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The Effects and Processes for Removal of Chromium in Activated Sludge Treatment

The Effects and Processes for Removal of Chromium in Activated Sludge Treatment. Jenny Merical. Introduction. Chromium Sources Biological Removal Methods Activated Sludge Absorption Capacity Biomass Growth Nitrification COD Removal Toxicity of Chromium. www.euroleather.com/.

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The Effects and Processes for Removal of Chromium in Activated Sludge Treatment

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  1. The Effects and Processes for Removal of Chromium in Activated Sludge Treatment 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 Nitrobacter sp. • 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

  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 Acinetobacter www.cns.fr Cellulomonas www.sci.muni.cz

  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 Vorticella plantphys.info Opercularia www2.ac-lyon.fr

  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

  19. Thank you

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