The hybrid zero-valent-iron (hZVI) process is a novel chemical treatment process that has shown great potential in previous laboratory and field bench-top scale tests for removing selenium, mercury and nutrients from various industrial wastewaters. In this study, a pilot-scale demonstration was conducted to continuously treat 3.8-7.6 L/min (1-2 gpm) of the flue-gas-desulfurization (FGD) wastewater at a coal-fired power plant for five months. Results show that the hZVI process could simultaneously reduce selenate-Se from 1 to 3 mg/L to below 10 μg/L and mercury from over 100 μg/L to below 10 ng/L in compliance with the new stringent effluent discharge limits planned by the U.S. EPA for Se and Hg. A three-stage hZVI system with a combined hydraulic retention time of 12 h is sufficient for Se treatment, while a single-stage system can meet Hg treatment requirement. The successful pilot study demonstrated that the hZVI process is scalable and could be a reliable, low-cost, high-performance treatment platform with many application potentials, particularly, for solving some of the toughest heavy metal water problems.
The hybrid zero-valent-iron (hZVI) process is a novel chemical treatment process that has shown promise for removing heavy metals and nutrients from industrial wastewaters. In this study, a pilot-scale demonstration was conducted to continuously treat 3.8-7.6 L/min (1-2 gpm) of the flue-gas-desulfurization (FGD) wastewater at a coal-fired power plant for 5 months. In this paper, a spike test was conducted to evaluate performance of the hZVI process for removing selected toxic metals at artificially elevated concentrations. The results showed that a multiple-stage hZVI process could decrease selenate-Se from 22 mg/L to ~10 μg/L and dissolved Hg(2+) from 1.15 mg/L to ~10 ng/L. In addition, the process simultaneously removed a broad spectrum of heavy metals such as As(III), As(V), Cr(VI), Cd(II), Pb(II) and Cu(II) from mg/L to near or sub-ppb (μg/L) level after a single-stage treatment. The process consumed about 0.3 kg ZVI per 1 m(3) FGD wastewater treated at a cost of about US$0.6/m(3). Solid waste production and energy consumption were reasonably low. The successful pilot study demonstrated that the hZVI technology can be a low-cost, high-performance treatment platform for solving some of the toughest heavy metal water problems.
The Activated Iron Process (AIP), a novel chemical water treatment platform, was developed for removing various micro-pollutants and impurities from a liquid stream. This integrated treatment system employs certain iron chemistry to create a hybridized reactive solid mixture that comprises three reactive components: zero-valent iron (ZVI) particles with activated surface, redox reactive iron oxide crystalline (FeOx), and certain labile Fe(II) species. The hybrid ZVI/FeOx/Fe(II) system can overcome the surface passivation problem of a conventional ZVI system, providing sustainable reactive power from the activated irons to react, transform, precipitate, and mineralize various heavy metals and nutrients from wastewater.In this study, a pilot-scale AIP prototype capable of treating 2 gpm was demonstrated in a fivemonth continuous-flow test at a power plant. The treatment system accepted raw FGD wastewater, reduced all major pollutants of concern and produced a high quality effluent. The system consistently reduced total mercury (Hg), mostly in dissolved form, from about 100 µg/L to below 0.010 µg/L. Total selenium (Se), of which most was selenate, was decreased from about 2,000 µg/L to below 10 µg/L. Nitrate was lowered from 10-25 mg/L to below 0.2 mg/L. Moreover, the AIP system achieved high reduction for many other heavy metals; e.g., arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and copper (Cu) were all rapidly reduced from 1-5 mg/L level to near or below 1 µg/L in a control spike test. The process uses inexpensive iron based chemicals and produces a limited amount of solid waste.This advanced technology can be commercialized to provide a cost-effective and reliable solution to the FGD wastewater and other metal-contaminated waste streams in various industries. This technology can help industries meet the most stringent effluent discharge regulations for heavy metals and nutrients. KEYWORDS activated iron process, zero-valent iron, hZVI, FGD wastewater, heavy metals, selenium removal, mercury removal 7134 WEFTEC 2012
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