Effect of chemical additives on biomass deposition onto beaded adsorbents

Common limitations encountered during the direct recovery of bioproducts from an unclarified feedstock are related to the presence of biomass in such processing systems. Biomass-related effects can be described as biomass-to-support deposition and cell-to-cell aggregation. In this work, a number of chemical additives were screened for their ability to inhibit either biomass deposition, cell aggregation, or a combination of both effects. Several interacting pairs were screened. These were composed of (i) a commercial chromatographic matrix harbouring a variety of ligand types and (ii) intact yeast cells - as a model biomass type. Studies were performed based on partitioning tests, colloid deposition experiments, and sorption performance studies in expanded beds. Results indicated that the coating of anion-exchanger beads with the synthetic polymer PVP 360 alleviated biomass deposition and consequently restored EBA process performance. This behaviour correlated well with calculations performed according to the XDLVO approach: the secondary (interaction) free energy pockets decreased from -230 kT to -100 kT in the absence and in the presence of PVP 360, respectively. Experiments performed in parallel demonstrated that total binding capacity for the model protein (BSA) - under dynamic conditions - remained almost constant (≈ 55.7 kg m(-3)). Other combinations of additives and adsorbents were tested. However, no solution chemistry was able to inhibit biomass deposition onto strong (composite) ion exchangers. Moreover, yeast cell deposition was only marginally decreased when hydrophobic interaction and pseudo-affinity supports were explored. The utilization of non-toxic polymers could help to avoid detrimental biomass deposition during expanded bed adsorption of bioproducts and other direct contact sequestration methods.