Biological Cr(VI) removal coupled with biomass growth, biomass decay, and multiple substrate limitation

E.M. CONTRERAS; A.M. FERRO OROZCO; N.E. ZARITZKY

WATER RESEARCH

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2011 vol. 45 p. 3034 - 3046

0043-1354

In this work, a mathematical model for the biological reduction of Cr(VI), carbon andnitrogen sources consumption, and biomass growth under fully aerobic conditions wasdeveloped. The model comprises three types of aerobic heterotrophic cells (non-growingcells, growing cells with chromate reductase activity, and growing cells that have lost thechromate reductase activity), and five soluble compounds (organic substrate, ammonianitrogen, non-metabolizable soluble products, dissolved oxygen, and hexavalent chromium).Two processes are considered responsible for the reduction of Cr(VI). The first oneis the reduction of Cr(VI) coupled with growth, the second process is coupled with theendogenous decay of the biomass. The model was calibrated using the results obtained inbatch cultures in the absence of carbon and nitrogen sources, using different initial Cr(VI)concentrations (0-100 mgCr/L), two carbon sources (cheese whey and lactose), anddifferent initial nitrogen to carbon ratio (0-50 mgN/gCOD). The calibrated model wasused to calculate steady-state values of TSS, soluble COD, TAN and Cr(VI) in continuoussystems, obtaining a good agreement with the experimental data. The model also accuratelypredicted the transient concentration of Cr(VI) as a function of time in response tostep changes of the inlet Cr(VI) concentration in continuous systems.