Recyclable polyampholyte flocculants for the cost-effective dewatering of microalgae and cyanobacteria

Flocculation provides an attractive route for the primary dewatering of dilute suspensions of microalgae and cyanobacteria, however, economical harvesting and separations remain challenging. In this article, recyclable flocculants are demonstrated in a novel approach for the harvesting of fresh- and saltwater microalgae and cyanobacteria. Polyampholytes, based on model acrylamide polymers, provide reversible electrostatic interactions with negatively-charged cellular microorganisms through changes in pH. The behavior of the polyampholytic flocculants is characterized for the harvesting of Chlamydomonas reinhardtii (Chlamydomonas Genetics Center CC124), Synechococcus PCC 7002, Aulacoseira ambigua (Varsity Lake, CU Boulder), Nannochloropsis gaditana (CCMP526), and Chlorella vulgaris (UTEX 395). The polyampholytic flocculants, with reversible electrostatic interactions, achieve greater than 97% flocculation efficiencies, can be recovered at greater than 90% yields following flocculation, and when recycled retain flocculation efficiencies of at least 95%. Additionally, the recyclable polymer flocculants, in contrast to what is possible with single-use commercial flocculants, are demonstrated to be more robust for the dewatering process, regardless of culture salinity and other differences (e.g., structural, motility, or surface charge) exhibited by themicroorganisms. A techno-economic analysis of the dewatering process is also performed, with recyclable polyampholytic flocculants providing an opportunity to reduce flocculant operating costs by similar to 85% at standard conditions. (C) 2015 Elsevier B.V. All rights reserved.