2016 Excellence in Environmental Engineering and Science™ Awards Competition Winner

E3S Grand Prize

Grand Prize - University Research

Kinetics and Mechanistic Framework for Pollution Control Using Activated Iron Processes

Entrant: University of Nebraska-Lincoln and Texas A&M University
Engineer in Charge: Tian C. Zhang, Ph.D., P.E., D.WRE, BCEE, F.ASCE, A.EASA, F.AAAS
Location: College Station, Texas
Media Contact: Tian C. Zhang

Entrant Profile

Tian C. Zhang, Ph.D., P.E., D.WRE, BCEE, F.ASCE, A.EASA, F.AAAS is Professor in the department of Civil Engineering (CE) at the University of Nebraska-Lincoln (UNL). He received his Ph.D. from University of Cincinnati and joined the UNL faculty in August 1994. Professor Zhang has published > 100 peer-reviewed journal papers, 62 book chapters and 11 books since 1994. Professor Zhang is a Diplomate of Water Resources Engineer (D.WRE) of the American Academy of Water Resources Engineers, Board Certified Environmental Engineers (BCEE) of the American Academy of Environmental Engineers (since 2013), Fellow of American Society of Civil Engineers (F. ASCE), Academician of European Academy of Sciences and Arts, and Fellow of American Association for the Advancement of Science (F.AAAS). Professor Zhang is the Associate Editor of Journal of Environmental Engineering (since 2007), Journal of Hazardous, Toxic, and Radioactive Waste (since 2006), and Water Environment Research (since 2008). He has been a registered professional engineer in Nebraska since 2000. In this nominated zero-valent (ZVI) project, as the project principal investigator (PI), he directed research conducted in the Civil Engineering Department while collaborating with other researchers at UNL. He advised graduate students in the CE dept. and co-advised students in the interdisciplinary Environmental Engineering program. Specific contributions included development of experimental procedures, identification of research directions, integrative analysis and interpretation of the experimental, preparing project reports, publishing scientific papers, promoting technology transfer, working with Prof. Huang (since 2007) continuously on the project, and moving toward new directions (e.g., development of nano-ZVI processes).

Yongheng Huang, Ph.D., P.E., is an Associated Professor with the Department of Biological and Agricultural Engineering at Texas A&M University (TAMU). In this project, Dr. Huang worked as a Ph.D. student and then a postdoc under the supervision of Prof. Zhang at UNL in 1999−2005. Together they discovered the role of dissolved Fe2+ in reversing ZVI surface passivation and proposed a semiconducting corrosion model to describe the chemistry involved. In Nov. 2006 Dr. Huang joined TAMU. There, he discovered the role of the discrete FeOx phase in multiplying the ZVI system's reactivity and then invented the Activated Iron technology, a new chemical water treatment platform that can remove a broad spectrum of heavy metals from some of the most challenging and high-impact industrial waste streams. Dr. Huang worked with industrial partners to demonstrate and scale up the new treatment systems. The technology was globally licensed to and being commercialized by Siemens Water (currently Evoqua Water Technologies LLC) under the name of the Pironox™ Advanced Reactive Media System. Pironox™ has received broad attentions from industries and the USEPA for its potential in heavy metal-impaired wastewater treatment in steam-electric power, mining, and refinery industries. Dr. Huang also developed a ceramic nanomaterial that can effectively capture mercury vapor with a specific sorption capacity of about 100 times of that of the current mainstream sorbents used by industries. The new sorbent technology can significantly reduce the compliance cost for industries and could have positive impacts on global mercury emission reduction in the long term.

Post-doc and Graduate Students involved in the project:
ZAWAIDEH, Laura (M.S. student at UNL); Chew, Chin (Ph.D. student at UNL); HUANG, Yongheng (Ph.D. student and Post-Doc at UNL,1999-2005); ZHEN, Hui (M.S. student at UNL and Post-Doc at TAMU); TANG, Ci-Lai (PhD student at TAMU); LIN, Sin-Hong (PhD student at TAMU); PEDDI, Phani K. (MS student at TAMU); WANG, Xiao (PhD student at TAMU); LIN, Xin (Post-Doc at TAMU)

Project Description

Complexity of the Problem

In 1994, the National Research Council has estimated that in the U.S., 300,000 to 400,000 sites have contaminated groundwater/soils; at these sites, hazardous wastes pose a myriad of threats to human health and the environment; up to $1 trillion would be spent to clean up these sites over the next 30 years. Since 1990, zerovalent iron (Fe0) technology has emerged as a potential solution to various pollutants. However, problems associated with Fe0 passivation hampers application of Fe0 technology. Elucidating the mechanisms that describe these relationships has been a critical challenge for researchers in this field since 1994.

Demonstration of a Comprehensive and Integrated Approach

This research project focused on kinetics and mechanistic framework for pollution control using activated iron processes, and had three primary thrusts: 1) application of Fe0 processes for remediation of different contaminants in multiple media[1-4]; 2) elucidation of the functions of iron oxides and relationships among Fe0, Fe2+ and iron oxides under different conditions[2-4]; and 3) development of the activated iron technology and promotion of its applications[5-8]. This study found that a series of chemical reactions and mechanisms that in tandem could overcome Fe0 passivation. This study invented a hybridized system of surface reactive Fe0 + FeOx + Fe(II)−the so-called Activated Iron technology (AIT). The technology has been used as a platform for a) removing heavy metals (e.g., Se, Hg, As) from flue- gas desulfurization (FGD) wastewater, refinery stripped sour water, and acid mining drainage; b) removing dissolved silica for many industrial water supplies; c) remediation of groundwater contaminated with multi-pollutants; and d) air purification of different sources.

Quality and Importance of This Research

Remediation of pollutants from different media is very important but often costly. This study developed a new treatment platform that uses reactive power of the rapid iron corrosion process to remove various contaminants/impurities from all environmental media. The cumulative work has resulted in publications in peer-reviewed journals, presentations in conferences and technique reports for technology transfer. The AIT processes has been commercialized by Siemens Water (currently Evoqua Water Technologies LLC) under the name of the Pironox™ Advanced Reactive Media System[5,7].

Originality and Innovation

Little is known about how to rejuvenate passivated iron grains. This study systematically investigated formation and effects of Iron corrosion coatings on performance of Fe0 or AIT systems. This study found that the formation of magnetite (Fe3O4) on Fe0 granules could significantly accelerate reduction of pollutants if Fe2+ or other cations (e.g. Cu2+, Al3+) are available in bulk solution[2,4]. The hybridized AIT system of surface reactive Fe0 + FeOx + Fe(II) would promote synergistic effects for enhanced removal of different contaminants, which could overcome Fe0 surface passivation, and thus, is an effective chemical platform for much wider environmental applications. For example, using AIT to treat FGD wastewater could result in < 10 ppb Se and < 10 ppt Hg in treated effluent with only 0.1−0.3 g Fe0/L ($1,200/ton Fe0), < 0.1 g/L acid (35% HCL), < 0.1 g/L lime (Ca(OH)2), which is 10−20 times more efficient than the conventional treatment method (e.g., Fe0 cementation) with only 1/10 to 1/20 reagent usage of the conventional method. Thus, AIT has the advantages of simplicity, versatility/ robustness, high efficiency, low operation/maintenance cost, and limited sludge production. AIT is effective for decreasing a broad spectrum of heavy metals and metalloids of different forms to near or below ppb level, including Se, Hg, U, Tl, As, Cr, Cd, V, Cu, Zn, Pb, Ni, Mo, Te, Sn, and Sb[5-9]. In addition, this study extends previous research by relaxing reaction conditions for nitrate to react with Fe(II) at near-neutral pH, which could add an important link between the nitrogen cycle and the Fe(II)/Fe(III) redox couple in the bio-/geo-sphere[10].

Project Contributions and Broader Impacts

The project advanced fundamentals of how to rejuvenate passivated iron with improved understanding of mechanisms and kinetics related to the Fe0 process. Results of this study have direct transferability for people to develop new activated iron processes. The invented AIT can be used as a platform for remediation and pollution control in all environmental media, which will contribute to reduction of public health risk, promotion of economic growth, and development of sustainable society.

References (selected from 29 peer-reviewed journal papers)

  1. Huang, Y.H., and Zhang, T.C. (2004). Effects of low pH on nitrate removal with iron powder. Water Research, 38, 2631-2642.
  2. Huang, Y.H., and Zhang, T.C. (2005). Effects of dissolved oxygen on formation of corrosion products and concomitant oxygen and nitrate reduction in zero-valent iron systems with or without aqueous Fe2+. Water Research, 39(9), 1751-1760.
  3. Zhang, T.C., and Huang, Y.H. (2006). Profiling iron corrosion coating on iron grains in a zero- valent iron system under the influence of dissolved oxygen. Water Research 40, 2311-2320.
  4. Zhang, T.C., and Huang, Y.H. (2006). Effects of surface-bound Fe2+ on nitrate reduction and transformation of iron oxide(s) in zero-valent iron systems at near-neutral pH. J. Environ. Eng. 132(5), 527-536.
  5. Huang, Y.H., Peddi, P.K., Zeng, H., Tang, C.L., and Teng, X.J. (2012). Pilot-scale demonstration of the hybrid zero-valent iron process for treating flue-gas-desulfurization wastewater: Part I. Water Science & Technology, 67(1), 16-23.
  6. Huang, Y.H., Tang, C.L., and Zeng, H. (2012). Removing molybdate from water using a hybridized zero-valent iron/magnetite/Fe(II) treatment system. Chemical Engineering J., 200-202, 257-263.
  7. Huang, Y.H., Peddi, P.K., Tang, C.L., Zeng, H., and Teng, X. (2013). Hybrid zero-valent iron process for removing heavy metals and nitrate from flue-gas-desulfurization wastewater. Separation and Purification Technology, 118, 690-698.
  8. Tang, C.L., Huang, Y.H., Zeng, H., and Zhang, Z. (2014). Promotion effect of Mn2+ and Co2+ on selenate reduction by zero-valent iron. Chemical Engineering Journal, 2014, 97-104.
  9. Tang, C., Huang, Y., Zhang, Z., Chen, J., Zeng, H., and Huang, Y.H. (2016) Rapid removal of selenate in a zero-valent iron/Fe3O4/Fe2+synergetic system. Applied Catalysis B: Environmental, 184(5), 320-327.
  10. Huang, Y.H., and Zhang, T.C. (2016). Nitrate reduction by surface-bound Fe(II) on solid surfaces at near-neutral pH and ambient temperature. J. Environ. Eng., 142 (in press).

The following is a news release about Activated Iron Technology: http://baen.tamu.edu/2011/05/innovative-water-treatment-technology/

Click images to enlarge in separate window.

E3S Photos

The prototype has been continuously operated for 4 months with minimal maintenance consistently produced excellent results.

E3S Photos

The reactive solids are strongly magnetic and highly settleable.

E3S Photos

Time courses of NO3-N, NH4-N, total N, aqueous Fe and pH in batch reactors (Initial conditions: 5% Fe0 + 30 mg/l NO3-N + pH adjusted by HCl to 2.3). Three stages were observed in the test: 1) (< 30 min): anaerobic iron corrosion, rapid production of Fe2+, nitrate reduction, and pH increase; 2) (0.5–10 h): magnetite coating and precipitation, slow nitrate reduction and Fe2+ depletion; and 3) (> 10 h): rapid nitrate reduction, Fe2+ consumption, and a further rise in pH. Results indicate that activated iron (Fe0 coated with Fe3O4 + Fe2+ in the bulk solution) can be made with this method.

E3S Photos

Morphology (SEM pictures) of the iron particles and corrosion coating over the course of O2- Fe0 reaction. (Top left) typical surface of iron grains. (Top right) lepidocrocite coating, sampled at reaction time (t) = 1 h. (bottom left) magnetite crystalline predominant in the inner layer of the iron oxide coating, sampled at t = 4 hr after 1 min sonication to strip off the outer layer of lepidocrocite. (bottom right) vertical profile of the oxide coating shown as a broken edge, from t = 1 h before sonication. The inner magnetite layer would grow with time by transforming the lipidocrocite (outer) layer into an activated iron oxide layer (i.e., the magnetite layer).

E3S Photos
E3S Photos

Field demonstration of using bench-scale continuous-flow activated iron system to remove heavy metals (e.g., Se, Hg, As) from flue-gas-desulfurization (FGD) wastewater. (Left) Location of the activated iron treatment system (red cycle) in the field. (Right) the treatment train with a capacity of 30 L/d.

E3S Photos

Schematic representation (top) and a picture (bottom) of the pilot-scale continuous-flow hybrid activated iron system to treat flue-gas-desulfurization (FGD) wastewater between Jan. 15 to June 22, 2011 for field demonstration. The system, mounted on a 40-ft flat-bed trailer, has a treatment capacity of 1−2 gal/min (5−10 m3/d) and a total hydraulic retention time of 8−16 h. The four reactors have a total volumn of 1000 gal (250 gal/each reactor). Raw FGD wastewater strength: Hg2+ (50-195 μg/L), 1−3 ppm SO42--Se; 10-30 mg/L NO3--N, high persulfate (~300 mg/L) and varied flow rate.

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