Rice straw to Biogas (R2B)

点击翻译按钮获取中文摘要

The research at Southampton seeks to maximise biogas from rice straw through the use of innovative pre-treatment techniques, evaluation of nutritional requirements of the anaerobic consortium, and optimisation of the bioreactor in terms of its configuration and physical environment. The work will build on the rich but fragmented knowledge which represents the state of the art in rice straw digestion. This suggests that mechanical pre-treatment may be effective, although reliable quantitative data are not available. Batch methane potential tests will be carried out to assess the reaction kinetics of the straw after the application of mechanical treatments. The flail mill is targeted as a preferred technology because of its simple and robust construction, lack of reliance on cutting blades that are rapidly blunted in rice straw applications, and history of successful use in developing countries e.g. in the tea industry. Its performance will be compared with that of other systems such as hammer and ball mills. The batch tests will be followed by more extensive trials using semi-continuous fed digesters to establish specific and volumetric gas productivities and digester operational stability. Compositional analysis of the straw will indicate not only of its theoretical methane potential but also its nutritional value and buffering capacity, as a basis for selective additions of essential elements to improve digester performance. The semi-continuous trials will be conducted at both mesophilic and thermophilic temperatures over a range of loading conditions, with monitoring of key operating parameters to establish baseline kinetic data against which pilot plant performance can be compared and optimised. Prior art also suggests that rice straw may be deficient in natural pH buffering and performance can be enhanced through co-digestion with animal slurries. To date, work has mainly focused on cattle and swine manures. The planned work will additionally consider duck and poultry manure, as these are readily available in the Philippines and other parts of the world where rice is extensively cultivated. Both shredding and manure addition will significantly alter the rheology of the substrate, which will impact on the operating mode of a dry digestion system. Permeability tests will therefore be conducted at various stages through the batch dry digestion process. This will involve running small-scale 'dry' digesters that simulate the pilot plant and provide data for direct comparison and assessment of factors of scale. The propensity for acidification will also be assessed, and the potential requirement for second-stage methane recovery from the leachate will be considered: if necessary this could be achieved by coupling to a low-tech second stage reactor (e.g. anaerobic filter) with recycling of acid-stripped liquid to overcome buffering issues. Other control measures, such as batch sequencing of the dry digesters and optimisation of the substrate-to-inoculum ratio at start-up, will also be evaluated as part of an operational strategy to match harvesting schedules and minimise storage requirements. Where permeability is an issue the use of inert bulking material will be tested to improve hydraulic distribution and reduce short circuiting. Previous work has shown that agricultural residues with a high solids content require long operating periods to reach the pseudo steady state conditions needed to determine the nutritional needs of the anaerobic consortia and the digestate properties. This provides the opportunity to monitor changes in biomass characteristics and population structure using advanced microscopy, Raman spectroscopy and gene techniques. Of key importance is the overall sustainability of the rice straw energy production system, and the laboratory and pilot plant data will feed into previously developed energy balance models to provide processed data output for the work of the Manchester team.