(583c) Performance of Ion Selective Electrodes (ISE) on Wastewaters from Power Plants

The latest U.S. Environmental Protection Agency (EPA) effluent limitations guidelines and standards for the steam electric power generating point source category’s final rule published in November 2015 mandates the limitations of toxic metals and other chemical compounds from coal-fired power plants. On an annual basis, the rule reduces the amount of toxic metals, nutrients, and other pollutants that steam electric power plants are allowed to discharge (no more than 1.4 billion pounds per year) and it also reduces water withdrawal by 57 billion gallons per year. Currently, a Flue Gas Desulphurization (FGD) system is used to remove SO₂ from flue gas produced from the coal-fired power plant boiler. In the FGD system, limestone reacts with SO₂, producing gypsum. The system also uses various chemicals, like organosulfides, to remove trace heavy metals (e.g., selenium, mercury, arsenic etc.) from FGD wastewater. Chemicals required for the FGD system are calculated based on coal sulfur and heavy metal content, and the numerical discharge limit regulated by EPA. The plant operators manually collect samples of the discharge water as well as the FGD wastewater periodically, and measure the chemical quantity by spectroscopy in the laboratory, which is time consuming, costly, and tedious. Often, response to a parameter tuning takes days and the plant may discharge over the limit in the meantime.

As of 2015, more than 66 companies are manufacturing water related sensors in the world but only a handful of them market Ion Selective Electrodes (ISE). An ISE (with its own internal reference electrode) is immersed in an aqueous solution containing the ions to be measured, together with a separate, external reference electrode. The external reference can be completely separate or incorporated in the body of the ISE to form a Combination Electrode). The electrochemical circuit is completed by connecting the electrodes to a sensitive (milli)volt meter using special low-noise cables and connectors. A potential difference is developed across the ISE membrane when the target ions diffuse through from the high concentration side to the lower concentration side.

In this project, we have investigated the feasibility of using inexpensive sensors for FGD water measurements and ISE sensors for chemical composition. FGD wastewaters were collected from AEP’s coal-fired power plant. Before testing the ISE electrodes in FGD wastewaters, it is important to quantify the targeted compounds in the FGD wastewater. Therefore, we have used high accuracy gas chromatography, ion chromatography, high-performance liquid chromatography, and induced coupled plasma available for organic and inorganic compounds detection and quantification. Targeted compounds for this project were mercury, selenium, arsenic, nitrate, nitrites, calcium, and chloride. ISEs purchased from Thermo-scientific and NIKO (London, UK) were tested on the known FGD wastewaters individually to determine the performance of each electrodes.

In future, we will select the working electrodes and make a sensor package for wastewater quality monitoring. The package will be designed as a self-powered, wireless, water-resistant, robust, and cheap. The sensor package is expected to demonstrate at the AEP’s site for the real-time data monitoring.