Evaluation And Correlation Of Biomass/Adsorbent Interactions In Expanded Bed Adsorption

Expanded bed adsorption (EBA) is a novel bioseparation technique, which integrates clarification, concentration and initial purification into one unit operation. It enables the target products to be adsorbed directly from uhclarified fermentation broth or microorganism homogenate. However, the interactions between biomass and adsorbents often lead to the flocculation of adsorbents and destroy the stable fluidization of adsorbents in expanded bed. Therefore it is necessary to analyze and evaluate the impact of biomass/adsorbent interactions in EBA, because the strong biomass/adsorbent interactions would weaken the separate effect and even break down expanded bed.The thesis is divided into four sections. Section 1 is the review of expanded bed adsorption, including the history, principles and operation. Then the biomass/adsorbent interactions in expanded bed and zeta potential, a practical parameter to characterize surface charges of charged particles, are introduced. Furthermore, the research idea is put forward: the biomass pulse response method might be set up firstly to obtain biomass transmission index (BTI) estimating biomass/adsorbent interactions, then zeta potential would be measured and a relation between zeta potential and BTI should be established in order to evaluate the biomass/adsorbent interactions in the early phase of EBA process design.Section 2 established the biomass pulse response method. Three important factors were investigated as biomass concentration in biomass suspension, the volume of biomass pulse and expanded factor. The appropriate operation conditions of the biomass pulse response method were chosen as the OD600 of biomass pulse at the range of 0.5~0.6, pulse I volume equal to 80% volume of sedimented bed, expansion factor at 2.5.Section 3 investigated the interactions between different biomass (intact cells or homogenate of yeast, E.coli, Pichia Pastoris and Bacillus subtilis) and different adsorbents(STREAMLINE DEAE, STREAMLINE Q XL, FASTLINE SP and cellulose/ stainless steel powder composite matrix) under varying pH and ions concentration. The values of BTI were measured and analyzed. The rule of BTI>0.9 indicates that there are no or quite slight interactions between biomass and adsorbents, resulting a stable expanded bed even in the unclarifiedfeedstock.Section 4 measured zeta potential of different biomass (intact cells or homogenate of yeast, E.coli, Pichia Pastoris and Bacillus subtilis) and different adsorbents (STREAMLINE DEAE, STREAMLINE Q XL, FASTLINE SP and cellulose/ stainless steel powder composite matrix) under varying pH and ions concentration. The relations among zeta potential of biomass (b), zeta potential of adsorbents (a), biomass size (d) and BTI were found out. The results showed that there is a good linear relation between (-abd) and BTI. When (-abd) < 130 mV2 m, the value of BTI reaches 0.9. This rule could be used to simplify and improve EBA process design.