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Cách đo pH của nước thải

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Industrial and municipal wastewater needs to be treated before it re-enters our lakes, canals and rivers. Extreme pH levels, particulates, toxic contaminants, and high levels of alkalinity are common problems in wastewater. Wastewater treatment is a serious environmental concern. The use of pH in the treatment of wastewater requires a quick, accurate and robust measurement.

Direct measurement of the pH level of wastewater effluent can vary dramatically due to variation in water temperature, water flow and the chemical makeup of the substances present in the water. Therefore, an accurate measurement of the wastewater’s pH value also requires the measurement of the water’s temperature.


Chemical and particulate contamination in wastewater can be destructive to standard pH electrodes; prematurely killing the junction. So specialized pH electrodes are recommended for wastewater testing. A double junction electrode will block chemical interferences in the wastewater, and prevent the common chemical damages to the reference junction. A flushable junction will easily deal with chemical and particulates in the wastewater. A flushable junction is ideal for paper-pulp, sludge, and dirty samples; the easy-to-clean junction never clogs.

Testing the pH of your wastewater sample

Equipment

You will need a standard pH meter, a durable pH electrode (see below), an ATC (automatic temperature compensation) 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; we recommend a double junction electrode (ex. Cole-Parmer® double junction 59001-70); or for very dirty samples, the flushable junction electrode (ex.Thermo Scientific Orion ROSS SureFlow 05718-53).

Sampling

Grab two to three representative 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.

Refence source:  http://www.coleparmer.com/TechLibraryArticle/1371