Sewage treatment plant operation index monitoring list!

Pay more attention to the public account: environmental protection water treatment

The normal operation of the sewage treatment plant is the fundamental guarantee to ensure the normal effluent. Scientific and effective operation and management of sewage plants is an important means to ensure normal operation. Among them, the regular and accurate monitoring of the operation indicators of the sewage plant, and the analysis and statistics of the obtained data, so as to guide the operation of the sewage treatment plant are the foundation of the work of the sewage plant.

1. Physical properties of sewage

1, Temperature

It has a direct impact on the physical, chemical and biological properties of sewage and sludge. In the aeration tank of the activated sludge system, it mainly relies on a large number of active microorganisms (microbial micelles) for treatment, and the temperature they are more suitable for is generally about 20~30 °C, so if you want to ensure a better organic matter treatment effect, the temperature should be controlled at about 20~30 °C as much as possible.

Temperature monitoring is carried out in the field, and the commonly used methods are water thermometer method, deep water thermometer method, inverted thermometer method and thermal thermometer method.

2. Chromaticity

The color of the sewage from the municipal sewage treatment plant is not very obvious from the sewage from the industrial wastewater, but it does not mean that the monitoring of the color is not important. In fact, the freshness of the sewage can be judged by observing the color of the sewage entering the sewage treatment plant. Normally, fresh municipal sewage is gray in color, but if it is anaerobic and rotten during the pipeline process, and there is little DO, the sewage will be black and smelly. In addition, in mainland China, because a drainage system is usually used to discharge industrial wastewater and domestic sewage, the color of urban sewage plants sometimes varies greatly. Chromaticity gives people a feeling of displeasure, and the mainland has discharge requirements for chromaticity in the discharge standards of sewage plants, so if the chromaticity of the inlet water is large, the chromaticity of the effluent should be paid attention to in the monitoring index.

3. Odor

The odor in the water mainly comes from the decay of organic matter, which will also bring unpleasantness to people, and even affect human physiology, breathing difficulties, vomiting, etc. Therefore, odor is a relatively important physical indicator, however, there is no special monitoring of odor in sewage treatment plants.

2. Chemical (including biochemical) properties of sewage

The chemical indicators of sewage water quality include suspended solids, pH, alkalinity, heavy metal ions, sulfides, biochemical oxygen demand, chemical oxygen demand, total oxygen demand, total organic carbon, organic nitrogen, dissolved oxygen, etc.

1. Chemical Oxygen Demand (COD)

Chemical oxygen demand (COD) is the amount of oxidation consumed when a water sample is treated with a certain strong oxidant under certain conditions. It is an indicator of the amount of reducing substances in the water. The reducing substances in the water include various organic substances, nitrites, sulfides, ferrous salts, etc. But the main thing is organics. For this reason, chemical oxygen demand (COD) is often used as a measure of the amount of organic matter in the water. The higher the chemical oxygen demand, the more serious the pollution of the water body by organic matter.

The determination of COD is the main daily monitoring item of the sewage treatment plant, through the measurement of the COD of the inlet and outlet water of different structures, the operation of the structure can be accurately grasped, and the operation of the structure can be appropriately adjusted through the data analysis of a period of time, so as to ensure the treatment effect of the sewage. In addition, COD is a project that must be monitored for the effluent of the sewage plant, and the effluent should meet the corresponding national standards.

The determination of chemical oxygen demand (COD) varies depending on the reducing substances in the water sample and the method of measurement. At present, the most common applications are acid potassium permanganate oxidation method and potassium dichromate oxidation method. Potassium permanganate (KmnO4), which has a low oxidation rate but is relatively simple, can be used in the determination of the relative comparison value of organic matter content in water samples. The potassium dichromate (K2CrO7) method has high oxidation rate and good reproducibility, and is suitable for determining the total amount of organic matter in water samples.

2. Biochemical oxygen demand (BOD)

Biochemical oxygen demand (BOD) is the amount of oxygen consumed when the organic matter that can be decomposed in water is completely oxidized and decomposed due to the action of microorganisms under aerobic conditions, which is called biochemical oxygen demand. It is expressed as the amount of dissolved oxygen reduced (mg/L) by a water sample at a certain temperature (e.g., 20 °C) in a closed container after a certain period of time. When the temperature is at 20 °C, it takes about 20 days for the general organic matter to be basically completed, and it takes 100 days to complete the decomposition process. However, such a long time is lost for actual production control. Practical value. Therefore, a 5-day incubation at 20 °C is currently prescribed as the standard for the determination of biochemical oxygen demand. At this time, the measured biochemical oxygen demand is called the five-day biochemical oxygen demand, which is expressed as BOD5. If the amount and composition of organic matter in sewage are relatively stable, there may be a certain proportional relationship between the two, which can be extrapolated from each other. The ratio of BOD to COD of domestic sewage is roughly 0.4~0.8. For a certain amount of sewage, generally speaking, COD> BOD20>BOD5.

BOD5 is also one of the important daily monitoring items in sewage treatment plants. The specific significance of BOD5 monitoring is basically the same as that of COD.

However, due to the drainage system of rivers existing in the mainland, the sewage of urban sewage plants contains a certain amount of industrial wastewater, and the water quality of industrial wastewater varies greatly and is difficult to degrade compared with domestic sewage.

The classic method for determining biochemical oxygen demand is the dilution inoculation method.

3. Dissolved oxygen DO

The molecular oxygen dissolved in water is called dissolved oxygen, and the dissolved oxygen content of natural water depends on the balance of oxygen in the water body and the atmosphere. The saturation content of the dissolved side is closely related to the partial pressure of oxygen in the air, atmospheric pressure, and water temperature. The solubility of surface water in clean ground is generally close to saturation. Dissolved oxygen may be supersaturated due to algae growth, and dissolved oxygen is reduced when the water is contaminated with organic and inorganic reducing substances. When the oxygen in the atmosphere is too late to replenish, the dissolved oxygen in the water gradually decreases to close to zero, and the anaerobic bacteria are slightly multiplied, and the water quality deteriorates, resulting in the death of fish and shrimp.

The amount of dissolved oxygen in wastewater depends on the treatment process before the wastewater is discharged, and is generally low and varies greatly. Fish mortality accidents are mostly due to a large amount of sewage, which increases the amount of oxygen-depleting substances in the water body, and the dissolved oxygen is very low, resulting in fish suffocation and death, so lolytic oxygen is one of the important indicators to evaluate water quality.

During the entire operation of the wastewater treatment plant, great attention is paid to the determination of dissolved oxygen in the water.

The main treatment system for urban sewage treatment at home and abroad is the biological secondary treatment system, which is mostly aerobic method. As the name suggests, it uses the metabolic process of aerobic microorganisms to decompose and remove organic matter from water. It can also be seen that the control of DO oxygen is very important, first of all, it should be ensured that there is enough dissolved oxygen in the water, so that aerobic microorganisms can work normally, which is the premise of achieving better operation results. However, if there is too much oxygenation, it will cause waste and increase operating costs. Therefore, the DO in the aeration tank is generally controlled between 2~4mg/L.

When there is a lack of dissolved oxygen due to equipment problems or other reasons, the treatment system fails. For example, insufficient DO in the aeration tank often leads to the expansion of filamentous bacteria in the activated sludge. The reason is that bacteria and filamentous bacteria compete for insufficient DO, but under the condition of insufficient DO, filamentous bacteria are far more competitive than bacteria, therefore, bacteria will get less DO, their growth will be inhibited, on the contrary, filamentous bacteria get the opportunity to multiply, and the final result is filamentous swelling.

In A/O, A2/O and other processes with certain denitrification and phosphorus removal, the control of DO is also very important. In order to obtain the desired removal rate of N and P, it is necessary to ensure that there is an appropriate DO value.

It can be seen that in the monitoring of the daily operation of the sewage plant, the monitoring of DO is very meaningful. The methods used in singing include the iodine measurement method and its correction method, the membrane electrode method and the on-site rapid dissolved oxygen meter method.

4. Total Oxygen Demand (TOD)

Total Oxygen Demand (TOD). Organic matter contains C, H, N, S and other elements, when all the organic matter is oxidized, these elements are oxidized to CO2, H20, NO2 and SO2 respectively, and the oxygen demand at this time is called total oxygen demand (TOD).

The principle and process of total oxygen demand determination is to inject a certain amount of water sample into the oxygen content, and send it into the combustion tube with platinum steel as the catalyst, and burn it at a high temperature of 900 °C, the organic matter in the water sample consumes the oxygen in the carrier gas because it is combusted, and the remaining oxygen is measured with an electrode, and recorded with an automatic recorder, and the remaining oxygen after the combustion of the water sample is subtracted from the original oxygen of the carrier gas, which is the total oxygen demand.

Compared with the determination of BOD and COD, the determination of this index is faster and easier, and the results are closer to the theoretical oxygen demand than COD.

5. Total organic carbon (TOC)

Total Organic Carbon (TOC). It represents the total carbon content of all organic pollutants in water, and is a comprehensive parameter for evaluating organic pollutants in water. It is a comprehensive measurement index to reflect the total amount of organic matter in water by measuring the total amount of organic carbon in water samples by combustion method. The measurement result is expressed in C content in mg/L.

Its determination principle and process are: the water sample is acidized, the inorganic carbonate in the water is blown out by compressed air to eliminate interference, and then the water sample is quantitatively injected into the combustion tube with platinum steel as the catalyst, and the oxygen content is sufficient and a certain gas flow, and the high temperature of 900 °C is burned, and carbon dioxide is produced in the combustion process, which is measured by the infrared gas analyzer and recorded by the automatic recorder, and then the amount of carbon is converted.

TOC is determined by combustion, so it can oxidize all organic matter, and it is more direct than BOD5 or COD to represent the total amount of organic matter, so it is often used to evaluate the degree of organic matter pollution in water bodies.

In recent years, various types of TOC analyzers have been developed at home and abroad. According to the different working principles, it can be divided into combustion oxidation-non-dispersive infrared absorption method, conductivity method, gas chromatography, wet method, L-non-dispersion infrared absorption method, etc.: among them, the combustion oxidation-non-dispersion infrared absorption method only needs a one-time conversion, the process is simple, the reproducibility is good, and the sensitivity is high, so this TOC analyzer is widely used at home and abroad.

6. Nitrogen (organic nitrogen, ammonia nitrogen, total nitrogen)

Organic nitrogen is a water quality index that reflects the total amount of nitrogen-containing organic compounds such as protein, amino acids, and urea in water.

If organic nitrogen is biooxidized under aerobic conditions, it can be gradually decomposed into NH3, NH4+, N02-, NO3- and other forms, NH3 and NH4+ are called ammonia nitrogen, NO2- is called nitrite nitrogen, and NO3- is called nitrate nitrogen, and the content of these forms can be used as water quality indicators, representing the different stages of organic nitrogen conversion into inorganic substances.

Total nitrogen (TN) is a water quality indicator that covers everything from organic nitrogen to nitrate. Ammonia nitrogen (NH3-N) is an important monitoring index of effluent from sewage plants, and the source of ammonia nitrogen in water is the decomposition products of nitrogen-containing organic matter in domestic sewage by microbial action, some industrial wastewater, such as coking wastewater and synthetic ammonia fertilizer plant wastewater, as well as farmland drainage. In addition, in an oxygen-free environment, the nitrite present in the water can also be reduced to ammonia by microbial action. In an aerobic environment, ammonia in water can also be converted to nitrite and even continue to be converted to nitrate.

The determination of nitrogen compounds in various forms of water is useful for evaluating the polluted and "self-purifying" status of water bodies. Fish are sensitive to ammonia nitrogen in the water, and high levels of ammonia nitrogen can lead to fish death.

It is present in water in the form of free ammonia NH3) or ammonium salt (NH4-), and the composition ratio of the two depends on the pH and temperature of the water. When the pH value is high, the proportion of free ammonia is higher. Conversely, the proportion of ammonium salts is high, and the water temperature is reversed. Therefore, sufficient attention should be paid to pH and water temperature when monitoring.

Methods for the determination of ammonia nitrogen usually include Nessler colorimetric method, gas-phase molecular absorption method, phenol-hypochlorite (or salicylic acid-hypochlorite) colorimetric method and electrode method.

N in the water will lead to eutrophication of the water body, and the N in the effluent of the sewage plant should be treated in accordance with the corresponding requirements of the national and local governments before being discharged. Therefore, the monitoring of N in effluent is one of the important items for water quality monitoring in sewage plants.

In addition, for the urban sewage plant that widely adopts secondary treatment, in order to ensure the normal operation of the sewage plant, it is necessary to ensure the nutrient demand of microorganisms in the biochemical tank, and the aerobic method is generally controlled at: BOD:N:P=100:5:1, therefore, for the monitoring of the inlet water N of the sewage plant, it is conducive to the control of microbial nutrition, and when the proportion of phosphorus in the sewage is less, it needs to be artificially supplemented to ensure the nutritional needs of microorganisms, and then ensure the normal operation of the sewage treatment system.

7. Phosphorus (total phosphorus, dissolved phosphate and total dissolved phosphorus)

In natural water and wastewater, phosphorus is almost always present in the form of various phosphates, which are divided into orthophosphate, condensation phosphate (pyrophosphate, metaphosphate and polyphosphate) and organically bound phosphorus (such as phospholipids, etc.), which are found in solution, humus particles or in aquatic organisms.

In general, the phosphate content in natural water is not high. Industrial wastewater and domestic sewage collected by fertilizers, smelting, synthetic detergents and other banks often contain large amounts of phosphorus. Phosphorus is one of the essential nutrients for biological growth. However, high phosphorus levels in water bodies (e.g., more than 0.2 mg/L) can cause algae to overbloom until they reach a harmful level (called eutrophication), resulting in reduced transparency of lakes and rivers and deterioration of water quality. Phosphorus is an important indicator for evaluating water quality.

In order to further prevent the eutrophication of the water body caused by P in the water, the P in the effluent of the sewage treatment plant should be treated and discharged in accordance with the corresponding requirements of the national and local governments. Therefore, the monitoring of P in effluent is one of the important items for water quality monitoring in sewage plants.

In addition, for the urban sewage plant that widely adopts secondary treatment, in order to ensure the normal operation of the sewage plant, it is necessary to ensure the nutrient demand of microorganisms in the biochemical tank, and the aerobic method is generally controlled in: BOD:N:P=100:5:1, therefore, for the monitoring of the inlet water P of the sewage plant, it is conducive to the control of microbial nutrition, and when the proportion of phosphorus in the sewage is less, it needs to be artificially supplemented to ensure the nutritional needs of microorganisms, and then ensure the normal operation of the sewage treatment system.

8. pH value

pH is an important indicator of the acidity and alkalinity of water, which is numerically equal to the negative logarithm of the concentration of hydrogen ions. The determination of pH value is usually based on the electrochemical principle using the glass electrode method, but it can also be determined by colorimetry.

The pH value can represent the most basic properties of water, which has an impact on the change of water quality and the effect of water treatment, and has important practical significance for the determination and control of pH value, for maintaining the normal operation of sewage treatment facilities, preventing the corrosion of sewage treatment and conveying equipment, protecting the growth of aquatic organisms and the self-purification function of water bodies.

If the pH of the wastewater is too high or too low, it will affect the biochemical treatment, as the pH range suitable for biological survival is often very narrow and sensitive. For example, in the aeration tank of the activated sludge system, if the pH changes, such as from the normal 6.5~8.5 to 5.5, then the system is likely to have the expansion of the filamentous bacteria of the activated sludge. This will directly affect the quality of the effluent, resulting in a deterioration of the effluent. The main reason is that bacteria should be dominant in activated sludge, and the optimal pH range is 6.5~8.5, when the pH value is normal, bacteria dominate, and the number of filamentous bacteria is limited. However, when the pH changes to 5.5, the lack of bacteria is inhibited because it is very suitable for the growth of filamentous bacteria, which will cause filamentous bacteria to dominate the activated sludge and cause the sludge to swell.

In addition, special attention should be paid to pH control when anaerobic digestion of sludge or high-concentration wastewater. Because, in the process of anaerobic digestion, it is mainly methanogenic and non-methanogenic bacteria that act. Among them, the methanogenic flora has very strict requirements for pH value, which needs to be controlled at 6.5~7.5, and it is best to control it between 6.8~7.2, otherwise, the methane gas production rate will be significantly reduced, which will affect the digestion effect. Generally, the pH value of the treated sewage is 6~9, and when the pH value is less than 5, the general fish can be killed.

9. Suspended solids (SS)

Suspended solids (SS) are solids that cannot pass through a filter (filter paper or membrane). Solids in sewage include suspended solids and dissolved solids. Suspended solids are solid substances suspended in water. Suspended solids, also known as suspended matter or suspended solids, are usually denoted by SS. Suspended solids have poor light transmittance, which makes the water quality turbid, affects the growth of aquatic organisms, and a large number of suspended solids will also cause river blockage. From the perspective of the corresponding national and local sewage discharge standards, SS is one of the important items for monitoring.

10. Toxic substances

Toxic substances refer to substances that can endanger human health, endanger aquatic organisms in water bodies, or affect the biological treatment of sewage after reaching a certain concentration. Due to the greater harm of this kind of substance, therefore, the content of toxic substances is an important water quality indicator in sewage discharge, water monitoring and sewage treatment, toxic substances are a common concern, toxic substances can be divided into inorganic poisons and organic poisons.

The main representatives of inorganic substances are some heavy metal ions such as mercury, chromium, cadmium, etc., if these ions are not removed in water or the treatment effect is not good, they will enter the natural water body or biological system, and eventually can be transferred to the human body through the food chain for a large amount of payment, and eventually lead to the emergence of various public health diseases. Such as Minamata disease, bone pain, etc.

Typical representatives of organic poisons are cyanide, phenols, organochlorides, etc. These substances can also cause serious injury accidents.

Therefore, it is necessary to carry out serious, strict and scientific monitoring of toxic and harmful substances in the effluent and sludge of urban sewage treatment plants. Only when the emission standards are really met can be discharged or do what he has.

3. Biological indicators

Water is a natural environment where microorganisms are widely distributed, whether it is surface water, groundwater, or even rain or snow water, it contains a variety of microorganisms. When the water body is polluted by human or animal manure, domestic sewage or some industrial wastewater, the number of microorganisms in the water can increase significantly. Therefore, the bacteriological determination of effluent from urban sewage plants, especially the detection of intestinal bacteria, is of great significance in environmental quality evaluation and environmental sanitation supervision. However, the direct detection of various pathogenic microorganisms in water is more complicated and difficult, and a negative test result does not guarantee absolute safety. Therefore, in practice, the total number of bacteria in the water is often checked, especially the indicator bacteria that are used as fecal pollution, to indirectly judge the pollution status of the water body. The total number of bacteria in the water has a certain relationship with the water pollution status, but it cannot directly indicate the presence of pathogenic microorganisms. Fecal contamination indicator bacteria generally refer to the presence of the indicator bacteria in the water body, which means that the water body has been polluted with feces, and there may be intestinal pathogenic microorganisms. Then the water is not hygienically safe.

1. Total number of bacteria

The total number of bacteria refers to the total number of various bacteria contained in 1 mL of water. An indicator of the degree of bacterial contamination of water.

In water quality analysis, a certain amount of water is inoculated in agar medium, incubated at 37°C for 24 hours, the number of bacterial colonies that grow and grows is counted, and then the number of bacteria contained in each milliliter of water is calculated.

Bacterial total count determination is a method for determining the density of aerobic bacteria, facultative anaerobes, and anaerobic bacteria in water. Because bacteria can exist in the form of individual individuals, pairs, chains, clusters, etc., and no single medium can meet the physiological requirements of all bacteria in a water sample. As a result, the resulting colonies may be lower than the total number of viable bacteria actually present.

2. Coliform count

Coliform count refers to the number of coliform bacteria contained in 1L of water. Although coliform bacteria themselves are not pathogenic bacteria, because the living conditions of coliform bacteria in the external environment are similar to those of bacteria and parasite eggs of intestinal infectious diseases, and the number of coliform bacteria is large, it is relatively easy to test, so the number of coliform bacteria is used as a biological indicator. The more common pathogenic microorganisms are typhoid, hepatitis virus, adenovirus, etc., and there are also some parasites.

Among the methods for the detection of total coliforms, the multi-tube fermentation method can be applied to various water samples (including sediment), but the operation is more complicated and takes a long time. The membrane method is mainly suitable for water samples with less impurities, and the operation is simple and fast.

If the membrane method is used, the total coliform bacteria can be redefined as the ability to produce aerobic and facultative anaerobic gram-negative bacilli with a metallic dark color on lactose-containing Wonteng's medium within 24 hours at 37 °C. In addition, in addition to the monitoring of microorganisms in the effluent, it is necessary to pay attention to the monitoring of microorganisms in the operation process.

For example, the sewage treatment plant for sludge microscopic inspection, mainly to observe the shape of the biological phase, composition, etc., through regular microscopic inspection, you can judge the normal operation of the facilities, and can even prevent some abnormal phenomena in advance, such as: if through the inspection, it is found that there is a tendency for filamentous bacteria to proliferate in the sludge, you can take certain measures to eliminate the expansion of the activated sludge filamentous bacteria that may occur in the bud, effectively ensure the operation of the sewage plant, and ensure that the effluent meets the requirements.

To sum up, if you want to ensure normal operation, its fundamental guarantee comes from scientific and effective operation management.

From this, the regular and accurate monitoring of the operation indicators of the sewage plant, and the analysis and statistics of the obtained data, so as to guide the operation of the sewage treatment plant are the foundation of the work of the sewage plant.