Four Ways to Improve Wastewater pH Adjustment Systems

Does your facility routinely exceed your permitted wastewater pH range? Often, pH adjustment is the source of headaches as a result of poorly designed systems.  If your system is having difficulties, check these common issues first:

1. Dirty pH sensor.  All types of wastewater deposit scale and film on the sensor glass that eventually causes the sensor to drift or completely fail to return useful signal.  Use a soft brush, place into dilute (0.5 – 1%) hydrochloric acid to remove scale, rinse, place into alkaline cleaner or detergent to remove oily films and rinse; an alternative method is to use inhibited acidic toilet bowl cleaner.  Perform this sensor cleaning prior to sensor calibration on a weekly basis (although some very dirty wastewaters may need daily cleaning to avoid issues).
2. Non-calibrated pH sensor. Over time, pH sensors tend to drift.  Weekly or monthly calibration with two buffer solutions (pH 4 and pH 10) will help keep your system in tune.  If the pH responds sluggishly between buffer solutions, this is a sign that the sensor needs to be replaced.
3. Low and high pH set points too close together. Having pH set points too close causes the system to “fight” itself.  This scenario occurs when acid is added, driving the pH below the lower set point. This causes the system to add caustic and the pH then rises above the high set point, causing an acid addition.  The cycle then repeats.  If it doesn’t interfere with other system parameters, try increasing the distance between set points while still allowing a reasonable margin within the permit limits.
4. Inadequate mixing.  Chemical costs can be reduced by a system with vigorous mixing that rapidly disperses the chemicals, achieving complete reactions prior to measurement by the pH sensor controlling the system.  Vigorous mixing is typically indicated by an occasional vortex around the mixer shaft and a rolling, boiling action at the liquid surface with minimal splashing.  If this is not apparent, a larger mixer may be needed as well as several anti-swirl baffles.  Since mixing is a function of many variables, including viscosity and tank dimensions, it may be necessary to consult a mixing specialist (mixer supplier).

Hixson’s Environmental team would be happy to help you evaluate and solve your wastewater pH difficulties.  Contact Steve Schulte at 513-241-1230 to learn more.

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