Analysis in sewage treatment plants is a very important operation method. The analysis results are the basis for sewage regulation. Therefore, the accuracy of the analysis is very demanding. The accuracy of the analysis values must be ensured to ensure that the normal operation of the system is correct and reasonable!
1. Determination of chemical oxygen demand (CODcr)
Chemical oxygen demand: refers to the amount of oxidant consumed when potassium dichromate is used as an oxidant to treat water samples under strong acid and heating conditions, the unit is mg/L. In my country, the potassium dichromate method is generally used as the basis.
1. Method principle
In a strong acidic solution, a certain amount of potassium dichromate is used to oxidize the reducing substances in the water sample. The excess potassium dichromate is used as an indicator and ferrous ammonium sulfate solution is used to drip back. Calculate the amount of oxygen consumed by reducing substances in the water sample based on the amount of ferrous ammonium sulfate used.
2. Instruments
(1) Reflux device: an all-glass reflux device with a 250ml conical flask (if the sampling volume is more than 30ml, use an all-glass reflux device with a 500ml conical flask).
(2) Heating device: electric heating plate or variable electric furnace.
(3) 50ml acid titrant.
3. Reagents
(1) Potassium dichromate standard solution (1/6=0.2500mol/L:) Weigh 12.258g of standard or superior grade pure potassium dichromate that has been dried at 120°C for 2 hours, dissolve it in water, and transfer it to a 1000ml volumetric flask. Dilute to the mark and shake well.
(2) Test ferrousin indicator solution: Weigh 1.485g of phenanthroline, dissolve 0.695g of ferrous sulfate in water, dilute to 100ml, and store in a brown bottle.
(3) Ferrous ammonium sulfate standard solution: Weigh 39.5g of ferrous ammonium sulfate and dissolve it in water. While stirring, slowly add 20ml of concentrated sulfuric acid. After cooling, transfer it to a 1000ml volumetric flask, add water to dilute to the mark, and shake well. Before use, calibrate with potassium dichromate standard solution.
Calibration method: Accurately absorb 10.00ml potassium dichromate standard solution and 500ml Erlenmeyer flask, add water to dilute to about 110ml, slowly add 30ml concentrated sulfuric acid, and mix. After cooling, add three drops of ferroline indicator solution (about 0.15ml) and titrate with ferrous ammonium sulfate. The color of the solution changes from yellow to blue-green to reddish brown and is the end point.
C[(NH4)2Fe(SO4)2]=0.2500×10.00/V
In the formula, c—the concentration of ferrous ammonium sulfate standard solution (mol/L); V—the dosage of ferrous ammonium sulfate standard titration solution (ml).
(4) Sulfuric acid-silver sulfate solution: Add 25g of silver sulfate to 2500ml of concentrated sulfuric acid. Leave it for 1-2 days and shake it from time to time to dissolve (if there is no 2500ml container, add 5g silver sulfate to 500ml concentrated sulfuric acid).
(5) Mercury sulfate: crystal or powder.
4. Things to note
(1) The maximum amount of chloride ions that can be complexed using 0.4g of mercury sulfate can reach 40mL. For example, if a 20.00mL water sample is taken, it can complex a water sample with a maximum chloride ion concentration of 2000mg/L. If the chloride ion concentration is low, you can add less mercury sulfate to maintain the mercury sulfate:chloride ion = 10:1 (W/W). If a small amount of mercury chloride precipitates, it does not affect the measurement.
(2) The water sample removal volume can be in the range of 10.00-50.00mL, but the reagent dosage and concentration can be adjusted accordingly to obtain satisfactory results.
(3) For water samples with chemical oxygen demand less than 50mol/L, it should be 0.0250mol/L potassium dichromate standard solution. When back dripping, use 0.01/L ferrous ammonium sulfate standard solution.
(4) After the water sample is heated and refluxed, the remaining amount of potassium dichromate in the solution should be 1/5-4/5 of the small amount added.
(5) When using the standard solution of potassium hydrogen phthalate to test the quality and operating technology of the reagent, since the theoretical CODCr per gram of potassium hydrogen phthalate is 1.167g, dissolve 0.4251L potassium hydrogen phthalate and double-distilled water. , transfer it to a 1000mL volumetric flask, and dilute to the mark with double-distilled water to make it a 500mg/L CODCr standard solution. Newly prepared when used.
(6) The measurement results of CODCr should retain three significant figures.
(7) In each experiment, the ferrous ammonium sulfate standard titration solution should be calibrated, and special attention should be paid to changes in its concentration when the room temperature is high.
5. Measurement steps
(1) Shake the retrieved inlet water sample and outlet water sample evenly.
(2) Take 3 ground-mouth Erlenmeyer flasks, numbered 0, 1, and 2; add 6 glass beads to each of the 3 Erlenmeyer flasks.
(3) Add 20 mL of distilled water to the No. 0 Erlenmeyer flask (use a fat pipette); add 5 mL of feed water sample to the No. 1 Erlenmeyer flask (use a 5 mL pipette, and use feed water to rinse the pipette). tube 3 times), then add 15 mL distilled water (use a fat pipette); add 20 mL of effluent sample to the No. 2 Erlenmeyer flask (use a fat pipette, rinse the pipette 3 times with incoming water ).
(4) Add 10 mL of potassium dichromate non-standard solution to each of the 3 Erlenmeyer flasks (use a 10 mL potassium dichromate non-standard solution pipette, and rinse the pipette 3 with potassium dichromate non-standard solution) Second-rate).
(5) Place the Erlenmeyer flasks on the electronic multi-purpose furnace, then open the tap water pipe to fill the condenser tube with water (do not open the tap too large, based on experience).
(6) Add 30 mL of silver sulfate (using a 25 mL small measuring cylinder) into the three Erlenmeyer flasks from the upper part of the condenser tube, and then shake the three Erlenmeyer flasks evenly.
(7) Plug in the electronic multi-purpose furnace, start timing from boiling, and heat for 2 hours.
(8) After heating is completed, unplug the electronic multi-purpose furnace and allow it to cool for a period of time (how long depends on experience).
(9) Add 90 mL of distilled water from the upper part of the condenser tube to the three Erlenmeyer flasks (reasons for adding distilled water: 1. Add water from the condenser tube to allow the residual water sample on the inner wall of the condenser tube to flow into the Erlenmeyer flask during the heating process to reduce errors. .2. Add a certain amount of distilled water to make the color reaction during the titration process more obvious).
(10) After adding distilled water, heat will be released. Remove the Erlenmeyer flask and cool it.
(11) After cooling completely, add 3 drops of test ferrous indicator to each of the three Erlenmeyer flasks, and then shake the three Erlenmeyer flasks evenly.
(12) Titrate with ferrous ammonium sulfate. The color of the solution changes from yellow to blue-green to reddish brown as the end point. (Pay attention to the use of fully automatic burettes. After a titration, remember to read and raise the liquid level of the automatic burette to the highest level before proceeding to the next titration).
(13) Record the readings and calculate the results.
2. Determination of biochemical oxygen demand (BOD5)
Domestic sewage and industrial wastewater contain large amounts of various organic matter. When they pollute waters, these organic matter will consume a large amount of dissolved oxygen when decomposing in the water body, thus destroying the oxygen balance in the water body and deteriorating the water quality. The lack of oxygen in water bodies causes the death of fish and other aquatic life.
The composition of organic matter contained in water bodies is complex, and it is difficult to determine their components one by one. People often use the oxygen consumed by organic matter in water under certain conditions to indirectly represent the content of organic matter in water. Biochemical oxygen demand is an important indicator of this type.
The classic method of measuring biochemical oxygen demand is the dilution inoculation method.
Water samples for measuring biochemical oxygen demand should be filled and sealed in bottles when collected. Store at 0-4 degrees Celsius. Generally, analysis should be performed within 6 hours. If long distance transportation is required. In any case, storage time should not exceed 24 hours.
1. Method principle
Biochemical oxygen demand refers to the amount of dissolved oxygen consumed in the biochemical process of microorganisms decomposing certain oxidizable substances, especially organic matter, in the water under specified conditions. The whole process of biological oxidation takes a long time. For example, when cultured at 20 degrees Celsius, it takes more than 100 days to complete the process. At present, it is generally prescribed at home and abroad to incubate for 5 days at 20 plus or minus 1 degree Celsius, and measure the dissolved oxygen of the sample before and after incubation. The difference between the two is the BOD5 value, expressed in milligrams/liter of oxygen.
For some surface water and most industrial wastewater, because it contains a lot of organic matter, it needs to be diluted before culture and measurement to reduce its concentration and ensure sufficient dissolved oxygen. The degree of dilution should be such that the dissolved oxygen consumed in the culture is greater than 2 mg/L, and the remaining dissolved oxygen is more than 1 mg/L.
In order to ensure that there is enough dissolved oxygen after the water sample is diluted, the diluted water is usually aerated with air, so that the dissolved oxygen in the diluted water is close to saturation. A certain amount of inorganic nutrients and buffer substances should also be added to the dilution water to ensure the growth of microorganisms.
For industrial wastewater that contains little or no microorganisms, including acidic wastewater, alkaline wastewater, high-temperature wastewater or chlorinated wastewater, inoculation should be carried out when measuring BOD5 to introduce microorganisms that can decompose organic matter in the wastewater. When there are organic matter in the wastewater that is difficult to be degraded by microorganisms in general domestic sewage at normal speed or contain highly toxic substances, domesticated microorganisms should be introduced into the water sample for inoculation. This method is suitable for the determination of water samples with BOD5 greater than or equal to 2mg/L, and the maximum does not exceed 6000mg/L. When the BOD5 of the water sample is greater than 6000mg/L, certain errors will occur due to dilution.
2. Instruments
(1) Constant temperature incubator
(2)5-20L narrow mouth glass bottle.
(3)1000——2000ml measuring cylinder
(4) Glass stirring rod: The length of the rod should be 200mm longer than the height of the measuring cylinder used. A hard rubber plate with a smaller diameter than the bottom of the measuring cylinder and several small holes is fixed to the bottom of the rod.
(5) Dissolved oxygen bottle: between 250ml and 300ml, with ground glass stopper and bell-shaped mouth for water supply sealing.
(6) Siphon, used for taking water samples and adding dilution water.
3. Reagents
(1) Phosphate buffer solution: Dissolve 8.5 potassium dihydrogen phosphate, 21.75g dipotassium hydrogen phosphate, 33.4 sodium hydrogen phosphate heptahydrate and 1.7g ammonium chloride in water and dilute to 1000ml. The pH of this solution should be 7.2
(2) Magnesium sulfate solution: Dissolve 22.5g magnesium sulfate heptahydrate in water and dilute to 1000ml.
(3) Calcium chloride solution: Dissolve 27.5% anhydrous calcium chloride in water and dilute to 1000ml.
(4) Ferric chloride solution: Dissolve 0.25g ferric chloride hexahydrate in water and dilute to 1000ml.
(5) Hydrochloric acid solution: Dissolve 40ml hydrochloric acid in water and dilute to 1000ml.
(6) Sodium hydroxide solution: Dissolve 20g sodium hydroxide in water and dilute to 1000ml
(7) Sodium sulfite solution: Dissolve 1.575g sodium sulfite in water and dilute to 1000ml. This solution is unstable and needs to be prepared daily.
(8) Glucose-glutamic acid standard solution: After drying glucose and glutamic acid at 103 degrees Celsius for 1 hour, weigh 150ml of each and dissolve it in water, transfer it to a 1000ml volumetric flask and dilute to the mark, and mix evenly. Prepare this standard solution just before use.
(9) Dilution water: The pH value of dilution water should be 7.2, and its BOD5 should be less than 0.2ml/L.
(10) Inoculation solution: Generally, domestic sewage is used, left at room temperature for a day and night, and the supernatant is used.
(11) Inoculation dilution water: Take an appropriate amount of inoculation solution, add it to the dilution water, and mix well. The amount of inoculation solution added per liter of diluted water is 1-10ml of domestic sewage; or 20-30ml of surface soil exudate; the pH value of the inoculation dilution water should be 7.2. The BOD value should be between 0.3-1.0 mg/L. The inoculation dilution water should be used immediately after preparation.
4. Calculation
1. Water samples cultured directly without dilution
BOD5(mg/L)=C1-C2
In the formula: C1——dissolved oxygen concentration of water sample before culture (mg/L);
C2——Remaining dissolved oxygen concentration (mg/L) after the water sample has been incubated for 5 days.
2. Water samples cultured after dilution
BOD5(mg/L)=[(C1-C2)—(B1-B2)f1]∕f2
In the formula: C1——dissolved oxygen concentration of water sample before culture (mg/L);
C2——Remaining dissolved oxygen concentration (mg/L) after 5 days of incubation of the water sample;
B1——Dissolved oxygen concentration of dilution water (or inoculation dilution water) before culture (mg/L);
B2——Dissolved oxygen concentration of dilution water (or inoculation dilution water) after culture (mg/L);
f1——The proportion of dilution water (or inoculation dilution water) in the culture medium;
f2——The proportion of water sample in the culture medium.
B1——Dissolved oxygen of dilution water before culture;
B2——Dissolved oxygen of dilution water after cultivation;
f1——The proportion of dilution water in the culture medium;
f2——The proportion of water sample in the culture medium.
Note: Calculation of f1 and f2: For example, if the dilution ratio of the culture medium is 3%, that is, 3 parts of water sample and 97 parts of dilution water, then f1=0.97 and f2=0.03.
5. Things to note
(1) The biological oxidation process of organic matter in water can be divided into two stages. The first stage is the oxidation of carbon and hydrogen in organic matter to produce carbon dioxide and water. This stage is called the carbonization stage. It takes about 20 days to complete the carbonization stage at 20 degrees Celsius. In the second stage, nitrogen-containing substances and part of the nitrogen are oxidized into nitrite and nitrate, which is called the nitrification stage. It takes about 100 days to complete the nitrification stage at 20 degrees Celsius. Therefore, when measuring BOD5 of water samples, nitrification is generally insignificant or does not occur at all. However, the effluent from the biological treatment tank contains a large number of nitrifying bacteria. Therefore, when measuring BOD5, the oxygen demand of some nitrogen-containing compounds is also included. For such water samples, nitrification inhibitors can be added to inhibit the nitrification process. For this purpose, 1 ml of propylene thiourea with a concentration of 500 mg/L or a certain amount of 2-chlorozone-6-trichloromethyldine fixed on sodium chloride can be added to each liter of diluted water sample to make TCMP at The concentration in the diluted sample is approximately 0.5 mg/L.
(2) Glassware should be cleaned thoroughly. First soak and clean with detergent, then soak with dilute hydrochloric acid, and finally wash with tap water and distilled water.
(3) In order to check the quality of the dilution water and inoculum solution, as well as the operating level of the laboratory technician, dilute 20ml of glucose-glutamic acid standard solution with inoculation dilution water to 1000ml, and follow the steps for measuring BOD5. The measured BOD5 value should be between 180-230mg/L. Otherwise, check whether there are any problems with the quality of the inoculum solution, dilution water or operating techniques.
(4) When the dilution factor of the water sample exceeds 100 times, it should be preliminarily diluted with water in a volumetric flask, and then an appropriate amount should be taken for final dilution culture.
3. Determination of suspended solids (SS)
Suspended solids represent the amount of undissolved solid matter in water.
1. Method principle
The measurement curve is built-in, and the absorbance of the sample at a specific wavelength is converted into the concentration value of the parameter to be measured, and is displayed on the LCD screen.
2. Measurement steps
(1) Shake the retrieved inlet water sample and outlet water sample evenly.
(2) Take 1 colorimetric tube and add 25 mL of incoming water sample, and then add distilled water to the mark (because the incoming water SS is large, if not diluted, it may exceed the maximum limit of the suspended solids tester) limits, making the results inaccurate. Of course, the sampling volume of the incoming water is not fixed. If the incoming water is too dirty, take 10mL and add distilled water to the scale).
(3) Turn on the suspended solids tester, add distilled water to 2/3 of the small box similar to a cuvette, dry the outer wall, press the selection button while shaking, then quickly put the suspended solids tester into it, and then press Press the reading key. If it is not zero, press the clear key to clear the instrument (just measure once).
(4) Measure the incoming water SS: Pour the incoming water sample in the colorimetric tube into the small box and rinse it three times, then add the incoming water sample to 2/3, dry the outer wall, and press the selection key while shaking. Then quickly put it into the suspended solids tester, then press the reading button, measure three times, and calculate the average value.
(5) Measure the water SS: Shake the water sample evenly and rinse the small box three times…(The method is the same as above)
3. Calculation
The result of the inlet water SS is: dilution ratio * measured inlet water sample reading. The result of the outlet water SS is directly the instrument reading of the measured water sample.
4. Determination of total phosphorus (TP)
1. Method principle
Under acidic conditions, orthophosphate reacts with ammonium molybdate and potassium antimonyl tartrate to form phosphomolybdenum heteropoly acid, which is reduced by the reducing agent ascorbic acid and becomes a blue complex, usually integrated with phosphomolybdenum blue.
The minimum detectable concentration of this method is 0.01mg/L (the concentration corresponding to the absorbance A=0.01); the upper limit of determination is 0.6mg/L. It can be applied to the analysis of orthophosphate in ground water, domestic sewage and industrial wastewater from daily chemicals, phosphate fertilizers, machined metal surface phosphating treatment, pesticides, steel, coking and other industries.
2. Instruments
Spectrophotometer
3. Reagents
(1)1+1 sulfuric acid.
(2) 10% (m/V) ascorbic acid solution: Dissolve 10g ascorbic acid in water and dilute to 100ml. The solution is stored in a brown glass bottle and is stable for several weeks in a cold place. If the color turns yellow, discard and remix.
(3) Molybdate solution: Dissolve 13g of ammonium molybdate [(NH4)6Mo7O24˙4H2O] in 100ml of water. Dissolve 0.35g potassium antimonyl tartrate [K(SbO)C4H4O6˙1/2H2O] in 100ml water. Under constant stirring, slowly add the ammonium molybdate solution to 300ml (1+1) sulfuric acid, add potassium antimony tartrate solution and mix evenly. Store reagents in brown glass bottles in a cold place. Stable for at least 2 months.
(4) Turbidity-color compensation solution: Mix two volumes of (1+1) sulfuric acid and one volume of 10% (m/V) ascorbic acid solution. This solution is prepared on the same day.
(5) Phosphate stock solution: Dry potassium dihydrogen phosphate (KH2PO4) at 110°C for 2 hours and let cool in a desiccator. Weigh 0.217g, dissolve it in water, and transfer it to a 1000ml volumetric flask. Add 5ml of (1+1) sulfuric acid and dilute with water to the mark. This solution contains 50.0ug phosphorus per milliliter.
(6) Phosphate standard solution: Take 10.00ml of phosphate stock solution into a 250ml volumetric flask, and dilute to the mark with water. This solution contains 2.00ug phosphorus per milliliter. Prepared for immediate use.
4. Measurement steps (only taking the measurement of inlet and outlet water samples as an example)
(1) Shake the retrieved inlet water sample and outlet water sample well (the water sample taken from the biochemical pool should be shaken well and left for a period of time to take the supernatant).
(2) Take 3 stoppered scale tubes, add distilled water to the first stoppered scale tube to the upper scale line; add 5mL of water sample to the second stoppered scale tube, and then add distilled water to the upper scale line; the third stoppered scale tube Brace plug graduated tube
Soak in hydrochloric acid for 2 hours, or scrub with phosphate-free detergent.
(3) The cuvette should be soaked in dilute nitric acid or chromic acid washing solution for a moment after use to remove the adsorbed molybdenum blue colorant.
5. Determination of total nitrogen (TN)
1. Method principle
In an aqueous solution above 60°C, potassium persulfate decomposes according to the following reaction formula to generate hydrogen ions and oxygen. K2S2O8+H2O→2KHSO4+1/2O2KHSO4→K++HSO4_HSO4→H++SO42-
Add sodium hydroxide to neutralize the hydrogen ions and complete the decomposition of potassium persulfate. Under the alkaline medium condition of 120℃-124℃, using potassium persulfate as the oxidant, not only can the ammonia nitrogen and nitrite nitrogen in the water sample be oxidized into nitrate, but also most of the organic nitrogen compounds in the water sample can be oxidized into Nitrates. Then use ultraviolet spectrophotometry to measure the absorbance at wavelengths of 220nm and 275nm respectively, and calculate the absorbance of nitrate nitrogen according to the following formula: A=A220-2A275 to calculate the total nitrogen content. Its molar absorption coefficient is 1.47×103
2. Interference and elimination
(1) When the water sample contains hexavalent chromium ions and ferric ions, 1-2 ml of 5% hydroxylamine hydrochloride solution can be added to eliminate their influence on the measurement.
(2) Iodide ions and bromide ions interfere with the determination. There is no interference when the iodide ion content is 0.2 times the total nitrogen content. There is no interference when the bromide ion content is 3.4 times the total nitrogen content.
(3) The influence of carbonate and bicarbonate on the determination can be eliminated by adding a certain amount of hydrochloric acid.
(4) Sulfate and chloride have no effect on the determination.
3. Scope of application of the method
This method is mainly suitable for the determination of total nitrogen in lakes, reservoirs, and rivers. The lower detection limit of the method is 0.05 mg/L; the upper limit of determination is 4 mg/L.
4. Instruments
(1) UV spectrophotometer.
(2) Pressure steam sterilizer or household pressure cooker.
(3) Glass tube with stopper and ground mouth.
5. Reagents
(1) Ammonia-free water, add 0.1ml concentrated sulfuric acid per liter of water and distill. Collect the effluent in a glass container.
(2) 20% (m/V) sodium hydroxide: Weigh 20g of sodium hydroxide, dissolve in ammonia-free water, and dilute to 100ml.
(3) Alkaline potassium persulfate solution: Weigh 40g potassium persulfate and 15g sodium hydroxide, dissolve them in ammonia-free water, and dilute to 1000ml. The solution is stored in a polyethylene bottle and can be stored for one week.
(4)1+9 hydrochloric acid.
(5) Potassium nitrate standard solution: a. Standard stock solution: Weigh 0.7218g of potassium nitrate that has been dried at 105-110°C for 4 hours, dissolve it in ammonia-free water, and transfer it to a 1000ml volumetric flask to adjust to volume. This solution contains 100 mg of nitrate nitrogen per ml. Add 2ml chloroform as a protective agent and it will be stable for at least 6 months. b. Potassium nitrate standard solution: Dilute the stock solution 10 times with ammonia-free water. This solution contains 10 mg of nitrate nitrogen per ml.
6. Measurement steps
(1) Shake the retrieved inlet water sample and outlet water sample evenly.
(2) Take three 25mL colorimetric tubes (note that they are not large colorimetric tubes). Add distilled water to the first colorimetric tube and add it to the lower scale line; add 1mL of inlet water sample to the second colorimetric tube, and then add distilled water to the lower scale line; add 2mL of outlet water sample to the third colorimetric tube, and then add distilled water to it. Add to the lower tick mark.
(3) Add 5 mL of basic potassium persulfate to the three colorimetric tubes respectively.
(4) Put the three colorimetric tubes into a plastic beaker, and then heat them in a pressure cooker. Carry out digestion.
(5) After heating, remove the gauze and allow to cool naturally.
(6) After cooling, add 1 mL of 1+9 hydrochloric acid to each of the three colorimetric tubes.
(7) Add distilled water to each of the three colorimetric tubes up to the upper mark and shake well.
(8) Use two wavelengths and measure with a spectrophotometer. First, use a 10mm quartz cuvette with a wavelength of 275nm (a slightly older one) to measure the blank, inlet water, and outlet water samples and count them; then use a 10mm quartz cuvette with a wavelength of 220nm (a slightly older one) to measure the blank, inlet, and outlet water samples. Take in and out water samples and count them.
(9) Calculation results.
6. Determination of ammonia nitrogen (NH3-N)
1. Method principle
Alkaline solutions of mercury and potassium react with ammonia to form a light reddish-brown colloidal compound. This color has strong absorption over a wide wavelength range. Usually the wavelength used for measurement is in the range of 410-425nm.
2. Preservation of water samples
Water samples are collected in polyethylene bottles or glass bottles and should be analyzed as soon as possible. If necessary, add sulfuric acid to the water sample to acidify it to pH<2, and store it at 2-5°C. Acidified samples should be taken to prevent absorption of ammonia in the air and contamination.
3. Interference and elimination
Organic compounds such as aliphatic amines, aromatic amines, aldehydes, acetone, alcohols and organic nitrogen amines, as well as inorganic ions such as iron, manganese, magnesium and sulfur, cause interference due to the production of different colors or turbidity. The color and turbidity of the water also affect Colorimetric. For this purpose, flocculation, sedimentation, filtration or distillation pretreatment is required. Volatile reducing interfering substances can also be heated under acidic conditions to remove interference with metal ions, and an appropriate amount of masking agent can also be added to eliminate them.
4. Scope of application of the method
The lowest detectable concentration of this method is 0.025 mg/l (photometric method), and the upper limit of determination is 2 mg/l. Using visual colorimetry, the lowest detectable concentration is 0.02 mg/l. After appropriate pretreatment of water samples, this method can be applied to surface water, groundwater, industrial wastewater and domestic sewage.
5. Instruments
(1) Spectrophotometer.
(2)PH meter
6. Reagents
All water used for preparing reagents should be ammonia-free.
(1) Nessler’s reagent
You can choose one of the following methods to prepare:
1. Weigh 20g of potassium iodide and dissolve it in about 25ml of water. Add mercury dichloride (HgCl2) crystal powder (about 10g) in small portions while stirring. When a vermilion precipitate appears and is difficult to dissolve, it is time to add saturated dioxide dropwise. Mercury solution and stir thoroughly. When vermilion precipitate appears and no longer dissolves, stop adding mercuric chloride solution.
Weigh another 60g of potassium hydroxide and dissolve it in water, and dilute it to 250ml. After cooling to room temperature, slowly pour the above solution into the potassium hydroxide solution while stirring, dilute it with water to 400ml, and mix well. Let stand overnight, transfer the supernatant to a polyethylene bottle, and store it with a tight stopper.
2. Weigh 16g of sodium hydroxide, dissolve it in 50ml of water, and fully cool to room temperature.
Weigh another 7g of potassium iodide and 10g of mercury iodide (HgI2) and dissolve it in water. Then slowly inject this solution into the sodium hydroxide solution while stirring, dilute it with water to 100ml, store it in a polyethylene bottle, and keep it tightly closed.
(2) Potassium sodium acid solution
Weigh 50g of potassium sodium tartrate (KNaC4H4O6.4H2O) and dissolve it in 100ml of water, heat and boil to remove ammonia, cool and dissolve to 100ml.
(3)Ammonium standard stock solution
Weigh 3.819g of ammonium chloride (NH4Cl) that has been dried at 100 degrees Celsius, dissolve it in water, transfer it to a 1000ml volumetric flask, and dilute to the mark. This solution contains 1.00mg ammonia nitrogen per ml.
(4)Ammonium standard solution
Pipette 5.00ml of amine standard stock solution into a 500ml volumetric flask and dilute with water to the mark. This solution contains 0.010mg ammonia nitrogen per ml.
7. Calculation
Find the ammonia nitrogen content (mg) from the calibration curve
Ammonia nitrogen (N, mg/l)=m/v*1000
In the formula, m – the amount of ammonia nitrogen found from the calibration (mg), V – the volume of the water sample (ml).
8. Things to note
(1) The ratio of sodium iodide and potassium iodide has a great influence on the sensitivity of color reaction. The precipitate formed after resting should be removed.
(2) The filter paper often contains trace amounts of ammonium salts, so be sure to wash it with ammonia-free water when using it. All glassware should be protected from ammonia contamination in laboratory air.
9. Measurement steps
(1) Shake the retrieved inlet water sample and outlet water sample evenly.
(2) Pour the inlet water sample and outlet water sample into 100mL beakers respectively.
(3) Add 1 mL of 10% zinc sulfate and 5 drops of sodium hydroxide into the two beakers respectively, and stir with two glass rods.
(4) Let it sit for 3 minutes and then start filtering.
(5) Pour the standing water sample into the filter funnel. After filtering, pour out the filtrate in the bottom beaker. Then use this beaker to collect the remaining water sample in the funnel. Until the filtration is completed, pour the filtrate in the bottom beaker again. Pour away the filtrate. (In other words, use the filtrate from one funnel to wash the beaker twice)
(6) Filter the remaining water samples in the beakers respectively.
(7) Take 3 colorimetric tubes. Add distilled water to the first colorimetric tube and add to the scale; add 3–5mL of the inlet water sample filtrate to the second colorimetric tube, and then add distilled water to the scale; add 2mL of the outlet water sample filtrate to the third colorimetric tube. Then add distilled water to the mark. (The amount of incoming and outgoing water sample filtrate is not fixed)
(8) Add 1 mL potassium sodium tartrate and 1.5 mL Nessler’s reagent to the three colorimetric tubes respectively.
(9) Shake well and time for 10 minutes. Use a spectrophotometer to measure, using a wavelength of 420nm and a 20mm cuvette. Calculate.
(10) Calculation results.
7. Determination of nitrate nitrogen (NO3-N)
1. Method principle
In the water sample in the alkaline medium, nitrate can be quantitatively reduced to ammonia by the reducing agent (Daisler alloy) under heating. After distillation, it is absorbed into the boric acid solution and measured using Nessler’s reagent photometry or acid titration. .
2. Interference and elimination
Under these conditions, nitrite is also reduced to ammonia and needs to be removed in advance. Ammonia and ammonia salts in water samples can also be removed by pre-distillation before adding Daisch alloy.
This method is particularly suitable for the determination of nitrate nitrogen in severely polluted water samples. At the same time, it can also be used for the determination of nitrite nitrogen in water samples (the water sample is determined by alkaline pre-distillation to remove ammonia and ammonium salts, and then the nitrite The total amount of salt, minus the amount of nitrate measured separately, is the amount of nitrite).
3. Instruments
Nitrogen-fixing distillation device with nitrogen balls.
4. Reagents
(1) Sulfamic acid solution: Weigh 1g of sulfamic acid (HOSO2NH2), dissolve it in water, and dilute to 100ml.
(2)1+1 hydrochloric acid
(3) Sodium hydroxide solution: Weigh 300g of sodium hydroxide, dissolve it in water, and dilute to 1000ml.
(4) Daisch alloy (Cu50:Zn5:Al45) powder.
(5) Boric acid solution: Weigh 20g of boric acid (H3BO3), dissolve it in water, and dilute to 1000ml.
5. Measurement steps
(1) Shake the retrieved samples from point 3 and the reflux point and place them for clarification for a period of time.
(2) Take 3 colorimetric tubes. Add distilled water to the first colorimetric tube and add it to the scale; add 3mL of No. 3 spotting supernatant to the second colorimetric tube, and then add distilled water to the scale; add 5mL of reflux spotting supernatant to the third colorimetric tube , then add distilled water to the mark.
(3) Take 3 evaporating dishes and pour the liquid in the 3 colorimetric tubes into the evaporating dishes.
(4) Add 0.1 mol/L sodium hydroxide to three evaporating dishes respectively to adjust the pH to 8. (Use precision pH test paper, the range is between 5.5-9.0. Each requires about 20 drops of sodium hydroxide)
(5) Turn on the water bath, place the evaporating dish on the water bath, and set the temperature to 90°C until it is evaporated to dryness. (takes about 2 hours)
(6) After evaporating to dryness, remove the evaporating dish and cool it.
(7) After cooling, add 1 mL of phenol disulfonic acid to three evaporating dishes respectively, grind with a glass rod to make the reagent fully contact with the residue in the evaporating dish, let it stand for a while, and then grind again. After leaving it for 10 minutes,Add approximately 10 mL of distilled water respectively.
(8) Add 3–4mL ammonia water to the evaporating dishes while stirring, and then move them to the corresponding colorimetric tubes. Add distilled water to the mark respectively.
(9) Shake evenly and measure with a spectrophotometer, using a 10mm cuvette (ordinary glass, slightly newer) with a wavelength of 410nm. And keep count.
(10) Calculation results.
8. Determination of dissolved oxygen (DO)
Molecular oxygen dissolved in water is called dissolved oxygen. The dissolved oxygen content in natural water depends on the balance of oxygen in the water and the atmosphere.
Generally, the iodine method is used to measure dissolved oxygen.
1. Method principle
Manganese sulfate and alkaline potassium iodide are added to the water sample. The dissolved oxygen in the water oxidizes low-valent manganese to high-valent manganese, generating a brown precipitate of tetravalent manganese hydroxide. After adding acid, the hydroxide precipitate dissolves and reacts with iodide ions to release it. Free iodine. Using starch as an indicator and titrating the released iodine with sodium thiosulfate, the dissolved oxygen content can be calculated.
2. Measurement steps
(1) Take the sample at point 9 in a wide-mouth bottle and let it sit for ten minutes. (Please note that you are using a wide-mouth bottle and pay attention to the sampling method)
(2) Insert the glass elbow into the wide-mouth bottle sample, use the siphon method to suck the supernatant into the dissolved oxygen bottle, first suck a little less, rinse the dissolved oxygen bottle 3 times, and finally suck in the supernatant to fill it with dissolved oxygen. bottle.
(3) Add 1mL manganese sulfate and 2mL alkaline potassium iodide to the full dissolved oxygen bottle. (Pay attention to the precautions when adding, add from the middle)
(4) Cap the dissolved oxygen bottle, shake it up and down, shake it again every few minutes, and shake it three times.
(5) Add 2mL of concentrated sulfuric acid to the dissolved oxygen bottle and shake well. Let it sit in a dark place for five minutes.
(6) Pour sodium thiosulfate into the alkaline buret (with rubber tube and glass beads. Pay attention to the difference between acid and alkaline burettes) to the scale line and prepare for titration.
(7) After letting it stand for 5 minutes, take out the dissolved oxygen bottle placed in the dark, pour the liquid in the dissolved oxygen bottle into a 100mL plastic measuring cylinder, and rinse it three times. Finally pour to the 100mL mark of the measuring cylinder.
(8) Pour the liquid in the measuring cylinder into the Erlenmeyer flask.
(9) Titrate with sodium thiosulfate into the Erlenmeyer flask until it is colorless, then add a dropper of starch indicator, then titrate with sodium thiosulfate until it fades, and record the reading.
(10) Calculation results.
Dissolved oxygen (mg/L)=M*V*8*1000/100
M is the concentration of sodium thiosulfate solution (mol/L)
V is the volume of sodium thiosulfate solution consumed during titration (mL)
9. Total alkalinity
1. Measurement steps
(1) Shake the retrieved inlet water sample and outlet water sample evenly.
(2) Filter the incoming water sample (if the incoming water is relatively clean, no filtration is required), use a 100 mL graduated cylinder to take 100 mL of the filtrate into a 500 mL Erlenmeyer flask. Use a 100mL graduated cylinder to take 100mL of the shaken effluent sample into another 500mL Erlenmeyer flask.
(3) Add 3 drops of methyl red-methylene blue indicator to the two Erlenmeyer flasks respectively, which turns light green.
(4) Pour 0.01mol/L hydrogen ion standard solution into the alkaline buret (with rubber tube and glass beads, 50mL. The alkaline burette used in dissolved oxygen measurement is 25mL, pay attention to the distinction) to the mark. Wire.
(5) Titrate the hydrogen ion standard solution into two Erlenmeyer flasks to reveal a lavender color, and record the volume readings used. (Remember to read after titrating one and fill it up to titrate the other. The inlet water sample requires about forty milliliters, and the outlet water sample requires about ten milliliters)
(6) Calculation results. The amount of hydrogen ion standard solution *5 is the volume.
10. Determination of sludge settling ratio (SV30)
1. Measurement steps
(1) Take a 100mL measuring cylinder.
(2) Shake the retrieved sample at point 9 of the oxidation ditch evenly and pour it into the measuring cylinder to the upper mark.
(3) 30 minutes after starting the timing, read the scale reading on the interface and record it.
11. Determination of sludge volume index (SVI)
The SVI is measured by dividing the sludge settling ratio (SV30) by the sludge concentration (MLSS). But be careful about converting units. The unit of SVI is mL/g.
12. Determination of sludge concentration (MLSS)
1. Measurement steps
(1) Shake the retrieved sample at point 9 and the sample at the reflux point evenly.
(2) Take 100mL each of the sample at point 9 and the sample at the reflux point into a measuring cylinder. (The sample at point 9 can be obtained by measuring the sludge sedimentation ratio)
(3) Use a rotary vane vacuum pump to filter the sample at point 9 and the sample at the reflux point in the measuring cylinder respectively. (Pay attention to the selection of filter paper. The filter paper used is the filter paper weighed in advance. If the MLVSS is to be measured on the sample at point 9 on the same day, quantitative filter paper must be used to filter the sample at point 9. Anyway, qualitative filter paper should be used. In addition, pay attention to quantitative filter paper and qualitative filter paper. the difference)
(4) Take out the filtered filter paper mud sample and place it in an electric blast drying oven. The temperature of the drying oven rises to 105°C and starts drying for 2 hours.
(5) Take out the dried filter paper mud sample and place it in a glass desiccator to cool for half an hour.
(6) After cooling, weigh and count using a precision electronic balance.
(7) Calculation results. Sludge concentration (mg/L) = (balance reading – weight of filter paper) * 10000
13. Determination of volatile organic substances (MLVSS)
1. Measurement steps
(1) After weighing the filter paper mud sample at point 9 with a precision electronic balance, put the filter paper mud sample into a small porcelain crucible.
(2) Turn on the box-type resistance furnace, adjust the temperature to 620°C, and put the small porcelain crucible into the box-type resistance furnace for about 2 hours.
(3) After two hours, close the box-type resistance furnace. After cooling for 3 hours, open the door of the box-type resistance furnace a little and cool again for about half an hour to ensure that the temperature of the porcelain crucible does not exceed 100°C.
(4) Take out the porcelain crucible and place it in a glass desiccator to cool again for about half an hour, weigh it on a precision electronic balance, and record the reading.
(5) Calculation results.
Volatile organic substances (mg/L) = (weight of filter paper mud sample + weight of small crucible – balance reading) * 10000.
Post time: Mar-19-2024
