Multi-dimensional monitoring of water quality indicators(2)

- May 05, 2020-

The second method is to measure the changes in physical or chemical indicators of water caused by the action of organisms, especially microbes, to infer the changes in biological indicators to control the water treatment process. Taking sewage treatment as an example, most of the mainstream processes of sewage treatment in the world currently use biological treatment. As we all know, sewage biological treatment is a biological reaction process, and its core is the microbial activity in water. It is very important to accurately understand the microbial activity in sewage, but in the past, it was almost impossible to detect microbial activity in real time through online water quality analysis instruments. Water treatment experts have developed dissolved oxygen (DO), oxidation-reduction potential (ORP), aerobic rate (OUR), sludge volume index (SVI), MLSS (mixed liquid suspended solids (activated sewage) Mud) concentration), biological oxygen demand (BOD), etc. A large number of physical and chemical indicators related to microbial activity in sewage, or environmental condition parameters; of course, there are volatile fatty acids (VFA) and alkali for anaerobic processes Physical and chemical indicators such as degree, these indicators have become very important process parameters that play an important role in the process control of sewage biological treatment process, and online water quality analysis instruments for these indicators have also been widely used in actual sewage treatment processes. application. In spite of this, because the data of microbial activity cannot be obtained directly, the entire sewage treatment process is still in a black box operation state. In actual operation, it is often necessary to rely on the experience of the operator to deal with the occurrence of abnormal water quality.

The residual amount of disinfectant in drinking water is another valuable example. The purpose of adding disinfectant to drinking water is to kill pathogenic microorganisms and protozoa in the water. At the same time, in order to ensure the continuous maintenance of disinfection ability during the delivery and distribution of drinking water, it is necessary to ensure that there is a certain amount of disinfectant residue in the water. At present, the most widely used drinking water disinfectant in the world is chlorine preparation (including chlorine gas, sodium hypochlorite, etc.), and its residual amount is referred to as residual chlorine concentration. According to the World Health Organization (WHO) in the "Guidelines for Drinking Water Quality" (Fourth Edition): "Monitoring residual chlorine can quickly indicate problems that were originally reflected by direct measurement of microbial parameters ... It is difficult to maintain residual chlorine somewhere, or the residual chlorine gradually disappears, which may indicate that the water or pipeline has increased the demand for oxidants due to the growth of bacteria. "In addition, it is also recommended:" Coliform bacteria can be used to evaluate the cleanliness of the distribution system , Integrity and presence or absence of biofilm, but the detection is too slow and unreliable, it is better to directly detect the residual amount of disinfectant. "At present, the chlorine disinfection of water plants in the global drinking water industry all use residual chlorine concentration as drinking water control One of the most important indicators of microbial safety, China ’s “Sanitary Standards for Drinking Water” also stipulates that the residual chlorine concentration of tap water must be not less than 0.3mg / L when leaving the factory; the residual chlorine concentration of tap water at the end of the pipe network cannot be Less than 0.05mg / L. In spite of this, in the actual situation, in addition to bacteria in the water, there are other substances that will consume residual chlorine, and the presence of a large number of chlorine-resistant microorganisms, although the residual chlorine concentration is qualified, but the microbial index exceeds the standard. , Brings risks to drinking water safety. At the same time, due to the inability to obtain direct information on microbial pollution in water in a timely manner, in order to fully ensure the safety of water quality when water quality may be at risk, sometimes the method of excessively adding disinfectant is used, which wastes disinfectant and increases disinfection by-products Generated risk.


03

Online monitoring of biological indicators, online water quality analysis instruments usher in the 3D era


With the rapid development of biological science and technology, coupled with the growing attention of the water industry to biological contaminants represented by pathogenic bacteria, viruses and resistance genes in water, emerging biological science and technology and traditional online water quality analysis instrument technology are The field of analysis has been combined, and breakthroughs have been made in online water quality analysis instrument technology. Real-time online monitoring of biological indicators has been realized. Through online analysis technology, real-time detection of water quality indicators from the three dimensions of physics, chemistry, and biology, a comprehensive description of water quality status and safety Carrying out a quick and comprehensive assessment also makes it possible to control the water treatment process in multiple dimensions automatically. The online water quality analysis instrument technology has entered the "3D era".


The use of biotechnology can directly measure the biological composition and quantity of the water sample to be tested, such as algae concentration or microbial content, etc., and can also obtain microbial activity information by measuring the metabolites of microorganisms in water. So far, the most important new products in the former method are algae online analyzer, online flow cytometer, etc .; in the latter method, there are online E. coli analyzer and alkaline phosphatase (ALP) method for total bacterial analysis Instrument, adenosine triphosphate (ATP) online analyzer, etc.

The on-line algae analyzer uses photosynthetic pigments represented by chlorophyll and emits fluorescence under excitation light. The intensity of the fluorescence is related to the content of chlorophyll in the algae, and then to the total amount of algae in the water; and the photosynthetic pigments in the same category of algae The excitation light of a specific wavelength has a similar corresponding fluorescence spectrum. Because of the presence of this characteristic pigment, the fluorescence spectrum of different species of algae has a significant difference. According to the characteristic spectrum and intensity of algae, algae can be classified. And quantitative detection of the concentration of different species of algae. Online flow cytometry (FCM) is a technology that applies laboratory flow cytometry to online analysis of water quality. The instrument detects various scattered light and fluorescent signals to achieve the object to be measured (cell, RNA) at the molecular level \ DNA, protein, etc.) rapid detection of physical and biological characteristics, with the support of advanced algorithms and computing capabilities, these complex and numerous signals are quantitatively processed; flow cytometry measures the total number of cells (TCC), It has been included in the standard analysis method for drinking water in Switzerland. At present, flow cytometry online bacteria analyzer can quickly measure the total number of bacteria in the water, algae and other indicators, and can distinguish between live and dead bacteria through different fluorescent staining materials, to obtain a lot of valuable microbial information in water.


At present, the use of underwater 3D microscopic imaging lenses, with the support of artificial intelligence and image recognition technology, continuously obtains information on the number and classification of algae in the water body in real time; or on the protozoa and microbial populations and activities in the biological treatment of sewage Continuous monitoring has been carried out to help operators to control and optimize the sewage treatment process in real time.

 

Obtaining information on microbial activity in a timely manner by measuring microbial metabolites in water is also a rapidly developing online analytical instrument technology. Metabolism is the most basic symbol of living organisms. It reflects the ability of cells to obtain energy from the environment. The metabolism of organisms is carried out by enzymes. Certain organisms or biomes will produce specific enzymes. Measuring this specific enzyme to measure, you can get information about the metabolic activity of the target organism and calculate the concentration of the live target organism. Because laboratory microbiological analysis methods require manual cultivation and take a long time, when it comes to the requirements of water treatment process control, as well as water quality alarms and water quality safety warnings, the advantages of fast and automatic online water quality analysis instruments are fully reflected. Taking the analysis of E. coli as an example, there are currently two online E. coli analyzers. One is the enzyme substrate method. The enzyme substrate method is based on a standard laboratory method. The principle is to use E. coli in water through cultivation in the metabolic process. The β-glucuronidase produced in the product decomposes a specific substrate in the culture medium and generates fluorescence. The fluorescence intensity is mathematically related to the content of E. coli in the water. The concentration of E. coli can be calculated by measuring the fluorescence intensity. Since the enzyme substrate method still needs to be cultivated, the measurement time will be affected by the concentration of E. coli in the water sample to be tested, usually from 4-18 hours. At present, the online analytical instrument of this method can only be used for automatic analysis of water quality, and cannot To meet the needs of process control; the other is the direct measurement of enzyme activity. By establishing a standard curve of enzyme activity, the activity of β-glucuronidase in water is directly measured. The size of enzyme activity is highly related to the content of E. coli. The concentration of E. coli in the water is obtained; since the direct measurement of enzyme activity does not require the cultivation of the water sample, the measurement can be completed once in 15 minutes.

The alkaline phosphatase (ALP) method total bacterial count analyzer uses the correlation between the bacterial alkaline phosphatase activity and the total bacterial count to obtain relative data on the total bacterial count in the water by directly measuring the alkaline phosphatase activity in the water sample to be tested And through the comparison with the laboratory traditional cultivation method measurement results and calibration, to achieve online real-time monitoring of the total number of bacteria for a specific water sample, this principle of online water quality analysis instrument, the measurement cycle only needs 15 minutes, can meet The need for real-time monitoring and automatic control of the water treatment process.


The adenosine triphosphate (ATP) online analyzer measures adenosine triphosphate (ATP), an energy substance present in all living cells. Studies have shown that the ATP content in water is positively correlated with the number of living cells. By measuring the ATP content, the activity in water can be reflected indirectly. Biomass. The measurement method is: based on bioluminescence technology, the cell releases ATP after lysis, under the action of luciferase, the fluorescein in the reagent reacts with ATP, and finally emits a fixed wavelength of fluorescence. The fluorescence intensity and ATP concentration are With a certain proportional relationship, the fluorescence signal is detected by a fluorescence detector, and compared with the known ATP calibration curve, the ATP concentration can be obtained, and then the data of active biomass in water can be obtained. The luciferase in the reagent of this method needs to be stored at a low temperature, otherwise the enzyme activity will be affected, which will affect the accuracy of the measurement results. The online analysis instrument requires a built-in refrigeration device, and the instrument structure is slightly complicated.

The "3D era" of online water quality analysis instruments, through the online monitoring of biological indicators, solves the limitations of the previous indirect reaction of microbial activities in water through physical and chemical indicators, and truly controls the more comprehensive water quality safety assessment and water treatment process Provide more valuable data; as more biological indicators achieve online monitoring, and online monitoring of physical and chemical indicators synergistic, microbial pollution control of water treatment process and biological method of water treatment process will no longer be black box control The efficiency and safety of water treatment will be further improved.



As for the online biotoxicity meter, as mentioned earlier, the broad biological indicators also include the biological toxicity of water. Specifically, a certain organism is used as an experimental method to test its response to a specific water body to measure the comprehensive toxicity of water. Due to the wide variety and large number of toxic substances in water, it is almost impossible to exhaust these substances through physical or chemical analysis; and, even if the content and toxicity of these substances in water are known, there will still be Many different interaction methods such as synergy, antagonism, addition, and independence have an impact on the toxicity of water, making it impossible to determine the final water toxicity through physical and chemical methods. At this time, it is necessary to use organisms to directly evaluate the comprehensive toxicity of water.


The main organisms used as toxicity tests are: luminescent bacteria, fish, large fleas, algae, nitrifying bacteria, etc., and the application of microbial fuel cells (MFC) in toxicity tests has also been reported. At present, online toxicity analysis instruments using these organisms have mature products and market applications.

Among them, the luminescent bacteria method for measuring biological toxicity analysis is a very mature method. Both the International Organization for Standardization (ISO) and China have standard methods for laboratory measurement. The standard codes and names are: ISO11348-3: 2007 "Water quality — Determination of the inhibitory effect of water samples on the light emission of Vibrio fischeri (Luminescent bacteria test) — Part 3: Method using freeze-dried bacteria; The specific method is; use of some self-luminous bacteria, such as bright photobacterium, vibrio qinghai, vibrio fischeri, etc., when encountering toxic substances, the bacteria will die and the luminous intensity will be weakened, and their relative luminosity and water toxicity The concentration of the components is significantly negatively correlated (P≤0.05), so a certain amount of luminescent bacteria can be used as a test reagent to measure its relative luminosity in a specific water body to characterize the toxicity level of the water sample. The existing luminescent bacteria method online biotoxicity analyzer is to automatically analyze the above laboratory analysis methods and steps through automatic control from the water sample collection, transportation, reagent addition to the result calculation, so as to realize the synthesis of the water sample to be tested Real-time online monitoring of biological toxicity. At present, there are two main sampling methods of the luminescent bacteria method online biotoxicity analyzer. One is to use the batch sampling method commonly used in laboratory analyzers. One sample is injected, and the next water sample is completed after one analysis process. Because this kind of instrument analyzes non-continuous water samples, it is possible to lose some of the real data of the water samples when the water body changes suddenly. The other is the continuous sampling method. The water sample continuously enters the reactor and is mixed with the luminescent bacteria reagent. The instrument continuously detects the change in luminous intensity. This sampling method can ensure that the online biotoxicity analyzer analyzes the continuous water sample. Compared with the batch The second injection can reflect the changes of water toxicity in a more timely and continuous manner.