Biomass harvesting and concentration of microalgae scenedesmus sp. cultivated in a pilot phobioreactor

Samples of a culture of Scenedesmus sp. grown in a pilot raceway photo bioreactor were processed in the laboratory by flocculation and centrifugation, to assess the efficiency of solid concentration of both methods. Three flocculation agents were tested, ferrous sulfate (FeSO4), ferric chloride (FeCl3) and aluminum sulfate Al2(SO4)3 using concentrations of 0.05, 0.2, 0.8, 1.5, 3.0 y 7.0 g L−1 and pH range between 4.0 and 11.0 for the better concentration response of each flocculant. Additional flocculation tests were carried out to measure the sedimentation kinetics of the concentrated biomass. All these tests were performed with culture samples of 800 cm3 for 12 min of stirring and 10 min of sedimentation with three repetitions. In the case of centrifugation the testing was carried out using a laboratory centrifuge run at speeds of 1500, 1800 and 2200 rpm with culture samples of 300 cm3 for 15 min and three repetitions. In order to quantify the efficiency of the concentration, initial and final turbidity of the cleared water and concentrated portion were measured. The flocculation experiments showed that a limit of maximum concentration efficiency of 97.9% that was reached with 1.5 g L−1 of Al2(SO4)3 at pH of 8.5 and an average sedimentation velocity of about 2.7 cm min−1. Testing also showed that FeSO4 was the worst flocculant agent in the range tested. With respect to the centrifugation test, the solid concentration efficiency varied from 95.2% at speed of 1500 rpm up to 96.0% at speed of 2200 rpm.