Microarray to study microorganisms in biogas plants

Under the conditions of the Kyoto Protocol, the EU is committed to reducing its greenhouse gas emissions by 8 per cent below the 1990 level in the period from 2008-2012. It is expected that renewable energies such as wind power, solar energy, hydropower and biomass will play an important role in meeting this target. According to the EU- Directive 2004/8/EC, the co-generation of electricity and heat should be promoted. Biogas production is one of the options for accomplishing this. Alone in Austria, 65 million tonnes of agricultural by-products would be available for such a co-generation. In addition, an enormous potential is seen in energy crops as a possible source of substrates with amounts that greatly surpass the above figures. The Landfill Directive (99/31/EC) lays down that EU member states should strictly limit and control the biodegradable wastes dumped at landfills (http://www.europa.eu/comm/environment); biological treatments are the best option for the disposal of the putrescent fraction of separately collected biowaste, as these technologies maximise recycling and recovery of the waste components, and produce energy. Anaerobic digestion is the biological process for the decomposition of organic waste in the absence of oxygen. The performance of an anaerobic digester, in terms of its biogas production, is thought to be linked with both the microbial community structure and with the chemical and physical parameters of the digester. In order to improve the performance of biogas production from an anaerobic digester, it is important to better study the microbial communities associated with the different stages of the digestion process. The aim of this project is to study the microbial communities involved in an anaerobic digestion plant. A better knowledge of the microbial communities present and active in this process should result in a better understanding of the anaerobic degradation process and why it sometimes fails in methane production. This should allow for improved biogas production in anaerobic digestion plants. Milestones of the project: 1. To study the microbial communities present in different stages of the anaerobic digestion process by cloning the 16S rRNA gene from extracted DNA of samples from the anaerobic digestion process 2. To design a microarray with oligonucleotide probes specific to microorganisms (Bacteria and Archaea) present in the anaerobic digestion process, as determined by the clone libraries, from the literature, and from the findings of other researchers 3. To apply the microarray to sludge samples taken from efficiently operating (high biogas production) and not efficiently operating (low biogas production) anaerobic digestion processes in Austria, to determine if the changes in biogas production can be related to alterations in certain microbial communities. 4. To use the newly developed microarray to study the different microbial communities in different types of anaerobic digesters and digesters treating different types of waste. 5. To be able to follow the fate (survival) of pathogens, as well as the hygiene status of the final product (anaerobic sludge).

With increasing human population, the need for sustainable ways to manage the large amount of wastes produced is continually increasing and becoming more urgent. Anaerobic digestion is a biological process by which organic wastes are decomposed in the absence of oxygen, producing a sludge of agricultural value, as well as biogas, which can be used to generate electricity. The process requires specific environmental conditions and different microbial communities for the various stages. A better knowledge of the microbial communities present and active in well functioning anaerobic digestion processes should result in a deeper understanding of the process and why it can occaisionally fail in methane production. This study has resulted in the development of two new molecular tools, the BACCHIP microarray and the ANAEROCHIP microarray. These arrays are each printed with oligonucleotide probes targeting the 16S rRNA gene specific for different anaerobic bacteria (BACCHIP) and methanogens (ANAEROCHIP). The BACCHIP array probes target acetogens, hydrogenotrophs, hydrolytic bacteria, syntrophs, and sulphate and nitrogen reducing bacteria. Optimisation of this microarray so to yield more sensitive results is still required. The ANAEROCHIP array allows the determination of the presence or absence of most lineages of mesophilic and thermophilic methanogens within complex anaerobic samples in a single test. The microarray has been tested in numerous studies, and has revealed the presence of different methanogenic communities in different sludges, allowing links to be made between biotic and abiotic characteristics in anaerobic digesters. Based upon all the results of studies thus far, it would appear that reactors have relatively stable methanogenic communities, which do not change easily, even when reactor disturbances occur. Also, different populations of methanogens dominate in different reactors, depending on input materials and operating conditions.