Use of Natural pH Variation to Increase the Flocculation of the Marine Microalgae Nannochloropsis oculata

Abstract

Microalgae is largely used in aquaculture as feed. More recently, these microorganisms have been considered as an important feedstock for biodiesel production. However, the concentration of produced biomass represents a large parcel of production costs. In this study, we have evaluated the influence of natural pH variation of culture medium, caused by photosynthetic activity, on the flocculation of the marine microalgae Nannochloropsis oculata. Experiments were conducted with the same culture with different pH values (8.5 and 9.6), obtained after exposing the cells to different light conditions. For each pH value, different treatments were composed by adding 0, 5, 10, and 30 mM of NaOH and the flocculant Flopam® (FO4800 SH) at concentrations of 0, 0.5, 1, and 5 ppm. Higher flocculation efficiencies were obtained for the culture with pH 9.6 in comparison to 8.5 for the same NaOH and Flopam concentrations. Lower concentrations of base and flocculant were needed for flocculating the culture in higher pH, representing an economy of 20 % in the costs of crop harvesting.

Carotenoid production by the marine microalgae Nannochloropsis oculata in different low-cost culture media

“…It can be grown in wastewater (Uggetti, Sialve, Trably & Steyer, 2014) and in petrol production water (Arriada & Abreu, 2014). Recently, these microalgae have been widely used in several studies on biofuel production at the Microalgae Production Laboratory from the Aquaculture and Marine Biotechnology Center in the Oceanographic Institute of the Federal University of Rio Grande (Arriada & Abreu, 2014;do Valle Borges, de Farias, Odebrecht & de Abreu, 2007; L. Borges, Mor on-Villarreyes, D'Oca & Abreu, 2011;Roselet, Maic a, Martins & Abreu, 2013;Roselet, Vandamme, Roselet, Muylaert & Abreu, 2015;Sales & Abreu, 2014).…”

Concentrated microalgal biomass as a substitute for fresh microalgae produced on site at hatcheries

“…For example, out of the concentrates produced by using NaOH and polyelectrolytes, in 45% of studies reported total replacement of the fresh microalgal culture by the concentrates, 13% partially and in 42%, replacement was not feasible. Flocculation by pH variation, followed by addition of a polyelectrolyte, is considered a promising method, essentially because it results in reduced electrical demand and leaves no toxic residues in the biomass (Sales & Abreu, 2015). The flocculation of N. oculata culture using NaOH and the cationic polyacrylamide FLOPAM® did not alter the fatty acid profile of the biomass, while use of the anionic polyacrylamide Magnafloc® LT‐25 reduced the percentage of EPA (Borges et al, 2011).…”

“…For example, out of the concentrates produced by using NaOH and polyelectrolytes, in 45% of studies reported total replacement of the fresh microalgal culture by the concentrates, 13% partially and in 42%, replacement was not feasible. Flocculation by pH variation, followed by addition of a polyelectrolyte, is considered a promising method, essentially because it results in reduced electrical demand and leaves no toxic residues in the biomass (Sales & Abreu, 2015).…”

Floculacion de Nannochloropsis sp. inducida por hidroxido de sodio: eficiencia de floculacion, efecto sobre la viabilidad microalgal y su uso como alimento para rotiferos

“…El hidróxido de sodio es uno de los agentes alcalinos más ampliamente usados en la floculación de microalgas (Schlesinger et al, 2012). No obstante, es usual que sea aplicado junto con polisacáridos (Pestan ® ; Lee et al, 1998), almidón catiónico (Vandamme et al, 2010), quitosano (Guevara et al, 2011), polielectrolitos (Magnafloc ® ; Knuckey et al, 2006;Harith et al, 2009), polímeros orgánicos (Flopam ® ; Sales & Abreu, 2015); sulfato de aluminio (Shen et al, 2013) y cloruro férrico (Knuckey et al, 2006). La combinación con alguno de estos compuestos incrementa el pH y mejora el proceso de floculación.…”