If the pH of a waste stream goes down, the concentration of hydrogen ions [H+]

When the pH of a solution decreases, it indicates that the solution is becoming more acidic. The pH scale is logarithmic, meaning that each whole number change represents a tenfold change in hydrogen ion concentration. Specifically, a lower pH value corresponds to a higher concentration of hydrogen ions ([H^+]).

For instance, if the pH decreases from 7 to 6, that change reflects a tenfold increase in hydrogen ion concentration. Therefore, as the pH continues to decrease, the concentration of hydrogen ions increases significantly. This relationship is fundamental in understanding the chemistry of acids and bases. A decrease in pH directly translates to an increase in ([H^+]), making the solution more acidic and the hydrogen ion concentration greater.