As Green Bin programs began being implemented across North America a number of years ago, communities were faced with making decisions about program design; they made certain decisions without significant information that impacted program performance. Thankfully, operational experience allows program designers to choose a system that best suits the needs of their community.
Implementation of residential source-separated organics (SSO) programs requires many decisions: what materials to collect; how they should be stored in the home and collected at the curb; the processing approach used (composting or anaerobic digestion); policies that could increase participation and capture in residential SSO programs; and, the most appropriate end markets for finished compost.
One important decision is which type of kitchen catcher bag to allow for set-out of SSO in curbside bins. Until recently this had not been empirically studied.
The impacts of different bag choices (paper, plastic, biodegradable plastic or certified compostable plastic) on SSO program performance were examined in a study recently commissioned by Bag To Earth and carried out by this author and consultant Janet Robins. The study focussed on quantifying, to the extent possible, the impacts of the choice of bag on SSO program performance. Data collected from SSO programs across Canada, predominantly in the provinces of Ontario and Nova Scotia, included:
• Year that the SSO program was implemented;
• Households served;
• SSO tonnage collected annually since the program was initiated;
• Type of bags permitted in SSO bins (paper only, certified compostable plastic, biodegradable plastic or plastic);
• Frequency of garbage collection (weekly or bi-weekly);
• Curbside policies which would impact on participation in the SSO program(bag limits, PAYT programs, etc.);
• Facility where SSO was processed; and
• Residue rates at the processing operation.
The conclusion of the analysis was that many factors impact the performance of the SSO program. Some key factors are:
Size of curbside Green Bin containers provided, and the extent to which leaf-and-yard waste are collected in the Green Bin: Some communities chose small 46 litre Green Bin containers which collect kitchen waste only whereas other communities chose a larger Green Bin container, and allow some leaf and yard waste in the bin. Bin sizes in the programs studied included: 46, 80, 120, 140 and 240 litres. The community decision on the bin size is generally related to optimizing the collection system design. It also impacts on processing options chosen.
Age of the program (number of years in operation): Participation in SSO programs generally increases and the amount of SSO collected generally increases over time as residents become used to the program requirements.
Frequency of garbage collection: Participation in SSO programs and capture of SSO are both higher in communities which only collect garbage every other week. Less frequent garbage collection service encourages people to use the Green Bin more.
Curbside policies: SSO program performance is better in communities with lower garbage bag/container set out limits and in communities where extra bags or containers of garbage cost extra (through a tag system)
The research found that there was not sufficient evidence to indicate that the choice of a particular type of kitchen catcher bag (paper, plastic, certified compostable plastic or biodegradable plastic) significantly impacted participation or capture rates in the SSO programs examined. A number of factors are at play (including the list of the materials collected, the age of the program, frequency of garbage collection, curbside policies and size of Green Bin) that influence participation rates and capture rates.
Well performing programs include a blend of policies and practices which best meet community needs and diversion targets, while integrating collection decisions with the broader integrated waste management system, and taking account of the implications of program design decisions on the organics processing operation.
Compost facility operators contacted for the study preferred paper bags, as these compost readily in existing systems, and result in residue rates of “virtually zero.” All facility operators noted that certified compostable plastic bags compost more slowly than paper bags, and they experience higher residue rates from programs that use plastic bags, including biodegradable and certified compostable plastic bags. Operators commented that a well run composting operation should be able to achieve a residue rate of below five per cent.
Maria Kelleher is Principal at Kelleher Environmental in Toronto, Ontario. Contact Maria at email@example.com