1. Jenny Merical

2. Introduction Chromium Sources Biological Removal Methods Activated Sludge Absorption Capacity Biomass Growth Nitrification COD Removal Toxicity of Chromium www.euroleather.com/

3. Sources of Chromium Chromium Cr(VI) Cr(III) Sources Leather tanning Electroplating Wood Preservation Textile manufacturing www.seacoastventures.net www.galvanomondo.com

4. Activated Sludge Plants in Iowa www.iamu.org

5. Chromium Removal Methods Traditional: Chemical process Biological: Reduction of Cr(VI) to Cr(III) Adsorption Positive charged Cr(VI) attracted to negative charged microorganism cell wall

6. Reduction of Cr(VI) to Cr(III) Most common removal mechanism Reduced then precipitated as Cr(OH) 3 Metal Distribution for 1 mg/l Cr(III) Metal Distribution for 1 mg/l Cr(VI) Stasinakis, Thomaidis, Mamais, and Karivali et al., 2003

7. Activated Sludge Absorption Capacity 95% Cr(III) removal efficiency Increased removal Longer SRT Higher pH 96-99% chromium present in the form Cr(III) when anoxic selector precedes aerobic tank Stasinakis, Thomaidis, Mamais, and Karivali et al., 2003

8. Activated Sludge Characteristics Suspended Solids Concentration Cr(III) removal efficiency increases with a high SS concentration Cr(VI) removal did not correlate with SS concentration Sludge Age Cr(III) removal efficiency decreases as age increases Cr(VI) removal not affected by sludge age

9. Activated Sludge Acclimation Cr(VI) and Cr(III) increase biomass lag time Cr(III) more inhibitive at concentrations less than 70 mg/L Cr(VI) more inhibitive at concentrations greater than 70 mg/L Lag time increases with increased chromium concentration Optimum growth conditions: 10 mg/L Cr(III) or Cr(VI) 11 and 17 HRT, respectively

10. Biomass Growth 25 mg/L Cr(VI) stimulates biomass growth 15 mg/L Cr(III) stimulates biomass growth Higher concentrations limit growth Gikas and Romanos, 2006

11. Nitrification Cr(VI) interferes with nitrification Increases ammonium concentration Decreases nitrate concentration 5 mg/L decreased ammonium removal to 30% System recovery of about 12 days Cr(III) interferes at higher concentrations 25 mg/L or greater limit nitrification System recovery of about 7 days www.college.ucla.edu Nitrobacter sp.

12. COD Removal Cr(VI) limits COD removal capacity No significant impact with less than 5 mg/L 5 mg/L system required 3 days to recover from loading Higher Cr(VI) concentrations More pronounced effect on COD removal Longer system recovery time Cr(VI) shock loading does not impact COD

13. Toxicity of Chromium Microbiological effects Decrease biomass Decrease activity Decrease density Cr(VI) 100 times more toxic than Cr(III) Cr(III) less soluble Presence of sodium decreased Cr(VI) toxicity

14. Chromium Reducing Bacteria Acinetobacter Partially reduce Cr(VI) to Cr(III) Assist in chromium removal Ochrobactrum Aureobacterium Corynebacterium Hydrogenophaga Clavibacter www.cns.fr www.sci.muni.cz Acinetobacter Cellulomonas

15. Chromium loading on bacteria Nitrifying bacteria more sensitive than COD reducing bacteria Longer recovery time Smaller quantity/diversity of nitrifying bacteria Cr(VI) has to be toxic to several species to impact COD reducing bacteria Shock loading Lethal to Cr(VI) reducing bacteria 9.25-211 mg/L Range implies different toxicity levels

16. Chromium Reducing Protozoa Species: Vorticella Opercularia Stalked ciliates Free swimming ciliates Rotifers Free swimming ciliates dominate in high Cr(VI) concentration 5 mg/L Cr(VI) toxic to all protozoa www2.ac-lyon.fr Opercularia Vorticella plantphys.info

17. Activated Sludge Chromium Removal Advantages Drawbacks Inhibits nitrification process (25 mg/L) Inhibits filamentous bulking Increased biomass growth lag time Limits COD removal Limits microorganism diversity Self sufficient communities Stimulate biomass growth at optimum concentration Some microorganisms assist in chromium removal Possibly more economical

18. Conclusion Activated sludge sufficient for chromium removal 95% removal efficiency by absorption Reduction of Cr(VI) to Cr(III) Couple with nitrification process Improve chromium removal: Lower activated sludge age Avoid high concentrations Longer SRT Higher pH Increase Suspended Solids