Organic Matter and Microbial Cell Density Behavior during Ion Exchange Demineralization of Surface Water for Boiler Feedwater

Abstract

Chemical industries around the world show an increasing awareness of their ecological footprint, including their water use. A shift toward alternative water sources, such as wastewater streams or surface water, is slowly becoming a well-known concept to reduce the intake of ground and drinking water. However, a change of intake water often leads to unforeseen challenges (for example, faster breakthrough of organic matter and growth of biofilms) and requires a review of the currently used water treatment technology. A study of surface water used in various Antwerp companies was carried out, but the acquired knowledge can tackle multiple unexpected problems in different applications, as many industries undergo an alteration in their water management due to the increasing water scarcity. Demineralization of Biesbosch surface water by ion exchange and the associated removal of both total organic carbon and microbial cells were investigated with liquid chromatography in combination with organic carbon detection characterization and flow cytometric monitoring. The effect of monochloramine and sodium bisulfite on the ion exchange operation and the respective removal efficiencies were investigated. Considering a total organic carbon limit value of 250 ppb, the addition of both chemicals together had a positive effect on the demineralization operating time. On average, >93% of the organic matter was removed from the incoming feedwater. The organic matter removal mechanism by the anion exchange resins was mostly (acidic) adsorption at low pH in the scavenger and by ion exchange at neutral pH in the weak and strong anion exchange resins. The microbial cell concentration was reduced by almost 2 log units, from 8.16 × 105 cells/mL in the feedwater to 8.58 × 103 cells/mL in the demineralized water, and was the result of cell lysis due to a large pH drop over the consecutive resin columns. In addition, the end water quality was suited to be used as boiler feedwater, as little to no formation of corrosive organic acids occurred under boiler conditions.