Wednesday, November 3, 2010

Dioxins from WTE and coal-fired plants

QUESTION SENT TO Nickolas Themelis (NJT):

Dear Dr. Themelis,

My name is Nathan Walker and I work as an Environmental Scientist for the Shoshone-Bannock Tribes in SE Idaho. I have recently been doing research regarding waste to energy technologies for the tribes and just finished reading your 2009 Waste Management article entitle Waste-to-Energy: A review of the status and benefits in USA. I enjoyed the paper and found it informative, but was left with a nagging question that I thought you might be able to answer. The majority of the figures used to compare WTE technologies to fossil fuel energy production, especially coal, were not normalized to anything. For example, when you talk about dioxin emissions you attribute 12 g/year to WTE and 60 g/year to coal fired power plants, but fail to take into account how much coal and MSW was burned, or how many kWh were produced. If the mass/year emissions values were presented as mass/year/kWh, or mass/year/ton, or simply as a concentration of flue gas would the MSW emission values continue to hold up? I appreciate your time and look forward to your response.

Nathan Walker

Dear Nathan, there was no intention to castigate coal plants for dioxin emissions because both they and the WTE plants emit very little (by now 6 grams TEQ for WTEs and about 60 g TEG for coal fired power plants). The big dioxin emitter now according to EPA is "backyard barrel burning" (fireplaces, burning grass, etc. etc.,) amounting to about 550 grams TEQ, plus all the fireworks on the 4th of July. Even that 550 grams is insiginifant for a country the size of the U.S.

You cannot compare energy from coal and MSW because coal has about three times the energy of MSW, ton per ton. MSW is a poor fuel and the primary puropse for incineration is to get rid of the MSW with energy generation being a definite plus and much preferable in most urban settings to landfilling.
The U.S. combusts 30 million tons of MSW and about 900 million tons of coal (last time I looked it up some years back) so, ton per ton, MSW emits more dioxins than coal but both levels are insignificant as far as environmental/health effects are concerned. Regards NJT


  1. If we extract as much energy from waste as from coal, coal will emit lesser dioxins, but coal has to be mined, it is non-renewable and is a proper homogeneous fuel as compared to waste which is highly heterogeneous mixture which needs to be gotten rid off. Also, waste as a fuel is partly renewable.

    Main objective is to get rid of (manage) waste (as a resource). Energy is only a positive as explained in the post.

  2. When framing an argument for the benefits of WTE over landfills, it is beneficial to consider the dioxin, mercury and CO2 emissions of coal per kWh to show how much each ton of MSW incinerated can offset electricity generated by coal. This offset can be combined with estimated emissions from landfills per ton of MSW and compared to modern WTE facility emissions per ton of MSW showing the true benefit of MSW incineration.

    While doing a research paper, I too had this question and was unable to find it stated outright. I was able to find a generalized value for the amounts of dioxin, mercury and CO2 produced per ton of coal by combining data from several sources including The EPA, The Department for Environment, Food and Rural Affairs (DEFRA) and Natural Resources Defense Council (NRDC).
    I used the following-

    19.73 mmbtu per short ton coal- electric power sector 2009, source- (4 April 2014, EPA)
    19.73 mmbtu = 5786.7541944444 kWh per short ton coal at %35 efficiency, (Jeffrey Morris)
    = 2023.8025 actual kWh per ton of coal (this value will vary from facility to facility or if calculated from a different source)
    .078 ng/kg - dioxin in ng per kg of coal source- (EPA/600/P-03/002F November 2006)
    1 ton coal = 907.185 kg coal
    .078 ng x 907.185 kg/ton = 70.76043 ng dioxin per short ton of coal burned
    70.76043 ng dioxin/2023.8025 KWh
    0.0349640985225 ng dioxin per KWh of coal burned – rounded .035 ng dioxin/KWh from coal burning

    Mercury emissions rate = pounds of mercury per gigawatt hour (GWh) of electricity produced from coal -source- (Emissions of the 100 Largest Electric Power Producers, M. J. Bradley & Associates. (2012))
    .03 lbs/GWh average, 1 lb = 453.592 grams, .03 lbs = 13.6078 grams, 13.6078 g/GWh, 1GWh = 1000000 KWh, 0.0000136078 grams/kwh, 13607.8 ng/KWh or .0000136 g/kwh from coal burning

    2224 lbs CO2/MWh average of 100 coal plants (Emissions of the 100 Largest Electric Power Producers, M. J. Bradley & Associates. (2012)) data from 2010
    2.224 lbs CO2/kWh covert to kg- 1.0087894 kg CO2/kWh average or about 1 kg CO2/kWh from coal burning