Do you know the three major types of water quality indicators in sewage?
Kinglv Environmental tells you that water quality indicators can be divided into three categories: physical indicators, chemical indicators and main physical indicators.
1. the physical indicators
1.1. Solid matter (TS). Solid matter in water refers to the total amount of solid matter remaining when the water sample is evaporated to dryness at a certain temperature, also called evaporation residue. According to the solubility of solids in water, it can be divided into dissolved solids (DS) and suspended solids (SS). Dissolved solids are also referred to as "total filterable residues" and refer to the sum of various inorganic and organic substances dissolved in water. In the water quality analysis, the water sample is subjected to a filtration operation, and the solid matter obtained after the filtrate is evaporated to dryness at a temperature of 103 to 105 ° C is a dissolved solid. Suspended solids are also referred to as "total non-filterable residue". In the water quality analysis, the water sample is filtered through a 0.45 μm filter, and the solid particles that cannot pass through the filter are suspended solids.
1.2. Turbidity. The water contains muddy sand, fiber, organic matter, plankton, etc., which will show turbidity. The degree of turbidity of the water can be expressed by the amount of turbidity. The turbidity refers to the degree of hindrance caused by the insoluble matter in water to the passage of light. In the water quality analysis, the turbidity of 1 g of SiO2 in 1 L of water is defined as a standard turbidity unit, abbreviated as 1 degree. Turbidity using NTU units
1.3. Color. The color of water is divided into true color and color. The true color is caused by dissolved substances or colloidal substances contained in the water, that is, the color exhibited by the suspended matter in the water. The color of the table is the color caused by the dissolved substance, the colloidal substance and the suspended substance. The appearance of abnormal colors is a sign of water pollution. The physical water quality indicators of water include smell, temperature and conductivity.
2. Chemical index
2.1. Chemical oxygen demand (COD). Chemical oxygen demand refers to the amount of oxygen consumed by a strong oxidant to oxidize organic matter in sewage under certain conditions. Commonly used oxidants are potassium permanganate (KMnO4) and potassium dichromate (K2CrO7). China's prescribed sewage inspection standard uses potassium dichromate as the oxidant, which is recorded as CODCr in units of (mg/L). Because K2CrO7 has a strong oxidation capacity, it can oxidize 85%~95% of the organic matter in the sewage.
The determination of CODCr is simple and rapid, and the measurement time is only 2 hours, which is convenient for guiding production and is not limited by water quality. However, there are also disadvantages: since the reducing inorganic substance in the sewage can also consume oxygen, the CODCr value cannot accurately represent the amount of organic matter that can be oxidized by the microorganism.
2.2. Biochemical Oxygen Demand (BOD). Due to the wide variety of organic substances in the sewage, it is difficult to separately determine the content of various organic substances in the prior art (it is not necessary in general). However, most organic pollutants in sewage require oxygen when oxidatively decomposed by microorganisms, and the amount of organic matter is proportional to the amount of oxygen consumed. Therefore, biochemical oxygen demand has become a widely used indicator of sewage quality. Biochemical oxygen demand refers to the amount of dissolved oxygen consumed by the organic matter decomposed in water due to the action of microorganisms under the conditions of constant temperature and time, and its unit is mg/L. The decomposition process of organic matter in sewage can generally be divided into two stages. The first stage is the carbonization stage, in which the carbon in the organic matter is oxidized to carbon dioxide, and the nitrogen in the organic matter is converted into ammonia. The amount of oxygen consumed in the carbonization stage is called carbonized oxygen demand. The second stage is the nitrification stage, in which nitrogen is oxidized to nitrite and nitrate by the action of nitrifying bacteria. The amount of oxygen consumed during the nitrification stage is called nitrification.
The rate at which microorganisms decompose organic matter is closely related to temperature and time. In order to make the measured BOD values comparable, the Environmental Monitoring Technical Specification prepared by the State Environmental Protection Administration stipulates that the sewage should be cultured at 20 ° C for 5 days as a standard condition for the determination of biochemical oxygen demand. The result measured under these conditions is the 5-day biochemical oxygen demand, which is recorded as BOD5. If the measured time is 20 days, the result is called 20-day biochemical oxygen demand, which is recorded as BOD20.
The BOD value, as the main indicator of organic matter concentration, basically reflects the amount of organic matter that can be decomposed by microbial oxidation. However, there are also defects such as difficulty in controlling measurement error and slow feedback information under certain conditions.
Generally speaking, for a certain amount of sewage, the difference between COD>BOD20>BOD5, BOD, and COD roughly reflects the content of organic matter that cannot be biodegraded.
2.3. Total Organic Carbon (TOC) Total organic carbon refers to the carbon content of all organic matter in wastewater. In the TOC meter, when the sample is burned at 950 ° C, all organic carbon and inorganic carbon in the sample form CO 2 , which is total carbon (TC). When the sample is burned at 150 ° C, only organic carbon is converted to CO 2 , and the remainder is the total inorganic carbon TIC. The difference between total carbon and inorganic carbon is the total organic carbon TOC, namely:
The TOC value approximately represents the amount of oxygen consumed when all the organic matter in the water sample is oxidized, and the conversion coefficient of the COD value and the TOC value is 2.67, that is,
2.4. Organic nitrogen. Organic nitrogen is a water quality indicator of the total amount of nitrogen-containing organic matter such as protein, amino acid and urea in water. If the organic nitrogen is biooxidized under aerobic conditions, it can be gradually decomposed into NH3, NH4+, NO2-, NO3-, etc., NH3 and NH4+ are called ammonia nitrogen, NO2- is called nitrite nitrogen, and NO3- is called Nitrate nitrogen. The sum of organic nitrogen and ammonia nitrogen, nitrite nitrogen and nitrate nitrogen is called total nitrogen (TN).
2.5. pH value. The pH value refers to the concentration of hydrogen ion concentration in water, that is, pH = -1 g [H + ].
2.6. Toxic substance indicators. The toxic substances in the water mainly include cyanide, mercury, arsenide, cadmium, chromium, lead, phenol, etc., and their contents are used as separate water quality indicators.
3. Biological indicator
The biological indicators mainly include the total number of bacteria and the number of coliform bacteria. The total number of bacteria refers to the total number of bacteria contained in 1 mg of water; the number of coliforms refers to the number of coliforms per 1 L of water.
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