Anaerobic Digestion

ANAEROBIC DIGESTION AND BIOGAS

TECHNOLOGY

A contribution to Environmental Protection and

the Conservation of Natural Resources

1. Fundamentals

The main principle of anaerobic digestion technology is to feed biomass, including in particular waste materials and by-products (agricultural wastes; kitchen scraps; feaces; organic wastes) into a closed container, the biodigester. In the absence of oxygen, this digestion material is converted into high-value fertiliser 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, due to the fact that it is capable of converting waste material into germ -free fertiliser, anaerobic digestion technology is really predestined to being used also in the treatment und clarification of waste water, 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 seccessfull in environment-friendly sewage

disposal from hospitals and other community facilities.

Before reaching the biodigester, the waste water 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 in few millimetres under the water surface, so that there is no odour 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 (feaces, placentas etc.) is sucked into the biodigester by means of hydraulic control device, and there undergoes anaerobic digestion. The average retention time of 100 days guarantees a high degree of substrate hygienisation.

Te substrate can then be applied as a fertiliser on fields, gardens, orchards etc., and this aspect of the technology is in fact 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 as a valuable by-product of waste water treatment 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 this 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 motivation factor for the whole system. Hospital managements 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 waste water 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 waste

water produced by introducing appropriate water - saving measures. This means, for instance, to put 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 fresh water requirements for sanitation purposes by up to 50%!

The used water is fed into an underground tank and, as required and by means of an appropriate control 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