In recent years, the eutrophication of water bodies in my country has become increasingly serious. Today, with advanced science and technology, there have been a variety of methods and agents for phosphorus removal, most of which have stable effects. How to remove phosphorus quickly and efficiently is also a key topic of research.
Unlike nitrogen, phosphorus cannot become a gas, so if you want to remove phosphorus, you can only make phosphorus into a solid form. Most of the phosphorus in the wastewater is inorganic phosphorus, and chemical precipitation has an obvious effect on phosphorus removal. The use of certain drugs can make phosphorus into a solid. Aluminum salt can also form water-insoluble aluminum phosphate with phosphorus. Generally, aluminum sulfate or sodium aluminate is used, but the effect of phosphorus removal is similar.
1. Discharge standard for wastewater dephosphorization
In 1998, the State Environmental Protection Administration issued the "Notice on Phosphate and Its Monitoring Methods in GB 8978-1996 "Integrated Wastewater Discharge Standard", which clearly stated that phosphate in GB 8978-1996 "Integrated Wastewater Discharge Standard" refers to total Phosphorus is the sum of particulate organic phosphorus and inorganic phosphorus dissolved in wastewater.
Studies have shown that the various forms of phosphorus in sewage are not equal. Taking domestic sewage as an example, total soluble phosphate> soluble orthophosphate> particulate phosphorus content> other dissolved phosphorus, but due to differences in water, the total The same phosphorus will also cause differences in the proportion of phosphorus in different wastewaters.
2. Difficulties and analysis of phosphorus removal technology
Commonly used methods for phosphorus removal include lime phosphorus removal, biological phosphorus removal, and aluminum salt phosphorus removal. But today with serious pollution, it is difficult to reduce the phosphorus content with a single method.
Lime for phosphorus removal
The use of slaked lime can generate phosphoric lime with phosphorus. The characteristic is that the higher the pH value, the worse the solubility, and the slaked lime is just alkaline after it is dissolved. When the pH of the wastewater is 10.5-11, the lime phosphorus removal method can reduce the total phosphorus to 0.5mg/L. Relatively speaking, it has a certain effect, but the shortcomings are also extremely obvious. The water pipes are blocked, causing irreversible losses, and in the end the gains outweigh the losses.
Biological phosphorus removal
The principle of using biological phosphorus removal is that microbes need to take in phosphorus to survive, and convert phosphorus into polyphosphate and store it as an energy reserve. This type of microbe is called phosphorus accumulating bacteria. Phosphorus-accumulating bacteria have a good appetite only in aerobic conditions, otherwise a state of dilute phosphorus will appear. A complete biological phosphorus removal process needs to include an anaerobic section and an aerobic section. Although biological phosphorus removal is one of the more popular methods so far, its price is relatively high, and the treatment cost is high. For general water plants, the investment is relatively large, and it is difficult for small and medium-sized treatment plants to accept it.
Aluminum salt dephosphorization
Most of the phosphorus in wastewater is inorganic phosphorus, and the phosphorus removal effect of chemical precipitation is the most obvious. The use of certain drugs can turn phosphorus into solid. Aluminum salt can also form water-insoluble aluminum phosphate with phosphorus. Generally, aluminum sulfate or sodium aluminate is used, and the effect of phosphorus removal is similar. The difference is that sodium aluminate will increase the pH of wastewater, while aluminum sulfate will decrease. However, the amount of phosphorus removal using aluminum salt is relatively large, and the effluent cannot be stabilized.
Iron salt dephosphorization
Iron salt can form water-insoluble iron phosphate with phosphorus, the most commonly used is ferric chloride, and occasionally ferrous chloride, ferrous sulfate, and ferric sulfate are also used. Iron salt is as flexible as aluminum salt. The only drawback is that the phosphorus removal effect is erratic and fluctuates according to pH. Generally speaking, it is better than aluminum salt.
3 New and efficient phosphorus removal technology
The biological treatment method has limited phosphorus removal effect. When the phosphorus emission standard is very high, it is often necessary to use chemical phosphorus removal or a combination of biological and chemical phosphorus removal. Therefore, for the current industrial phosphorus removal, using a chemical to remove phosphorus is simpler and more efficient than using traditional processes and equipment. How to use a special agent and treatment method to make sewage treatment with a small amount of chemicals, stable effluent, and cost savings will be a major difficulty in the current stage of phosphorus removal technology.
The new type of high-efficiency polyaluminum chloride (PPAC) developed by Shenzhen Changlong Technology Co., Ltd. is a kind of significant increase in the hydrolysis-polymerization process of Al(Ⅲ) solution by the use of a polymerizing factor. Molecular compound flocculant.
The hydroxide ions are incorporated into the sewage, forming a large number of positive charge clusters and negative charge clusters in the water, and finally flocculate and precipitate, and the sewage is degraded. Its adsorption, aggregation and precipitation functions determine that it is suitable for printing and dyeing. A variety of complex water quality such as papermaking, textile, chemical industry, etc. It has good effects such as speeding up the reaction rate, improving the hydrogenation capacity and controlling the pH of the solution
1. It has a strong positive charge density and higher molecular weight;
2. It has excellent performance of adsorption, condensation, precipitation, etc.;
3. The treatment cost of ton of water is low, and the corrosiveness is weak, which is suitable for most water plants;
4. It has the functions of dephosphorization, decolorization and COD removal;
5. There are iron/iron-free and various content options, freely adjusted according to water quality.
Scope of application:
1. Used in the treatment of industrial wastewater from printing and dyeing plants, paper mills, electroplating plants, circuit board plants, food plants, pharmaceutical plants, fertilizer plants, pesticide plants, mineral processing and metallurgy;
2. Suitable for phosphorus removal in domestic sewage treatment plants;
3. It is suitable for sludge filter press, and it has an excellent effect with a small amount of polyacrylamide;
4. It is suitable for sewage with darker chroma and difficult to remove.
Four, application cases
Project: Standard treatment of a sewage treatment plant in Zhuhai
Water plant situation: the water volume is 38,000 tons/day, the consumption is 50 tons/month, the CASS process, the original use of a certain brand of polyiron is large, and the color of the effluent is not good.
Treatment target: total phosphorus <0.5mg/L, and the cost of drug consumption is reduced by 20%.
Specific plan: switch to high-efficiency polyaluminum chloride (PPAC), and select a suitable dosage to determine the color of the effluent.
From left to right, the dosage of medicament is 30ppm, 40ppm, 50ppm, 60ppm respectively. The dosage is 40% less than that of poly-iron and the effluent is clearer.