Abstract
Large amounts of fibre-rich organic waste material from public green and private gardens have to be treated environmentally friendly; however, this fibre-rich biomass has low biogas yields. This study investigated the presence of fungi in full-scale biogas plants as well as in laboratory reactors and elucidated the importance of fungi for the biogas process. The dominating members of the eukaryotic community were identified by analyzing 18S rRNA gene and internal transcribed spacer 1 (ITS1) region fragments of clone libraries. These identifications were accompanied by diverse microscopic techniques such as fluorescence microscopy and conventional scanning electron microscopy. Cells of presumably fungal origin were characterized by intensive fluorescence and were about 1 order of magnitude larger than prokaryotic cells. Molecular techniques enabled to identify fungi from the subphyla Agaricomycotina, Mucoromycotina, Pezizomycotina, Pucciniomycotina and Saccharomycotina and from the class Neocallimastigomycetes. Members of these groups can be important for microbial degradation of complex compounds, due to the ability to penetrate cell walls, and thus open the cells for the influx of bacteria, further enhancing degradation. Optimal treatment of biowaste depends on the amount of lignocelluloses. Targeted application of fungi to the biogas process will open wider possibilities for anaerobic treatment of fibre-rich biomass and can result in better biomass utilization as a renewable energy resource. Due to higher temperature optima of fungal cellulolytic enzymes, the thermophilic process is suggested for anaerobic degradation of fibre-rich biomass.
Highlights
Large amounts of fibre-rich organic waste material from public green and private gardens have to be treated environmentally friendly; this fibre-rich biomass has low biogas yields
Amounts of municipal solid waste (MSW) as well as of organic waste are closely correlated to gross domestic product (GDP) and are increasing sharply in many countries [2]
The anaerobic decomposition of organic compounds in the first steps of biogas production provides the basic substrates for the methanogens [5,6]
Summary
Large amounts of fibre-rich organic waste material from public green and private gardens have to be treated environmentally friendly; this fibre-rich biomass has low biogas yields. In Germany, the organic fraction of MSW amounts up to 3.8 Mt a−1 and source sorting is implemented at 72% of the municipalities with a further increasing share. Another large source of organic waste material is urban gardening waste from public green and. Anaerobic fungi are known to form co-cultures with ruminal methanogenic archaea which utilize the fungal hydrogen production [13]. Fungal penetration results in faster and more complete decomposition of fodder that enters the rumen [13] Such fungal enhancement of decomposition could be used in the biogas process; until recently, there is only limited knowledge about the occurrence of fungi in a biogas plant
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