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  • To support claims of benefit in terms of

    2018-11-05

    To support claims of benefit, in terms of reduced environmental burden or increased process sustainability, rigorous process analysis is required using tools such as Life Cycle Assessment or carbon- and water footprinting. These approaches require availability of material and special health care needs inventories, as do techno-economic assessments. Where these are available at an early stage of process design, they can be used to inform process selection. Further, such analysis can be used to target process improvements. In order to perform the environmental or economic studies required, a good knowledge of the process as well as the material and energy balance data are needed. This information is often found through physical data collection or from a detailed software modelling exercise (including, for example, AspenPlus or SuperPro Designer). Such an exercise typically requires a software package that is more complex than needed, may not be freely available, is unsuitable for biological processes or requires a specialist user to manipulate. Alternative, simplified tools are also available but concentrate on costing only, are limited to a single product, include pharmaceutical processes only and/or use modified results from the software mentioned earlier as inputs to a next step (Boukouvala et al., 2012, 2013; Claypool and Raman, 2013; Sen et al., 2013).
    Model specifications
    Sterilization Two basic options are included: to allow for feed at ambient temperature (20 °C) or partially pre-heated feed (60 °C) (partial heat integration from recycled steam). It is assumed there is a constant rate of heat loss of 0.003 kW/m2 °C during the holding phase, an accepted value for insulated vessels (Woods, 1994). After heating, the raw materials are cooled by heat exchange with cooling water.
    Microbial growth and product formation
    Agitation Nienow has described agitation in microbial systems in various papers (including, Nienow, 1968, 1997, 2006). The model presented uses power numbers (Np) as described in these and other sources (Bakker, 2000; Doran, 1995; Fasano et al., 1994; Fraser et al., 1993; Oldshue et al., 1988; Philadelphia Mixing Solut, 2009; Post Mixing, 2003; Rushton et al., 1950; Weetman and Coyle, 1989) to determine agitation power in turbulent flow regimes. The power per unit volume is then calculated (Coulson and Sinnott, 1999), using power number, and/or impeller speed, diameter and type, the number and dimensions of the tanks agitation efficiency, together with corrections for different ratios of blade width to impeller diameter (W/D) and gassed systems (Dickey, 2004; Atkinson and Mavituna, 1983). In the current model, the heat added due to agitation is not considered.
    Case study: penicillin V production
    Conclusions This paper provided an introduction to the sterilization and microbial growth/product formation of a generic flowsheet model (CeBER Bioprocess Modeller) for fast, first estimate material and energy balance inventories of industrial bioprocesses. Presented in an MS-Excel format, the model uses a stoichiometric approach, together with first principles and rules of thumb. The model allows for batch or continuous production by aerobic or anaerobic and intra- or extracellular means. Typical information from bioprocess systems are stored in a database which include relevant constants and physical data. Downstream processing units allowing for accurate representation of typical downstream bioprocess setups are given in an accompanying paper (Harding and Harrison, 2016). With the framework in place, it is now possible to add more complex models to each unit, introduce economic modelling and expand the work to include photosynthetic processes, pretreatment steps and others.
    Acknowledgements The financial support of the National Research Foundation and the DST, South Africa, through the Competitive Industries program and the SARChI Research Chair in Bioprocess Engineering is gratefully acknowledged.