First of all, when it comes to the indicators of organic matter in water, everyone should be able to think that they can be divided into two categories. One is an indicator expressed by oxygen demand (O2) equivalent to the amount of organic matter in water, and the other is an indicator expressed by carbon (c). Among them, the oxygen demand index is: BOD
/TOD, and the carbon index is: TOC. The following editor will introduce the above indicators of organic matter in water in detail. Firstly, the order of the above indicators according to the numerical value is: TOD>COD>BOD>TOC. The specific analysis is as follows: [Total oxygen demand TOD] The total oxygen demand TOD refers to the amount of oxygen required when reducing substances in water burn at high temperature and become stable oxides, and the result is expressed in mg/L. The TOD value can reflect the oxygen consumed when almost all organic substances in water (including carbon C, hydrogen H, oxygen O, nitrogen N, phosphorus P, sulfur S, etc.) become CO2, H2O, NOx, SO2, etc. after combustion quantity. 【Total Organic Carbon TOC】Total organic carbon TOC is a comprehensive indicator that indirectly indicates the content of organic matter in water. The data displayed is the total carbon content of organic matter in sewage, and the unit is expressed in mg/L of carbon (c). The TOC of general urban sewage can reach 200mg/L, and the TOC of industrial sewage has a wide range, up to tens of thousands of mg/L. The TOC of sewage after secondary biological treatment is generally<50mg/L. [Biochemical Oxygen Demand BOD] Biochemical Oxygen Demand is called Biochemical Oxygen Demand, abbreviated as BOD, which means that under the condition of temperature of 20 ℃ and aerobic conditions, aerobic microorganisms decompose the organic matter in water during the biochemical oxidation process. The amount of dissolved oxygen, that is, the amount of oxygen required for the stabilization of biodegradable organic matter in water, is in mg/L. BOD includes not only the oxygen consumed by the growth and reproduction of aerobic microorganisms or respiration in water, but also the oxygen consumed by reducing inorganic substances such as sulfide and ferrous, but the proportion of this part is usually very small. Under natural conditions at 20°C, the time required for organic matter to oxidize to the nitrification stage, that is, to achieve complete decomposition and stability, is more than 100 days. In production and application, 20 days is still considered too long, and the biochemical oxygen demand BOD5 of 5 days at 20°C is generally used as an index to measure the organic matter content in sewage. [Chemical Oxygen Demand COD] Chemical oxygen demand COD refers to the amount of oxidant converted into oxygen consumed by the action of organic matter in water and strong oxidant under certain conditions, expressed in mg/L of oxygen. When potassium dichromate is used as the oxidant, almost all (90% to 95%) of the organic matter in the water can be oxidized. At this time, the amount of the consumed oxidant converted into oxygen is commonly referred to as the chemical oxygen demand, often abbreviated as CODcr. The CODcr value of sewage not only includes the oxygen consumption for the oxidation of almost all organic substances in the water, but also includes the oxygen consumption for the oxidation of reducing inorganic substances such as nitrite, ferrous salt, and sulfide in the water.
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