The influence of solid retention time on cadmium uptake by activated sludge at different concentrations of the metal was studied. Activated sludge was cultivated in a lab-scale bioreactor with plug-flow pattern. Respirometric measurements were applied to evaluate the inhibitive effects of cadmium on activated sludge. The obtained values of the conditional adsorption constant indicate a similar affnity of cadmium to activated sludges cultivated in both plug-flow and complete-mixing reactors. The decrease of the metal affinity to activated sludge cultivated in a semicontinuous system with an increasing solid retention time was observed. High value of the mass ratio of cadmium in the activated sludge to metal in the surrounding liquid phase at equilibrium conditions made possible subsequent cadmium recovery. Maximum inhibition of cadmium to non-acclimated activated sludge was observed after 6 to 10 hours of exposure. The highest toxicity of this metal was observed between 2 and 5 hours after cadmium dosing of the acclimated sludge. A beneficial influence of solid retention time on the toxicity of the metal with regard to non-acclimated activated sludge resulted from this work.
BROWN R.E., Significance of trace metals and nitrates in sludge soils. Journal WPCF, 47, 2863—2875,1975.
WOBER S.A., SHERRARD J.H., Effects of cadmium on the completely mixed activated sludge process. Journal WPCF, 52, 2378—2388,1980.
LESTER J.N., Heavy Metals in Wastewater and Sludge Treatment Processes. Vol. 1 Sources, Analysis, and Legislation. CRC Press, Inc.: Boca Raton, Florida, pp 183,1987.
NEUFELD R. D„ HERMANN E.R., Heavy metal removal by acclimated activated sludge. Journal WPCF 47 311 329 1975
NEUFELD R.D., GUTIERREZ J., NOVAK R.A., A kinetic model and equilibrium relationship for heavy metal accumulation. Journal WPCF, 49, 489—498,1977.
NELSON P.O., CHUNG A.K., HUDSON M.C., Factor affecting the fate of heavy metals in the activated sludge process. Journal WPCF, 53, 1323—1332,1981.
BATTISTONI P., FAVA G., RUELLO M.L., Heavy metal shock load in activated sludge uptake and toxic effects. Water Res., 27, 821—827,1993.
ARTOLA A., RIGOLA M., Selection of optimum biological sludge for zinc removal from wastewater by a biosorption process. Biotechnology Letters. 14, 1199—1204, 1992.
LESTER J.N., Heavy metals in wastewater and slu¬dge treatment processes. Vol 2 Treatm ent and Dis¬posal Legislation. CRC Press, Inc.: Boca Raton, Flo¬rida, pp 145,1987.
NEUFELD R.D., Heavy metals induced deflocculation of activated sludge. Journal WPCF, 48, 1940—1948,1976.
MO WAT A., Measurement of metal toxicity by biochemical oxygen demand. Journal WPCF, 48, 853—867,1976.
GREENBERG A.E., CLESCERI L.S., EATON A.D., Standard methods for the examination of wa¬ter and wastewater, 18 th ed.: American Public He¬alth Association: Washington, pp 10-137,1992.
CECH J.S., CHUDOBA J., GRAU P., Determination of kinetic constants of activated sludge microorganisms. Wat. Sci, Technol. 17, 259—272,1984.
CHENG M.H., PATTERSON J.W., MINEAR R.A., Heavy metals uptake by activated sludge. Journal WPCF. 47, 362—376,1975.