Continuous Flow Process for Cr(VI) Removal from Drinking Water - - PowerPoint PPT Presentation
Continuous Flow Process for Cr(VI) Removal from Drinking Water through Reduction onto FeOOH by ISRs E. Kaprara, F. Pinakidou, E. Paloura, A. Zouboulis and M. Mitrakas Aristotle University of Thessaloniki, Greece 13th IWA Specialized Conference on
Aristotle University of Thessaloniki, Greece
13th IWA Specialized Conference on Small Water and Wastewater Systems (SWWS) 5th IWA Specialized Conference on Resources‐Oriented Sanitation
Chromium
Special interest
ultramafic sediments and ophiolitic rocks.
as metal’s plating. Cr(VI) origin in water
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13th IWA Specialized Conference on Small Water and Wastewater Systems (SWWS) 5th IWA Specialized Conference on Resources‐Oriented Sanitation
Cr(VI) priority pollutant Crtotal < 0.1 mg/L Crtotal < 0.05 mg/L (‐) Lack of regulation limit for Cr(VI). (‐) Total Cr limit underestimates the risk. (!) Strong intention for establishing regulation limit for Cr(VI) in drinking water.
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(!!!) U.S. State of California: MCL=10 μg Cr(VI)/L (1/7/2014).
13th IWA Specialized Conference on Small Water and Wastewater Systems (SWWS) 5th IWA Specialized Conference on Resources‐Oriented Sanitation
Kaprara et al (2015), J. Hazard. Mater. 281, 2–11.
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Contact with ultramafic rocks activates Cr(VI) formation by a catalytic mechanism. Cr(VI) concentration in water samples accounts for 96% of total chromium in average.
2Cr3+ + 3MnO2(s) + 2H2O → 2HCrO4
‐ + 3Mn2+ + 2H+
Cr(OH)2
+ + 3MnO2(s) + 2OH‐ → HCrO4 ‐ + 3MnΟΟΗ(s)
MnO2(s) + Mn2+ → MnO2(s) • Mn2+ MnO2(s) • Mn2+ + O2 → 2MnO2(s) 2MnO2(s) + 2MnΟΟΗ(s) → 2MnO2• MnΟΟΗ(s) 2MnO2• MnΟΟΗ(s) + 1/2O2 → 4MnO2 + H2O
6 Chemical reduction and precipitation. Adsorption. Ion exchange. Membrane separation NF, RO. Electro‐dialysis. Electro‐coagulation. Phyto‐remediation. Flotation. Solvent extraction.
13th IWA Specialized Conference on Small Water and Wastewater Systems (SWWS) 5th IWA Specialized Conference on Resources‐Oriented Sanitation
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Residual concentration of Cr(VI) at low ppb level. Low reaction time. Feasibility for full scale operation. Sustenance of physical and chemical characteristics of water. Low capital and running cost.
13th IWA Specialized Conference on Small Water and Wastewater Systems (SWWS) 5th IWA Specialized Conference on Resources‐Oriented Sanitation
hemical reduction of Cr(VI) and removal of C(III) by: ‐ precipitation ‐ adsorption
ighly efficient and fast and educes Cr(VI) to the non‐toxic insoluble Cr(III) form mon reductants ro‐valent iron (ZVI) surface passivation, enriches treated water with dissolved Fe(II) rrous iron salts (FeSO4, FeCl2) BAT ‐ production of sludge
eresting results high dose demand
mical reduction and precipitation norganic Sulfur Reductants
perimental batch evaluation: e maximum dose 50 mg S/L (increase SO4
2‐by 150 mg/L)
ISRs proved very effective at pH ≤ 4 (!) eptable efficiency at pH 7 only by sodium dithionite (Na2S2O4)
uence of reaction pH on Cr(VI) removal
(Cr(VI)=100μg/L, CISR=10 mg S/L, reaction time 24 h, 20±1oC)
Influence of ISRs dose on Cr(VI) removal
(Cr(VI)=100μg/L, pH 7, reaction time 24 h, 20±1oC)
imization of Cr(VI) removal from drinking water by ISRs Through surface “catalysis” Under continuous flow configuration.
nts
ants examined: NaHSO3, Na2S2O3, Na2S2O4, Na2S2O5 and Na2S. catalyst: synthesized FeOOH mainly consisting of Fe16O16(OH)10(SO4)3 ∙10H2O.
Cations (mg/L) Anions (mg/L) Na+ 88.8 HCO3
‐
183 Ca2+ 40.0 SO4
2‐
50 Mg2+ 12.7 Cl‐ 71 NO3‐‐N 2 F‐ 1 PO4
3‐‐P
0.04
Artificial water prepared with composition close to that of natural ones according to the NSF standard.
rimental procedure
d Small Scale Column Tests (RSSCTs) sment of treatment efficiency r continuous flow conditions. rption columns: OOH granules (0.25 – 0.5 mm). CT: 3 min, pH: 7.0, T: 20o C. /h of 100 μg/L Cr(VI) in artificial water. 5 L/h of ISR solution. ation y to decrease Cr(VI) concentration below 10 μg/L S: Investigation of Cr(VI) sorption mechanism
ugh curve of Cr(VI) adsorption at FeOOH column (initial Cr(VI):
Assessment of FeOOH effectiveness to adsorb Cr(VI) under continuous flow conditions (‐) low adsorption capacity (+) ability to decrease residual Cr(VI) to sub‐ppb levels. (+) Promotes electron transfer Cr(VI) + 3e+ → Cr(III)
ISR inflow ISR outflow Cr(VI) outflow O2outflow mg S/L mg S/L μg/L mg/L O3 20 8 47 3.5 40 26 26 2.5 O3 20 14 50 3.5 40 33 28 2.5 O4 20 13 ND 4.5 40 31 ND 2.5 O5 20 4 42 1.5 40 21 29 <1 S 20 <1 ND <1
Addition of ISRs solution at doses
Na2S2O4, Na2S: highest efficiency. Na2S: unpleasant odour to treated water. NaHSO3, Na2S2O3, Na2S2O5: (‐) failed to decease Cr(VI) to single ppb levels, Na2S2O4: qualified and further examined at column experiments.
kthrough curves of Cr(VI) uptake by FeOOH column different Na S O concentrations (i iti l C (VI) 100
For better estimation of Na2S2O4 dose:
at 100 μg/L Cr(VI)and
slope 10 mg/L S‐Na2S2O4: Cr(VI) 5±2 μg/L 15 and 20 mg S‐Na2S2O4: Cr(VI) < 1 μg/L (+) “buffer” adsorption capacity of FeOOH column.
gation of Cr(VI) reduction reaction and sorption mechanism of Cr. measurements H / absence of ISRs: Cr(VI) is physisorbed onto the FeOOH surface. H / addition of Na2S2O4: Cr(III) forms inner sphere complexes, Cr(VI) involved in sphere complexes.
Cr(III) Fe Fe Fe
Mononuclear (2E) (3.00‐3.05Å) (2C) 6Å)
Bidentate
Mononuclear (1V) (3.60Å)
Chemisorption inner sphere complexes Physisorption
Cr
Monodentate
dsorption mechanism of Cr oxyanions onto surfaces
Significant contribution of FeOOH on Cr(VI) removal by ISRs. Highest efficiency: Na2S2O4, Na2S. Na2S: residual unpleasant odour additional treatment step (‐) Continuous flow configuration:
concentration below the upcoming limit of 10 μg/L.
EXAFS study: chromium uptake onto FeOOH proceeds via both physisorption and chemisorption.
tinuous Flow Process of Cr(VI) Removal from Drinking Water through Reduction onto FeOOH by ISRs