1. The main source of phosphorus-containing wastewater
The main sources of phosphorus-containing wastewater are as follows:
① According to the source classification, it mainly comes from the production process of various detergents, industrial raw materials, agricultural fertilizers, and human excretion;
② According to the existence form of phosphorus, it can be divided into inorganic phosphorus wastewater (phosphate, polyphosphate) and organic phosphorus wastewater (phosphorus-containing organic compounds mixed in water). Phosphorus-containing laundry powder is one of the main sources of phosphorus-containing wastewater. The "Biwa Lake Incident" in Japan in the mid-1960s aroused people's attention to the eutrophication of phosphorus, so the problem of non-phosphorization of detergents became a research hotspot. People have achieved good results by restructuring the product formula and using 4A zeolite instead of phosphate as the main auxiliary to synthesize phosphorus-free laundry powder to replace the original phosphorus-containing laundry powder; for agricultural fertilizers, part of the phosphorus is absorbed by plants and part of it is absorbed by the soil. There is also a part with soil and water loss, so when using fertilizers, you should consider minimizing soil loss.You can minimize soil and water loss by means of greening barren mountains and deserts, scientifically farming according to local conditions, establishing farmland shelter forests, and establishing green belts in rivers and lakes. This is also an important aspect of reducing the phosphorus content of wastewater; for human excretion, it can be used for agricultural fertilizer after special treatment.
2. Treatment method of phosphorus-containing wastewater
At present, domestic and foreign sewage phosphorus removal technologies mainly include biological methods and chemical methods. Biological methods such as A / O, A2 / O, and UCT processes are mainly suitable for treating low-concentration and organic phosphorus-containing wastewater. Chemical methods mainly include coagulation sedimentation, crystallization, ion exchange adsorption, electrodialysis, reverse osmosis and other processes, which are mainly suitable for treating inorganic phosphorus-containing wastewater. Among them, coagulation sedimentation and crystallization comprehensive treatment technology can treat high-concentration phosphorus-containing wastewater. It has a high phosphorus removal rate and is a reliable treatment method for high-phosphorus wastewater.
2.1 Biological Law
In the 1970s, Spector in the United States discovered that microorganisms can take up phosphorus in an aerobic state and release phosphorus in an anaerobic state in which organic matter exists. The biological treatment method of phosphorus-containing wastewater is gradually formed and improved on this basis. At present, there are mainly three types of biological dephosphorization technologies commonly used in foreign countries: first, adding coagulants to dephosphorization in aerated storage tanks; second, using soil treatment, orthophosphate ions interact with Fe and Al in the soil. Oxides react or replace with OH- or SiO22- in clay to generate insoluble phosphate compounds. The third method is activated sludge method, which is the most widely used biological dephosphorization technology at home and abroad. The biological phosphorus removal method has a good treatment effect, without the disadvantages of chemical sedimentation sludge being difficult to treat, and does not need to add a precipitating agent. For the secondary activated sludge process, there is no need to add a lot of equipment, and only the operation process can be changed to achieve the effect of biological phosphorus removal. However, strict management is required. In order to form VFA, the anaerobic conditions in the anaerobic stage must be guaranteed.
Zhang Linsheng and others used lime precipitation crystallization to treat high-concentration phosphorus-containing wastewater successfully. This method combines the advantages of precipitation and crystallization, overcomes the shortcomings of the two, and has good development prospects. Experimental results and engineering practice show that this method has high phosphorus removal efficiency in treating phosphorus-containing wastewater, and the effluent water quality is stable and can be reused.
2.2 Chemical precipitation method
By adding a chemical precipitant and phosphate in the wastewater to form a poorly soluble precipitate, the phosphorus can be separated out, and the formed floc also has an adsorption and removal effect on the phosphorus. Commonly used coagulating and precipitating agents are lime, alum, ferric chloride, a mixture of lime and ferric chloride, and the like. The main factors affecting such reactions are pH, concentration ratio, and reaction time.
In order to reduce the cost of wastewater treatment and improve the treatment effect, scholars have done a lot of work in the development of new and cheap chemical precipitants. Wang Guanghui found that when the raw water contains 10mg / L of phosphorus, adding 300mg / L of Al2 (SO4) 3 or 90mg / L of FeCl3 can remove about 70% of phosphorus, and adding excess lime during initial sedimentation can generally remove total phosphorus. About 80%. He added the new type of water purification agent basic aluminum chloride based on chemical coacervation to increase the sedimentation rate of sedimentable substances, and the sedimentation effect reached 80% to 85%, which solved the problem of PO43-pollution of production water. Coagulation sedimentation method is a traditional method of phosphorus removal, which has the advantages of simple and easy operation and good treatment effect. However, long-term operation results show that the addition of chemical precipitants will cause the pH value of wastewater to rise, form hard scales in the ponds and water pipes, and produce a certain amount of sludge. In addition, research shows that the curve of phosphorus removal efficiency corresponding to the amount of precipitant is exponential. When the chemical precipitant exceeds a certain amount, the curve reaches the stagnation period. Therefore, it is not economical to try to reduce the mass concentration of phosphorus in the wastewater to less than 0.1 mg / L by the precipitation method.
The A / O reconstruction practice of Dalian Development Zone Sewage Plant hosted by Cong Guangzhi and others shows that the system can achieve better purification effect under the following parameters: BOD5 load is 0.2 ～ 0.3kg / (kgMLSS˙d), TP load is (2.8 ～ 3.0 ) × 10-3kg / (kgMLSS˙d). Volume of anaerobic section: volume of aerobic section = 1: 2, DO of anaerobic section is less than 0.6mg / L, DO of aerobic section is 3 ～ 3.5mg / L, water temperature is 12 ℃. The effluent phosphorus content is stable below 10mg / L. The anaerobic and aerobic activated sludge dephosphorization process can remove phosphorus more thoroughly without increasing the capital investment and maintenance costs of the standard activated sludge process, and the operation is stable. This process not only inherits the advantages of the traditional standard activated sludge process, but also increases the biological phosphorus removal function.
The inverted A2 / O process chaired by Huang Lihui and others overcome the shortcomings of the relatively complex A2 / O process and the obvious inadequacy in the use of phosphorus absorption power. Several return systems. The test results show that for 2/3 of urban sewage with industrial wastewater, the inverted A2 / O process has higher ability to remove organic matter and nitrogen and phosphorus in the production operation. The whole process has the characteristics of simple process, low energy consumption, stable operation and strong impact resistance, which is suitable for the transformation of old factories.
2.3 Adsorption method
In the 1980s, porous materials were used as adsorbents and ion exchangers in water purification and pollution control. Huang Wei et al. Used fly ash as an adsorbent to study the characteristics of dephosphorization of simulated wastewater containing 50 ～ 120mg / L phosphorus. Studies have shown that fly ash contains more activated alumina and silica, etc., and has a considerable adsorption effect. Fly ash does not simply adsorb inorganic phosphates, among which CaO, FeO, Al2O3, etc. can be insoluble with phosphate or Directly soluble precipitation phenomenon has broad application prospects in wastewater treatment. The test results show that fly ash is an effective adsorbent. The mass concentration of P is 50 ～ 120mg / L, the amount of fly ash per 50mg is 2 ～ 2.5g, the particle size range is 140 ～ 160 mesh, and the pH is neutral. Under the experimental conditions, the removal rate of phosphorus can reach more than 99%. Ding Wenming, Huang Xia and other synthetic iron-cerium composite phosphorus removal agents have better phosphorus removal effect. It is synthesized by reacting a mixed solution of iron salt and cerium salt with an lye, and has a high-efficiency adsorption effect on phosphate in aqueous solution. Orthogonal experiments show that the content of iron and cerium ions in the salt solution is the most important factor affecting the effect of phosphorus removal. In addition, the synthesis temperature and drying temperature also have a certain effect on the adsorption performance. Various tests have proven that crystal breakage is the main reason for the increase in specific surface area of the compound phosphorus removal agent, and the increase in specific surface area is the main reason for the efficient adsorption of phosphorus removal. It is expected that there will be more adsorbents for phosphorus removal in the future.
2.4 Other phosphorus removal methods
The new double sludge denitrification and phosphorus removal process system studied by Zou Weiguo and others succeeded in treating domestic sewage. Traditional denitrification and phosphorus removal processes mostly use a single sludge system, so there is a contradiction between nitrification and phosphorus removal sludge age. Combining activated sludge method with biofilm method can solve this problem. The experimental results show that the removal rate of PO43- reaches 90%, the treatment effect is stable, and the adaptability to water quality is very strong. Chen Yun et al. Carried out research on low-dissolved oxygen SBR phosphorus removal process. The experimental results show that phosphorus accumulating bacteria can be enriched in the SBR system with low-oxygen aeration, and obvious phosphorus release and excessive phosphorus absorption have occurred. This method should pay attention to that the sludge load has a greater impact on the COD removal rate and phosphorus removal effect, so it is necessary to choose an appropriate sludge load. Excessive sludge loading will cause swelling of non-filamentous sludge. Fang Qian et al. Made progress in the treatment of low-carbon urban sewage by using the SBR method, and solved the difficult point of how to ensure the efficient removal of nitrogen and phosphorus in the treatment of unbalanced carbon, nitrogen, and phosphorus ratios (low carbon content). The results show that by using this method to treat low-carbon urban sewage in Guangzhou, the effluent organic matter, ammonia nitrogen, and total phosphorus meet the standards, and the greater the amount of phosphorus released, the lower the total phosphorus concentration in the effluent. Practice has proved that the SBR method has the characteristics of simple process, no need for sludge reflux, and good nitrogen and phosphorus removal effect.
3. Control of discharged wastewater pollution
The discharged phosphorus-containing wastewater must not be allowed to flow freely, and necessary measures and measures should be taken to control and restore it. First of all, the trends of the discharged wastewater should be closely monitored to control it within a certain range, so as to prevent more areas from being polluted; then, strict measures should be taken for the phosphorus-containing wastewater that is being discharged and will be discharged. It is forbidden to discharge, so that the total amount of discharged wastewater can be controlled within a certain range, which facilitates the subsequent wastewater treatment. Finally, the phosphorus-containing wastewater that has been discharged should be treated in a timely manner. Since the discharged wastewater is not easy to collect for systematic treatment, we can use chemical precipitation method for purification. For the areas that have been polluted, the functions of the original ecosystem have been destroyed, and the ability to self-recovery becomes more fragile. Therefore, it is especially critical to prevent them from being polluted again.
4. Recovery of polluted waters
The ultimate goal of wastewater treatment is to restore its original appearance and maintain a benign state for people and the surrounding environment. Therefore, the restoration of polluted waters has become extremely important. The main methods currently applied are: physical measures, chemical measures, biological measures, etc. Physical measures are mainly to reduce the amount of nutrients entering the water body; mechanical agitation and aeration are used to destroy the water body layering and increase the fluidity of the water body; mechanically harvesting blue-green algae, etc., but the effect is not ideal. Chemical measures are to use algicides and algicides as emergency measures. Practice has proved that water quality eutrophication cannot be effectively controlled, and new pollution is caused. Biological measures are to cultivate phosphorus-eating bacteria, animals or plants to absorb nitrogen and phosphorus in water. The governance of Dianchi Lake in Yunnan is a typical example. In recent years, a large amount of urban sewage has been discharged into Dianchi Lake, causing rapid deterioration of water quality and severe blue-green algae blooms. The scientist selected an area for a demonstration biological experiment. More than 180 kinds of insects were planted in this area, and aquatic plants were planted. For sturgeon and sturgeon, the main food is cyanobacteria. Researchers put a large amount of sturgeon and sturgeon in the demonstration area. Research shows that each catfish can grow an average of 3 to 4kg per year, and for each 1kg, it needs to consume 40-50kg of cyanobacteria, and one catfish can consume an average of 150kg of cyanobacteria per year. The amount of cyanobacteria. At the demonstration site, the entire water surface was very pure. It is understood that this algae-control fishery demonstration project ended in 2003, and its scientific research results provide a useful attempt for the ecological management of Dian Lake in the future.
5.Summary
The treatment of phosphorus-containing wastewater is a systematic project, which mainly consists of pollution source control, sewage treatment, and control and recovery of discharged sewage. Based on my understanding of wastewater treatment issues, the author summarizes the following points:
(1) The control and restoration of the discharged wastewater pollution can be considered as a follow-up to the phosphorus removal problem and an important supplement to the former. Therefore, we should attach great importance to it and adopt a proactive and effective method for timely governance.
(2) The phosphorus-containing wastewater treatment technology is the key to the treatment of phosphorus-containing wastewater. As a traditional method of phosphorus removal, the precipitation method is relatively mature in terms of theoretical process technology, but there are still problems such as the generation of sludge in the phosphorus removal process and incomplete phosphorus removal. If it can be solved, there is still a lot of room for development; biological The method has successfully solved the disadvantages of the sludge sedimentation method which is difficult to handle and has no secondary pollution. It has great market competitive advantages. For the adsorption method and other new phosphorus removal technologies, although it has high phosphorus removal efficiency and stable operation, etc. Advantages, but there are still deficiencies in theoretical and technical aspects, and continuous improvement and improvement are needed. In practical applications, according to the different characteristics of phosphorus-containing wastewater, appropriate process technologies should be selected for reasonable matching, so as to achieve simultaneous optimization of economic and environmental benefits.
(3) The main source of phosphorus-containing wastewater is controlled by certain methods and means, which is the primary link of wastewater treatment. Just do this
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