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 × 10 5 cells/mL in the feedwater to 8.58 × 10 3 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.

Revealing the effect of anion exchange resin conditioning on the pH and natural organic matter model compounds removal mechanisms

“…In the framework of sustainable use of water, industries tend to switch from ground water to surface water [8]. Here, NOM concentrations are typically higher causing several issues such as an increased risk on disinfection by-product formation and biofouling during drinking water production or corrosion in steam-water cycles [2,5].…”

“…Humic substances, the most abundant NOM fraction in ground and surface water, are anionic under neutral to basic pH and therefore a good overall removal by anion exchange resins (AER) is expected and experimentally confirmed. For the BP and LMWN fraction, having a lower charge density under these pH conditions, removal using AER is more challenging, resulting in low removal efficiencies [3,8,[14][15][16][17][18]. However, the remaining NOM can be of concern since biopolymers can e.g.…”

“…The cationic and anionic resins applied in a water demineralization unit, are in the H + , resp. OHform to prevent the release of other ions in the water as consequence of the IEX process [8,29,37]. However, very few comparative studies between the conventional Cl -, as used in potable water treatment, and this OHform (or FB in the case of weak basic anion exchange (WBA) resins) have been published.…”

Stress Corrosion Cracking of Steam Turbine Steel: The Influence of Organic Acid Characteristics

“…One of the causes for this is climate change, resulting in less rainfall and therefore leading to higher concentrations of organic compounds [10,11]. Another cause is the shift to alternative water sources in industry, for example from the use of tap water to surface water, or reuse of effluent [12]. Different water sources require other water treatment practices, therefore also influencing the boiler feed water quality [13][14][15].…”

Effect of Film-Forming Amines on the Acidic Stress-Corrosion Cracking Resistance of Steam Turbine Steel

“…Especially the increasing amount of organic acids in the first condensate of low-pressure steam turbine sections can cause serious corrosion damage, such as SCC [26][27][28][29][30][31][32][33][34][35]. These organic acids originate from the breakdown of organic impurities by hydrothermolysis in boilers and superheaters [19,[36][37][38][39][40][41]. Film-forming amines, added during operation, might also tackle the issues resulting from impurities in the water.…”