1. Fundamentals The main principle of anaerobic digestion technology is to feed biomass, including particular waste materials and byproducts (agricultural wastes; kitchen scraps; feces, organic wastes) into a closed container, the biodigester. In the absence of oxygen, this digestion material is converted into high-value fertilizer humus, and pathogenic germs are eliminated at the same time. The bacteria involved in this process produce a biogas mixture composed of 35% carbon dioxide and 65% methane.
Biogas can be used as an alternative source of energy in many ways. The whole system works without any external energy input.
2. Areas of use For a very long time, biogas units used to be regarded only as sources of energy for cooking, baking, and lighting. However, because it is capable of converting waste material into germ-free fertilizer, anaerobic digestion technology is predestined to be used also in the treatment and clarification of wastewater, in the field of sanitation in general, and in particular in the treatment of organic waste from households, hospitals, and agricultural production including abattoirs.
These aspects of using anaerobic digestion or fermentation technology for reasons of hygiene and environmental health have become increasingly relevant and popular in recent years.
2.1 Thus, anaerobic and biogas systems have been very successful in environment-friendly sewage disposal from hospitals and other community facilities. Before reaching the biodigester, the wastewater is separated mechanically / hydraulically from the solid matter and runs into a clarification pond or over a reed bed for treatment.
The anaerobic process is already going on a few millimeters under the water surface so that there is no odor nuisance. The water is then used for irrigation of gardening and crop farming areas, and thus fed back into the natural cycle. The solid matter (feces, placentas, etc.) is sucked into the biodigester using the hydraulic control device, and there undergoes anaerobic digestion. The average retention time of 100 days guarantees a high degree of substrate hygienist. The substrate can then be applied as a fertilizer on fields, gardens, orchards, etc., and this aspect of the technology is becoming increasingly accepted and popular. The best indicator of a well-functioning biodigester is the production of biogas. The proper use of a biogas unit can be an important contribution to an improved economic and ecological balance of a hospital. Biogas is a valuable by-product of wastewater treatment and is used as a source of energy for a variety of purposes, including, for example, the cooking of meals, the heating of water in laundries, and, to an increasing extent, the baking of bread. In all these cases, biogas effectively replaces vast amounts of firewood. As soon as people become aware of the opportunities and advantages involved, biogas tends to serve as a strong motivating factor for the whole system. Hospital management starting to look into possibilities of further increasing their biogas energy production are a more and more frequent occurrence. This awareness-building process is of course very welcome, and also produces rather surprising spring-offs. For instance, the purified wastewater may be used, among other things, to irrigate lawns or parkland areas; as a result, more grass will grow and these areas, which, after appropriate shredding, can, in turn, be fed into the biodigester, and will thus bring about an enormous increase in biogas production.
2.2 As with all disposal problems, however, top priority must be given to bringing down the levels of wastewater produced by introducing appropriate water-saving measures. This means, for instance, putting an end to using fresh and drinking water to flush toilets. Indeed, the water from kitchens, baths, and wash – basins can be used again to flush sewer toilets, thus reducing freshwater requirements for sanitation purposes by up to 50%! The used water is fed into an underground tank and, as required and using an appropriate control, the device is allowed to flow through a trench under the latrines. As a result of the way the trench is designed, only a fraction of the amount of water required per person for the use of flush toilets will be necessary to make the contents of the latrines are properly washed towards the biodigester. The control device will prevent the trench from running dry so that even in the event of a water shortage for several days there will be no odor nuisance and the system will not block up.
2.3 Biogas units for smallholding peasant families in the so-called Third World have been praised as an ideal improvement for many years because they allow people to save firewood and produce organic fertilizer. The world over it has been maintained as a fundamental truth that manure produced in a zero-grazing unit from 3 cows will be sufficient to provide the amount of biogas needed for cooking and lighting in the farm household. However, are people really in a position to actually set up an appropriate zero-grazing unit and feed the cattle there? What about the necessary natural conditions? Is the whole venture financially viable for those concerned? And what about those who cannot afford it? Experiences show that for many peasant farmers the investment required to build a cowshed and set up a biogas plant is simply out of reach. They will always have to rely on financial assistance. In these situations, preference should be given to agroforestry, i.e. mixed cultivation providing firewood from fast-growing trees and stabilizing soil fertility through erosion control and prevention. Programs designed to promote the dissemination of stoves using a minimum of firewood will reach much larger target groups than efforts to promote the setting – up of biogas plants; and, what is more, these target groups will be less dependent on external aid.
3. OperationDuring the operation of a biogas plant continuous feeding is required, as well as regular supervision by a competent person taking responsibility for the running of the unit. In addition to that, it is advisable to set aside some money as a reserve fund to cover possible expenses incurred through maintenance work, replacement, and repairs. However, at the end of the day, the operating costs of a biogas unit are still very low as compared to the benefits achieved, in particular the fact that enormous amounts of firewood are saved. Any cost-benefit analysis will show how fast investing in a biogas plant pays off.
4. Further effects were anaerobic / biogas systems are introduced, and a market is created with new income opportunities for small local businesses. The people employed or self-employed in this sector can be given appropriate training on the job in all stages of planning, setting up, monitoring and maintenance.
MISEREOR provides Consulting – Planning – Training to partners all over the world who wish to make use of anaerobic / biogas technology. To an increasing extent, well-trained and experienced people from developing countries are taking on consulting assignments in neighboring regions. A network facilitating the exchange of professional experience at that level is currently being prepared, with the data of already implemented projects serving as an information basis.