Physical disintegration techniques (substrate conditioning systems) for the optimization of dry fermentation systems : a sample analysis for a standardized biogas plant

Abstract

The development of biogas production has been very successful in some European countries. Germany is one of the leading markets, followed by some other countries in the EU like Italy, Belgium, Sweden and Spain. As a renewable energy source, biogas production has an important role. It can be produced from a broad variety of energy crops, animal manures and by-products from industrial processes. The feeding material can be adapted to the specific needs of contrasting locations and farm managements. The use of biogas (methane content 50-70%) produced, is very flexible. For instance, it can be used for electricity production in a CHP gas engine, where the waste heat from the engine can be used for heating the digester and surrounding facilities (for cooking, space heating, and water heating). Moreover it can be used in vehicles and if concentrated via a biogas upgrading system it can be introduced in the natural gas grid. Compared to other renewable energies, there must be given particular attention to the economic efficiency of the biogas plant, primarily because of the high fixed costs of feeding material (energy crops) and the work intensiveness. To run a biogas plant efficiently, high biogas yields are required. Some key factors play therefore a central role: the energy crop production has to be optimized as well as the harvesting time; also the nutrient composition and conservation are important to preserve essential nutrients for biogas production; last but not least pretreatment technology must be developed to enhance the biogas production. The aim of a pretreatment method is to enhance the hydrolysis step in the anaerobic digestion process by decomposing complex carbohydrate structures in order to increase the availability of readily degradable organic material and hence increase the biogas and methane production in the digester. Such pretreatment technologies can be either physical (thermal, electrical, mechanical), or chemical (acid, alkaline, oxidation, carbon dioxide etc.) or biological. But, these technologies have a wide range of complexity and can be also combined to each other in order to further optimize AD performance. Following this study, several pre-treatment methods are carefully investigated from literature and results on the biogas yield are presented. If an adequate disintegration technique is found, an increase of 10-20% of biogas production can be expected, leading to a higher profitability of the biogas plant.