Source-Separation and Mixed Waste Recycling Systems for Multifamily Buildings: A Comparative Analysis

Feb. 20, 2014

Interest in the recycling of the organic fraction of the municipal solid waste (MSW) stream is at an all-time high. As a result, municipal solid waste managers are facing a watershed moment as they are now being tasked with the implementation of collection and processing systems for organic wastes.  As with materials recycling, there is a need to implement collection services that are efficient, cost-effective and convenient to the resident.

In this regard, many communities are staying with the source-separation approach and instructing residents to place their food waste and other organics in the yard waste bin.  Some communities, however, are starting to consider and implement other residential recycling options.

Managing municipal solid waste is more than landfilling: publicity, education, engineering, long-term planning, and landfill gas waste-to-energy are specialties needed in today’s complex environment. We’ve created a handy infographic featuring 6 tips to improve landfill management and achieve excellence in operations.  6 Tips for Excellence in Landfill Operations. Download it now!

The city of Houston, TX, for example, was recently awarded a $1 million grant from the Bloomberg Philanthropies “2012-2013 Mayors Challenge” to support the city’s implementation of its “One Bin For All” residential recycling program. (The Mayors Challenge is a competition to inspire American cities to generate innovative ideas that solve major challenges and improve city life-and that ultimately can be shared with cities across the nation.) As described in its grant application, this program will instruct residents to place all their discards into a single bin for collection and will rely on processing technologies to separate out recyclables and organics from the mixed waste at a central processing facility.

The Recycling Group of the SWANA Applied Research Foundation (ARF) decided to conduct a comparative analysis of the source-separation and mixed waste recycling approaches during FY2013 (July 2012 through June 2013). The goal of the research project was to conduct a comparative analysis of the costs, benefits, and issues associated with source-separation and mixed waste recycling systems. Because of funding constraints, the analysis that was conducted was preliminary in nature and was limited to multifamily residences. However, it provides an initial review of the benefits, risks, and costs associated with each option.

This article presents highlights from the project report, which was developed with input and support from the FY2013 ARF Recycling and Collection Group Subscribers who are listed in Table 1.

Source-Separation Recycling in Seattle
The implementation of residential source-separation recycling programs began in earnest in the early 1990s. By 2011, it was estimated that there were more than 9,800 curbside collection programs in the US to collect source-separated recyclables, serving over 70% of the population. (US EPA Office of Solid Waste. Municipal Solid Waste in the United States: 2011 Facts and Figures. [EPA-530-R-13-001]. May 2013. http://www.epa.org.)

Residential source-separation programs typically involve the provision of three regularly scheduled curbside collection services for residential customers: mixed waste, yardwaste, and recyclables. Residents are required to assist in these services by separating their discards into these three categories and placing them in their assigned bins or wheeled containers at the curb.

One of the premier residential source-separation programs in the US has been implemented by the city of Seattle, a city well known for its strong environmental ethic and commitment to recycling. In addition to achieving very high diversion rates, the city has made a commitment to the principles of full-cost accounting, accurate accounting of diversion rates, and public transparency with respect to the costs and performance levels associated with each of its recycling services.

For these reasons, the city of Seattle was selected for analysis as an excellent representative of a modern residential source-separation recycling system.

Seattle Public Utilities (SPU), a department in the government of the city of Seattle, is responsible for the provision of water supply, wastewater and stormwater management, and solid waste management services to the residents, businesses, and industries in the city’s jurisdiction.

Almost 714,000 tons of MSW were generated in Seattle and managed in 2012. (Seattle Public Utilities. 2012 Recycling Rate Report.) The city’s 2012 estimated population of 634,535 is divided into single-family (163,483 households) and multifamily residents (132,840 households). (Seattle Public Utilities, Economic Services Section. Seattle Garbage Report-2nd Quarter 2013.)

The Seattle Solid Waste Plan-2011 Revision includes a graphic of the city’s MSW system, which is presented in Figure 2-1 and summarized below:

  • SPU has divided the city into two residential franchise collection districts, each of which is provided with garbage, organics collection, and recyclables collection services. For single-family residences, garbage and organics are collected on a weekly basis while recyclables are collected every other week. For multifamily residences, the collection frequency for garbage varies according to the needs of the building, while organics are still collected weekly and recyclables every other week.
  • The collected wastes are transported to either of two transfer facilities (north or south), while the organics and recyclables are hauled directly to processors. From the transfer facilities, waste is trucked to an intermodal rail station, from which it is transported by train approximately 250 miles to the Columbia Ridge Landfill-located near Arlington, OR, and owned by Waste Management, Inc.-for disposal.

About 45% of Seattle’s population of 634,535 persons live in multifamily apartment buildings. The 132,840 apartment units contained in the approximately 6,000 multifamily buildings equate to about 22 units per building. As described above, multifamily buildings are defined by SPU to contain more than four apartment units and utilize dumpsters for garbage collection.

The following collection services are provided to multifamily apartment buildings in Seattle:

Recyclables collection-Multifamily building managers can use 1-, 1.5-, or 2-cubic-yard dumpsters, or either 64-gallon or 96-gallon rollout containers, which are provided free of charge, for the collection of recyclables from their residents. Residents are instructed to place recyclables commingled into the container, which is collected on an every-other-week basis at the curb. For larger buildings, the dumpsters are collected once per week. SPU does not charge multifamily residents for the recyclables collection service.

Organics collection-Seattle apartment and condominium properties of five or more units are required by law to provide a foodwaste collection cart for residents to use. In this regard, it is important to note that multifamily residents are not allowed to use plastic bags to contain foodwaste when participating in organics recycling.

SPU has developed guidelines for the cart sizes and collection frequencies that are likely to be needed by apartment buildings of different sizes. The monthly rate charged by SPU for the weekly collection of a 32-gallon organics rollout cart is $27.68. Since this size container can serve up to 20 units, the equivalent cost is $1.38 per multifamily household per month.

SPU acknowledges that odors and flies are potential problems associated with the organics collection service, for which plastic bags are prohibited for containing organic discards but compostable bags are allowed. The following guidelines have been issued to help residents to address these issues:

  • Use old newspaper to line carts and kitchen containers and/or or wrap food scraps in newspaper or paper towels.
  • To reduce odors, sprinkle baking soda in the kitchen container.
  • Wash kitchen containers thoroughly with detergent and water after every use.
  • Use a vacuum cleaner to remove fruit flies.
  • Rub vinegar around the rim of kitchen containers.

Garbage collection-SPU provides a dumpster-based garbage collection service for multifamily buildings. The most common service level is for a 1-cubic-yard, uncompacted container serviced once per week. In FY2012, SPU reported that 50,497 tons of waste was disposed from the city’s 132,840 multifamily households, which equates to 0.38 tons per household per year. Assuming an uncompacted bulk density of 250 pounds per cubic yard, it is estimated that the 1-cubic-yard service would serve 17 multifamily households. The rate charged by SPU for this service is $188.57 per month, which equates to $11.03 per multifamily household per month. As noted above, this rate covers the costs of both recyclables as well as waste collection and disposal.

Mixed Waste Recycling in San José
The city of San José has been a leader in the field of recycling materials from solid waste for over 20 years and was one of the first municipalities in the United States to develop a zero waste plan. The California Department of Resources Recycling and Recovery (CalRecycle) reported a 74% waste diversion rate for the city in 2010. (City of San José Environmental Services Department. Integrated Waste Management Zero Waste Strategic Plan. November 2008. http://www.sanjoseca.gov/documentcenter/view/1020.)

Despite this success, the city found that the achievement of high recycling rates for its multifamily residents presented a persistent problem for a number of reasons. First, effective outreach to this population has been challenging since apartment dwellers are a more transient population with diverse language requirements. In addition, multifamily buildings often suffer from the “tragedy of the commons” problem, where no one takes responsibility for shared trash and recycling areas. For these reasons, the diversion rate achieved by this residential subsector was historically low. In 2003, for example, the city’s multifamily collection contractor reported a diversion rate of only 18% achieved by the multi-family source-separation recycling program. (Ibid.)

To enhance the recovery of recyclables and organics from multifamily residents, the city modified its diversion program for multifamily complexes in 2008 to include the processing of mixed waste generated by these complexes.

The city’s contractor, GreenTeam of San José, provides recycling and garbage collection services to all of the 100,000 multifamily housing units located in the 3,337 apartment and condominium complexes in San José.

The mixed solid waste collected from multifamily residences is delivered to the GreenWaste Materials Recovery Facility (MRF) for processing. Located in the city of San José, this 96,000-square-foot facility processes residential and commercial waste, yard trimmings, curbside recyclables, foodwaste, and construction-and-demolition debris. (http://greenwaste.com/about-us/material-recovery-facility-mrf.)

The GreenWaste MRF, which was constructed in 1999, was originally designed to process recyclable materials, yard trimmings, and construction-and-demolition debris. (GreenWaste/Zaner Sustainability Report. 2012.) In 2008, a massive reconstruction project was undertaken that involved the installation of two side-by-side processing lines-one for source-separated recyclables and another for mixed waste processing. As a result, the MRF is now permitted to process up to 2,000 tons per day of mixed solid waste and single-stream recyclables. The side-by-side design results in reduced costs due to economies of scale and the combined processing of recovered materials from both lines.

Processing at the facility starts with the manual sorting, which is followed by mechanical processing and then manual sorting of separated materials for quality control. The mechanical sorting equipment and processes include bag breakers, screens, separators, magnets, optical sorters, and an eddy-current separator. The bulk of the wastes and recyclables processed at the MRF come from San José’s multifamily residences.

The mixed waste processing line, which can process up to 30 tons per hour, consists of presort stations, a bag breaker, a trommel screen, a drum separator, a polishing screen, and quality-control post-sort stations. To maximize materials recovery, mixed recyclables pulled from the MSW line during the presort step are transferred to the presort conveyor of the single-stream line for processing. Unsorted materials, consisting largely of organics, are composted at the Z-Best Composting Facility in Gilroy, California.

An analysis of the costs of the San José mixed waste recycling system was conducted as a part of the project. In this regard, the service rates charged to multifamily building owners cover the costs of both recyclables and garbage collection and processing. The monthly service fee is based on the frequency of collection and the number and sizes of the garbage containers in use at each complex.

The most popular collection service contracted for by multifamily building owners is a 3-cubic-yard waste container serviced twice a week. The monthly charge for this service-covering the two weekly waste collection services, two weekly recyclables collections service, and the costs for processing the waste at the GreenWaste MRF-is $376.11, which equates to $4,513.32 per year.

A multifamily household in San José generated 0.74 tons of waste (excluding recyclables) in FY 2012-2013. Assuming a bulk density of 250 pounds per cubic yard, this equates to 5.92 cubic yards of waste. Therefore the 3-cubic-yard container collected twice per week service would serve about 53 multifamily households, which equates to a cost of $85.64 per household per year.

The city currently pays GreenWaste $81.51 to process each ton of MSW at its mixed waste MRF, which equates to $60.32 per multifamily household. Subtracting this amount from the total household cost of $85.64 leaves $25.32 per year to cover the four weekly collection services or $6.33 per collection service per household per year. Since two of the three weekly services are for waste collection, a multifamily household incurs costs of $60.32 for waste processing and $12.66 for waste collection, for a total of $72.98 per year or $6.08 per household per month for waste collection and processing.

Similarly, a monthly cost of $1.05 per household per month is incurred for recyclables collection and processing.

Comparative Analysis
The costs and performance parameters associated with the two types of residential recycling systems-source-separation recycling and mixed waste recycling-are summarized in Table 2.

Based on this preliminary analysis, the cost per multifamily residential unit being served by the source-separated recycling system in Seattle appear to be significantly higher than the costs being incurred for the  mixed waste recycling system in San José. This may indicate that the cost of providing the additional collection services to collect the source-separated recyclables and organics exceeds the cost of processing the mixed waste stream for the recovery of recyclables and compost. Additional research and analysis will be needed to confirm this conclusion.

As indicated, the source-separation recycling approach in Seattle is achieving a higher materials recycling rate for multifamily residences than the mixed waste recycling approach implemented in San José. However, as the table indicates, 19% of the multifamily wastestream is recovered through the source-separation collection service provided by San José to multifamily buildings before the remaining waste is processed at the mixed waste recycling facility. It is uncertain what portion of these recyclables would be recovered at the mixed waste recycling facility if the source-separation recycling service was not being provided. In this regard, if 65% of the source-separated recyclables were recovered at the facility, then the materials recycling rate of the mixed waste recycling system would equal the rate being achieved in Seattle’s source-separation recycling system.

The total diversion rate for multifamily households achieved by the mixed waste recycling system in San José-57%-is higher than Seattle’s diversion rate of 33% because of the significantly higher recovery rate for organics.

It is generally conceded that the source-separation recycling approach results in higher-quality recyclables and compost than the mixed waste recycling system. It is unclear what impact the difference in the quality of recovered recyclables has on the market prices received for the recovered recyclables. Both systems have been able to market the recovered recyclables and compost.

Managing municipal solid waste is more than landfilling: publicity, education, engineering, long-term planning, and landfill gas waste-to-energy are specialties needed in today’s complex environment. We’ve created a handy infographic featuring 6 tips to improve landfill management and achieve excellence in operations. 6 Tips for Excellence in Landfill Operations. Download it now!  

The source-separated recycling system is more inconvenient for residents and results in a higher degree of unpleasantness associated with organics diversion due to odors and vector issues.

Finally, the mixed waste recycling option provides a community capability of producing a process-engineered fuel (PEF) from the non-recyclable portion of the mixed wastestream. PEFs that meet EPA regulations can be combusted in existing industrial or utility boilers, which are subject to the Section 112 Clean Air Act requirements, as opposed to the more stringent Section 129 CAA requirements that apply to WTE facilities. For both of these reasons, the recovery of PEFs from MSW should have significantly lower associated costs than traditional WTE systems. PEFs can be marketed to industries and utilities and can potentially displace the use of fossil fuels for electricity and heating.

The SWANA Applied Research Foundation will continue to conduct research on the comparison of source-separation recycling versus mixed waste recycling in FY2014. If you think that your organization might be interested in participating in the foundation and supporting this research, please contact Jeremy K. O’Brien, PE, SWANA’s director of applied research, at mailto:[email protected]
About the Author

Jeremy O'Brien

Jeremy K. O'Brien, P.E., is director of applied research for the Solid Waste Association of North America.

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