The pH value of the test solution was determined every day, the appearance changes and odor emission were observed, and the number of bacteria and fungi were determined after 5 days of ventilation and 2 days of deaeration. Repeat until the water-based metal cutting fluid deteriorates. Due to the microbial reproduction process, cellular respiration releases CO2 and the organic acids produced in the degradation process will cause the pH value to drop. Therefore, the biological stability of water-based metal cutting fluid can be evaluated by the degree of pH reduction and the degree of microbial reproduction

​The main reasons for the deterioration and odor of metal cutting fluids come from anaerobic bacteria and aerobic bacteria. Aerobic bacteria have a characteristic.

The main reasons for the deterioration and smell of metal cutting fluid are anaerobic bacteria and aerobic bacteria. Aerobic bacteria have a characteristic. They must have sufficient oxygen in the process of survival and reproduction.