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Chromium species behaviour in the activated sludge process
Athanasios S Stasinakis1, Nikolaos S Thomaidis, Daniel Mamais
1Laboratory of Air and Water Quality, Department of Environmental Studies, University of the Aegean, University Hill, 81 100, Mytilene, Greece.
Chemosphere
|June 5, 2003
Summary
Activated sludge effectively removes trivalent chromium (Cr(III)) through adsorption and precipitation. Hexavalent chromium (Cr(VI)) removal is minimal, but Cr(VI) can be reduced by activated sludge with sufficient organic substrate.
Area of Science:
- Environmental Science
- Environmental Engineering
- Microbiology
Background:
- Chromium contamination in wastewater poses environmental risks.
- Understanding chromium speciation (Cr(III) vs. Cr(VI)) is crucial for effective treatment.
- Activated sludge is a common biological wastewater treatment method.
Purpose of the Study:
- To compare the removal efficiency of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) using activated sludge.
- To investigate the occurrence of Cr(VI) reduction and Cr(III) oxidation within wastewater treatment systems.
Main Methods:
- Batch experiments were conducted using activated sludge from sequencing batch reactors.
- Chromium removal was quantified and analyzed using adsorption isotherm models.
- Factors influencing removal, such as sludge age, suspended solids, and organic substrate concentration, were investigated.
Main Results:
- Activated sludge demonstrated high removal of Cr(III) (approx. 90% via adsorption/precipitation).
- Cr(VI) removal was significantly lower (≤15%), with no observed Cr(III) oxidation to Cr(VI).
- Cr(VI) reduction was confirmed, primarily dependent on organic substrate availability (COD > 1000 mg/L) and initial Cr(VI) concentration.
Conclusions:
- Activated sludge is effective for Cr(III) removal but not for Cr(VI) removal.
- Biological reduction of Cr(VI) to less toxic Cr(III) is feasible in activated sludge systems under specific conditions.
- Wastewater treatment strategies should consider chromium speciation and optimize conditions for Cr(VI) reduction.