Wednesday, June 29, 2011

Response to criticism of biodegradability paper

Waste & Recycling News has a new post up criticizing the paper that I co-wrote with my advisor Dr. Morton Barlaz entitled Is Biodegradability a Desirable Attribute for Discarded Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory Model. The criticisms are from the Berlin-based European Bioplastics BV. Their main criticism is that the conclusions reached in the study are too broad. I would argue that they interpreted the results of the study too broadly, and that their criticisms are not aimed at things actually said in the study. They start by saying:
There are bio-based, non-biodegradable bioplastics -- such as bio-based versions of PET and polyethylene -- that do not produce methane because they are not biodegradable, explained the association. They, however, constitute a significant proportion of the current bioplastics production.
Firstly, it should go without saying that “non-biodegradable plastics” are not biodegradable, and therefore not being referenced in the title of the manuscript. Secondly, our study's only mention of bio-based non-biodegradable products was to say that they would lead to the least greenhouse gas emissions in a landfill.

From the paper:
These results suggest that for a national average landfill, in which not all gas is collected and converted to energy, optimal performance would be achieved for biogenic materials that are recalcitrant under anaerobic conditions.
So, these materials are out of the scope of the question asked in the title of paper, and we still addressed the fact that they are preferable from a greenhouse gas emission standpoint. Perhaps, instead of criticizing our work they should be highlighting the fact that we have shown the benefits of bio-based, non-biodegradable plastics which "constitute a significant proportion of the current bioplastics production".

Their second point is similiar:
In addition, biodegradable and bio-based materials do not all behave the same way under landfill conditions.... In sanitary landfill the moisture level is low and not conducive for biodegradation as shown by some studies.
Once again we have a problem of definitions. The U.S. FTC states that claims of "biodegradable or photodegradable should be substantiated by competent and reliable scientific evidence that the entire product or package will completely break down and return to nature, i.e., decompose into elements found in nature within a reasonably short period of time after customary disposal". I do not see how a compelling case can be made that a material that is in a landfill is "not conducive for biodegradation" degrades "within a reasonably short period of time after customary disposal". Landfills may not be considered customary disposal of these materials in Europe, but that is certainly not the case in the U.S.

Finally, they also say that we did not consider "the fact that, compared with other waste going to landfills and potentially emitting methane, bioplastics only enter landfill in very low amounts" which is totally irrelevant for a couple of reasons. Firstly, our calculations were performed on a per mass basis, which means we calculated the amount of greenhouse gas emissions per ton of waste discarded in a landfill. Therefore, it makes no difference that other waste materials are landfilled in greater amounts. Secondly, it's irrelevant from a planning perspective because we can't substitute biodegradable plastics for food waste or yard waste or paper, which constitute traditional biodegradable materials. The fact that some of those materials may emit more methane (which we quantify and discuss in the paper), is completely irrelevant since those materials perform completely different functions. People can't substitute food for bioplastics, so it doesn't matter from a decision standpoint that food waste may lead to more emissions. In the end, the first step to rectifying both problems is aggressive landfill gas collection as was stated in my first post on the subject.

Cited Literature

  1. Levis, J. W., Barlaz, M. A. “Is Biodegradability a Desirable Attribute for Discarded Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory Model” Environ Sci Technol, 2011, doi: 10.1021/es200721s

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