Please wait a minute...

Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2020, Vol. 14 Issue (5) : 88
Hexavalent chromium in drinking water: Chemistry, challenges and future outlook on Sn(II)- and photocatalyst-based treatment
Haizhou Liu(), Xuejun Yu
Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, CA 92521, USA
Download: PDF(1292 KB)   HTML
Export: BibTeX | EndNote | Reference Manager | ProCite | RefWorks

• Wide occurrence of Cr(VI) in US source drinking water.

• A strong dependence of occurrence on groundwater sources.

• Elucidate Redox and equilibrium chemistry of Cr(VI).

• Sn(II)-based and TiO2-based reductive treatments hold extreme promise.

• Key challenges include residual waste, Cr(VI) re-generation and socioeconomic drivers.

Chromium (Cr) typically exists in either trivalent and hexavalent oxidation states in drinking water, i.e., Cr(III) and Cr(VI), with Cr(VI) of particular concern in recent years due to its high toxicity and new regulatory standards. This Account presented a critical analysis of the sources and occurrence of Cr(VI) in drinking water in the United States, analyzed the equilibrium chemistry of Cr(VI) species, summarized important redox reaction relevant to the fate of Cr(VI) in drinking water, and critically reviewed emerging Cr(VI) treatment technologies. There is a wide occurrence of Cr(VI) in US source drinking water, with a strong dependence on groundwater sources, mainly due to naturally weathering of chromium-containing aquifers. Challenges regarding traditional Cr(VI) treatment include chemical cost, generation of secondary waste and inadvertent re-generation of Cr(VI) after treatment. To overcome these challenges, reductive Cr(VI) treatment technologies based on the application of stannous tin or electron-releasing titanium dioxide photocatalyst hold extreme promise in the future. To moving forward in the right direction, three key questions need further exploration for the technology implementation, including effective management of residual waste, minimizing the risks of Cr(VI) re-occurrence downstream of drinking water treatment plant, and promote the socioeconomic drivers for Cr(VI) control in the future.

Keywords Chromium      Chemistry      Treatment      Future outlook     
This article is part of themed collection: Accounts of Aquatic Chemistry and Technology Research (Responsible Editors: Jinyong Liu, Haoran Wei & Yin Wang)
Corresponding Author(s): Haizhou Liu   
Issue Date: 19 August 2020
 Cite this article:   
Haizhou Liu,Xuejun Yu. Hexavalent chromium in drinking water: Chemistry, challenges and future outlook on Sn(II)- and photocatalyst-based treatment[J]. Front. Environ. Sci. Eng., 2020, 14(5): 88.
E-mail this article
E-mail Alert
Articles by authors
Haizhou Liu
Xuejun Yu
Fig.1  Distributions of Cr(VI) concentrations in source drinking water and at the exit point of the drinking water distribution systems in the United States. This analysis is based on data from 4,583 water utilities and 22,734 drinking water samples in the USPEA UCMR3 database. (A) Cr(VI) distribution at the entry point to the water distribution systems based on 22,734 detections. (B) Cr(VI) distribution at the maximum residence time of the exist to the distribution systems based on 4583 public water utilities.
Fig.2  Speciation of hexavalent chromium as a function of drinking water pH. The total Cr(VI) level is modeled at 100 µg/L, i.e., the US EPA drinking water maximum contaminant level for total chromium. T = 25°C.
Fig.3  Redox potentials of different redox couples in typical drinking water chemical conditions. The calculation is based on the following condition: [HOCl] = 1 mg/L as Cl2; [Cl] = 3.5 mg/L; [CrO42–] = 100 µg/L; [Fe2+] = 2 mg/L; [Sn2+] = 0.5 mg/L, pH= 7, T = 25°C. The actual redox potentials are calculated based on the standard redox potential values obtained from Benjamin, 2004.
Fig.4  Promising treatment technologies for hexavalent chromium in drinking water. (A) A schematic illustration of Sn(II)-based reductive treatment for hexavalent chromium in drinking water. (B) The molecular structure of a DEG-capped TiO2 catalyst.
Fig.5  (A) Reaction mechanism for photocatalytic reduction of Cr(VI) in aqueous suspension of TiO2 nanocrystals. (B) The molecular structure of a diethylene glycol (DEG)-capped TiO2 catalyst.
1 M M Benjamin (2004). Water Chemistry. Chapter 12: Redox Chemistry. Long Grove: Waveland Press, Inc.
2 N Blute, X Y Wu, C Cron, R Abueg, D Froelich, L Fong (2014). Hexavalent chromium treatment implementation in Glendale, Calif. Journal- American Water Works Association, 106(3): E160–E175
3 M Chebeir, G Chen, H Liu (2016). Frontier review: Occurrence and speciation of chromium in drinking water distribution systems. Environmental Science. Water Research & Technology, 2(6): 906–914
4 M Chebeir, H Liu (2016). Kinetics and mechanisms of Cr(VI) formation via the oxidation of Cr(III) solid phases by chlorine in drinking water. Environmental Science & Technology, 50(2): 701–710
5 M Chebeir, H Liu (2018). Oxidation of Cr(III)–Fe(III) mixed-phase hydroxides by chlorine: Implications on the control of hexavalent chromium in drinking water. Environmental Science & Technology, 52(14): 7663–7670
6 G Chen, J Feng, W Wang, Y Yin, H Liu (2017). Photocatalytic removal of hexavalent chromium by newly designed and highly reductive TiO2 nanocrystals. Water Research, 108: 383–390
7 G Chen, H Liu (2020). Photochemical removal of hexavalent chromium and nitrate from ion-exchange brine waste using carbon-centered radicals. Chemical Engineering Journal, 396: 125236
8 Y S Choi, J J Shim, J G Kim (2004). Corrosion behavior of low alloy steels containing Cr, Co and W in synthetic potable water. Materials Science and Engineering, 385(1-2): 148–156
9 R Coyte, K L McKinley, S Jiang, J Karr, G S Dryer, A J Keyworth, C C Davis, A J Kondash, A Vengosh (2020). Occurrence and distribution of hexavalent chromium in groundwater from North Carolina, USA. Science of the Total Environment, 711: 135135
10 E L Eary, D Rai (1987). Kinetics of chromium(III) oxidation to chromium(VI) by reaction with manganese dioxide. Environmental Science & Technology, 21(12): 1187–1193
11 L E Eary, D Rai (1988). Chromate removal from aqueous wastes by reduction with ferrous iron. Environmental Science & Technology, 22(8): 972–977
12 S Gonzalez, R Lopez-Roldan, J L Cortina (2013). Presence of metals in drinking water distribution networks due to pipe material leaching: A review. Toxicological and Environmental Chemistry, 95(6): 870–889
13 T Henrie, S Plummer, J Orta, S Bigley, C Gorman, C Seidel, K Shimabuku, H Liu (2019). Full-scale demonstration testing of hexavalent chromium reduction via stannous chloride application. AWWA Water Science, 1(2): e1136
14 J G Hering, T C Harmon (2004). Geochemical controls on chromium occurrence, speciation, and treatability. Water Research Foundation Report. Denver, USA
15 J A Izbicki, K Groover (2018). Natural and man-made hexavalent chromium, Cr(VI), in groundwater near a mapped plume, Hinkley, California—study progress as of May 2017, and a summative-scale approach to estimate background Cr(VI) concentrations. U.S. Department of the Interior – U.S. Geological Survey. Reston, Virginia
16 J Jacobs, S M Testa (2005). Cr(VI) Handbook. Boca Raton: CRC Press
17 A Kennedy, R Croft, L Flint, M Arias‐Paić (2020). Stannous chloride reduction–filtration for hexavalent and total chromium removal from groundwater. AWWA Water Science, 2(2): e1174
18 S K Loeb, P J Alvarez, J A Brame, E L Cates, W Choi, J Crittenden, D D Dionysiou, Q Li, G Li-Puma, X Quan, D L Sedlak, T D Waite, P Westerhoff, J H Kim (2019). The technology horizon for photocatalytic water treatment: sunrise or sunset? Environmental Science & Technology, 53(6): 2937–2947
19 C Oze, D K Bird, S Fendorf (2007). Genesis of hexavalent chromium from natural sources in soil and groundwater. Proceedings of the National Academy of Sciences of the United States of America, 104(16): 6544–6549
20 C Oze, S Fendorf, D K Bird, R G Coleman (2004). Chromium geochemistry in serpentinized ultramafic rocks and serpentine soils from the Franciscan complex of California. American Journal of Science, 304(1): 67–101
21 C Pan, H Liu, J G Catalano, A Qian, Z M Wang, D E Giammar (2017). Rates of Cr(VI) generation from CrxFe1–x(OH)3 solids upon reaction with manganese oxide. Environmental Science & Technology, 51(21): 12416–12423
22 C Pan, L D Troyer, J G Catalano, D E Giammar (2016). Dynamics of chromium (VI) removal from drinking water by iron electrocoagulation. Environmental Science & Technology, 50(24): 13502–13510
23 Z Pan, X Zhu, A Satpathy, W Li, J D Fortner, D E Giammar (2019). Cr(VI) adsorption on engineered iron oxide nanoparticles: Exploring complexation processes and water chemistry. Environmental Science & Technology, 53(20): 11913–11921
24 C Y Peng, A S Hill, M J Friedman, R L Valentine, G S Larson, A M Y Romero, S H Reiber, G V Korshin (2012). Occurrence of trace inorganic contaminants in drinking water distribution systems. Journal- American Water Works Association, 104(3): E181–E193
25 S L Percival, J S Knapp, R G J Edyvean, D S Wales (1998). Biofilms, mains water and stainless steel. Water Research, 32(7): 2187–2201
26 S Plummer, C Gorman, T Henrie, K Shimabuku, R Thompson, C Seidel (2018). Optimization of strong-base anion exchange O&M costs for hexavalent chromium treatment. Water Research, 139: 420–433
27 C J Seidel, I N Najm, N K Blute, C J Corwin, X Y Wu (2013). National and California treatment costs to comply with potential hexavalent chromium MCLs. Journal- American Water Works Association, 105(6): E320–E336.
28 United States Environmental Protection Agency (2015). Unregulated Contaminant Monitoring Rule 3 (UCMR3). Access at the website of
29 A Vengosh, R Coyte, J Karr, J S Harkness, A J Kondash, L S Ruhl, R B Merola, G S Dywer (2016). Origin of hexavalent chromium in drinking water wells from the piedmont aquifers of North Carolina. Environmental Science & Technology Letters, 3 (12): 409–414
Related articles from Frontiers Journals
[1] Zhiling Wu, Xianchun Tang, Hongbin Chen. Seasonal and treatment-process variations in invertebrates in drinking water treatment plants[J]. Front. Environ. Sci. Eng., 2021, 15(4): 62-.
[2] Ting Chen, Yingying Zhao, Xiaopeng Qiu, Xiaoyan Zhu, Xiaojie Liu, Jun Yin, Dongsheng Shen, Huajun Feng. Economics analysis of food waste treatment in China and its influencing factors[J]. Front. Environ. Sci. Eng., 2021, 15(2): 33-.
[3] Milan Malhotra, Anurag Garg. Characterization of value-added chemicals derived from the thermal hydrolysis and wet oxidation of sewage sludge[J]. Front. Environ. Sci. Eng., 2021, 15(1): 13-.
[4] Wenyue Li, Min Chen, Zhaoxiang Zhong, Ming Zhou, Weihong Xing. Hydroxyl radical intensified Cu2O NPs/H2O2 process in ceramic membrane reactor for degradation on DMAc wastewater from polymeric membrane manufacturer[J]. Front. Environ. Sci. Eng., 2020, 14(6): 102-.
[5] Lu Song, Can Wang, Yizhu Wang. Optimized determination of airborne tetracycline resistance genes in laboratory atmosphere[J]. Front. Environ. Sci. Eng., 2020, 14(6): 95-.
[6] Yang Yang. Recent advances in the electrochemical oxidation water treatment: Spotlight on byproduct control[J]. Front. Environ. Sci. Eng., 2020, 14(5): 85-.
[7] Chao Pan, Daniel Giammar. Interplay of transport processes and interfacial chemistry affecting chromium reduction and reoxidation with iron and manganese[J]. Front. Environ. Sci. Eng., 2020, 14(5): 81-.
[8] Haiyan Yang, Shangping Xu, Derek E. Chitwood, Yin Wang. Ceramic water filter for point-of-use water treatment in developing countries: Principles, challenges and opportunities[J]. Front. Environ. Sci. Eng., 2020, 14(5): 79-.
[9] Jianfeng Zhou, Ting Wang, Cecilia Yu, Xing Xie. Locally enhanced electric field treatment (LEEFT) for water disinfection[J]. Front. Environ. Sci. Eng., 2020, 14(5): 78-.
[10] Rongrong Zhang, Daohao Li, Jin Sun, Yuqian Cui, Yuanyuan Sun. In situ synthesis of FeS/Carbon fibers for the effective removal of Cr(VI) in aqueous solution[J]. Front. Environ. Sci. Eng., 2020, 14(4): 68-.
[11] Quan Zheng, Minglu Zhang, Tingting Zhang, Xinhui Li, Minghan Zhu, Xiaohui Wang. Insights from metagenomic, metatranscriptomic, and molecular ecological network analyses into the effects of chromium nanoparticles on activated sludge system[J]. Front. Environ. Sci. Eng., 2020, 14(4): 60-.
[12] Quan Yuan, Hui Gong, Hao Xi, Kaijun Wang. Aerobic granular sludge formation based on substrate availability: Effects of flow pattern and fermentation pretreatment[J]. Front. Environ. Sci. Eng., 2020, 14(3): 49-.
[13] Ting Zhang, Heze Liu, Yiyuan Zhang, Wenjun Sun, Xiuwei Ao. Comparative genotoxicity of water processed by three drinking water treatment plants with different water treatment procedures[J]. Front. Environ. Sci. Eng., 2020, 14(3): 39-.
[14] Jianguo Liu, Shuyao Yu, Yixuan Shang. Toward separation at source: Evolution of Municipal Solid Waste management in China[J]. Front. Environ. Sci. Eng., 2020, 14(2): 36-.
[15] Luman Zhou, Chengyang Wu, Yuwei Xie, Siqing Xia. Biogenic palladium prepared by activated sludge microbes for the hexavalent chromium catalytic reduction: Impact of relative biomass[J]. Front. Environ. Sci. Eng., 2020, 14(2): 27-.
Full text