Reasonable waste digestion plants

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Courtesy of ORBIT e.V.

During the last years it became quite clear that in the area of utilisation of organic waste the anaerobic digestion has developed a leading position. This is not only based on its well known advantages:
- abhigh rate degradation of organics
- abcontained process
- ablow emissions
- abhigh yield of CO2-neutral produced biogas and high quality compost as its products
but also on the fact that customers confidence in this technology is increased, due to its greater presence at the market. Also the long lasting claimed disadvantage referring higher investment costs of digestion plants in comparison with composting facilities has been proved to be wrong. The standard of composting facilities was essentially increased, among others caused by the positive examples in the area of emission and working protection given by digestion plants. But there was still one hurdle to take by the digestion: investment costs for a plant capacity of more than 15,000  t/a with digestion or composting were nearly comparable. But in the field of smaller plants designed for up to 10,000 t/a the digestion technology was mostly at a disadvantage. To be competitive was normally only possible by giving up or minimising well experienced characteristics.

But there really is a request for plants designed for up to 10,000 t/a. So there was to develop a concept, which would keep to the high standards but also fix the investment costs at the ton-capacity of plants designed for more than 15,000 t/a. Now deductions got necessary.

The treatment of organic waste can be divided in two major steps: the pre-treatment - which means the separation of contaminants - first and following the biological treatment. This sequence is not absolute. Many biological treatment plants are carrying out the contaminant separation completely or partially at the end of the process.

That plant, which should be presented here, is the biowaste digestion plant in Erkheim. Referring its concept it was quite clear from the beginning not to make any cuts on the pre-treatment and the standards as set. Thus the deductions had to be made on the technical effort of the biological treatment and based on experiences this option was decided to be achievable.

Experiences of more than ten years have shown: a well pre-treated waste causes less effort in the biological treatment step (digestion or composting). So the basis for the development of this concept was: if the waste is pretreated in a way to become similar to an agricultural material (this means slurry/manure) it can be then treated in a simple constructed agricultural manure plant. The key was the quality of the waste pre-treatment, to be able to realise following a reasonable digestion. Consistently the plant concept in Erkheim is combining a fully automated pre-treatment with a following digestion in a reactor of agricultural standard.

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