ON THE POTENTIAL TOXICITY OF “PROMISING” CHROMIUM EXTRACTANTS G ON THE POTENTIAL TOXICITY OF “PROMISING” CHROMIUM EXTRACTANTS G. Lytras, G. Malavetas, C. Lytras, G. Lyberatos ICEHT/FORTH and NTUA

Approximately 4.500 kg/d chromium are discharged into the environment.

Chromium in water & wastewater Two stable oxidation states: Hexavalent [Cr(VI)] Trivalent [Cr(III)]. Hexavalent chromium is highly toxic and can cause serious damage to the environment and human beings. Trivalent chromium is less toxic and can be readily precipitated out of solution in the form of Cr(OH)3. Hexavalent [Cr(VI)] Hexavalent chromium is highly toxic and can cause serious damage to the environment and human beings.

Presence of Cr(VI) in the Environment Chromium from the anthropogenic sources is discharged into the environment mainly as hexavalent chromium. Recent studies have shown that Cr(VI) can be formed naturally in the environment.

Legislation for Chromium and Cr(VI) Potable water: Both in U.S.A. and E.U. the maximum Cr (VI) concentration in potable water is 0.05 ppm. Wastewater: In E.U. the maximum daily effluent concentration for industrial wastewater should not exceed 3 ppm.

Ways for Cr(VI) removal Chemical reduction to Cr(III) which can be precipitated as hydroxides. Ion Exchange Adsorption Reverse Osmosis Biological removal of Cr(VI) Liquid-Liquid Extraction

Liquid-Liquid Extraction During Liquid- Liquid Extraction (LLE) Cr(VI)  contained in an aqueous phase  is transferred to another organic phase which is water immiscible. Cr(VI) ions Cr(VI) ions Organic Phase Aqueous Phase

Advantages of LLE LLE can selectively extract a desired metallic ion from a feed solution containing a significant amount of metallic impurities. LLE can concentrate the desired ion in final aqueous solution so that it can be treated by methods inappropriate for the initial dilute feed. LLE is well suited for process automation and efficient metal recovery from a mixed-metal hydroxide slurry. (Knocke et al., 1978; Petersen et al., 1981)

Organic & Aqueous Phase Organic phase: Organic solvent Extractant (Modifier or stabilizer) Aqueous phase: Wastewater containing 1000 ppm Cr(VI)

Organic Solvent The organic solvent must be: Bio-compatible Non- biodegradable Non- volatile Water-immiscible

Organic Solvents The following organic solvents were screened: Hexane [C6H14] Heptane [C7H16] Chloroform [CHCl3] Ethyl acetate [C4H8O2] Kerosene

Extractants The following extractants were used: N-Methyl-N,N-dioctyloctan-1-ammonium chloride (Aliquat 336) [C25H54CIN]  Tri-n-octylphosphine oxide (TOPO) [C24H51OP] Tri-n-butyl phosphate (TBP) [C12H27O4P]

Experimental procedure Stir at 25oC at 35rpm for 24 hours Transfer to a separation funnel and leave it for 45 minutes Organic phase Aqueous phase with Cr(VI) Separation of organic and aqueous phase

Toxicity of organic solvents Growth Hexane, C6H14 - Heptane, C7H16 + Chloroform, CHCl3 ­­- Ethyl acetate,C4H8O2 Kerosene ++ Microorganisms derived from anaerobic sludge of the Municipal Wastewater Treatment Plant of Lycovrisi, Attica, Greece 24 hours at 35rpm 25oC

Stabilizer The kerosene/Aliquat 336 forms an intense interphase. So, we used 1-hexanol as a stabilizer. +10% v/v 1-Hexanol Organic phase: 5% v/v Aliquat 336 Kerosene Aqueous phase: 1000ppm Cr(VI) 20 ml organic phase: 20 ml aqueous phase

Optimization of conditions during Cr(VI) extraction from aqueous solutions with kerosene/Aliquat 336/1-hexanol mixture

Effect of pH on the Cr(VI) extraction efficiency Initial Cr(VI) concentration: 1000 ppm Shaking time: 24 hours Organic: Aqueous phase: 1:1 Temperature: 25 oC

Effect of organic:aqueous phase ratio on the Cr(VI) extraction efficiency Initial Cr(VI) concentration: 1000 ppm Shaking time: 24 hours Temperature: 25 oC

Effect of the initial Cr(VI) concentration on the Cr(VI) extraction efficiency Shaking time: 24 hours Organic: Aqueous phase: 1:1 Temperature: 25 oC pH: 7

Effect of shaking time on the Cr(VI) extraction efficiency Initial Cr(VI) concentration (ppm) Final Cr(VI) concentration (ppm) Standard Deviation (SD) % Extraction of Cr(VI) 0 min 1000 69,8 4,51 93,0 5 min 66,1 7,11 93,4 10 min 78,8 2,03 92,1 20 min 75,8 6,71 92,4 40 min 66,4 5,18 2 h 79,4 7,28 4 h 82,5 1,53 91,8 24 h 66,3 6,73 Organic:Aqueous phase: 1:1 Temperature: 25 oC pH: 7

Toxicity of Organic Phase Microorganisms derived from the anaerobic sludge of a Municipal Wastewater Treatment Plant, grown either in YPD or in a Basal Medium, were incubated with the organic phase. 100% mortality of both cultures during the second day of incubation. YPD: 20 g/L Glucose, 10 g/L Yeast Extract, 20 g/L Bactopeptone Basal Medium: 4 g/L Glucose, 1 g/L NH4Cl, 1.75 g/L KH2PO4, 0.25 K2HPO4, 7 ml/L trace elements’ solution

Toxicity of Organic Phase Incubation: 2 days Temperature: 25oC 17 ml Kerosene + 2ml 1-Hexanol +1ml Aliquat 336 20 ml of mixed culture+ 20 ml sterile H2O 18 ml Kerosene + 2ml 1-Hexanol 20 ml of mixed culture 20 ml of mixed culture Aliquat 336 is the toxic ingredient of the organic phase YPD Basal Medium

Toxicity of Aliquat 336 Addition of 200 μl of Aliquat 336 in 20 ml of the mixed culture growing in Basal Medium led to 100% mortality during the second day of the incubation. The mixtures Aliquat 336/Heptane, Aliquat 336/Kerosene, Aliquat 336/Olive pomace oil were also toxic.

Toxicity of Aliquat 336 The addition of 200 ml Organic Phase in a 2L anaerobic bioreactor led to 100% mortality during the first days of the operation. The bioreactor was inoculated with an acclimated mixed culture with high Cr(VI) reduction rate (15ppm/day) and tolerance to the organic solvents.

Aliquat 336

Uses of Aliquat 336 Extraction of Chromium Vanadium extraction Arsenic extraction Separation of platinum group metals Copper extraction Saeed et al., 2009

Concerns about the use of Aliquat 336 as Extractant

Safety information Acute toxicity (oral, dermal, inhalation) Hazardous to the aquatic environment Acute hazard Chronic hazard Corrosive to metals Skin corrosion Serious eye damage

Concerns Aliquat 336 has high water solubility (Torma and Itzkovitch, 1976). Aliquat 336 is an inhibitor of growth of intact algal cells. Ιt also inhibits the photosynthesis in intact plant cells and in isolated spinach chloroplasts (Egneus et al, 1977). Aliquat 336 is toxic to Lactobacillus delbrueckii (Roffler et al., 1984). Aliquat 336 is toxic to Activated sludge (Quijano et al., 2011). Aliquat 336 is toxic to anaerobic sludge (this study).

Thank you very much for your attention! Acknowledgements This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.