After saccharification (via pretreatment and enzymatic hydrolysis), residual biomass solids can have a detrimental impact on downstream fermentation or catalytic conversion processes. These solids are commonly deformable, porous, asymmetric, and have a wide particle size distribution, making them extremely difficult to remove from solution. Here we utilize polyelectrolyte-flocculating agents to enhance the solid-liquid separation of enzymatically-hydrolyzed (EH) corn stover and acid pretreated (PT) algae slurries.<br/><br/>The EH corn stover slurries are a two-phase system with 5-10 wt% insoluble solids suspended in an aqueous phase at pH 4-5. The zeta potential of the corn stover particles was found to be negative over the measurable range of pH (1-13), and the particles were easily flocculated with various cationic flocculants. Initial studies evaluated flocculant dosing and separation effectiveness using centrifugation. However, economics for a centrifugation process are not expected to be favorable. Therefore, the focus of the work was vacuum-driven bulk filtration aided by flocculation. The use of flocculation increased the overall capacity of vacuum filtration (for the slurries tested) by ~50-fold.<br/><br/>The acid PT algae slurries, on the other hand, are a three-phase mixture of solid cell debris (5-8 wt%), lipids, and a protein- and carbohydrate-rich aqueous phase. The solid-liquid separation process for the algae slurries is more complex than the EH corn stover slurries due to the buoyant lipid phase, which tends to associate with the solids. In addition, the acid PT algae slurries (unadjusted pH of 1-2), have a positive zeta potential from pH 1-4 and then display a charge inversion at pH values &gt;4. We found that the flocculants tested were not stable at pH &lt; 3, and as a result, pH adjustments of the PT algal slurries were performed to optimize the flocculation process. Centrifugation was determined to be an ineffective technique because the buoyant lipids complicated the isolation of the aqueous layer. Vacuum filtration was again pursued as the preferred separation technique. The use of flocculation and pH control increased the vacuum filtration flux of the PT algae slurries by 1-2 orders of magnitude compared to untreated slurries.

Flocculant-aided solid-liquid separation of algal and lignocellulosic biomass slurries

249th National Meeting (2015)

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