br Introduction In order to obtain easy access to

Introduction In order to obtain easy access to accurate material and po1 inventory data for the modelling of industrial bioprocesses at the early stages of process design, a Microsoft® Excel model has been developed, termed the CeBER Bioprocess Modeller (Centre for Bioprocess Engineering Research at the University of Cape Town, Department of Chemical Engineering). This model allows for the use of a limited set of inputs to calculate the material and energy balance data. The approach to the generic flowsheet model is based on first principles in many instances, supplemented by data from advanced modelling studies, as well as industrial practice. A corresponding paper described the development of the microbial growth and product formation (Harding and Harrison, 2016), while the current paper focuses on the downstream processing. Additional information can also be obtained for specific unit systems (Harding, 2009). The model allows for solid liquid separation, cell disruption, further solid liquid separation, up to six recovery, concentration and purification steps and a final formulation stage. All of these units are based on commonly used process units as shown in Table 1, with each unit having a product recovery based in part on the information in Table 2. Recovery, concentration and purification steps allow for the addition of reactive and/or non-reactive chemicals. A waste water treatment step is also included in the model. The output from the model is a material and energy balance table (Fig. 1) as well as a breakdown of the energy sources and nominal volumes of each of the units in tabular (Fig. 2) and graphical formats. This downstream processing package has application in analysing the recovery of products from microbial processes as well as conventional extraction of fine chemicals from plants and products of biocatalysis. The model allows for fast results at an early stage of design; even by users not familiar with modelling software such as AspenPlus or SuperPro Designer. The model also includes a database and default values based on industrial norms and academic studies. Should specific information not be known, the model selects the most feasible values and automatically uses these. All automatic values can be overwritten with more suitable data as this becomes available. More detailed calculations and equations can be obtained (Harding, 2009).
Solid liquid separation
Cell disruption
Concentration and purification
Formulation
Wastewater treatment A simplified wastewater treatment scenario is included whereby wastewater collected in the discarded streams may be neutralized by the addition of up to three chemicals. A stoichiometric oxygen demand (StOD) value (IChemE, 2003), has been included and can be used as a water pollution value. Opportunities exist to expand the model to include more appropriate wastewater treatment scenarios; including anaerobic digestion and other systems.
Case study: penicillin V production
Conclusions This paper provides 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 CeBER Bioprocess Modeller allows for batch or continuous production by aerobic or anaerobic and intra- or extracellular means, the details of which are presented in an accompanying paper (Harding and Harrison, 2016). Downstream processing units were included to allow for accurate representation of typical process setups for biomass separation, cell disruption (where needed), product recovery, concentration, purification and formulation. In this paper, following review, appropriate approaches to the modelling of each unit operation are described, with indication of simplifying assumptions and opportunity to expand the level of detail. Typical data required for these analyses have been collected from bioprocess systems and are stored in a database. These include relevant constants and physical data that are required by the model. The framework of the CeBER Bioprocess Modeller ensures that maximum flexibility is maintained in terms of process flowsheets that can be analysed using this tool. From the outputs in the model, techno-economic evaluations or environmental analyses, e.g. life-cycle assessments, could be performed, since all required information (mass/energy balance data, vessel sizes and more) is calculated and provided.