If the pH of a plant influent changes suddenly and consistently at the same time each week, what is a probable cause?

A sudden and consistent change in the pH of plant influent at the same time each week is most likely attributable to industrial waste. This scenario suggests that there is a regular discharge from a nearby industrial facility that introduces specific contaminants and chemicals into the wastewater system, which can dramatically affect the pH levels. Many industrial processes generate wastewater with pH values that are either highly acidic or basic, depending on the chemicals being used. The timing of these changes implies that the industrial discharge occurs on a set schedule, which correlates with the observed fluctuations in pH.

The other potential causes are less likely to create such consistent and sudden pH changes. Seasonal temperature changes might influence biological processes and chemical reactions but would not typically result in a consistent weekly swing in pH. Heavy rainfall could dilute effluents and might cause short-term fluctuations, but it would not necessarily create a regular, predictable pattern in pH levels. Natural decomposition processes are more gradual and would not likely lead to sudden, consistent pH fluctuations. Therefore, industrial waste is the most plausible explanation for the described phenomenon.