I have a question regarding the pH of the aromatic hydrocarbon extraction water system; thank you

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I have a question that has been bothering me for a long time. Here’s what happened: last year, in March, I increased the feed load to its maximum design value one day; as a result, the interface level in the extraction tower kept dropping, and the liquid level in the recovery tower also kept falling. Due to these large fluctuations in the liquid levels, I reduced the load again, and both the interface level and the liquid levels returned to normal. However, two days later, the water from the wash towers of the recovery tower in the aromatic hydrocarbon extraction water system, the water from the wash towers used for washing the raffinate oil, and the water from the reflux tank of the stripping unit all suddenly became acidic (with a pH as low as 3), while the pH of the solvent remained normal (around pH 7). Prior to this, the pH of the water system was fine. System oxygen leakage has been ruled out, and the raw materials contain no chloride ions. The current measure taken is to add monoethanolamine regularly, but the pH of the water system still drops after about 2 months, while the pH of the solvent remains normal. I would like to ask what causes the pH of only the water system to drop suddenly, while the pH of the solvent remains normal? Thank you so much