Water Treatment Sludge Can Be Used As An
Adsorbent For Heavy Metals
In Wastewater Streams
Author(s)
Y.-F. Zhou & R. J. Haynes
Abstract
Throughout the world, alum is the most widely used coagulant in drinking water
treatment. The waste stream from water treatment is alum-derived water
treatment sludge and in most localities large quantities of this material are
deposited in waste disposal areas. Reuse of this waste stream in an
environmentally sustainable manner is therefore a priority. Research has shown
that the material is an effective adsorbent of phosphate from aqueous solutions,
but its use as an adsorbent for heavy metals has not been investigated. Our
research showed that water treatment sludge was an effective adsorbent for
Pb(II), Cr(III) and Cr(VI). Adsorption isotherm data fitted equally well to
Freundlich and Langmuir equations and kinetic data correlated well to a pseudosecond-
order kinetic model, suggesting that the mechanism involved was
chemisorption. Adsorption was pH-dependant with percentage sorption of Pb(II)
and Cr(III) increasing greatly with increasing pH and that of Cr(VI) decreasing.
Cr(VI) could be removed from sludge surfaces with 0.1 M NaOH. At a
concentration of 0.1M, HNO3 was effective at removing adsorbed Cr(III) and
Pb(II) from the sludge surfaces and regeneration was successful for eight
sorption/removal cycles. Other work showed that water treatment sludge had
adsorbent properties for Cu, Zn, Cd, As and Se. It was concluded that water
treatment sludge is a suitable material from which to develop a low-cost
adsorbent for removal of both heavy metal cations and anions from wastewater
streams.
Keywords: water treatment sludge, adsorption isotherms, Cr(III), Cr(VI), Pb(II).
Keywords
water treatment sludge, adsorption isotherms, Cr(III), Cr(VI), Pb(II)
Related Book
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