Sigrid Kusch

Effect of various leachate recirculation strategies on batch anaerobic digestion of solid substrates

Various leachate recirculation strategies were applied to a batch-wise operated solid-phase digestion system in laboratory-scale tests. Comparative experiments with both continuous and intermittent leachate recirculation revealed no advantages of a continuous flow. Results suggest that leachate recirculation should not be carried out continuously during process initialisation when methanogenesis is the rate-limiting step. Continuous watering resulted in the accumulation of Volatile Fatty Acids (VFA) during process start-up. In addition, no need for continuous water circulation was found for the following digestion process when hydrolysis was rate-limiting. Even in the absence of liquid recirculation, degradation was only slightly retarded when the biomass moisture content was adjusted.

Anaerobic Digestion of Waste

All sustainable development closely links to the context of energy and to appropriate solutions to cope with challenges arising from trends of increasing urbanisation, by at the same time allowing for development of rural areas. Biogas production through anaerobic digestion of biomass, including the organic fraction of waste materials and residues, is a particularly promising choice and experiences increasing interest worldwide. It does not only supply a clean and versatile energy carrier, but is well suited to contribute towards appropriate waste management schemes in urban areas and in agriculture. Biogas production has high potential worldwide, and in this chapter special focus is given to its implementation in countries with economies in development or transition. China and India are countries where biogas production is already well-known and often adopted, and more widespread implementation is to be expected. This book chapter also highlights the topic anaerobic digestion in countries in Latin America and Africa.

Dry Digestion of Organic Residues

Sustainable development closely links to the context of energy. Replacing fossil fuels with sustainably produced biomass or organic residues will not only be a way to cope with the depletion of fossil fuel resources but also to reduce the CO2 emissions into the atmosphere and therefore minimise the risk of global warming. A large variety of methods of biomass energy conversion are available today. Some technologies produce secondary fuel such as methanol or biomass oil which then can be utilized for various purposes. Especially for electricity generation efficient processes might be direct combustion, thermal gasification or the production of biogas. Anaerobic digestion (AD) with biogas production, including utilisation of the organic fraction of waste materials and of residues, is a particularly promising choice and experiences increasing interest worldwide. AD does not only supply a clean and versatile energy carrier, thus displacing other energy sources such as fossil energy, but is well suited to contribute towards appropriate waste management schemes in urban areas and in agriculture. Biogas production has high potential worldwide, and it is in particular digestion of solid materials which is of increasing interest. As a result, it is to be expected that so-called dry digestion systems, operated with an elevated content of total solids (TS) in the reactor, will experience more widespread implementation. Agricultural residues in general are left on field or are brought back to field in order to supply fertilizers and to improve soil quality. Anaerobic digestion offers the possibility to produce renewable energy, and at the same time generates a digestate with an improved fertilizer value. Currently the most common strategy for management of municipal solid waste (MSW) worldwide is still landfill. As a result of higher environmental awareness, and often based on favourable legislative backgrounds, more and more emphasis is given to recycling and recovery, and in particular to efficient use of organic materials. Composting and anaerobic digestion are state-of-the-art for treating organic substrates. Germany today is leading in the area of biogas production. Around 6,000 AD plants are in operation, and the number is further increasing. Most plants are in the agricultural sector, but currently at least 100 plants are run solely on the organic fraction of MSW, a direct result

Meeting the growing demand for food and bioenergy in the 21st century: synergies through efficient waste management

1University of Southampton, Faculty of Engineering and the Environment, Highfield Campus, Southampton, Hampshire, SO17 1BJ, UK 2Economic & Urban Policy Analysts, 65 Edgewood Avenue, Yonkers, NY 10704, USA *Author for correspondence: Tel.: +49 911 30037333; Fax: +49 911 30037334; E-mail: S.Kusch@soton.ac.uk

Editorial: Progress in biogas – State of the art and future perspectives: Engineering in Life Sciences 3'12

We are all aware that the fossil fuel reserves are limited and because they are of such importance for our daily life we will run dry in a foreseeable future. Especially mineral oil, which has currently manifold applications, will not be available anymore within few generations or hardly affordable. Other energy sources like natural gas and coal as well as nuclear energy will follow in its footsteps. In addition, the use of fossil fuels has a critical impact on the environment, as their combustion leads to an accumulation of carbon dioxide in the atmosphere, thus promoting global warming. It is therefore essential by several means to push the use of renewable energy sources for energy supply and to promote progress in this area. An obvious possibility is the use of renewable resources for energy generation, such as the production of biogas. Some countries, particularly Germany, are implementing legal regulations and assistance measures for renewable energy sources to promote the progress of biogas technology and to increase the efficiency of these systems. As a result, the number of biogas plants grows continuously and exceeded 7 000 plants with an installed electrical capacity of 2.8 GW by the end of 2011. In addition, a growing number of biogas upgrading plants, supplying the gas grid with purified substitute natural gas (SNG) can be recorded, represented by 60 large-scale plants operated in Germany. Researchers at the University of Hohenheim, Stuttgart, Germany, have invested in research in the field of fermentative conversion of biomass into biogas for more than three decades. The international conference “Progress in Biogas II”, which was mainly organized by the International Biogas Center of Competence (IBBK), was held in March 2011 at the University of Hohenheim and brought together about 400 biogas experts from 40 countries. This Special issue in Engineering in Life Sciences, features contributions made at this conference. The potentials of biogas and the control to make use of them were a main conference topic. To assess the impact of potential fermentation substrates, laboratory batch tests are typically used, as they allow reliable statements about the potential yields from certain substrates. Mittweg et al. [1] showed that only a careful implementation of such tests provides a meaningful result for the efficiency and planning of the biogas process. One more important topic of the congress was the description of new approaches for the production engineering of biogas generation. Several systems, for example for mechanical or thermal conditioning especially of high fiber substrates, were presented to expand the usable substrate spectrum and to allow a higher biogas yield from these substrates.