Removal of heavy metals by the nuisance cyanobacteria Microcystis in continuous cultures: an eco-sustainable technology

Abstract

The blue-green alga Microcystis was grown under continuous culture 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. The present work used artificial wastewater with low free ion activities due to the presence of a strong chelating agent EDTA but with total concentrations not appropriate for acceptable environments. Chromium (VI) and cadmium (II) had a positive interaction that increased the removal percentages of both these metals; the work, however, could not detect any interaction with copper (II). Microcystis was able to remove all the tested metals to some extent (24-76%), but bivalent metals were not removed as efficiently as reported in batch cultures. Chromium (VI) was more efficiently removed in continuous cultures than in batch culture, because the uptake of chromate could be favoured by actively growing algae. The work demonstrated the efficiency of Microcystis in metal removal from single bimetallic as well as multimetallic conditions. Since Microcystis is a nuisance and bloom-forming cyanobacteria, its biotechnological exploitation in metal removal at the field scale should follow an eco-sustainable approach.