Status quo and development trend of water treatment technology at home and abroad

Current status and development trends of related technologies at home and abroad Many regions in the world are facing the most serious shortage of water. According to the statistics of the World Bank, 80% of the countries and regions in the world are short of domestic and industrial fresh water. With the rising cost of resources and increasing awareness of environmental protection, many companies have begun to use green technologies to reduce carbon emissions and minimize waste generation. Among them, water treatment technology is a very important green technology.

According to United Nations statistics, by 2025, two-thirds of the world's population may face a shortage of water resources, so water treatment technology will receive more and more attention, including efficient water resource management and sewage treatment. For example: in North America and especially in Canada, the problems facing water management and sewage treatment facilities are very urgent. 63% of currently operating facilities are overdue and their average operating time has reached 18.3 years. Of these, 52% of sewage treatment facilities are running overtime. In the dry regions of the United States, the demand for desalination technology is increasing. The main limitation of desalination technology is efficiency, and with the shortage of desalinated water, these limitations are gradually diluted and ignored. The development of water treatment technology has great prospects, and many countries are implementing water treatment policies and projects. According to the forecast of the world's leading growth consulting firm, by 2010, the global water resource management and sewage treatment technology market size is expected to reach 350 billion US dollars.

Current advanced water management and sewage treatment technologies and their development trends include water recycling, reverse osmosis desalination, and ozonation. For example, reverse osmosis desalination technology is rapidly occupying the large-scale facility market, which used to be dominated by thermal process equipment.

host. The improvement in treatment efficiency and the fall in the price of permeable membranes have prompted the rapid development of the reverse osmosis desalination market in the past five years. Now the application of reverse osmosis desalination technology is no longer small-scale factories, large-scale reverse osmosis desalination Desalination plants are commonplace.

In terms of sewage treatment, Australian researchers have proposed a new rotary bio-electrochemical contactor in the field of biopower generation. This technology can be used in the sewage treatment industry for 30 years. The efficiency of the rotary biological sewage treatment technology of the Only one tenth of the original through storage and chemical handling methods. This technique is currently considered to be the simplest, easiest to use and economical processing technique.

China is also currently facing a huge shortage of fresh water and water pollution. As a country with the smallest amount of water resources per capita, measures must be taken to avoid serious crises in the future. The problem of water shortage in northern China is extremely serious, so the country has launched a huge "South-to-North Water Diversion" project. The pollution problem also plagues China, where an estimated 300 million people have polluted drinking water. From 2004 to 2008, the annual growth rate of sewage discharge reached 18%, from 48.2 billion tons to 57.2 billion tons. It is estimated that in 2010, China's sewage emissions will reach 64 billion tons. China's continuous industrialization, urbanization and rapid economic growth are the main reasons for the continuous increase in sewage emissions; in contrast, China's sewage treatment plants are basically

Failed to run at full capacity. Taking 2008 as an example, the sewage treatment capacity of China's sewage treatment plants only reached 64% of the design load, mainly because the operating costs were too high. In this case, China's sewage treatment industry will require more investment and more advanced technology

technique. Between the 11th 5-year plan (2006 to 2010), the government expects to spend more than 300 billion RMB in water treatment. As of 2009, there were 1,572 sewage treatment plants in China, and 2,063 were under construction.

With the development of social economy and urbanization, shortage of water resources and pollution of water environment have become global problems in this century and are becoming more and more serious. Some people even believe that the water problem may surpass the energy problem and become the most important problem in the world in the 21st century. Therefore, great attention must be paid to the problem of water. Correctly mastering and rationally utilizing existing water treatment technologies and researching new water treatment technologies are important ways to solve water pollution and rationally utilize water resources. Correctly grasp the development trend of water treatment technology in the future. In view of this, the development trend of my country's water treatment technology is prospected through a review of the development status of my country's water treatment technology and an analysis of the current common water treatment modes and problems faced.

1. Development Status and Existing Mode of Water Treatment Technology

1 Development status of water treatment technology

The water supply treatment recorded in our country starts with alum water purification, and the relatively complete modern water supply is the Shanghai Yangpu Waterworks founded in 1882. Since then, the water purification technology has undergone simple precipitation and slow filtration treatment, relying on foreign experts to "copy and copy" new large-scale water plants, using advection pools, double-layer filtration technology, flocculation, and disinfection. Since the 1960s, urban water supply has been fully popularized, and water treatment has emerged from the Soviet model, and has gradually formed its own system in terms of academic theory, norm formulation, talent training, and equipment supply. For example, in water treatment, attention has been paid to the mixing after drug administration, using "details" such as static pipeline mixers, and promoting the application of technologies such as flocculation, which can reduce water loss, improve flocculation effect, and reduce drug consumption, etc.

Many studies have been carried out in

In the 1980s, there was corresponding research on the water distribution of the filter, and the application of the coagulant.

After the 1980s, with the deepening of reform and opening up, the water treatment introduced and absorbed foreign advanced technology and equipment, improved the automation level of flocculation and dosing, and began to improve water quality and micro-polluted water treatment. With the development of technology, disinfectants are widely used and show a trend of diversification, the water quality of water supply pipes has been automatically detected, and the conventional water treatment technology has been strengthened. ?At present, biological pretreatment technology for water pollution caused by economic development and advanced water treatment technology such as ozone activated carbon

In the process of practical development, small-scale membrane treatment equipment has also been applied to high-quality drinking water treatment systems.

At the same time, many studies and applications have also been carried out in industrial water treatment, such as

The pretreatment of industrial water is carried out by sedimentation and filtration, and the treatment of boiler water by ion exchange, softening, iron removal, etc., but in the treatment of industrial circulating water, due to the lack of automatic

The main technology, the concept of water quality stability in foreign tap water treatment was followed in the early days, mainly to control the scaling of CaCO3, ignoring other salts and compounds of scaling, and it has a great impact on the characteristics and characteristics of industrial water temperature changes. Corrosion of water and the influence of microbial slime caused by bacteria and algae in the water have not been considered, which leads to a detour. At present, in industrial circulating water treatment, the addition of corrosion inhibitors, scale inhibitors, fungicides and other chemicals is mainly used to control water corrosion, scaling and microbial sludge. It should be noted that the corrosion inhibitors used in industrial water treatment were mainly chromate and nitrite in the 1960s. Due to their high toxicity, phosphoric acid gradually became phosphoric acid due to the limitation of environmental protection in the 1970s. replaced by salt.

However, in recent years, the eutrophication of waters caused by the release of phosphorus with

Therefore, the organic series of molybdenum series, tungsten series, silicon series and other pollution-free water treatment corrosion inhibitors have been developed and gradually promoted.

In terms of scale inhibitors, pigments, starches and humic acids have been used, and currently the most widely used ones are organic phosphates and polymer polycarboxylic acids. In the early stage of fungicides, such as chlorine, sodium hypochlorite, calcium hypochlorite, etc., were the most common, and later, two chlorine oxides were developed. However, the by-product trihalomethane (THM3) produced after chlorine disinfection has been confirmed as a carcinogen, so the currently used bactericidal and algicides have been expanded to non-chlorine-containing oxidation such as ozone and hydrogen peroxide. type bactericides and non-oxidizing bactericides represented by quaternary ammonium salts such as tetraalkyl benzyl ammonium bromide.

In the treatment of waste (sewage) water, methods such as neutralization, precipitation, exposure, biological treatment, mixed dilution and filtration are mainly used at present. The purpose of treatment is to basically meet the requirements of discharge water quality, and, The overall processing rate is not very high.

In terms of aquaculture water treatment, since the 1960s, some countries, such as Japan, the United States, Germany, Canada, Denmark, etc., have carried out research on circulating water aquaculture water treatment technology to varying degrees. At present, water treatment technologies and facilities such as ozone, ultraviolet rays and biological filters have been widely used in aquaculture abroad, and they are developing in the direction of mechanization and modernization. my country started late in this regard, but it has developed rapidly in recent years. With the concerted efforts of large-scale scientific and technological workers, a series of achievements have been made, and various types of circulating aquaculture water treatment have been developed. facility.

2 Several main modes of current water treatment applications

1) Sewage treatment? The most widely used sewage treatment mode at present, this mode takes the exposure tank (oxidation ditch) and the sub-sink as the main functional units, which are constructed according to the structures in the exposure tank (oxidation ditch) The difference in form can distinguish various water treatment processes. The main application of this mode

For the treatment of urban domestic sewage and industrial waste, the treatment goal is to meet the sewage discharge requirements, such as reducing ammonia nitrogen and chemical oxygen consumption to below 525mg/L and 50100mg/L respectively.

2) Drinking water treatment

On June 7, 2001, my country promulgated a new "Living and Drinking Water Hygiene Standard", which requires the CODMn of living water to be less than 3mg/L; January 1, 2000

The "Environmental Quality Standard for Surface Water" implemented today requires that the concentration of ammonia nitrogen in the effluent from water source treatment be below 0.5mg/L. The implementation of these relevant standards has greatly improved the water quality standards for water treatment, and the country is still considering formulating industry standards for water quality. On the basis of safeguarding public health in economically and technologically developed regions and cities, higher standards will be proposed.

In addition to strictly controlling toxic and harmful items, microorganism items will also be added. At the same time, sensory items and requirements for appropriately improving water quality will also be considered to meet the needs of improving living standards. . It should be pointed out that the current conventional water treatment cannot meet the requirements for COD and ammonia nitrogen removal, and adding high doses of chlorine for disinfection will lead to mutagenic effects such as trihalomethanes and haloacids.

The disinfection by-products used in water pose a threat to the safety of drinking water. The removal of ammonia nitrogen depends on biological pretreatment, and the improvement of color, smell and taste requires the use of activated carbon or ozone activated carbon adsorption and biodegradation processes. Therefore, it is necessary to consider adding preprocessing or advanced processing links to improve water quality.

From the current research at home and abroad, various pre-oxidation treatments (ozone, potassium permanganate, chlorine dioxide, hydrogen peroxide), biological treatment and activated carbon adsorption are combined with conventional treatment to optimize the combination of new clean water. The technology is the basic technical countermeasure for the water purification of the polluted water source. ?3) Purified water treatment

4) Boiler water treatment

The development trend of water treatment technology

Looking at the above-mentioned development status of water treatment technology and the problems faced by my country's current water treatment, studying the development history of foreign water treatment technology, combined with the requirements of rational development and utilization of water resources in the new century, we can roughly outline the water treatment technology in my country. The following development trends.

1 General water treatment

Conventional processes aimed at removing suspended solids, colloids and bacteria cannot have a good removal effect on color, ammonia nitrogen and oxygen consumption. The initial stage of the process is continued, but it is not a simple repetition, but an "enhanced" or "optimized" process combination, supplemented by pretreatment and advanced treatment for different water source conditions and water quality requirements.

When the content of ammonia nitrogen and nitrite in the raw water is high, there are many organic substances, and it is easier to biodegrade, biological pretreatment will be suitable, because the effluent quality can be comprehensively improved, and the operating cost is low. When the amount of organic matter in the original water is large and difficult to degrade, in order to ensure that the effluent quality of the clean water fully reaches the specified organic matter (including disinfection by-products) index and reduces the mutagenic activity of the effluent (Ames test was negative), The use of activated carbon filtration will be necessary and will be the direction of future development.

2 Biological pretreatment? Biological pretreatment technology can effectively remove ammonia nitrogen and partially degradable organic matter in raw water. In view of the current status and trend of water pollution, biological pretreatment process as a powerful weapon to remove ammonia nitrogen will not change for a long time, but extensive research on practical application is still needed. , especially to conduct more extensive and in-depth research on the technological measures to deal with the outbreak period in the treatment of algal water.

The density of algae is generally small, so its flocs are not easy to settle, and the use of flotation can achieve better results.

algae removal effect. The main problems of the air float method are that the algal residue is difficult to handle, the odor near the air float tank is heavy, and the operating environment is poor.

3 Deep processing technology

At present, advanced water treatment technologies such as ozone oxidation and ozone activated carbon adsorption, which are still in the application research stage in my country, have been widely used in developed countries such as Europe and the United States. The application should work for a while.

4 Development of water treatment chemicals

In terms of disinfection and sterilization, although the problem of THM3 has attracted the attention of the world, it is currently limited to technical and economic conditions in my country, and liquid chlorine disinfection is still used by most waters. With the research and development of new high-efficiency, low-toxic or non-toxic alternatives in foreign countries, my country will gradually limit and eliminate the method of liquid chlorine sterilization. The chemicals in industrial water treatment will develop from toxic and polluting chemicals to low-toxicity, non-toxic and pollution-free chemicals, from non-biodegradable chemicals to easily biodegradable chemicals, and from a single water treatment agent Towards the development of compound multifunctional medicines.

5 Membrane treatment technology? Membrane technology is a technology composed of ion exchange membranes or organic polymer synthetic membranes. It has developed rapidly in recent years. For water treatment, it may be a new technology in the 21st century.

Membrane treatment technology is known as the key technology of water treatment technology in the 21st century, and it is the best choice to replace traditional processes. The main working principle of membrane separation technology is the mechanical sieving effect of membrane separation by using pressure gradient as the driving force to separate ions, molecules and impurities in water by using the permeation performance of specific membranes. From the chemical field to the water treatment field, the result of the development. ?In the past 10 years, my country has been mainly used for the treatment of high-quality drinking water in barrels and bottles, while in Europe and the United States, water has been built with a daily water treatment capacity of tens of thousands to tens of thousands of cubic meters. The current membrane treatment technology is under water

The main applications in management are reverse osmosis (Reverse Osmotic, RO), electrodialysis (Electrodialysis, ED or EDR), sodium filtration (Nano

There are five types of filtration, including ultrafiltration (NF), ultrafiltration (UF) and microfiltration (MF). UF and MF have low pressure required for operation and low cost of membrane, which can replace the coagulation process of traditional water treatment, which is worthy of promotion; RO and NF can separate particles with a diameter of 0.0001µm to 0.001µm, which is not suitable for viruses, organic matter, etc. It can effectively remove the dissolved inorganic matter and can be used for both industrial water treatment and drinking water treatment.

Problems and conventional disinfection by-product generation, especially addressing the inability to remove and kill cryptic spores by conventional methods newly discovered since the 1990s. With the improvement of drinking water quality requirements and the development of membrane technology, membrane technology and membrane products will be widely developed and applied. However, the integration of membrane modules, the detection of membrane damage, the control and washing of membrane fouling, the treatment of sewage in membrane treatment and the reduction of membrane costs still need to be further studied.

Microfiltration, ultrafiltration and reverse osmosis are filtration technologies that rely on pressure to drive water through a semi-permeable membrane and retain impurities in the water: colloids, inorganic ions, organic matter, microorganisms, etc. The difference between them is mainly the pore size of the membrane and the diameter of the retained particles. General particle media (sand, coal, etc.) filtration technology can remove particles above 2-5µm. Microfiltration can remove

The particles of 0.1-0.2µm can remove most of the particles that form turbidity. Ultrafiltration can remove particles with a molecular weight of 0.005µm and more than 1000, including bacteria and viruses. Reverse osmosis can remove 0.3-1.2nm organic matter (molecular weight 200-500) and

Inorganic ions for desalination, sea talk. Nanofiltration is a low-pressure reverse osmosis that removes nanoscale particles, organic matter (molecular weight 300), and inorganic ions for softening and desalination.

The application of membrane technology needs to be combined with other technologies (such as pre-treatment and post-treatment) to give full play to its characteristics. Raw water of good quality can be used for drinking after microfiltration and disinfection. The microfiltration membrane equipment produced by a company in Australia can be automatically flushed (anti-clogging) or cleaned with chemicals on a regular basis (Ningbo Water Supply Company has introduced this equipment to produce pure water for sale). For raw water with high salt content, high hardness and organic pollution, reverse osmosis can be used to produce high-quality water. Considering the need to retain some ions that are beneficial to health, mineralization, calcification and other treatments can be performed after reverse osmosis, or nanofiltration can be used to remove less ions. In the application of membrane technology, the key is to prevent membrane fouling. The scale formed by inorganic salts, the adhesion of organic matter and the accumulation and growth of microorganisms will cause the blockage of the membrane and reduce the water flux of the membrane (if the temperature is maintained, the inlet pressure needs to be increased). Therefore, it is extremely important to select the necessary pretreatment according to the original water quality, otherwise the service life of the membrane will be affected, and the membrane will be damaged.

Frequent replacement increases operating costs. ?Aiming at different pollution on the membrane, it is also an important link in the application of membrane technology to use cleaning solution to clean the membrane regularly. Some countries are studying the use of microfiltration and ultrafiltration to replace conventional water purification processes, and the results show that the technology is feasible, but economic considerations need to be cautious. With the large-scale application of organic membranes and the rapid reduction of the cost of membranes due to the high-speed production of membranes, it can be considered that membrane technology will be more and more applied in the water supply business. ?6 Quality water supply and water efficient utilization technology? Water recycling technology and waste (polluted) water treatment and reuse technology will develop rapidly, which is the current reality of water shortages and water treatment requirements. The specific performance of technical level improvement. The high degree of recycling and reuse of water will save a lot of water resources, alleviate the water crisis and meet the requirements of sustainable development and environmental protection, and will also promote the development and growth of the water treatment industry, and eventually form a highly Developed water industry system.