Total phosphorus is an important water quality indicator, which has a great impact on the ecological environment of water bodies and human health. Total phosphorus is one of the nutrients necessary for the growth of plants and algae, but if the total phosphorus in the water is too high, it will lead to eutrophication of the water body, accelerate the reproduction of algae and bacteria, cause algal blooms, and seriously affect the ecological environment of the water body. And in some cases, such as drinking water and swimming pool water, high levels of total phosphorus may cause harm to human health, especially to infants and pregnant women.
Sources of total phosphorus in water
(1) Agricultural pollution
Agricultural pollution is mainly due to the extensive use of chemical fertilizers, and the phosphorus in chemical fertilizers flows into water bodies through rainwater or agricultural irrigation. Normally, only 10%-25% of the fertilizer can be used by plants, and the remaining 75%-90% is left in the soil. According to previous research results, 24%-71% of phosphorus in water comes from agricultural fertilization, so phosphorus pollution in water is mainly due to the migration of phosphorus in soil to water. According to statistics, the utilization rate of phosphate fertilizer is generally only 10%-20%. Excessive use of phosphate fertilizer not only causes waste of resources, but also causes excess phosphate fertilizer to pollute water sources through surface runoff.
(2) domestic sewage
Domestic sewage includes public building sewage, residential domestic sewage, and industrial sewage discharged into sewers. The main source of phosphorus in domestic sewage is the use of phosphorus-containing washing products, human excrement, and domestic garbage. The washing products mainly use sodium phosphate and polysodium phosphate, and the phosphorus in the detergent flows into the water body with the sewage.
(3) Industrial wastewater
Industrial wastewater is one of the main factors causing excess phosphorus in water bodies. Industrial wastewater has the characteristics of high pollutant concentration, many types of pollutants, difficult to degrade, and complex components. If industrial wastewater is discharged directly without treatment, it will cause a huge impact on the water body. Adverse effects on the environment and the health of residents.
Sewage Phosphorus Removal Method
(1) Electrolysis
Through the principle of electrolysis, the harmful substances in the wastewater undergo a reduction reaction and an oxidation reaction at the negative and positive poles respectively, and the harmful substances are converted into harmless substances to achieve the purpose of water purification. The electrolysis process has the advantages of high efficiency, simple equipment, easy operation, high removal efficiency, and industrialization of equipment; it does not need to add coagulants, cleaning agents and other chemicals, avoids the impact on the natural environment, and reduces costs at the same time. A small amount of sludge will be produced. However, the electrolysis method needs to consume electric energy and steel materials, the operating cost is high, the maintenance and management are complicated, and the problem of comprehensive utilization of sediment needs further research and solution.
(2) Electrodialysis
In the electrodialysis method, through the action of an external electric field, the anions and cations in the aqueous solution move to the anode and the cathode respectively, so that the ion concentration in the middle of the electrode is greatly reduced, and the ion concentration near the electrode is increased. If an ion exchange membrane is added in the middle of the electrode, separation and concentration can be achieved. the goal of. The difference between electrodialysis and electrolysis is that although the voltage of electrodialysis is high, the current is not large, which cannot maintain the continuous redox reaction required, while electrolysis is just the opposite. Electrodialysis technology has the advantages of no need for any chemicals, simple equipment and assembly process, and convenient operation. However, there are also some disadvantages that limit its wide application, such as high energy consumption, high requirements for raw water pretreatment, and poor treatment stability.
(3) Adsorption method
The adsorption method is a method in which certain pollutants in water are adsorbed and fixed by porous solids (adsorbents) to remove pollutants in water. Generally, the adsorption method is divided into three steps. First, the adsorbent is in full contact with the wastewater so that the pollutants are adsorbed; second, the separation of the adsorbent and the wastewater; third, the regeneration or renewal of the adsorbent. In addition to widely used activated carbon as adsorbent, synthetic macroporous adsorption resin is also widely used in water treatment adsorption. The adsorption method has the advantages of simple operation, good treatment effect and rapid treatment. However, the cost is high, and the adsorption saturation effect will decrease. If resin adsorption is used, analysis is required after adsorption saturation, and the analysis waste liquid is difficult to deal with.
(4) Ion exchange method
The ion exchange method is under the action of ion exchange, the ions in the water are exchanged for phosphorus in the solid matter, and the phosphorus is removed by anion exchange resin, which can quickly remove phosphorus and have high phosphorus removal efficiency. However, the exchange resin has the disadvantages of easy poisoning and difficult regeneration.
(5) Crystallization method
Phosphorus removal by crystallization is to add a substance similar to the surface and structure of insoluble phosphate to the wastewater, destroy the metastable state of ions in the wastewater, and precipitate phosphate crystals on the surface of the crystallization agent as the crystal nucleus, and then separate and remove phosphorus. Calcium-containing mineral materials can be used as crystallization agents, such as phosphate rock, bone char, slag, etc., among which phosphate rock and bone char are more effective. It saves floor space and is easy to control, but has high pH requirements and a certain calcium ion concentration.
(6) Artificial wetland
Constructed wetland phosphorus removal combines the advantages of biological phosphorus removal, chemical precipitation phosphorus removal, and adsorption phosphorus removal. It reduces phosphorus content through biological absorption and assimilation, and substrate adsorption. Phosphorus removal is mainly through substrate adsorption of phosphorus.
In summary, the above methods can remove phosphorus in wastewater conveniently and quickly, but they all have certain disadvantages. If one of the methods is used alone, the actual application may face more problems. The above methods are more suitable for pretreatment or advanced treatment for phosphorus removal, and combined with biological phosphorus removal may achieve better results.
Method for Determination of Total Phosphorus
1. Molybdenum-antimony anti-spectrophotometry: The principle of analysis and determination of molybdenum-antimony anti-spectrophotometry is: under acidic conditions, phosphorus in water samples can react with molybdenum acid and antimony potassium tartrate in the form of ions to form acid molybdenum complexes. Polyacid, and this substance can be reduced by the reducing agent ascorbic acid to form a blue complex, which we call molybdenum blue. When using this method to analyze water samples, different digestion methods should be used according to the degree of water pollution. The digestion of potassium persulfate is generally aimed at water samples with a low degree of pollution, and if the water sample is highly polluted, it will generally appear in the form of low oxygen, high metal salts and organic matter. At this time, we need to use oxidizing Stronger reagent digestion. After continuous improvement and perfection, using this method to determine the phosphorus content in water samples can not only shorten the monitoring time, but also have high accuracy, good sensitivity and low detection limit. From a comprehensive comparison, this is the best a detection method.
2. Ferrous chloride reduction method: Mix the water sample with sulfuric acid and heat it to boiling, then add ferrous chloride and sulfuric acid to reduce total phosphorus to phosphate ion. Then use ammonium molybdate for color reaction, and use colorimetry or spectrophotometry to measure the absorbance to calculate the total phosphorus concentration.
3. High-temperature digestion-spectrophotometry: Digest the water sample at high temperature to convert total phosphorus into inorganic phosphorus ions. Then use an acidic potassium dichromate solution to reduce the phosphate ion and potassium dichromate under acidic conditions to generate Cr(III) and phosphate. The absorption value of Cr(III) was measured, and the content of phosphorus was calculated by the standard curve.
4. Atomic fluorescence method: the total phosphorus in the water sample is first converted into inorganic phosphorus form, and then analyzed by atomic fluorescence analyzer to determine its content.
5. Gas chromatography: The total phosphorus in the water sample is separated and detected by gas chromatography. The water sample was treated first to extract phosphate ions, and then acetonitrile-water (9:1) mixture was used as solvent for pre-column derivatization, and finally the total phosphorus content was determined by gas chromatography.
6. Isothermal turbidimetry: convert the total phosphorus in the water sample into phosphate ions, then add buffer and Molybdovanadophosphoric Acid (MVPA) reagent to react to form a yellow complex, measure the absorbance value with a colorimeter, and then The calibration curve was used to calculate the total phosphorus content.
Post time: Jul-06-2023
