BioCycle June 2005, Vol. 46, No. 6, p. 44
Newer collection vehicles and containers provide managers with more choices to collect food residuals, yard trimmings and other organics in lower cost systems.
Bronwen Smith and Dan Lantz
AS HOUSEHOLD organics programs have been developing in Ontario, there has been much discussion about how to best collect the material – both in terms of containers and vehicles, and what other materials should be cocollected with the organics as a means of keeping costs to a minimum. The overall trend in the province has been to set out material curbside in small (< 50L) containers and tip them manually, in a split body truck with either recyclables or garbage. Although this is the current trend, below is a discussion of all collection container systems that have been investigated and used by municipalities across Ontario.
Plastic bags for food residuals are being used in selected municipalities, both as the primary collection container, as well as part of a cart-based program. A key issue that needs to be managed upfront in the selection of any bag-based system is the means to debag the materials at the facility as well as to remove any plastic film from the product prior to sale. The use of plastic bags does offer residents a number of key advantages: Control of liquids; Control of odors; Easy to manage in the home; No container to clean; and No residual odors in in-house container.
Bins and carts range in size from the small 35 to 45 litre (9-11 gallon) container (e.g. the Norseman 42 L bin is used in Toronto) to the large 90-240 litre (32-60 gallon) cart (e.g. 240 L carts are used in St. Thomas and Caledon). The cart choices serve very different purposes. The smaller 42 litre cart is sized to manage the typical amount of food residuals generated by a single family on a weekly basis (i.e., 3 to 5 kg). It is too small to handle any yard trimmings. The bin is picked up manually at the curb and dumped into a compartment on the truck. In some municipalities, residents are allowed to put their food scraps into plastic bags ahead of placing the material in the small bin. In other programs, food residuals can only be set out in the bin either loose or in degradable bags. The choice is dependent on the processing technology in use by the municipality.
The larger cart is designed to handle both kitchen residuals and leaves and yard trimmings. Some carts are designed with aeration vents, which help reduce odors in the cart by allowing air to pass over the organics. They also reduce the quantity of material to be collected because the vents allow moisture to evaporate. To keep vermin to a minimum, residents are advised to wrap their food residuals in newspaper or, in some municipalities, place the material in boxboard cartons (e.g., a cereal box). The clay content in both the newspaper and boxboard, beyond absorbing excess liquid, also acts to reduce odors (similar to clay in kitty litter).
The larger carts cannot be handled manually at the curb, but rather require a semi or fully automated collection vehicle. With the semiautomated system, the vehicle operator places the cart on a lifting arm, which then empties the cart’s contents into the truck. With the fully automated collection system, the vehicle operator maneuvers the vehicles’ arm, which grabs the cart, lifts it and empties the contents into the truck.
Kitchen organics should be cocollected with another material to increase the efficiency of collection. Although it can be done separately, work completed in the mid-1990s for the Region of Peel showed that because of the small quantities generated per household per week, the collection vehicle would never be properly utilized and the collection cost would exceed $1,000 per metric tons for separate collection. The high cost of separate collection was one of the main reasons that household organics were not introduced in Ontario earlier.
Over the past ten years, the collection vehicle industry has been developing cocollection vehicles. The early innovations had the walls between the two compartments that were flexed, allowing a variable amount of space within the two compartments, rather than being solid and rigid. Although this type of vehicle was sufficient for dry streams of materials, it was not appropriate for the collection of food residuals because the liquids from that stream had a tendency to migrate to the other compartment (i.e., under the partition) and contaminate the materials there. In systems where the food residuals were cocollected with the recyclables, the liquids ended up making the recyclables unmarketable.
The current cocollection vehicles have eliminated the cross contamination problem by changing the body structure. These new truck bodies are comprised of two separate “halves,” which can range from a split of 80:20 to 50:50, with separate hoppers and compaction hydraulics, fused together to make one truck. The two halves work independently of one another. Because they are built as separate compartments, there is no opportunity for contamination between the two compartments. These cocollection vehicles can be configured for manual, semiautomated and fully automated collection.
A number of key benefits are associated with the new cocollection vehicles including:
o Compaction of both compartments has increased on-route time – in some instances trucks do not return at midday to empty, i.e. they stay out on the route all day;
o There is less deadhead time; and
o Compaction provides the opportunity to increase the efficiency of recyclables collection (when organics are cocollected with recyclables).
In a recent study examining future collection system options for a regional municipality of 400,000 in southern Ontario, several different scenarios were run on a collection model to determine the most efficient way to collect household organics. Three of the options examined were:
1. Weekly cocollection of kitchen organics with recyclables alternating fibre/container; Weekly (or biweekly) collection of garbage;
2. Weekly cocollection of kitchen organics and single stream recyclables; Weekly (or biweekly) garbage collection; and
3. Weekly cocollection of kitchen organics with garbage; Weekly collection of two stream recyclables.
It was determined that all three of these options required little or no additional fleet to cocollect organics. No additional fleet would be required to switch from a weekly two stream recyclable collection to cocollection of recyclables (fibers and containers on alternating weeks) and organics in a two-compartment, 70:30 (recyclables:organics), compacting truck and collecting both on a weekly basis.
The second option of cocollecting single stream recyclables with organics in a two-compartment, 70:30 (recyclables: organics), compacting truck would result in a 10 percent decrease in collection trucks required compared to weekly two-stream collection.
The third option examined, the cocollection of organics and garbage in a two-compartment, 70:30 (garbage: organics), compacting truck, would increase fleet requirements only slightly (approximately 10 percent increase) over the existing weekly garbage collection.
One of the main concerns when deciding which collection is most suitable for a city or region is the distance between the organics processing facility/transfer station and the MRF versus the distance to the landfill or waste transfer station. The shorter the distance between the organics processing facility and processing facility of the material cocollected with the organics, the more efficient the resulting cocollection system.
One final benefit of providing curbside collection of food residuals is that it eliminates the need to collect garbage on a weekly basis. Moving to biweekly garbage collection, currently practiced in Toronto and proposed in a number of large urban centers in Southern Ontario (i.e., Niagara, Peel, Halton and Durham Regions), provides another opportunity for municipalities to reduce their collection costs, in some instances up to 30 percent.
COLLECTING FOOD RESIDUALS WITH YARD TRIMMINGS
In some jurisdictions, consideration is being given to cocollecting food residuals and yard trimmings in the same single compartment vehicle, as in currently done in Prince Edward Island and Nova Scotia, Canada. The premise behind this approach is that it provides a lower cost option for the collection of food residuals (as on a typical route they only typically take up approximately 4-5 m3 of space on a collection truck) and the food residuals can be mixed in with the yard trimmings in the same curbside cart (i.e., it does not require a separate collection vessel). In jurisdictions where yard trimmings are generated year round, thus the need to collect them throughout the year, adding food residuals to the cart may be a reasonable option. However this is not the case in Ontario where leaf and yard trimmings collection is offered only a seasonal basis.
The major disadvantage of adding food residuals to the yard trimmings is the potential impact on processing costs. Yard trimmings can be composted very easily and inexpensively in a typical windrow system or static pile system. In fact, with few exceptions, this is how yard trimmings are processed in programs across North America. Depending on the windrow operation, including distance to neighbors, windrow operations, adding food residuals may cause problems (e.g., increased frequency of turning, etc.). Although windrows can be used for food residuals processing (e.g., Region of Niagara, Ontario), it requires additional diligence to control the composting process, including management of possible odors.
MORE CHOICES, LOWER COSTS
With the arrival of compacting cocollection vehicles, the cocollection of kitchen organics with recyclables or garbage provides the benefit of collecting a second stream of materials with little or no increase to future fleet requirements. There are numerous types of collection systems that can be employed to create a successful household organics program although there is no “ideal” scenario to fit every region. Decisions for programs should be made to meet an area’s individual characteristics and needs. Finally, keeping food residuals separate from leaf and yard trimmings collection allows cities and regions to be more selective in their processing choice, thereby keeping overall costs for organics management to a minimum.
Bronwen Smith, Technical Analyst, and Dan Lantz, Business and Practice Leader, are in Solid Waste Management at MacViro Consultants Inc. in Markham, Ontario.
June 15, 2005 | General
FINDING THE BEST ORGANICS COLLECTION SYSTEMS
BioCycle June 2005, Vol. 46, No. 6, p. 44