Field Demonstration of the Activated Iron Technology for Removing Heavy Metals from Flue-Gas-Desulfurization Wastewater

The Activated Iron Process (AIP) technology, which is renamed from the hybrid zero-valent-iron (hZVI) process, is a novel chemical treatment process that has shown great potential in previous laboratory and field bench-scale tests for removing selenium, mercury, and nutrients from the flue-gas-desulfurization wastewater. In this study, a pilot-scale demonstration was conducted to continuously treat 3.8-7.6 L/min (1-2 gpm) of the FGD wastewater at a coal-fired power plant for five months. Results show that the AIP process could simultaneously reduce selenate-Se from 1-3 mg/L to below 10 μg/L and mercury from over 100 μg/L to below 10 ng/L, in compliance with new stringent effluent discharge limits planned by the USEPA for Se and Hg. Moreover, the process efficiently removed a broad spectrum of heavy metals such as As(III), As(V), Cr(VI), Cd(II), Pb(II) and Cu(II) from ppm level to near or sub-ppb level. A 3-stage AIP reactor with a combined hydraulic retention time of 8-12 h was sufficient for Se treatment and a single stage for Hg and other heavy metals. The process had a competitive economics and consumed ~0.3 kg ZVI per 1 m FGD wastewater treated at a cost of about $0.6/m. Solid waste production and energy consumption were reasonably low. The AIP process is scalable. The successful pilot study demonstrates that the AIP technology can be a reliable, low-cost, high-performance treatment platform with numerous application potentials, particularly, for solving some of the toughest heavy metal water problems