如何使用高錳酸鉀(Potassium Permanaganate)淨水?

Municipal Drinking Water Treatment with Potassium Permanganate

Potassium permanganate has a long history of successful application in municipal drinking water treatment, providing both primary and secondary benefits. It is widely used by facilities to help meet regulatory rules and public pressures to produce quality drinking water.

Municipal Drinking Water Treatment for Arsenic Removal

Potassium permanganate is used to remove arsenic (As) in ground water treatment systems that employ filtration. Permanganate oxidizes arsenic (As3+) to As5+ that can adsorb to insoluable precipitates such as hydros manganese hydroxides or ferric hydroxide. The precipitates are then removed from the drinking water supply in the clarification and filtration processes. Permanganate can also be used for arsenic removal in surface water treatment plants that have filtration.

Factors that affect removal efficiency include water chemistry, pH, temperature, contact time, and application point. Reaction times are rapid under normal conditions of temperature and pH. However, temperatures <35°F, and pH values <5.5 require reaction times longer than two minutes. In most cases, 5 to 10 minutes of reaction time is sufficient.

It has been demonstrated that the presence or addition of iron (Fe2+) will enhance the efficiency of As removal for municipal drinking water treatment. A ratio of Fe to As of 20:1 is recommended.

Application of Permanganate

Precipitates (e.g. MnO2) are removed more easily in hard water than soft water. Sufficient time (approximately 30 minutes) is suggested for coagulation of the oxidation by-products. The preferred location for feeding potassium permanganate is the point that gives the longest contact time ahead of coagulation, usually at the intake or well head of the drinking water treatment plant.

Chemistry

3As3+ + 2MnO4- + 4H2O -> 2MnO2 + 3As5+ + 8OH-

Dosage

1 part of soluble arsenic requires 1.26 parts of potassium permanganate.

Treatment Facility Requirements

Proper feed equipment specially designed to handle potassium permanganate is recommended and available from Carus. For proper removal of As with municipal drinking water treatment, the utility must have water filtration or coagulation/filtration to remove the arsenic containing precipitates formed during oxidation. In addition, alkalinity and hardness > 50 mg/L are recommended for proper coagulation of these precipitants.

Benefits of Permanganate

Potassium permanganate quickly oxidizes As3+ in most cases without pH adjustment. The freshly precipitated arsenic and manganese floc will further adsorb metal ions and organic compounds while enhancing the effectiveness of the coagulation process.

Treatment with permanganate also:

removes iron, manganese, hydrogen sulfide and other undesirable compounds,
helps control tastes and odors of drinking water, and
acts as a substitute oxidant to chlorine in a disinfection by-product (DBP) control program.

References
Lauf, G. F., Waer, M. A., Arsenic Removal Using Potassium Permanganate, AWWA WQTC, 1993
Ficek, K. J., “The Potassium Permanganate/Greensand Process for Water Treatment” Water Quality Association Conference, 1994