Zimbabwe: Turn Human Waste Into Energy

Source from:  The Herald (Harare) 9 October 2008 10/10/2008

TO many people, the term "biogas" is something they come across sometime in their secondary school education and is quickly forgotten once examinations are over. But there is immense energy potential for the country if biogas is harnessed and used for the development of the nation. Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. One type of biogas is produced by anaerobic, that is without air, digestion or fermentation of biodegradable materials such as biomass manure or sewage, municipal waste and energy crops. According to a Herald report sometime in February this year, the Zimbabwe National Water Authority indicated that it was considering reviving the biogas digesters that have been lying idle at Firle and Crowborough waterworks in Harare to cut down on energy costs. Studies done at the Crowborough site in Kuwadzana revealed that the gas produced has a chemical composition of 66,4 percent methane, 32,2 percent carbon dioxide and the rest hydrogen sulphide. "If revived, the digesters also have the capacity of producing enough energy to drive several other industrial operations that require large amounts of power. "According to water experts, Crowborough wastewater in Kuwadzana, currently consumes almost 215 000 kilowatts each month, costing the water authority billions of dollars yet it has the potential of producing about 12 500 cubic metres of biogas a day," the authority said then. An interesting success story of biogas technology deployment in Africa is in Rwanda. This followed the exponential rise in prisoner population following the 1994 genocide. With some of Rwanda's prisons holding five times the intended number of inmates, it was not surprising that the original septic tanks and settling pools were unable to cope. The appearance and stench was just the beginning of the problem. Faced with these threats, the Kigali Institute of Science and Technology developed a way to convert the human sewage to biogas, thus cleaning up the waste hygienically and creating a sustainable energy source. Talk about killing two birds with one stone. Biomass technology is a very mature and old technology that formalises the decomposition of waste into a fuel (biogas) and some fertilizer (waste). This process is part of the natural carbon cycle of life. Sunlight produces food in plants that we eat and discard as waste. As we have been taught in secondary school, you can neither create nor destroy energy but convert it to one form or another. Methane (CH4) is the combustible component of biogas and on average biogas has about 60 percent methane. Developing countries like Vietnam, Brazil, Thailand, Philippines and, of late, Tanzania and Rwanda have matured and stabilised in this technology. Here is a quick summary of the actual digestion process or decomposition. Anaerobic digestion is one of the most common biological procedures in nature. As the name implies, it means to carry out digestion or breakdown in the absence of air. Anaerobic decomposition will produce methane, carbon dioxide, some hydrogen and other gases in traces, with very little heat. Biogas technology simply formalises the natural decomposition process. Anaerobic decomposition is a two-stage process as specific bacteria feed on certain organic materials at a specific pH level. In the process, the bacteria emit gases, mostly methane. But instead of being vented into the air, they are piped into a storage canister. Depending on temperature and moisture content, it takes about six to 25 days to fully process a batch as temperatures are pretty favourable for this process in most parts of Zimbabwe. The end product is about 60-70 percent methane, 20-30 percent carbon dioxide and small amounts of hydrogen sulphide and other impurities. Constraints of biogas production arise from the production rate limitations. The process of anaerobic decomposition is relatively slow, so production of gas at useful rates requires a large volume of permanent culture. Biogas is not easily bottled and thus must be used near its sources. Thus biogas cannot be produced on an as-needed basis or where-needed basis. Thus it makes economic sense for public municipalities like Harare, Bulawayo, Gweru, Mutare etc to be the initiators of such projects since they own and or operate water/waste management systems. Beyond concerns about sanitation, successful adoption of biogas in the developing world is highly dependent on political, economic, logistical and social factors. It is important that decision-makers understand what this biomass technology is if it is to be rolled out effectively. Like any other technology, adoption is usually problematic. A healthy prospect for Zimbabwe is the development of anaerobic wastewater treatment systems with biomass as a by-product. There is no shortage of raw materials to be used as stockfeed as we are aware that some urban centres in Zimbabwe are literally flowing with raw sewage. Biomass technologies will not totally eradicate power shortages in Zimbabwe, but will go a long way in alleviating Zesa of its burden if executed properly. Municipalities, hospitals, prisons, colleges, schools etc should seriously consider adopting this technology, which is already being used in various parts of the world. It is not a question of its suitability and cost effectiveness, but a question of whether the decision-makers have enough vision to comprehend the advantages of biomass technologies. It takes one to two cows, five to eight pigs, or four adult humans to supply adequate daily feedstock for a single-household biodigester, according to a United Nations Development Programme Global Environment Facility fact sheet. Hence the use of biodigesters makes sense for institutions like prisons, hospitals and colleges where human population density is higher than elsewhere. The cost per unit of energy over a digester's 15 to 20-year life cycle is lower than both solar electrification and the cost of extending a conventional electrical grid. For agriculture, this is particularly crucial to the farmers who need energy and/or electricity to process their produce or to cure their tobacco. The departments responsible for energy must think outside the box in Zimbabwe and tap into this very old but very stable technology. There are some biomass plants somewhere in Chishawasha that were installed as far back as 1979. Many organisations have been rolling out biomass plants in Africa for years now and there is no shortage of technology or funding for such projects. What has remained elusive is commitment, focus and accountability on the part of developing countries. Biomass digesters, which can be plastic containers or made out of brick and cement, range in cost from US$400 to US$1 500 depending on type and capacity. There are many designs of biogas plants that are available, but the most common are the floating canopy (Indian) and fixed dome (Chinese) models. The polyethylene tubular biodigester technology is a cheap and simple way to produce gas for small-scale farmers. It is appealing to rural people because of the low cost of installation and, therefore, of the gas, and the improvement in the environment that the installation allows. It can be applied in rural or urban areas, both in low and hilly lands. We need to confront the problems that face us at the same level at which they occur. Naturally, pessimists and critics alike might think that these efforts are far fetched since the economy has challenges. But no one has ever considered that the present economic under-performance could actually be a result of looking for solutions in the wrong places while failing to see the things that are right under our noses. If we fail to turn around the economy, we have no one to blame but ourselves. We do not stop planning and building for the future just because there is a political impasse. Human waste may be a stinky business, but to some it smells like money! Enditem