Harvesting Microalgae Grown on Wastewater

Abstract

This project investigated the lifecycle costs of coagulants used for harvesting microalgae for biofuel production. Algae were grown in semi-continuous culture in pilot-scale photobioreactors (PBRs) under natural light conditions with anaerobic digester centrate as the feed source. Algae suspensions were collected from the PBRs, and the optimal coagulant dosages for metal salts (alum, ferric chloride), cationic polymer (Zetag 8819), anionic polymer (E-38) and natural coagulants (Moringa Oleifera and Opuntia ficus-indica cactus) were determined using jar tests. The relative dewaterability of the algae cake was estimated by centrifugation. Alum, ferric chloride and cationic polymer were all capable of > 91% algae recovery at optimal dosages of 170 (alum), 185 (ferric) and 44 (polymer) kg coagulant/MT of algae. Economic analysis and life cycle assessment studies revealed the polymer had the lowest cost but the highest greenhouse gas emissions and energy usage, while ferric chloride had the highest cost but the lowest greenhouse gas emissions and energy usage.

Harvesting of freshwater and marine microalgae by common flocculants and magnetic microparticles

“…Inorganic flocculants such as ferric chloride and aluminum sulfate are widely used in water and wastewater treatment, due to their effectiveness and understanding of their behavior (Molina Grima et al 2003;Chesters et al 2009;Vandamme et al 2013). Recently, inorganic flocculants are investigated for microalgae harvesting (Vandamme et al 2013;Udom et al 2013). The use of inorganic salts is associated with high doses, and the decrease in lipids or fatty acids in harvested cells after flocculation (Papazi et al 2010;Borges et al 2011).…”

Integration of microalgal cultivation system for wastewater remediation and sustainable biomass production

“…The bulk harvesting process delivers an algal solution of approximately 0.1 % total solids (Richardson et al 2014). Further concentration of the algal solution is achieved during the second step of harvesting, in which the microalgal slurry is thickened or dewatered by filtration, centrifugation or thermal processes (Udom et al 2013). Harvesting of algal biomass involves solid-liquid separation steps and is a challenging part of the production chain and can have a high impact on the resultant cost of biomass production.…”

“…Moreover, centrifugation can contribute to up to 480 kg CO 2 eq. ton -1 dry algae and is not feasible for large scale operations (Udom et al 2013).…”

Exploring the Use of Everglades Agricultural Area Canal Water as Base Medium for the Mass Production of Algae for Biofuels

“…Research addressed by the United Nations cited fresh water supply and energy intensification involved in culture collection, drying and lipid extraction for algae to be major concerns for third generation biofuels (Waltz, 2013). As a response to these concerns, several authors have suggested wastewater as growth medium for microalgae (Oswald and Gotaas, 1957;Goldman, 1979;Soedes, 1980;Udoma, et al, 2012;Yuan, et al, 2012;Christenson & Sims, 2011); however, empirical data are not abundant. My research aims at utilizing agricultural waste water obtained from the canals in the Everglades Agricultural Area (EAA).…”

“…(Oswald and Gotaas, 1957;Goldman, 1979;Soedes, 1980;Udoma, et al, 2012;Yuan, et al, 2012;Christenson & Sims, 2011). The potential use of algae obtained from water treatment plants is important for biofuel economics as algae are a bi-product of nutrient mitigation operations; thus, also reducing the feedstock cost.…”