Multi-dimensional monitoring of water quality indicators(1)

- May 04, 2020-

Related nouns

Online water quality analysis instrument is a kind of automatic analysis instrument specially used for water quality analysis. The instrument can realize continuous operation from water sample collection to real-time output of water quality index data without manual intervention. The online water quality analysis instrument has the characteristics of real-time, in-situ and automatic analysis, and has important application value in real-time water pollution alarm, rapid assessment of water quality safety and early warning, especially in water treatment process control.


Water quality index is a parameter that characterizes various physical, chemical, biological characteristics and radioactivity of water, specifically refers to the concentration of other substances (impurities) in the water except water molecules or the physical, chemical, biological Changes in characteristics and radioactivity. Taking drinking water as an example, the drinking water standards of all countries in the world, including the World Health Organization (WHO), contain the contents of these four types of indicators. They hope to pass a comprehensive study on the physical, chemical, biological and radioactive indicators of water. Obtain and analyze, conduct a comprehensive assessment of water quality, and achieve the purpose of ensuring drinking water safety.

In practical applications, since the water radioactivity indicators of fixed water sources generally do not change much, in addition to natural mineral water and domestic drinking water, sea water, and nuclear power plant water and drainage, in terms of overall water quality assessment and water treatment process control, It has been widely concerned and studied more physical, chemical and biological water quality indicators and their analysis techniques. Taking the Clean Water Act as an example, Section 101. (a) of Part 101 clearly states: The objective of this Act is to restore and maintain the chemical, physical, and biological integrity of The Nation's water (Chinese: The purpose of this regulation is to restore and maintain the chemical, physical and biological integrity of the national water body); In addition, China ’s GB / T 33087-2016 “Specifications and Test Methods for High-Purity Water for Instrumental Analysis” The requirements for high-purity water are only six indicators, which also cover physical (resistivity), chemical (chloride, sodium, silicate, total organic carbon or COD) and biological indicators (total bacteria).


Biological indicators of water quality refer to organisms in water, mainly microorganisms, algae, protozoa and their constituents (such as enzymes, chlorophyll, endotoxins, resistance genes, etc.), quantity, activity, and microbial community. The biological indicators in a broad sense also include biological toxicity indicators, specifically referring to the use of organisms as a means of detection to evaluate the water quality by testing the changes in certain characteristics of the organisms when facing specific water samples.

02


Physical and chemical index monitoring, "2D era" of online water quality analysis instruments


In the early days of online water quality analysis instrument technology development, the water quality indicators that online water quality analysis instruments can measure are mainly relatively simple physical indicators and chemical composition indicators, such as water temperature, conductivity, pH, ORP, dissolved oxygen, turbidity, and suspended solids concentration. Wait. Although, with the development of analytical chemistry, materials science, electronic science, computer technology and communication technology, online water quality analysis instrument technology has also been rapidly developed, water quality indicators that can be monitored online are increasing, and COD, SDI (pollution index) have appeared ), SiO2, total phosphorus (TP), total nitrogen (TN) and a large number of on-line water quality analysis instruments with complex structures. However, subject to the development level of biotechnology, the data of biological indicators can only be obtained through laboratory analysis methods, and there is a large time lag. Due to the lack of real-time change data of biological indicators, it is impossible to fully understand the real-time changes of water quality data from the three dimensions of water physical, chemical and biological indicators, to realize the prediction and early warning of water quality changes or to optimize the water treatment process And automatic control is still subject to many constraints. Some people call this stage where online water quality analysis instruments can only measure physical and chemical indicators of water the "2D era" of online water quality analysis technology.

During this period, in order to cope with the limitation that biological indicators cannot be directly monitored online in real time, water quality scientists and water treatment process experts have proposed many indirect measurement methods. There are mainly two categories: one is to use water quality replacement indicators, and water quality replacement indicators Refers to a specific type of water quality parameter, which can comprehensively reflect the water pollution of a certain type of water body or some of the water treatment process can not achieve online monitoring and laboratory analysis is also very cumbersome changes in water quality indicators. Turbidity is one of the most representative water quality substitution parameters. Turbidity was originally a limnology concept. It originally refers to the degree of turbidity caused by various plankton and suspended matter in natural water bodies. It is visually observed or optically measured. To take measurements. Because turbidity can reflect the content of sediment, clay, algae, microorganisms and other organic substances in the water, it has quickly become the most important key process parameter for water purification treatment. At the same time, turbidity can also reflect the most direct evaluation of water quality by human senses. , Drinking water standards in countries around the world, including the World Health Organization, take turbidity as a required indicator. In the United States drinking water quality standards, turbidity and total heterotrophic bacteria, E. coli, Legionella, viruses and other microbial indicators Also included in the series of microbiological indicators, the reason is: turbidity has an effect on disinfection and provides a place for bacterial growth. In drinking water standards and water purification processes, turbidity has become a substitute for pathogenic microorganisms such as "two insects" (Cryptosporidium and Giardia), heat-resistant Escherichia coli, and viruses. Degree of particulate matter can characterize the number of microorganisms in water to a certain extent. In addition, turbidity can also affect the disinfection effect of water:

Under the same water quality conditions, the lower the turbidity, the better the disinfection effect. More importantly, because the detection of microorganisms (especially "two insects") is very complicated, with large errors and poor timeliness, it is difficult to accurately characterize the removal effect of the water purification process on microorganisms in a timely manner. Using turbidity as a microbiological substitute index has the advantages of simple, rapid and accurate detection methods, which can facilitate the monitoring of the removal effect of water purification process on microorganisms, the evaluation of process operating conditions and the timely optimization and adjustment of process operating parameters.

PS: The measurement principle of the online turbidity analyzer is to use the principle of light scattering. When the light beam touches the surface of suspended particles in water, it will scatter and absorb the light passing through the water sample. When the scattered light is at a right angle of 90 degrees to the incident light The scattered light intensity has a linear relationship with the turbidity. The scattered light intensity is measured by the detector, and compared with the standard, the turbidity value of the water sample can be obtained. Today's online turbidity analyzer has become one of the most important monitoring equipment for water quality purification process control of drinking water, industrial process water, etc. due to its simple structure, fast response speed, and high reliability. Dozens of online turbidity analysis instrument products with different structures, different ranges, different test accuracy, and different installation methods can meet the real-time monitoring of turbidity from highly clean membrane filtered water to highly polluted and highly suspended water samples. (At present, the mainstream online suspended solids analyzer on the market also generally uses the principle of turbidity-based scattered light measurement. The method is to use the correlation between the suspended solids content in the water and the change in scattered light intensity. Comparing and correcting the concentration of suspended solids obtained by the method of weighing, filtering and drying in the chamber to the instrument, relatively accurate monitoring data of suspended solids can be obtained. Since the concentration of suspended solids refers to the amount of suspended solids in a certain volume of aqueous solution, The unit is mg / L; it should be noted that the turbidity unit NTU (scattered light turbidity unit) and mg / L as the concentration unit of suspended matter are two different concepts, the former is the optical unit and the latter is the mass concentration unit There is no numerical corresponding or equivalent relationship between the two. Suspended matter concentration is an important process parameter of sewage biological treatment method, and online suspended matter analyzer has a very wide range of applications in sewage treatment and industrial water treatment process control)