(539c) Molecular-Level Interactions in the Design of Reversible and Recyclable Flocculants

Morrissey, K., University of Colorado
He, C., University of Colorado
Chapman, R., University of Colorado
Zolnierowski, L., Yale Univeristy
Stoykovich, M. P., University of Colorado

Previously we have developed a novel approach for the dewatering and harvesting of microalgae using polyamphoteric flocculants that can be recovered and recycled in response to their pH-dependent properties.  Reversible and recyclable flocculants were shown to address the challenges of flocculant cost and downstream contamination that plague current algal biofuels processes.  Here ampholytic polyacrylamide-based flocculants, with a pH-tunable charge character ranging from net positively-charged to net negatively-charged, will be compared for the dewatering of the microalgae system Chlorella vulgaris (UTEX 395) and the flocculation of a model colloidal suspension of homogeneously-charged (negatively-charged) silica microparticles.  Direct comparison of the polyamphoteric flocculants with cationic, anionic, and nonionic commercial flocculants will also be provided.  Molecular-level interactions are elucidated that enable the polyamphoteric flocculants to 1) initially adsorb to the particle surface and cause aggregation and 2) undergo facilitated desorption from the particle surface.  By tuning these molecular interactions and operating conditions, the reversible and recyclable polyampholytes achieve similar initial flocculation efficiencies (>95%) as commercial cationic flocculants, however, can be recovered with >94% yields and recycled for over 5 flocculation processes.