Large scale human powered Biogas production: A solution whose time has arrived
The average human body produces .696 kilograms of solid waste every day, that’s 248 kilograms a year and 18,626 kilograms a lifetime (75). The city of Johannesburg in South Africa was home to 3,225,812 people in 2001, which would mean Joburgers on average produce over 2,245,165 kilograms of solid human waste every day. Waste being the operative word here because that’s what we do with it, we waste what is potentially a huge amount of energy and add to global warming at the same time by doing so. To understand how much potential energy is being wasted we must go to prison in Rwanda.
In 1997, The Kigali Institute of Science, Technology and Management (KIST) was formed in Rwanda to address the serious loss of professional manpower. In 2005 it was awarded The Ashden Award for Sustainable Energy for the large scale innovative implementation and use of a biogas system within the Rwandan prisons. The average Rwandan prison holds 5,000 people who together produce 50 m3 of toilet waste water per day. This is waste water is channelled into a 500 m3 capacity biogas system and produces a whopping 250 m3 of biogas per day.
Now although in the Rwandan systems the biogas is almost exclusively burnt for heat energy and accounts thus for a saving of over 60% in wood fuels, it also has the potential to produce electricity through natural gas generators. Approximately .6 m3 of biogas is needed to generate 1 kilowatt-hour (kW-h) of electricity in a gas generator system; this means in a single day one prison of 5,000 people could produce over 416 kW-h. Which bring us back to Johannesburg in 2001 which according to these latter figures could have been potentially producing nearly 161250 m3 of biogas per day or 268,750 kW-h/day. If we take the recent highest monthly electricity consumption for the whole of South Africa which was 20 631 Gigawatt-hours (GW-h) in July 2007, the biogas/electricity from Johannesburg alone could have accounted for 8,331,250 kW-h of that, or roughly 8,33 GW-h or .04% of the national monthly consumption for July at is highest peak. So why is this not the case, why is human and even animal biogas potential not exploited to the fullest extent possible? Are we so prudish and vain as to let this valuable resource literally go down the drain?
Biogas is not a new technology but is has for the most part been sidelined in the face of oil and natural gas resources. Whether this is just because of a seeming cheapness of oil and our carefully cultivated addiction to a petro-based economy, or has a simple prudish revulsion to using anything generated from our own waste or both, is debatable. To be sure it is not small scale biogas production I am talking about, that has proliferated, in China alone there were an estimated 7-10 million rural small scale biogas units in use by 1978. India and especially Nepal today make great use of rural small scale biogas units for primarily for heat and sometime electricity production. But whilst this is an important gain for global warming and less reliance on oil/coal etc. it has remained for the most part a small scale rural endeavour.
This is a point against biogas in being thought of only as a small scale rural solution that is until Rwanda. By the very nature of the required inputs into a biogas system it thrives on large consistent raw materials to feed the anaerobic reaction. It is a case of the more the better, the more efficient the system can become. And what can be more voluminous and consistent that the human waste from any city, as opposed to a small village which would need substantial extra inputs from farm animals to keep the system going.
In Rwanda for heating use alone a 500 m3 biogas system for a single prison cost only 50,000 pounds in total. A prison of 5,000 people before biogas used 50 m3 or 10 tonnes of wood per day. They cut that consumption in half with their biogas system or saved roughly 10,000 tonnes of carbon dioxide from being released and adding to global warming through the burning of wood. Which is great but we are after electricity here not just heat energy and that means adding two more steps to the process. First the gas must be cleaned of all impurities and this cost’s quite a bit more, but why does it need to be cleaned? Well that’s the next step the generating of electricity by the use of gas powered generators which require a cleaner grade of natural gas to function efficiently. And it’s these two steps combined with an unnecessary relegation that seem to keep biogas out of the larger picture, though I suspect it will not be for much longer.
Rwanda and KIST have laid down the blue prints for large scale biogas production. They have proved that all our cities and the lakes of sewage we pour out everyday are potential energy goldmines. If I take South Africa’s three main cities Johannesburg, Cape Town and Durban with a combined concentrated population or captive energy source of about 9,465,862 people (2001). In biogas terms these three cities could have potentially produced roughly 24,451,250 kW-h per month or 293,4 GW-h a year, back in 2001. And in a wholly sustainable and environmentally friendly way, because that’s the thing about human city biogas, it is a clean daily renewable energy resource and carbon neutral.
If more time and money is applied toward the research of large scale biogas systems for better converters, gas cleaners and more efficient gas powered electrical generators, these numbers can only get better. With a world population that’s out of control and our cities growing larger by the day combined with peak oil and climatic change it would seem the time has come. Time to get over any inhibitions we might have in using our own waste and to start seeing past the faded and cracked petro-based economy/dream. It is time to wake up before it is really too late and the damage is irreversible, we have all the tools and resources we need at our finger tips to do so, and biogas is one of them.
