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Fate of cyanobacterial species within full-scale water treatment/recycling processes and real-time treatment adjustment usingin-situfluorescence measurement.

Coagulation is an important step in the harvesting of algal biomass. This paper presents experimental results for a variety of prospective marine microalgal species using several inorganic and organic coagulants. Tetraselmis suecica and Chlorococcum sp. are readily coagulated using alum or iron(III) sulfate without any pH adjustment; doses of 3-5 mg L -1 or 0.2 mmol m -2 of Al 3+ or Fe 3+ yielding cell recoveries above 90% after only 5 min settling.Nannochloropsis salina, Dunaliella tertiolecta and Isochrysis galbana are harder to coagulate and require at least two times more coagulant to achieve similar recoveries. Several cationic polyacrylamides were investigated but were less effective than Al 3+ or Fe 3+ . Addition of NaOH to control pH improved the coagulation efficiency of N. salina but not of D. tertiolecta. The high coagulant demand of N. salina is due in part to its small size and large surface area, while that of D. tertiolecta may be attributable to its high production of extracellular polymer.The implications of cell surface properties for coagulation efficiency are discussed. At the coagulant doses used herein settled cells remain viable. Resuspension is a potential problem with some species, arising either from cell motility or from flotation of flocs by oxygen bubbles generated by photosynthesis. These effects can be eliminated by small additions of chlorine or by settling the algae in the dark.