Heavy metals removal by the microalga Scenedesmus incrassatulus in continuous cultures

The microalga Scenedesmus incrassatulus was grown under continuous regime in the presence of chromium(VI), cadmium(II) and copper(II), as single metal species and as mixtures of two or three metals, in a laboratory scale system. We used an artificial wastewater with low free ion activities (as determined by MINEQL+) due to the presence of EDTA (a strong chelating agent) but with total concentrations not suitable for acceptable environments. Chromium(VI) and cadmium(II) had positive interaction that increased the removal percentages of both these metals; we could not, however, detect any interaction with copper(II). S. incrassatulus was able to remove all the tested metals to some extent (25-78%), but bivalent metals were not removed as efficiently as reported in batch cultures, probably due to the high pH values there recorded. Chromium(VI) was more efficiently removed in continuous cultures than in batch culture, because the uptake of chromate could be favored by actively growing algae. (C) 2004 Published by Elsevier Ltd.