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[GreenYes] health and environmental concerns with anaerobic digestion and biogas

Dear folks:

Some enthusiasm is developing in Minnesota for anaerobic digestion of various wastes.  I share that enthusiasm somewhat but am not finding much about the health/environmental implications.  Some of my concerns are in the email below.  Can anybody point me towards some answers?



[heading deleted]

AD seems to have a lot of potential for managing various waste streams.  But possible health and environmental hazards should be considered in advance using the precautionary principle.

Exposure to nuisances and health hazards could come from several sources including (1) transporting feedstocks to the AD facility (diesel and gas engine exhaust, road dust, traffic accidents, etc), (2) fugitive emissions from the digester itself, (3) exposure to the biogas produced, and its products of combustion, and (4) exposures to the digestate and wastewater produced, including exposures from post-processing of these streams.

However, not much attention is being given so far to the issues of toxic constituents in biogas and its products of combustion, and the possible health implications.   these are the focus of the rest of this brief, non-comprehensive note.

I am not saying these issues are necessarily "deal killers," for AD generally, but I am saying the same level of scrutiny needs to be applied to AD as has been applied to, say, garbage incineration.

For example, wood burning ("biomass") has been widely promoted as a "green" activity.  People have assumed or pretended that wood is a clean fuel.  It isn't.   The permit documents for a proposed wood burner in Minneapolis ("Midtown" project by the Green Institute then Kandiyohi Development Partners) showed the emissions would be around a million pounds per year.  Neither the promoters nor the MPCA presented this information to the community in a meaningful way.  When the community found out the truth, the project went away.  The Virginia and Hibbing biomass burners have apparently been unable to comply with their permits and have been fined.  I am concerned that the MPCA's ultimate response may be to loosed up the permits.

What are the health implications of feeding AD gas into the natural gas distribution system?  People living near a digester might get a high proportion of AD gas, and some of it would be burned in gas stoves and unvented heaters, such that the products of combustion would be released directly into their homes and they would be breathing them directly.

None of the "feasibility studies" of AD that I've so far found have addressed this issue.

We know that households using gas stoves, as opposed to electric stoves, already experience measurable health effects such as increased asthma attacks.

What harmful constituents might be in digester gas, in addition to what is already in "natural gas?"

We know that "landfill gas," a biogas produced by anaerobic digestion in dumps and often misrepresented as a "green" fuel, contains hundreds of different contaminants, many of them toxic and/or carcinogenic.  According to an Energy Information Administration site, landfill gas contains an average of 2,700 ppmv of "non-methane-organic compounds" and 132 ppmv of halides. ( ). 

According to the Agency for Toxic Substances and Disease Registry (ATSDR): "NMOCs most commonly found in landfills include acrylonitrile, benzene, 1,1-dichloroethane, 1,2-cis dichloroethylene, dichloromethane, carbonyl sulfide, ethyl-benzene, hexane, methyl ethyl ketone, tetrachloroethylene, toluene, trichloroethylene, vinyl chloride, and xylenes." (

In 1991 EPA identified health effects from landfill gas including "leukemia, aplastic anemia, multiple myeloma, cytogenic changes, damage to liver, lung, kidney, central nervous system, possible embryotoxicity, brain, liver & lung cancer, possible teratogenicity" ( , Table 2.1)

In the same report, EPA "focused on nine carcinogenic constituents known to be present in MSW landfill air emissions, (benzene, carbon tetrachloride, chloroform, ethylene dichloride, methylene chloride, perchloroethylene, trichloroethylene, vinyl chloride, and vinylidene chloride ....)"

We know that landfill gas produces "hazardous air pollutants" when burned, including dioxins.

We know that landfill gas and sewage sludge digester gas contains siloxanes, compounds that when burned produce finely divided silicon dioxide (sand).  This tends to eat up the innards of engines and turbines burning digester gas, in a way similar to what would happen if you drove a car on dirt roads without an air filter element in place.  (Some interesting images and discussion here: )

Silicon dioxide is harmful when inhaled, and known to cause asthma, bronchitis, silicosis, and possibly lung cancer.   Is AD gas a credible exposure route if siloxane removal is not attended to?  I haven't looked into it enough to know, but I think it is important to know.

Now, people will point out correctly that AD gas is not the same as "landfill gas" and I agree.  I expect that AD gas would tend to be somewhat less contaminated than landfill gas, because the digester feed would hopefully be more controlled than dumping into a landfill.  it might be reasonable to consider LFG as a sort of "worst case" baseline.

But "the devil is in the details."  Incinerators tend to end up taking a wider range of stuff than originally stated, and this might also be the case for a digester.

Another question is how the permitting of a digester would be handled, and where the authority and responsibility would lie.  How rigorous would the permitting be, and would the impacts of digester gas at the points of consumption be fully considered?

Probably answers to many of my concerns exist in the literature.  I'm sure there are other issues I haven't thought of.  Since LHP&L has been looking into AD for some time, perhaps you could point me towards some answers? 

I hope that all those interested in AD can work together.


Alan Muller

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