Waste Wise: Mystery Machine

During the past decade, a tremendous amount of effort on the part of the solid waste industry, universities and EPA has been devoted to quantifying the amount of captured landfill gas and fugitive emissions. There is good reason to do this since landfills rank as the third highest source of man-made methane emissions, behind emissions from the natural gas industry and that associated with livestock management (think cow burps and flatulence next time you have that steak dinner).

For those unfamiliar with methane and its role in the greenhouse gas (GHG) equation, it is 25 times more potent as a GHG than carbon dioxide. This means 1 molecule of methane released into the atmosphere has the same global warming effect as 25 molecules of carbon dioxide. Thus, it’s easy to understand all the fuss in terms of wanting to accurately measure GHG emissions from landfills.

Despite this attention, GHG emissions from U.S. landfills represent approxi- mately 108 million tons of carbon dioxide equivalents, compared to the 1,745 million tons generated by transportation related activities. This means greenhouse gases from landfills equate to 6 percent of the total emissions from cars, trucks and other forms of transportation. Many efforts to quantify GHG emissions in recent years have focused on industry sectors in an effort to ascertain the effects of a particular industry on overall GHG emissions.

This perspective suggests that while material recovery facilities, landfills, waste-to-energy facilities and composting operations are primary end-points for the roughly 500 million tons of municipal solid waste (MSW), and construction and demolition waste disposed of in the United States each year, the majority of the energy is expended transporting these materials.

Thus, if transportation tends to be a substantial source of emissions in general and since waste transport plays a substantial role in how waste is managed, it stands to reason that GHG from waste collection vehicles may play a significant role in estimating overall GHG emissions for the solid waste industry. This premise led the Environmental Research and Education Foundation to fund a study, spearheaded by the University of Nebraska, to quantify air emissions from vehicles used to collect and transport MSW.

The study, which just began the data collection phase, evaluates the impact of variables such as ambient conditions, vehicle type and routing characteristics on garbage truck emissions. A secondary objective is to characterize fuel consumption as a function of vehicle and trip characteristics.

Emissions data for garbage trucks is virtually non-existent. This is partly due to the unique niche that garbage trucks occupy among a substantially larger fleet of over-the-road trucks. And the nature of how solid waste is collected, with vehicles continuously starting/stopping and engines being revved to drive hydraulic systems, makes its duty cycle complex compared to other types of trucks.

As the industry’s fleet composition shifts from standard diesel fueled trucks to dedicated or dual-fuel liquefied or compressed natural gas engines, data from this study can be used to track how such shifts are making waste collection greener. Additionally, the study is the first of its kind to ascertain garbage truck emissions under varying conditions and truck specs, which will help identify how variable truck emissions can be. The study is expected to be completed later this year. For more information, please see the EREF website or call 919-861-6876.