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Abstract
A series of batch experiments was conducted to compare the ability of 11 microalgal
species of the same cell density in removing nickel (Ni) and zinc (Zn) from synthetic
wastewater. These included Chlorella vulgaris (commercially available), Chlorella
sorokiniana and Scenedesmus quadricauda (isolates from polluted water of Wuhan, China),
and eight different isolates from Hong 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 after 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 treatment,
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 interfered 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 removing Ni and Zn. At the other extreme, one Hong Kong isolate
(Synechocystis 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 significantly reduced by
the presence of Zn. All algae tested were found to be viable, showing these 11 species
could tolerate a mixture of 30 mg/l Ni and 30 mg/l Zn in wastewater.