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[GreenYes] Re: Anaerobic digestion vs. landfill methane

Hi Dennis ~

Our county owns a typical "dry-tomb" landfill, and recovers methane gas to produce electricity, for which revenues exceed a million dollars a year. So, when there was discussion about recovering food scraps for compost or other uses, there was a concern about the potential loss of revenue at the landfill.

What we found is that the diversion of food scraps would have a negligible, if any, effect on the gas recovery revenue and would help the environment. This is due to the fact that food scraps have a half life of decomposition of between 6 months to 18 months, and, in a dry-tomb landfill, the gas extaction wells are not extended to the waste until it has been in place for at least 5 years, to avoid the suction/infiltration of oxygen. Thus, the food has largely decomposed by that time -- for example, if the half-life is 1 year, then after 1 year, only half is left, after 2 years, only a quarter, after 3 years, 12.5%, after 4 years, 6.25% and after 5 years, 3.125%.

The landfill will go anaerobic a few months after the waste is buried, and the methane that is produced prior to the gas extraction system being extended will probably largely go to the atmosphere, where it will contribute to global climate change. In addition, the food causes the landfill to enter an acid phase during its decomposition, and this acid dissolves out heavy metals that go into the leachate, causing problems for leachate treatment. Finally, it is the food that results in most of the landfill odor and bird and vector problems. Our conclusion was that it was benefical to divert the food scraps.

On the other hand, we also found that there are serious negative environmental consequences from setting up a household food collection program. We thus recommended encouraging better food management to produce fewer residues and on-site composting. Each spring, we hold composting seminars, have a booth at our garden show and sell compost bins. We are currently involved in a feasibility study for a livestock manure management system, and are considering the addition of food scraps, but only from food processors where there are not higher and better uses.

I hope that this helps. We would be glad to send you our food scrap recovery study.

Best wishes,

John Reindl, Recycling Manager
Dane County, WI

>-----Original Message-----
>From: GreenYes@no.address [mailto:GreenYes@no.address]On
>Behalf Of Dennis Sauer
>Sent: Wednesday, October 25, 2006 4:01 PM
>To: GreenYes
>Subject: [GreenYes] Anaerobic digestion vs. landfill methane
>I'm working on a proposal to build an anaerobic digester facility that
>would accept source separated food waste from businesses and schools
>and manure from local dairy farms for methane gas fired cogeneration.
>A landfill in our region generates energy from landfill methane and is
>in the process of expanding generating capacity. Some who support that
>effort argue that our proposed facility would, in essence, be taking
>potential feedstock from the landfill facility.
>Can anyone direct me to information and data pertaining to the benefits
>of source separation and AD vs. landfill gas capture to aid me in
>articultaing a response to that claim?
>Thanks in advance.

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