Joint Assessment of Bioreduction of Chromium(VI) and of Removals of Both Total Chromium and Total Organic Carbon (TOC) in Sequential Hybrid Bioreactors

Abstract

The overall purpose of this work was to evaluate the treatment system performance of sequential hybrid bioreactors, one without aeration and another with intermittent aeration, in the bioremoval of Cr(VI) and total chromium and in the removal of total organic carbon (TOC). The saturation kinetic curves were studied with initial concentrations of Cr(VI) of 80, 120 and 150 mg L⁻¹. A reference test was performed before adding chromium to the system, with the intention of checking the influence of the presence of chromium on the TOC removal. During the bioreactor regeneration, the chromium removal was evaluated, after each kinetic studied. For kinetics with 80 mg L⁻¹ of Cr(VI), the results showed that after 600 h of operation, there was no saturation of bioreactors, yielding 87 % overall removal of Cr(VI) and 62 % chromium total. For initial concentrations of Cr(VI) of 120 and 150 mg L⁻¹, only the non-aerated bioreactor reached saturation after 228 and 216 h of operation, respectively. In regeneration, it was found in all the assays performed that the chromium concentration at the outlet of the bioreactor became almost zero at a maximum of 72 h of operation. In the blank test, the TOC removal achieved was 64 %, while in the three tests in the presence of chromium, this was approximately 55 % (80 mg L⁻¹), 41 % (120 mg L⁻¹) and 31 % (150 mg L⁻¹). After cell lysis by ultrasound, it was found that the chromium concentration retained inside there was lower than the concentrations present in the environment.

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