and HHW (household hazardous waste) materials.
Until recent years, the vast majority of convenience sites in the U.S. collected paper, bottles and cans in separate containers, sometimes with as many as seven roll-offs for individual commodities or a whole series of 8-yard containers dedicated to specific materials. This setup has required citizens to do more work to recycle, having to walk between multiple containers one by one with their recyclables. Separated collection also has led counties (or their contractors) to make large investments in container equipment and to do many individual “pulls” of the various containers as they fill up. Compounding the inefficiency, loads of voluminous materials, such as plastic bottles, weigh very little even if filled to the brim. The small payloads make per-ton hauling costs very high.
MRFs offer single-stream possibilities
Over the past decade, North Carolina has seen an almost wholesale change in processing capacity with the statewide development of single-stream MRFs (material recovery facilities). Eighteen in-state MRFs and four out-of-state facilities present the opportunity for large areas of the state to adopt single-stream collection. In addition, the growing trend in “hub-and-spoke” transfer (more on that issue later) makes access to single-stream processing nearly universal in North Carolina.
The advent of this critical infrastructure, the state says, allowed North Carolina to undertake an intensive effort to convert curbside programs to cart-based collection. The state encouraged this process with a dedicated grant program from 2008 to 2013 that helped achieve an estimated 90 percent penetration of carts in curbside services. The transformation of the curbside recycling system in North Carolina to more efficient cart-based single-stream collection has resulted in a 100,000-ton increase of annual curbside materials. With that work basically complete, attention can turn to the state’s drop-off system, most prominently represented by the state’s 692 convenience centers.
Two leaps of efficiency are possible in convenience center recycling: 1) the use of single instead of multiple containers and 2) the use of compaction to maximize recyclable load weights. For counties with close, direct access to single-stream MRFs or indirect access through hub-and-spoke transfer, the conversion to single-stream collection using compacting roll-offs offers an opportunity to cut back on container purchases and maintenance as well as on the number of weekly hauls of individual, relatively light roll-offs.
For the average citizen, being able to bring all of his or her recyclables to a single container—essentially putting recycling on par with garbage—puts the “convenience” into convenience center recycling, helping to improve long-term recycling behavior.
Because commingling means not having to put in a separate container for the next new type of recyclables, counties have a golden opportunity to modernize their collection mixes by combining new recyclables (e.g., nonbottle plastics or cartons and aseptic containers) into mixed loads.
A number of North Carolina counties recognized these advantages early on and became the proving ground for commingled compacted collection at convenience centers. Among the leaders were Currituck, Franklin, Moore, Nash, Rutherford, Wake and Wilson counties, and the PCG Health Commission, covering three additional counties, Perquimans, Chowan and Gates.
In some cases, the state recycling program took an active role in encouraging the switch to single-stream collection by the early adopters, offering technical assistance and grant support through an annual general recycling grant cycle. The state also teamed with the North Carolina chapter of SWANA (Solid Waste Association of North America) in 2011 to offer workshops on convenience center operation where the concept of single-stream collection started to gain steam. In that training and in subsequent sessions at the conferences of North Carolina SWANA and the Carolina Recycling Association, as well as through a new round of workshops with North Carolina SWANA in 2014, the experiences of the early adopter counties have been shared widely to demonstrate the business case for compacted commingled recycling at convenience sites.
County experiences prove the concept
Individual county experiences have demonstrated the rewards of commingled convenience center recycling. One major gain is in the amount of recycling tonnage, as citizens respond to the new, more convenient collection format with increased material.
A second benefit, also demonstrated by the early adopter counties, was a substantial decrease in collection costs. In Moore County, for example, the cost of servicing full recyclable containers dropped from $144,573 per year to $53,775, a savings of 63 percent. In the first six months after switching to single stream, Rutherford County saved $2,592 in hauling costs at one site and $6,912 at another, where the county went from 12 trips per month to just two. In general, counties adopting commingled recycling collection using compacting roll-offs are experiencing a 3 to 1 reduction in recycling-related transportation costs.
Mix and squish
Commingling is an important step in its own right, but even greater efficiency can be gained by using compaction to optimize load weights. In North Carolina, counties are using one of two kinds of compactors: 1) a self-contained unit in which the compactor is integral to roll-off container body and 2) a stationary compactor with detachable roll-offs. Self-container roll-offs have a smaller footprint but also smaller capacity. For either type of unit, payloads can be between 5 and 9 tons, with an average of around 6 tons in a stationary unit—a tremendous contrast to loose roll-off loads that may have 2 or 3 tons when full.
A challenge with compactors is the expense, which entails the development of hard infrastructure, such as electrical access and concrete pads, in addition to the cost of the compacting unit itself.
Although this is a sizable investment for counties, especially those with 10 sites or more, the payback from hauling savings alone is relatively quick, in many cases two to three years. Considering avoided tipping fees, the ability to add materials and the improvement in recycling service for citizens, it is no wonder many counties have already made the switch and more are moving in that direction.
Nuances of transitioning to single stream
Although single-stream collection can be in many ways the ideal strategy for convenience center recycling, some variations on that theme may better fit a county’s needs. For example, some counties have collected corrugated cardboard separately for years, in some instances baling and selling the material for additional income. A case also can be made for glass to be kept separate to improve the value and quality of commingled loads, but so far attempts to do so by some counties, with assistance from the state, have not succeeded largely in light of a lack of price signals from MRFs. In general, although separation of one or two materials detracts from the simplicity of commingled recycling, it still may be worthwhile in some circumstances.
One of the most important benefits of converting to single stream is the freeing up of space at convenience centers for other services. As noted earlier, a number of counties have provided an array of recycling opportunities at their sites for years. When counties transition to commingled collection, they have the space to add more services because of the elimination of multiple roll-offs for separated recyclables.
Electronics have been an obvious addition, especially as counties have responded to the disposal bans on TVs and computer equipment in North Carolina, but other materials that can claim some collection space include automotive materials (oil, filters, antifreeze) and relatively newer discards, such as compact fluorescent lamps and used cooking oil. This chance to improve public waste diversion services is being embraced by communities who adopt single stream at their convenience sites, and it is encouraged by the state through its grant programs.
Using complementary hub-and-spoke transfer
Many North Carolina counties do not have a critical mass of recyclables to attract or justify their own MRF, and portions of the state are relatively distant (more than 50 miles) from the larger, more sophisticated MRFs that tend to be concentrated in urban areas. In addition, most existing MRFs serving North Carolina are operating under capacity; receiving more material would help maximize the return on investment that MRF operators need. The critical link between these two issues is the use of hub-and-spoke transfer of commingled recyclables, a strategy that works very well with adoption of single-stream collection at convenience centers.
Wilson County is a prime example. None of its 13 convenience centers is close enough to justify hauling recyclables directly to a MRF. In 2012, with the help of a state recycling grant, the county constructed a facility where recyclables from the convenience sites are consolidated into transfer trailer loads and then shipped to a MRF in Raleigh. With this increased transportation efficiency, Wilson County municipalities also can bring commingled recyclables from their curbside recycling programs to this facility.
Reflecting on this accomplishment in 2013, Andy Davis, the solid waste director responsible for the implementation of hub-and-spoke recycling, said this was the first time in Wilson County history where it was cheaper to recycle than to landfill materials.
Momentum behind commingled collection
Single streaming of recyclables at convenience centers already has made significant gains in North Carolina, with almost one-quarter of the sites fully transitioned to commingled collection and another quarter adopting single stream plus or minus a material or two. Only 41 percent of convenience centers have maintained source-separated collection.
Not all single-stream programs use compactors, nor is compacted collection appropriate or necessary in every case. But 26 North Carolina counties out of the 96 with convenience centers are using at least one compactor, and 105 individual sites now have a compacting container. As new sites are converted to single stream, compactors will see more usage. It is anticipated that many of the noncompacting single-stream centers also will make that conversion.
North Carolina has seen the almost comprehensive adoption of cart-based commingled curbside recycling and is now poised to make a similar transition in the statewide system of staffed convenience centers. As with curbside carts, this trend will be encouraged by a dedicated state grant program. The end result will be a more efficient recycling collection system across the state, with costs and services on par or better than garbage collection.
Scott Mouw is recycling section chief of the North Carolina Department of Environment and Natural Resources (NCDENR). He can be reached at firstname.lastname@example.org. Rob Taylor is the local government recycling team leader at the NCDENR. He can be reached at email@example.com.