Efficient harvesting of Chaetoceros calcitrans for biodiesel production

Abstract

Harvesting is one of the key challenges to determine the feasibility of producing biodiesel from algae. This paper presents experimental results for a cost-effective system to harvest Chaetoceros calcitrans, using natural sedimentation, flocculation, and inducing pH. No efficient sedimentation of microalgal cells was observed only by gravity. By alkalinity-induced flocculation, at a pH value of 9.51, 86% recovery of the cells was achieved with a sedimentation rate of 125 cm/h and a concentration factor (CF) of 4 (volume/volume (v/v)) in 10 min. The maximum photochemical quantum yield of photosystem II (F_v/F_m) of concentrated cells was almost the same as fresh culture (0.621). Commercial flocculants, aluminium sulphate and poly-aluminium chloride (PAC), were also successful in harvesting the studied algal cells. Optimum concentration of aluminium sulphate (AS) could be concluded as 10 ppm with 87.6% recovery and 7.10 CF (v/v) in 30 min for cost-efficient harvesting, whereas for PAC it was 20 ppm with 74% recovery and 6.6 CF (v/v). F_v/F_m yields of concentrated cells with AS and PAC showed a 1% reduction compared to fresh culture. Mg⁺² was the triggering ion for alkalinity-induced flocculation in the conditions studied. The rheology behaviour of the concentrated cells was Newtonian with values between 2.2 × 10⁻³ and 2.3 × 10⁻³ Pa s at 30°C.

Keywords:

• pre-concentration
• Chaetoceros calcitrans
• flocculation
• harvesting
• microalgae

Acknowledgements

The authors would like to thank Maria Pilar Rey Valera from IREC for valuable work with the algal cultures.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

Funding was obtained by projects: ENE2011-22761 ‘Biorrefineria de microalgas: optimización de las etapas de cosechado y de obtención de lípidos’ funded by the Spanish Ministry of Science and Innovation and ‘Fuels from Biomass’ (research programme funded by Excma. Diputació Tarragona). The research was supported by the European Regional Development Funds (ERDF, FEDER Programa Competitividad de Catalunya 2007–2013).

Supplementary data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/09593330.2015.1015456