Water quality analyzer in urban waste water treatment - Database & Sql Blog Articles

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With the rapid development of China's economy in recent years, the city's industrial and domestic waste has increased greatly, and the eutrophication of water has caused algal blooms to occur frequently. At present, the main method of treating garbage is sanitary landfill, and landfill is open-air. After the operation, the garbage is compacted, and as the waste in the garbage decomposes and encounters rain and snow, rain and snow water seep into the landfill area, and landfill leachate is generated. The leachate is a high-concentration organic wastewater with a wide range of concentration values, including hydrocarbons, nitrates, sulfates, and traces of heavy metal ions such as copper, cadmium, and lead. The bacterial index is high, and if it is not treated, it is directly discharged into the water body. It will seriously pollute the local water environment. In order to protect the water environment, monitoring of sewage discharge must be strengthened. The design of the inspection points and the quality of the instrumentation (mainly the water quality analyzer) play a crucial role in the monitoring of the water environment.

First, the working principle of water quality analyzer

There are two types of analyzers used in wastewater treatment plants: pH meters and dissolved oxygen analyzers.

1, the working principle of the pH meter

The pH of the water depends on the amount of material dissolved, so the pH can sensitively indicate changes in water quality. The change of pH has a great influence on the reproduction and survival of the organism, and also seriously affects the biochemical action of the activated sludge, that is, affects the treatment effect. The pH value of the sewage is generally controlled between 6.5 and 7.

Water is chemically neutral, and some water molecules spontaneously decompose according to the following formula: H2O=H++OH-, which is decomposed into hydrogen ions and hydroxide ions. In a neutral solution, the concentration of hydrogen ion H+ and hydroxide ion OH- is 10-7 mol/l, and the pH value is the negative of the logarithm of the base of hydrogen ion concentration: pH=-log, so neutral The pH of the solution is equal to 7. If there is an excess of hydrogen ions, the pH is less than 7, and the solution is acidic; otherwise, if the hydroxide ions are excessive, the solution is alkaline.

The pH value is usually measured by a potentiometric method. Usually, a reference electrode and a measuring electrode of a constant potential are used to form a primary battery. The magnitude of the electromotive force of the primary battery depends on the concentration of hydrogen ions and also depends on the pH of the solution. The plant uses a CPS11 pH sensor and a CPM151 pH transmitter. The specific structure is shown in Figure 1. The measuring electrode has a special pH-sensitive glass probe. It is made of special glass that can conduct electricity and penetrate hydrogen ions. It has high measurement accuracy and good anti-interference. When the glass probe is in contact with hydrogen ions, a potential is generated. The potential was measured by a silver wire reference electrode suspended in a silver chloride solution. The pH value is different, and the corresponding potential is different. It is converted into a standard 4-20mA output by the transmitter.

Second, the working principle of dissolved oxygen analyzer

The oxygen content in the water can fully indicate the degree of self-purification of the water. For biological treatment plants using activated sludge, it is important to understand the oxygen content of the aeration tank and the oxidation ditch. The increased dissolved oxygen in the sewage will promote biological activities other than anaerobic microorganisms, thus removing volatile substances and being easy. Naturally oxidized ions purify the sewage.

There are three main methods for determining oxygen content: automatic colorimetric analysis and chemical analysis measurement, paramagnetic measurement, and electrochemical measurement. The amount of dissolved oxygen in water is generally measured by electrochemical methods.

Oxygen is soluble in water and its solubility depends on temperature, total pressure on the water surface, partial pressure and salts dissolved in water. The higher the atmospheric pressure, the greater the ability of water to dissolve oxygen. The relationship is determined by Henry's law and Dalton's law. Henry's law states that the solubility of a gas is proportional to its partial pressure.