A paper I co-wrote with Dr. Morton Barlaz titled, “Is Biodegradability a Desirable Attribute for Discarded Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory Model,” has made news recently.
The headlines ranged from the measured (“Study: Biodegradable plastics can release methane”) to the reckless (“Biodegradable products are often worse for the planet”).
The foundation of this research is a life-cycle accounting of the greenhouse gas (GHG) emissions associated with discarding waste in both national-average and state-of-the-art landfills. A state-of-the-art landfill collects the generated methane and beneficially uses it. Only an estimated 35 percent of waste is discarded in state-of-the-art landfills, while about 31 percent of waste is in landfills without any gas collection. The rest is in landfills that collect and flare the gas.
The results of this research show that there are significant benefits to collecting and beneficially using landfill gas. Disposing of mixed municipal solid waste in a state-of-the-art landfill is carbon negative, but disposing of similar waste in a national-average landfill leads to positive GHG emissions. The results of this analysis also show that the more degradable a material is, the greater the GHG emissions it generates when disposed in a landfill.
The best material to have in a landfill, from a GHG emissions standpoint, is one that does not degrade at all.
Reactions to this research have been interesting and varied.
Numerous articles and comments written by anti-environmentalists have tried to use the results to portray environmentalists and environmentalism as naive and/or misguided. This argument is nonsensical when made by those who deny anthropogenic climate change. This research is meaningless if one does not first accept basic climate science. The purpose of the research is to allow us to more effectively mitigate GHG emissions by making informed decisions.
Another common response is that these materials are intended to be composted, therefore our results are irrelevant. But these materials are generally not composted, and most areas of the country do not have the infrastructure for source-separated “compostable” collection and treatment of these emerging biodegradable materials. Therefore, we need to understand the effects of their disposal in a landfill.
An additional response has been that the conclusions were too broad, that we neglected emerging materials (for example, some bioplastics) that do not appreciably degrade in landfills. This argument seems misguided because such materials are not technically biodegradable. The study's only mention of bio-based, non-biodegradable products was to say that it would lead to the least greenhouse gas emissions in a landfill. We also showed that materials that degrade more slowly or to less of an extent lead to reduced GHG emissions in landfills.
It must be reiterated that one needs to analyze the entire life cycle of a product to know if it is better to use a conventional or biodegradable material in its production. One should also look at additional environmental and economic factors (resource conservation, biodiversity impacts, etc.) before making a final judgment.
What the study does suggest is that the best first step is to aggressively collect methane from landfills. Increasing composting infrastructure could also be beneficial if additional life-cycle research shows benefits from composting these materials instead of landfilling.
Finally, this research is a good reminder that one must always take a systemic approach to analyzing complex problems.
James Levis is a researcher and doctoral student at North Carolina State University.