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This work evaluates three techniques of calibrating capacitance (dielectric) spectrometers used for on-line monitoring of biomass: modeling of cell properties using the theoretical Cole-Cole equation, linear regression of dual-frequency capacitance measurements on biomass concentration, and multivariate (PLS) modeling of scanning dielectric spectra. The performance and robustness of each technique is assessed during a sequence of validation batches in two experimental settings of differing signal noise. In more noisy conditions, the Cole-Cole model had significantly higher biomass concentration prediction errors than the linear and multivariate models. The PLS model was the most robust in handling signal noise. In less noisy conditions, the three models performed similarly. Estimates of the mean cell size were done additionally using the Cole-Cole and PLS models, the latter technique giving more satisfactory results.

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BACKGROUND The di‐carboxylic acids succinic acid and itaconic acid are promising building block chemicals that can be produced through fermentation, but the processes would benefit from enhancements in product recovery. While sorption has already been studied to some extent for succinate/succinic acid removal, literature on the potential of sorption for itaconic acid recovery is scarce. This work aimed to screen a range of sorbents and/or resins for their capacity to separate both acids from fermentation broths, envisaging both ex situ and in situ product recovery applications. RESULTS Static batch screening led to a shortlist of four promising products. These were further characterized in terms of dynamic sorption capacity, regenerability, acid recovery, ability to concentrate the product and stability during sorption–desorption cycles. Final tests with real fermentation broth gave unsatisfactory results for succinic acid recovery. For itaconic acid, promising results were obtained both on synthetic solutions and on a real fermentation broth. CONCLUSION While it is doubtful that adsorption will be the process of choice for in situ or ex situ succinic acid recovery, well performing sorbents could be identified for itaconic acid recovery from fermentation broths, offering perspectives for in situ product recovery applications. © 2017 Society of Chemical Industry