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Solid state fermentation of renewable resources in batch-operated systems - limitations and potentials

It could be shown that renewable resources in batch-operated solid state anaerobic digestion process act in a different way. Therefore the first step of plant operators should be a procedure specific choice of appropriate substrates.

The solid state fermentation in Germany has extended and consolidated its state in the agricultural sector, where plant sizes of 200 to 500 kW of installed electrical capacity dominate. By the majority this is caused by political measures supporting an exclusive utilisation of renewable resources. In the meantime even provider of sophisticated procedures, focus on the decentralized market of anaerobic digestion of energy crops. So far such systems have been reserved to applications in the field of waste management. Simplifications and cost minimisation took place to adjust these plants to the minor throughputs in agriculture. Besides this quasi-continuous plants often operated with a plug-flow reactor a number of batch processes using boxes or containers can be found. They are basic, less cost-intensive and using partly the already existing technology. The full scale operation of those solid state fermentations has shown that in many areas further research is needed. From time to time an inadequate blending or too close mixing ratios respectively leads to inhibited processes or even to a disruption of the biological degradation. Often a suboptimal structure of the packed bed is realised. Because there have been a lack of data for handling a project addresses to that task were carried out. Based on a substrate characterisation of selected renewable resources batch experiments in pilot plant size (120 litres, 60 days retention time, mesophilic conditions) were arranged. In the main focus have been physical parameters namely the interrelation between different installation densities in the reactor and the reachable biogas yield. A comparison of the both investigated processes - the percolated mono fermentation and the inoculated fermentation aims at statements on duration, the amount of biogas and its quality as well as the biological degradation. It was found that respective highest biogas yields base on different installation densities. In addition it could be shown that there is no overall coherence between density (dry and moist) and biogas yield. In the case of percolation the trend goes to lower densities whereby a better through-flow of the packed bed could be derived. In the inoculated case the maxima can be found at high compacted ranges by the majority. It is assumed that by stronger pressing a high contact and therefore a good mass transfer between microorganisms and substrate come into existence. This benefits the biogas production rate in processes without dynamic element. Such a distinct divergence would not have expected in advance. A combined representation in one matrix seems to be not purposeful. The substrates should observe in a specific way to filter optimal boundary conditions and procedures.

Copyright:	© European Compost Network ECN e.V.
Quelle:	Orbit 2008 (Oktober 2008)
Seiten:	8
Preis:	€ 7,00
Autor:	Dipl.-Ing. Thomas Haupt
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