Saturday, 15 December 2012

From cesspit conundrum to cooking fuel - Bahama school's biogas solution

© Copyright 2012 by
Waste disposal is a big problem when you're living in a confined space - and human waste doubly so. Without integrated sewage transport and treatment systems, some of the world's smallest islands struggle to deal with the noxious contents of septic tanks - especially when the waste burden from visiting tourists is taken into account.

But that mountain of human manure can be a veritable gold mine of renewable energy. Biogas can be harvested from such waste, and this can be used to power and heat homes - and even do the cooking. And it's the kitchens of Bahama's Eleuthra Island School that are one of the most recent beneficiaries of this full-circle thinking. The campus has just received its first biogas stove, donated by Cape Eleuthera Institute, an ecological research organisation.

The Institute is dedicated to developing ecologically-sensitive self-sufficiency solutions. Human waste disposal has been an environmental concern on the long slither of  island paradise that is Eleuthera. Cesspit contents are often stored in underground dumps, where there is a risk of leaching into the island's precarious freshwater reserves. But biogas production - which happens in sealed anaerobic biodigester units - transforms this disposal headache into both a useful energy sources, and a nutrient-rich fertilizer.

With organic fertilizer one resource that is often scarce on small islands, the biogas generation unit on the Island School can add another green feather to it's cap. By displacing expensive imported inorganic fertilizers, nitrate pollution can be reduced, and the islands nutrient-poor soils enriched - all from a low-cost indigenous source. It also helps make Eleuthera more self-sufficient.
As Island School's head Chris Maxey told The Bahamas Weekly: “Now we will literally be taking human waste and processing it into a safe and inexpensive form of energy that we can use to cook our food. And, we will be doing it all on-site, on our campus. What is more energy-independent than that?”


  1. (hint) For long lastin "Dark" Soil

    Mix Biochar with the resulting SLurry
    (from digester). It hold minerals and
    water (last refuge), helping plants
    grow faster, stronger.

    Biochar (see:

    and keep the other fuels (with biochar)

    example: (California)

    * works with any dry agro-waste

    Retired. Biochemistry, Systems, Economics,

  2. Very interesting point Jospeh.

    I've been following developments on these two approaches to unlocking the potential of various waste feedstocks (ie biochar & anaerobic digestion) for a while - but hadn't occurred to me that they could be complementary!

    What I'd be interested to investigate further, with biochar, is the effect on the total nutrient cycle for a range of soils. You're extracting plant wastes, but returning only the carbon. I know biochar has produced interesting results for nutrient-poor tropical soils, but would love to know results on acidic volcanic soils, for example. I'll check out those links


    1. I can imagine that compost/ biogas sludge is better for the soil than biochar. More food for bugs, more biological activity.