Tuesday, October 25, 2011

Word Cloud!

This is the tag cloud generated from the abstracts of my first four published journal papers. I hope to add a submitted paper to it soon. The word cloud was generated by Wordle

Wednesday, September 14, 2011

Looking for composting data

As part of the project I am working on for my dissertation (which I hope to write about soon), We are currently developing a publicly available life-cycle optimization model capable of analyzing solid waste management (SWM) performance – at both the individual process and integrated system levels – taking into account implications of greenhouse gas (GHG) mitigation policies and competing SWM objectives (e.g., costs,
emissions, and diversion targets). This life-cycle model is intended to estimate the costs, emissions, and environmental impacts associated with the processes (e.g., collection, separation, waste-to-energy, composting, anaerobic digestion, landfilling) that constitute the SWM system.

As part of this research we are developing and updating life-cycle models for composting operations. In order to ensure that our models are as accurate and up-to-date as possible we are trying to collect data from composting facility operators. Identifying information is not required and will not be shared if provided. The plan is aggregate
the data from a number of facilities to provide an up-to-date life-cycle model for composting operations.

If you would like to share any information or data that you have please visit this link. Feel free to share this link
with others that may be interested. The final composting model as well as the entire life-cycle optimization model will be publicly available upon completion. Please, email me if you have any questions orcomments.

Friday, August 12, 2011

Support the James Webb Space Telescope

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The James Webb Space Telescope (JWST) is meant to be the successor to the Hubble Space Telescope, which has peered further into the universe than any other scientific instrument to date and brought us hundreds of breathtaking pictures such as the Hubble Ultra Deep Field (HUDF) shown to the right. At several different times I have used the HUDF as a desktop wallpaper because I find it so inspiring. Every speck on that image is an entire galaxy, consisting of up to hundreds of trillions of stars each. It is also the furthest back in time that we have ever seen. The image shows what this tiny portion of the universe (roughly one thirteen-millionth of the total area of the sky) looked like approximately 13 billion years ago. It is an amazing glimpse of the magnitude of the universe that we inhabit, and I firmly believe that the Hubble is one of the greatest achievements of mankind in my lifetime. 
The JWST is an even more powerful space telescope with a planned launch in 2018. It will be able to see even further and earlier than the Hubble. From NASA:
Webb will find the first galaxies that formed in the early Universe, connecting the Big Bang to our own Milky Way Galaxy. Webb will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System.

Source
Unfortunately, the JWST is under threat of cancellation by Congress. In a short-sighted move the House Subcommittee on Commerce, Justice, Science and Related Agencies voted July 7 to cut funding for the telescope. Luckily, the full House and Senate have yet to vote to cancel funding for the JWST, so there is still time to influence votes. Northrop Grumman who is the lead contractor on JWST has a great tool for contacting your representatives to ask them to support the JWST. There is also a Facebook community devoted to saving the JWST. I would like to urge everyone reading this to do at least contact their representatives to show their support for continued scientific innovation and inspiration.

Thursday, July 7, 2011

Response to Statement by the Biodegradable Products Institute about the biodegradability paper.

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I found a statement by Steven A. Mojo, Executive Director of the Biodegradable Products Institute (BPI) about 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 that is patently false:
First, the author, James Lewis,[sic] leads the reader to believe that since a biobased material will quickly biodegrade under aerobic conditions, such as composting, that it will also do so under the anaerobic conditions found in landfills. 
Firstly, all publicity is good publicity IF they spell your name right. Secondly, this statement is not at all based in fact. Our results for the methane generation from PHBO were based on anaerobic reactor studies of PHBO published in Biomacromolecules in 2002 (Federle et al, 2002). We spend 400 words describing exactly how this was done in the section of the paper entitled Modeling of Individual Waste Components. Claiming that we used aerobic composting decomposition data or results to model anaerobic degradation in a landfill is completely false and clearly contradicted by the actual paper in question. I really hope that someone at BPI reads this and corrects the statement. 
His only other argument is that biodegradable plastics are a minuscule part of the waste stream, so their emissions aren't important. I rebutted that argument in my previous post:
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.
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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
  2. Federle, T. W.; Barlaz, M. A.; Pettigrew, C. A.; Kerr, K. M.; Kemper, J. J.; Nuck, B. A.; Schechtman, L. A. Anaerobic biodegradation of aliphatic polyesters: Poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) and poly(epsilon-caprolactone). Biomacromolecules 2002, 3, 813–822.

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.

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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

Tuesday, June 7, 2011

Is biodegradability a beneficial attribute for discarded solid waste?



A 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" has been making the news lately. The official press release can be found here. From what I've seen, a variety of people have taken the results to support a number of pre-conceived notions. But, I'll address that in a future post. I want this post to focus on what was done and what the results show.

Greenhouse gas flows in a landfill.

The foundation of this study is a life-cycle assessment (LCA) of the greenhouse gas (GHG) emissions from discarding waste in both national average landfills and state-of-the-art landfills. A state-of-the-are landfill is one where the landfill collects the generated methane and beneficially uses it. This LCA consisted of adding up all of the GHG emissions associated with every step of landfilling. The fundamental equation for determining the total GHG emissions from landfilling is shown below and is essentially a restatement of the image above (Sorry the equation is in picture form. I need to learn how to do equations in html.).


The units in each term of the equation are kg. Fossil fuels are used in the construction, operations, final cover, leachate management, and long term monitoring phases. These only amount to about 7 kg CO2 equivalents* (CO2e), though and aren't very important when compared to the other terms.

Source EPA
Fugitive methane is very important and pretty interesting from a modeling standpoint. But, I want to cover landfill gas modeling in a separate post. Basically, different materials decay at different rates, and landfills that collect gas tend to increase their collection efficiency over time. Collected methane is assumed to be destroyed with near 100% efficiency. It is also assumed that 10% of the methane passing through the soil will be oxidized to CO2, which is similar to combusting it, but is done by aerobic microbes. This 10% level is pretty conservative though, other studies have put the number at anywhere between 20-50% (Chanton et al., 2011). So, the methane that isn't collected or oxidized is emitted to the atmosphere.

The next major component is the electricity offsets. The EPA estimates that 69% of waste is in landfills that collect methane. About half of this waste is in landfills that beneficially use the methane. The others just flare the methane, which converts it to CO2. For this study we assumed all of the beneficially used methane was used for electricity generation. The electricity offsets are then due to the avoided emissions from the electricity that subsequently was not produced at either coal or natural gas plants. We only considered coal and natural gas because they are the two sources that can cost effectively adjust to changes in electricity demand. The marginal costs of nuclear and hydro are just too low for it to make any sense to reduce their output due to the availability of another source. So, we then assumed that our offset electricity was composed of 72% coal and 28% natural gas because this represents the adjusted national split. This leads to an offset of 1.02 kg CO2e per kWh.

The final component is the landfill carbon balance is carbon storage. Typical materials in solid waste do not fully degrade under anaerobic conditions (i.e. without oxygen). Since most of the typical materials that degrade at all are biogenic (i.e. plant or animal based) the carbon in those materials was recently removed from the atmosphere as plants were growing (e.g., trees for paper and food crops). This carbon is then considered sequestered in the landfill and will remain there as long as the landfill is undisturbed. On geological time scales this material could form peat or perhaps lignite. The amount of carbon stored for each material was measured based on previous laboratory studies (Staley and Barlaz, 2009; Federle et al., 2002).

So, what happens when you put all of these components together? The main results are shown in Figure 1 of the paper (reproduced below with modifications).
Greenhouse gas emissions from materials disposed in national average and state-of-the-art landfills. (Units and colors have changed for readability).
As I stated above, a state-of-the-art landfill is one where gas is collected and beneficially used. What these results really show that has been ignored by a lot of the articles that have reported on this study is that there are huge benefits to be had from collecting and beneficially using landfill gas. Disposing of mixed MSW in a state-of-the-art landfill  is actually carbon negative, but it is currently slightly positive using our current national average landfill infrastructure. Actually, all of the materials except for food waste have negative carbon emissions in a state-of-the-art landfill. This is fairly low hanging fruit for greenhouse gas mitigation efforts. So, when reporters have asked what consumers should do, the first thing that comes to mind is to ensure that their local landfill collects the generated methane and beneficially uses it if at all possible.

The main result that has been reported is an analysis of the effects of decay rate on greenhouse gas emissions in a national average landfill. Essentially, we exercised the model with 4 different theoretical biodegradable materials, and plotted the greenhouse gas emissions from disposing of those materials in a national average landfill as we vary the decay rate (i.e., how quickly the material releases its methane). The results of this analysis are shown below.
Greenhouse gas emissions from hypothetical biodegradable materials versus decay rate.  (Units and colors have changed for readability).
It is the results in this figure that have been widely reported for two reasons. Firstly, it shows that the more degradable a material is, the greater the CO2 emissions are from it. Basically, this means that degrading and generating methane is worse than just storing the carbon in the landfill. It also shows that a slower decay rate also leads to decreased greenhouse gas emissions. The best material is the one that does not degrade at all. It should be pointed out that this is for a national average landfill. The results would be somewhat different for a state-of-the-art landfill, but it can be easily shown that degradation of a carbohydrate or any degradable material with a hydrogen:oxygen atom ratio of 2:1 always leads to increased greenhouse gas emissions versus its non-degradable counterpart with standard electricity conversion efficiencies. Essentially, even with 100% gas collection the electricity offset is not large enough to offset the carbon storage.

It is this analysis that has led to headlines about biodegradable materials being bad for the environment. I would say it shows that there are negative global warming impacts associated with disposing of  biodegradable materials in landfills. One would need to study the entire life-cycle of the material to know if it was better or worse than the alternatives. One should also look at other environmental factors (i.e., resource conservation, biodiversity impacts, etc.) before making a final judgement. What this study does suggest is that the best first step is to ensure we are aggressively collecting methane from landfills. Increasing composting infrastructure could also be beneficial, and the development of non-degradable materials from biogenic sources may also be beneficial and worth further study. In the end, one must always take a systemic approach to analyzing complex problems.

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*kg CO2e = 1 x kg fossil CO2 + 25 x kg methane - (44/12) kg C stored

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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
  2. Chanton, J.; Abichou, T.; Langford, C.; Spokas, K.; Hater, G.; Goldsmith, D.; Barlaz, M. A. Observations on the methane oxidation capacity of landÔ¨Āll soils. Waste Manage. 2011, 31, 914 925.
  3. Staley, B. F.; Barlaz, M. A. Composition of municipal solid waste in the united states and implications for carbon sequestration and methane yield. J. Environ. Eng. -ASCE 2009, 135, 901–909.
  4. Federle, T. W.; Barlaz, M. A.; Pettigrew, C. A.; Kerr, K. M.; Kemper, J. J.; Nuck, B. A.; Schechtman, L. A. Anaerobic biodegradation of aliphatic polyesters: Poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) and poly(epsilon-caprolactone). Biomacromolecules 2002, 3, 813–822.

Saturday, April 2, 2011

Discussion of the safety, risks, and future of nuclear power

Fukushima-1
The The Sydney Morning Herald ran an editorial piece looking at the opinions of four experts on the safety, risks, and future of nuclear power. The whole piece is definitely worth a read, but I just wanted to go through some of the main points made and give my own opinion as well.

The first expert is Ben Heard, who is the director of ThinkClimate Consulting. I think he most mirrors my own thinking, saying
Rationally, we should all fear climate change. It threatens our occupation of this planet within a century. This, rather than nuclear power, is what keeps me awake at night.

The biggest contributor to climate change is coal. Renewables alone cannot displace coal quickly enough. But nuclear power plus renewables can, with minuscule risk. The only rational response is to be open to the further deployment of nuclear power, in partnership with growth in renewables.

The second commenter is Ian Lowe, who is president of the Australian Conservation Foundation. He agrees that climate change is a huge concern, but thinks the nuclear just isn't worth the risk.
By contrast, we do not have to worry about terrorists stealing wind turbine blades or earthquakes shattering solar panels. It is quite rational to see nuclear energy as a high-risk approach.
Things may be different in Australia, but I disagree with this because the real comparison is between nuclear and coal. Nuclear and coal both provide baseload power, and a shift away from nuclear, especially in this political climate is a shift towards coal. And, I haven't seen anyone make the case that the risks associated with coal are less than those associated with nuclear. According to the Clean Air Task Force:
Specifically, Abt Associate’s analysis finds that fine particle pollution from existing coal plants is expected to cause nearly 13,200 deaths in 2010.  Additional impacts include an estimated 9,700 hospitalizations and more than 20,000 heart attacks per year.  The total monetized value of these adverse health impacts adds up to more than $100 billion per year.
And this doesn't even include the climate impacts associated with coal use or the damage done by mountaintop removal, or the risks that coal miners face everyday. It was only a year ago this week that 29 coal miners died in the Upper Big Branch Mine in West Virginia, and that certainly lead to an international discussion about whether we need to shutter global coal plants. It's also been well documented that living near a coal plant will lead to higher radiation doses than living next to a nuclear plant operating under U.S. regulations.

The third expert is Ziggy Switkowski, who is chancellor of RMIT University and ANSTO's former chairman. I tend to agree with his assessment as well, since he essentially says that nuclear power has risks, but those risks are not unacceptable. He unfortunately doesn't provide any basis for comparison, though.
Experts will identify opportunities for improvement, and conclude that the best option for clean, industrial strength base-load power remains nuclear energy.
Finally, the last commenter is Beverley Raphael, who is a psychiatrist and international expert on the impact of disasters on mental health. She focuses mostly on understanding the psychological and sociological foundations of Japan's nuclear fears. She also rightly points out that people don't tend to quantitatively evaluate risk. We assess risk on a very emotional level. I don't really disagree with what she says, and her viewpoint is interesting, but it avoids the real question in my mind about what the future of nuclear power should be and how acceptable the risks actually are.
We all live with risk. We pursue risk as "thrill". Life involves the balancing of risks for the present and the future. This is part of our resilience, as individuals, as nations. We feel for, and with, the people of Japan, for whom such threat is so painfully evocative of their history.