Corrosion control using hydroxide and bicarbonate alkalising agents in water drinking processes

Abstract

<p><strong>Abstract.</strong> The water supply industry is faced with three phenomena of great importance: the aggressiveness, corrosion, and incrustation of water distribution systems (WDS), which are primarily due to the low alkalinity of water sources and the addition of chemicals used in water treatment processes, which require pH adjustments during the last stage of the treatment process before going into the WDS. This article presents the results of using Ca(OH)<sub>2</sub> and NaOH with doses between 2 and 20 mg L<sup>−1</sup> and NaHCO<sub>3</sub> and Na<sub>2</sub>CO<sub>3</sub> between 10 and 250 mg L<sup>−1</sup> to adjust the pH of water treated from the Cauca River, which is located in Cali, Colombia, using stabilisation indices normally used in water treatment plants for pH monitoring processes and to better predict the behaviour of water in the WDS. The results indicate that for the case of the surface water source studied, which exhibits low alkalinity levels, the evaluated alkalising agents, with the exception of NaHCO<sub>3</sub>, can create conditions that lead to the precipitation of a~protective calcium carbonate film. Because the pH values that guarantee an adequate pH adjustment are higher (8.7–9.0) than those specified by the Colombian water code and because other international rules indicate that these values do not compromise the health of consumers, it is advisable to review and adjust the code in this respect.</p>

Toxicity of Aqueous Alkaline Solutions to New Zealand Mudsnails, Asian Clams, and Quagga Mussels

“…Elevating freshwater pH with NaOH can be particularly appealing because the chemical is highly soluble, is available in liquid and powder forms, and is used widely in industrial and agricultural settings. Examples include the pulp and paper, food, and biodiesel industries as well as water treatments (Montresor et al 2013;Torres-Lozada et al 2015;Chaiyapong and Chavalparit 2016). Very little NaOH is needed to raise the pH of freshwater from neutral to a strong alkaline solution (U.S. Department of Health and Human Services 2002; ClearTech Industries Inc. 2017).…”