Jenny Merical. Introduction Chromium Sources Biological Removal Methods Activated Sludge Absorption...
-
Upload
ezra-hodges -
Category
Documents
-
view
216 -
download
1
Transcript of Jenny Merical. Introduction Chromium Sources Biological Removal Methods Activated Sludge Absorption...
Jenny Merical
IntroductionChromium Sources
Biological Removal Methods
Activated Sludge Absorption Capacity
Biomass Growth
Nitrification
COD Removal
Toxicity of Chromium
www.euroleather.com/
Sources of ChromiumChromium
Cr(VI)Cr(III)
SourcesLeather tanningElectroplatingWood PreservationTextile manufacturing
www.seacoastventures.net
www.galvanomondo.com
Activated Sludge Plants in Iowa
www.iamu.org
Chromium Removal MethodsTraditional:
Chemical process
Biological:
Reduction of Cr(VI) to Cr(III)
Adsorption
Positive charged Cr(VI) attracted to negative charged microorganism cell wall
Adsorbed90%
Precipitated9%
Dissolved1%
Dissolved86%
Adsorbed14%
Precipitated0%
Reduction of Cr(VI) to Cr(III)Most common removal mechanismReduced 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
Activated Sludge Absorption Capacity95% Cr(III) removal efficiencyIncreased removal
Longer SRTHigher pH
96-99% chromium present in the form Cr(III) when anoxic selector precedes aerobic tank
Stasinakis, Thomaidis, Mamais, and Karivali et al., 2003
Activated Sludge CharacteristicsSuspended Solids Concentration
Cr(III) removal efficiency increases with a high SS concentration
Cr(VI) removal did not correlate with SS concentration
Sludge AgeCr(III) removal efficiency decreases as age increasesCr(VI) removal not affected by sludge age
Activated Sludge AcclimationCr(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
Biomass Growth25 mg/L Cr(VI) stimulates biomass growth15 mg/L Cr(III) stimulates biomass growthHigher concentrations limit growth
Gikas and Romanos, 2006
NitrificationCr(VI) interferes with nitrification
Increases ammonium concentrationDecreases nitrate concentration5 mg/L decreased ammonium removal to
30%System recovery of about 12 days
Cr(III) interferes at higher concentrations25 mg/L or greater limit nitrificationSystem recovery of about 7 days
www.college.ucla.edu
Nitrobacter sp.
COD RemovalCr(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
Toxicity of ChromiumMicrobiological 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
Chromium Reducing BacteriaAcinetobacter
Partially reduce Cr(VI) to Cr(III)
Assist in chromium removal
Ochrobactrum
Aureobacterium
Corynebacterium
Hydrogenophaga
Clavibacter
www.cns.fr
www.sci.muni.cz
Aci
neto
bact
er
Cel
lulo
mon
as
Chromium loading on bacteriaNitrifying bacteria more sensitive than COD reducing
bacteriaLonger recovery timeSmaller quantity/diversity of nitrifying bacteriaCr(VI) has to be toxic to several species to impact
COD reducing bacteriaShock loading
Lethal to Cr(VI) reducing bacteria 9.25-211 mg/LRange implies different toxicity levels
Chromium Reducing ProtozoaSpecies:
VorticellaOperculariaStalked ciliatesFree swimming ciliatesRotifers
Free swimming ciliates dominate in high Cr(VI) concentration
5 mg/L Cr(VI) toxic to all protozoa
www2.ac-lyon.fr
Ope
rcul
aria
Vor
ticel
la
plantphys.info
Activated Sludge Chromium RemovalAdvantages 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
ConclusionActivated sludge sufficient for chromium removal
95% removal efficiency by absorptionReduction of Cr(VI) to Cr(III)Couple with nitrification process
Improve chromium removal:Lower activated sludge ageAvoid high concentrationsLonger SRTHigher pHIncrease Suspended Solids