The%20Effects%20and%20Processes%20for%20Removal%20of%20Chromium%20in%20Activated%20Sludge%20Treatment

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

• Jenny Merical

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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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Sources of Chromium

• Chromium
• Cr(VI)
• Cr(III)
• Sources
• Leather tanning
• Electroplating
• Wood Preservation
• Textile manufacturing

www.seacoastventures.net
www.galvanomondo.com
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Activated Sludge Plants in Iowa
www.iamu.org
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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

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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
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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
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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

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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

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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
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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
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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

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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

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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
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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

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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
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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

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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

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Thank you