Converting waste biomass resources through downdraft gasification can generate a producer gas for a combined heat and power unit. The study includes feedstock analysis, process modelling using ECLIPSE simulation software, and experimental analysis of materials in a pilot-scale fixed-bed downdraft gasifier. Anaerobic digestate and miscanthus were investigated for comparing the gasification potential of poultry litter as an energy source. Models validated through experimental analysis were applied to a case study based on a typical poultry farm in Northern Ireland.; Results found producer gas with a lower heating value up to 4.15 MJ/Nm3 can be generated. Sufficient poultry waste is generated on-site to produce the required heat and electricity for each shed, allowing the farm to switch from fossil fuels to a local renewable resource and addressing the waste disposal issue.; Downdraft gasification coupled with cogeneration could have a payback period of 4–5 years given the correct conditions. The net present value is positive for all technologies considered (i.e. internal combustion engine and the Organic Rankine cycle combined heat and power unit) under different subsidies, showing the economic viability of the solution. The break-even selling price could be lower than the current grid electricity selling price (£120/MWh) when incentives such as: (i) avoiding disposal cost of £30/tonne, (ii) selling the biochar by-product at £200/tonne and (iii) fuel displacement costs of 1.5p/kWh are considered.
Graphical abstract
Recently, there has been a resurgence of interest in continuous bioprocessing as a cost-optimised production strategy, driven by a rising global requirement for recombinant proteins used as biological drugs. This strategy could provide several benefits over traditional batch processing, including smaller bioreactors, smaller facilities, and overall reduced plant footprints and investment costs. Continuous processes may also offer improved product quality and minimise heterogeneity, both in the culture and in the product. In this paper, a model protein, green fluorescent protein (GFP) mut3*, was used to test the recombinant protein expression in an Escherichia coli strain with industrial relevance grown in chemostat. An important factor in enabling stable productivity in continuous cultures is the carbon source. We have studied the viability and heterogeneity of the chemostat cultures using a chemically defined medium based on glucose or glycerol as the single carbon source. As a by-product of biodiesel production, glycerol is expected to become a sustainable alternative substrate to glucose. We have found that although glycerol gives a higher cell density, it also generates higher heterogeneity in the culture and a less stable recombinant protein production. We suggest that manipulating the balance between different subpopulations to increase the proportion of productive cells may be a possible solution for making glycerol a successful alternative to glucose.
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