Please follow the link given below

https://www.google.co.in/amp/s/www.researchgate.net/publication/226369453_Comparison_of_Relationships_Between_pH_Dissolved_Oxygen_and_Chlorophyll_a_for_Aquaculture_and_Non-aquaculture_Waters/amp

Oxygen reduction on the cathode results in an alkaline pH. A traditional MFC can maintain two different pH conditions to optimize the anodic and cathodic reactions. It is however, impossible to do so in air - cathode MFCs, because only one electrolyte is present. The electrolyte pH is crucial to the MFCs power output. Generally, bacteria require a pH close to neutral for optimal growth; while oxygen reduction on the cathode electrode results in an alkaline pH.. For more information consult Bioelectrochemistry 74 ( 2008 ) 78 - 82.

As pH decreases (i.e. the concentration of H+ or the activity increases), the redox reaction is shifted to the right. Hydrogen ions and oxygen react with water, which results in a decrease of the DO. An increase of the pH value can shift the redox reaction to the left.

Let us consider pH and DO as control parameters for some biotechnological (fermentation) process. Parameter pH, if you change it by means of additions of acid or alcaline solutions, have no influence on DO value as itself. But an increase or decrease the pH value can influence on the respiration rate of mirobial culture, which in its turn, can results in changing the DO value. Parameter DO, if you change it by means of changing aeration or agitation rate, have no influence on pH value as itself. But an increase or decrease the DO value can influence on the growth or other biochemical rates of mirobial culture, which can result in changing the pH value. So, I suppose, that there is no relation between DO and pH, as control parameters.

I agree with Biryukov answer...." Let us consider pH and DO as control parameters for some biotechnological (fermentation) process. Parameter pH, if you change it by means of additions of acid or alcaline solutions, have no influence on DO value as itself. But an increase or decrease the pH value can influence on the respiration rate of mirobial culture, which in its turn, can results in changing the DO value. Parameter DO, if you change it by means of changing aeration or agitation rate, have no influence on pH value as itself. But an increase or decrease the DO value can influence on the growth or other biochemical rates of mirobial culture, which can result in changing the pH value. So, I suppose, that there is no relation between DO and pH, as control parameters".