Electrochemical Advanced Treatment of Desulfurization Wastewater from Coal-Fired Power Plants

Abstract

Zero-emission of desulfurization wastewater is one of the main demands for coal-fired power plants. As typical high salinity wastewater, it is hard to purify the desulfurization wastewater from coal-fired power plants through traditional physicochemical treatment or biochemical treatment, e.g., COD and Cl^-. A high concentration of Cl^- ion in desulfurization wastewater restricts wastewater reuse and zero-emission. Electrochemical technology is an attractive method for high salinity wastewater zero-emission, which provides a versatile, efficient, cost-effective, easily automatable, and clean industrial process. For advanced treatment of effluent after triple box process treatment in power plants, this paper reports an electrochemical method to remove COD and Cl^- from the desulfurization wastewater, which combines electrolysis with electrocoagulation. Aluminum plate and stainless steel plate were applied as the anode and the cathode, respectively, for electrocoagulation. Homemade β-PbO₂ coated Ti anode and stainless steel cathode were used for electrolysis. Homemade β-PbO₂ coated Ti anode was prepared with a two-step galvanostatic electrodeposition. The electrodeposition solution was 1 mol∙L^-1 Pb(CH₃SO₃)₂ solution with pH = 1~2. The temperature was set at 50 ^oC. Firstly, an 80 ~ 100 μm dense and smooth β-PbO₂ coating was electrodeposited onto the titanium mesh at 5 mA∙cm^-2, which is used to protect the titanium substrate. Secondly, the electrodeposition current density was increased to 20 mA∙cm^-2. About 0.5 mm more electroactive β-PbO₂ coating was deposited on the top layer. The electrooxidation mechanisms and dynamic parameters of SO₃^2-, HSO₃^-, and Cl^- on the homemade β-PbO₂/Ti were investigated particularly by linear scan voltammetry. It was testified that the homemade β-PbO₂/Ti is an excellent anode material for sulfite and chloride electrooxidations. A continuous plug flow electrolyser was homemade to test the feasibility and economy of the electrochemical method, which consisted of an electrocoagulation section and an electrolysis section. The electrocoagulation section could remove almost all suspended solids and a part of COD. To meet the industry-standard “Discharge standard of wastewater from limestone-gypsum flue gas desulfurization system in fossil fuel power plant” (COD < 150 mg∙L^-1), the energy consumptions of the electrolyser were 10.78 kWh∙m^-3 and 15.17 kWh∙m^-3 at 3.5 V and 4.0 V, respectively. For zero-emission, 91.43% of COD and 92.98% of Cl^- could be removed within 300 min at 4.0 V.

Keywords

desulfurization wastewater / lead dioxide / electrocatalysis / COD / sulfite / dechlorination

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