First-Principles Flocculation as the Key to Low Energy Algal Biofuels Processing

Technical Report · Sat Sep 01 00:00:00 EDT 2012

DOI:https://doi.org/10.2172/1090222· OSTI ID:1090222

Hewson, John C. ^[1]; Wyatt, Nicholas B. ^[1]; Pierce, Flint ^[1]; Brady, Patrick Vane ^[1]; Dwyer, Brian P. ^[1]; Grillet, Anne M. ^[1]; Hankins, Matthew G. ^[1]; Hughes, Lindsey Gloe ^[1]; Lechman, Jeremy B. ^[1]; Mondy, Lisa Ann ^[1]; Murton, Jaclyn K. ^[1]; O'Hern, Timothy J ^[1]; Parchert, Kylea Joy ^[1]; Pohl, Phillip Isabio ^[1]; Williams, Cecelia Victoria ^[1]; Zhang, Xuezhi ^[2]; Hu, Qiang ^[2]; Amendola, Pasquale ^[2]; Reynoso, Monica ^[2]; Sommerfeld, Milton ^[2]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2. Arizona State Univ., Mesa, AZ (United States)

This document summarizes a three year Laboratory Directed Research and Development (LDRD) program effort to improve our understanding of algal flocculation with a key to overcoming harvesting as a techno-economic barrier to algal biofuels. Flocculation is limited by the concentrations of deprotonated functional groups on the algal cell surface. Favorable charged groups on the surfaces of precipitates that form in solution and the interaction of both with ions in the water can favor flocculation. Measurements of algae cell-surface functional groups are reported and related to the quantity of flocculant required. Deprotonation of surface groups and complexation of surface groups with ions from the growth media are predicted in the context of PHREEQC. The understanding of surface chemistry is linked to boundaries of effective flocculation. We show that the phase-space of effective flocculation can be expanded by more frequent alga-alga or floc-floc collisions. The collision frequency is dependent on the floc structure, described in the fractal sense. The fractal floc structure is shown to depend on the rate of shear mixing. We present both experimental measurements of the floc structure variation and simulations using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Both show a densification of the flocs with increasing shear. The LAMMPS results show a combined change in the fractal dimension and a change in the coordination number leading to stronger flocs.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Arizona State Univ., Mesa, AZ (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1090222
• Report Number(s): SAND--2012-8099; 456461
• Country of Publication: United States
• Language: English