Using a pH Meter to Test Wastewater

Excessive pH levels, particulates, and contaminants are typically found in wastewater. Using pH in wastewater treatment requires an accurate and robust measurement with a pH meter. It also necessitates the measurement of the water's temperature.

Because chemical and particulate contamination in wastewater can destroy standard pH electrodes, prematurely killing the junction, specialized pH electrodes are recommended. A double junction electrode will block chemical interferences in the wastewater, and prevent common chemical damages to the reference junction. A flushable junction will handle chemical and particulates in the wastewater easily. A flushable junction is ideal for sludge, paper-pulp, and dirty samples as the easy-to-clean junction never clogs.

Testing the pH of a Wastewater Sample

Oakton® pH 5+ Meter with Probe

What's Needed: A standard pH meter, a durable pH electrode, an automatic temperature compensation (ATC) probe, a stirrer with stir bar, 100-mL graduated cylinder, 100-mL beaker, deionized water and buffers. The pH electrode will be exposed to chemical contaminates and particulates, so a double junction electrode is recommended or, for very dirty samples, a flushable junction electrode.

Sampling: Grab two to three samples from each site into a sealed container. Grab samples of wastewater will off-gas the volatile materials that are present, which could alter the pH level of the sample. Therefore, samples must be collected into a sealed container. Time delays between grabbing the sample and measuring the pH value should be avoided. No sample preservative or preparation required.

Laboratory Testing

1. We recommend a 2-point calibration with a pH 4 and a pH 7 buffer solution for more acidic waste and a pH 7 and a pH 10 buffer solution for more basic waste. The electrode slope should be between 92 and 102%.

2. Just before testing, use a graduated cylinder to measure 60 mL of the wastewater sample into a 100 mL beaker. Stir the sample. (Note: Allowing wastewater samples with a pH greater than 7 to be exposed to carbon dioxide (CO₂ ) in the atmosphere can result in the formation of carbonic acid, which will lower the sample's pH value—so minimize exposure to the air.)

3. Rinse electrode and ATC probe with DI water and blot dry. Place probes in the wastewater sample and allow the measurement to stabilize.

4. Record pH measurement. Rinse probes and repeat steps 2 to 4.

Results

A minor (<±0.5 pH) difference between results of the same wastewater sample indicates good technique and high confidence in results.