Digesters and waste food, a proposal

Interesting article on Report Buyer which says electricity could be generated from waste food  about using localised digesters to convert food waste into biofuels.

Digesters are one part of the answer perhaps. Another useful part could be the use of pyrolysis to convert the remaining biomass into gasses. These gases could be burned directly (like old fashioned town gas from coal) or converted into liquid fuel. There would still be the problem of disposing of the ash from this process but the volume would be considerably smaller than the volume of landfill. Such a two-pronged attack on the situation would yield more biofuel than simply digesting and would reduce volume.

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4 Responses to Digesters and waste food, a proposal

  1. Pradeep 24 October, 2008 at 3:30 pm #

    Simon,
    It is a neat idea. A few companies in the US are already doing heat/power from waste. Typical capacities range from 10s of kWs to 1 MW.
    Producing fuels will be more complicated. The main problem here is of scale. Fischer-Tropsch (F-T) synthesis of fuels from syngas (carbon monoxide + hydrogen mixture) produced from biomass/waste pyrolysis or gasification is not very economical at small scales. (For ex: Sasol produces ~16 million barrels of oil equivalent of F-T liquids, annually. In comparison, 1 MW of thermal energy is 0.05 million barrels of oil equivalents/year (accounting for efficiency losses)). Fermentation produces ethanol/alcohols, pyrolysis/gasification steps produce syngas which can be used to make either alcohols (mainly methanol) or CH2- type hydrocarbons. However, recently, a UK based company (Oxford Catalysts) is developing small-scale F-T technology.

  2. Drew 24 October, 2008 at 8:58 pm #

    My understanding is that the refuse left behind has a host of co-product application including fertilizer and heat. Adding a Pyrolysis unit to a Digester is probably more of an economic question then anything else.

    There are loads of articles on German advances on Anaerobic digesters. Turn a corner in Germany and pow, another digester. We haven’t caught up to the Germans yet, but the potential is certainly here, particularly since there are many digesters busily working away at the municipal level cleaning our sewage and leaving the rest of the potential energy uncaptured.

    I caught up to a mobile digester out of the University of Guelph (Canada). The premise is so simple, waste in methane out, but it appears that for the smaller operator, they take time and understanding. Digesters are like living ecosystems. They are healthy and productive when they eat well.

  3. David B. Benson 24 October, 2008 at 11:21 pm #

    The prylosis methods I know about produce heating oils and biochar. No ash, except after the biochar is burnt.

  4. larryhagedon 25 October, 2008 at 10:26 pm #

    Exactly right Simon, again and again I see a need for multiple processes to wring all the goodies from these feedstocks.

    I rather expect to see green algae coming into play again and again as a clean up process. Feed various waste substances from the other processes to the green algae.

    Some of the resulting high protein green algae cake will be used as an additive for people food and animal feed, pharmaceuticals and industrial chemicals, but we will massively overproduce our needs for that, so pyrolysis into gasses for more fuel will be one way of utilizing the last crumbs of the cake.

    larry

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