Performance of different microalgal species in removing nickel and zinc from industrial wastewater

A series of batch experiments was conducted to compare the ability of 11 mi croalgal species of the same cell density in removing nickel (Ni) and zinc (Zn) from synthetic wastewater. These included Chlorella vulgaris (commerci ally available), Chlorella sorokiniana and Scenedesmus quadricauda (isolate s from polluted water of Wuhan, China), and eight different isolates from H ong Kong. The Wuhan isolate of Scenedesmus removed most Ni, probably due to its large biomass. Nickel concentration was reduced from an initial 30 to 0.9 mg/l after 5 min (97% Ni removal), and further declined to 0.4 mg/l aft er 90 min of treatment. In wastewater containing 30 mg/l Ni and 30 mg/l Zn, more than 98% Ni and Zn were removed simultaneously at the end of 5 min tr eatment, indicating that the presence of Zn in wastewater did not affect Ni removal by this Scenedesmus isolate. The second most effective species for Ni removal was an isolate, tentatively identified as Chlorella miniata, Ni concentration was reduced to 10 mg/l after 90 min, and was only slightly i nterfered by the presence of Zn. In terms of metal removal per unit biomass or unit surface area of algal cells, C. miniata was the best species in re moving Ni and Zn. At the other extreme, one Hong Kong isolate (Synechocysti s sp.) did not remove any Ni and only achieved 40% Zn removal. Performance of the other isolates was comparable with the commercial C. vulgaris, less than 50% Ni was removed after 5 h of treatment and Ni removal was significa ntly reduced by the presence of Zn. All algae tested were found to be viabl e, showing these 11 species could tolerate a mixture of 30 mg/l Ni and 30 m g/l Zn in wastewater. (C) 2000 Elsevier Science Ltd. All rights reserved.