No abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. i.e. carbon, nitrogen and phosphorus; however other nutrients are also reviewed. M A N U S C R I P T A C C E P T E D 21Nutrients are generally taken up in the inorganic form, but several organic forms of 22 them are also assimilable. Some nutrients do not display any inhibition effect on believed that they will play a significant role in the sector of renewable energy nutrients for the production of microalgae using either synthetic fertilizers or 83 wastewater streams. The review will focus and discuss not only issues related to the 84 physiology of microalgae/cyanobacteria but also will discuss technical concerns 85 about the application of nutrients for biomass production. The main focus will be on 86 the nutrients carbon, nitrogen and phosphorus; however the minor nutrients 87 potassium, magnesium, sulfur and calcium will also be reviewed. CO2 is dissolved in water it reacts with the water molecules (H2O) and forms a weak104 acid-base buffer system, having the following equilibrium ( Fig Fig Fig Figure ure The above equilibrium depends on the pH of the solution, which means that 110 the relative amount of the dissolved inorganic carbon (DIC) species is strictly 111 related to the pH of the solution. Based on the equilibrium of the carbon species 112( Fig Fig Fig Figure ure Inorganic carbon is fixed inside the microalgal cells and is converted to 129Since the form and the amount of dissolved inorganic carbon depends on pH, 130 salinity, pressure and temperature ( Fig Fig Fig Figure ure 147The form of inorganic carbon utilization depends also on its concentration in the 148 medium; in high DIC concentration it seems that CO2 is preferred over HCO3 - 149(Aizawa and Miyachi 1986). It was shown that the active uptake of CO2 is 150 significantly faster than that of HCO3 - (Matsuda et al. 1999)

Microalgae hold great potential as a feedstock for biofuels or bulk protein or treatment of wastewater or flue gas. Realising these applications will require the development of a cost-efficient harvesting technology. Here, we explore the potential of flocculation induced by high pH for harvesting Chlorella vulgaris. Our results demonstrate that flocculation can be induced by increasing medium pH to 11. Although both calcium and magnesium precipitated when pH was increased, only magnesium (≥0.15 mM) proved to be essential to induce flocculation. The costs of four different bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and sodium carbonate) were calculated and evaluated and the use of lime appeared to be the most cost-efficient. Flocculation induced by high pH is therefore a potentially useful method to preconcentrate freshwater microalgal biomass during harvesting.

Due to their small size and low concentration in the culture medium, cost-efficient harvesting of microalgae is a major challenge. We evaluated the potential of cationic starch as a flocculant for harvesting microalgae using jar test experiments. Cationic starch was an efficient flocculant for freshwater (Parachlorella, Scenedesmus) but not for marine microalgae (Phaeodactylum, Nannochloropsis). At high cationic starch doses, dispersion restabilization was observed. The required cationic starch dose to induce flocculation increased linearly with the initial algal biomass concentration. Of the two commercial cationic starch flocculants tested, Greenfloc 120 (used in wastewater treatment) was more efficient than Cargill C*Bond HR 35.849 (used in paper manufacturing). For flocculation of Parachlorella using Greenfloc 120, the cationic starch to algal biomass ratio required to flocculate 80% of algal biomass was 0.1. For Scenedesmus, a lower dose was required (ratio 0.03). Flocculation of Parachlorella using Greenfloc 120 was independent of pH in the pH range of 5 to 10. Measurements of the maximum quantum yield of PSII suggest that Greenfloc 120 cationic starch was not toxic to Parachlorella. Cationic starch may be used as an efficient, nontoxic, cost-effective, and widely available flocculant for harvesting microalgal biomass.