Identify and Optimise Technologies for Prodcuing Biogas (Methane) from Grass Silage
Identify and Optimise Technologies for Producing Biogas
Researcher: David Wall
T: 021 490 1982
Funding Body: Teagasc
Programme: Walsh Fellowship
Project Type: PhD
Full Project Title: Identify and Optimise Technologies for Producing Biogas (and Specifically Methane) from Grass Silage
Period: July 2012- July 2016
Although there are more than 6,000 anaerobic digesters on German farms, much of their practical on-farm biogas production experience relates to the use of forage maize as the biomass source, and the design and operation of digesters has focused on optimizing the conditions for this feedstock. These systems are not ideally suited to grass digestion or to its subsequent mixing with digestate within the digester, and these issues are viewed as constraints to the more widespread use of grass for biogas. This project will identify and optimise technologies for producing biogas (and specifically methane) from grass silage. It will be a collaborative effort between Teagasc Grange, Environmental Research Institute at UCC-Cork and MTT Finland.
Replicated field plots and laboratory silos will be used to provide grass biomass for anaerobic digestion in continuous fermentation reactors – this will compare specific factors such as herbage species, herbage growth stage at harvest, type of silage fermentation and fibrolytic enzymes applied at ensilage, and relate these effects to those obtained in a parallel project using the biological methane potential (BMP) test. The methane output associated with digesting silage effluent will also be quantified. The effects of micronutrient/manure addition on the efficiency of methane production during the long-term digestion of herbages will be determined using both continuous laboratory-scale and pilot-scale digesters. Continuous laboratory- and pilot-scale digestion studies will be undertaken with selected herbage treatments in two digester types (CSTR, leach-bed) to identify optimal operational parameters, such as retention time, loading method and mixing procedure. Farm-scale co-digestion of manure and herbage (loading, mixing, feed ratio, feed interval etc.) will be optimised in order to maximise methane yield, minimise energy consumption, and ultimately provide guidelines for feasible digester design, feeding ratio and operational parameters. Desk-top exercises will be undertaken using the results from the above experiments and those from published literature to assess the economic, environmental and labour sustainability of a range of biogas production options.