The development process and background of industrial wastewater treatment

1. Development history and background of industrial sewage treatment

1.1 Development of foreign industrial sewage treatment The development of foreign sewage treatment industry started earlier than China, in 1914, the United Kingdom created the activated sludge process, applied to the sewage treatment process and achieved a certain degree of effect. Compared with European countries, our country is short of water resources per capita. In general, the water resources of Europe and the United States and other countries are relatively healthy, but the pollution caused by industrial sewage is a global problem, and the sewage treatment problem is the development of every country can not get rid of. As early as the 1990s, the European Community put forward requirements on water quality. Industrial and agricultural sewage flowing into water bodies caused the eutrophication of seawater lakes, which threatened the survival of water organisms, and the quality of underground drinking water was also affected. In 1975, the European Union enacted the law on surface water requirements, and in 1980, the law on drinking water requirements was enacted to regulate the water quality of groundwater, fishery and aquaculture water. In different countries and regions, the environmental background is different, the degree of water resources affected by sewage is different, and the development, requirements and process technology of sewage treatment are different. In some countries with rich water resources, sewage treatment regulations and facilities are simplified. For some industrially developed areas, water resources are regarded as wealth like crude oil, and the development and development of sewage treatment is relatively mature.

1.2 Development history and background of industrial sewage treatment in China

1.2.1 From 1920 to 1949, the construction of sewage treatment plants began one after another. In 1923, China's first urban sewage treatment plant was built in the northern district of Shanghai, and in the following years, urban sewage treatment plants in the western and eastern regions of Shanghai came out. Before this, industrial sewage, urban sewage and rainwater in various regions were directly diverted into rivers and lakes or the sea by ditches or pipes, and sewage was treated solely by drainage.

1.2.2 During the decade from 1950 to 1960, the main tasks were to organize and standardize the old pipes laid by direct sewage in the old city of Shanghai, remove unreasonable sewage pipes, strictly control the pollution of rivers and lakes in the area, and invest in the construction of a part of first-level sewage treatment plants after the completion of the transformation of standardized new sewage pipes. In Beijing, Shanghai and other places began to form a first-level sewage treatment plant with a daily treatment capacity of more than 100,000 tons.

1.2.3 From 1961 to 1978, land irrigation was applied to sewage treatment. In 1957, the relevant departments included this technical achievement in the national scientific research plan, and in the following years, multinational technical exchange meetings were held to actively develop and summarize the training and implementation of new technologies. At this stage, China invested in the construction of a large number of biological oxidation ponds; After the trial construction in many areas of China, the national sewage treatment capacity has been increased to one million tons per day, and the new sewage treatment pipeline has reached 19600km.

1.2.4 During this period from 1979 to 2000, China's sewage treatment officially entered the modern development in line with international standards, and the development speed was improved qualitatively. In the early 1980s, two production sewage treatment experimental bases were built successively in Tianjin and Beijing, and a large number of development and technical personnel joined together to conduct large-scale exploration experiments and research on sewage treatment technology and development routes in the two regions. The secondary biological treatment technology is deeply applied in the wastewater treatment process. After several years of continuous exploration, Tianjin built the largest sewage treatment plant in China in 1984, adding the new standard activated sludge biochemical process, and achieved remarkable results in local environmental improvement during a period of operation and production, and the treatment capacity was stable. Sewage treatment in our country has become large-scale and enterprise-oriented.

1.2.5 From 2001 to 2015, China in the 21st century is the world's China. With the reform and opening up, China's economic development has entered a stage of acceleration, and the development of sewage treatment industry is also a good momentum. As the country attaches more and more importance to environmental governance and puts forward the strategic goal of sustainable development, and constantly refining the requirements for sewage treatment, In the country, almost every industrial park has its own sewage treatment plant, urban sewage treatment plants are also entering the high-standard version of large-scale investment and construction, the development of sewage treatment industry benefited from the introduction of environmental protection laws and regulations to improve the continuous attention to environmental protection, environmental protection legislation.

Analysis of domestic and foreign sewage treatment development history, combined with China's development status of the 18th National Congress report pointed out: construction of ecological civilization, chemical enterprises towards green development, efficient development, low-carbon development direction transformation. Increase the intensity and requirements of pollution control and sewage treatment, and actively study and innovate to make our country have their own sewage treatment technology while constantly absorbing advanced technology of foreign sewage treatment. In the second half of 2015, the benefits of regional chemical enterprises began to decline, due to the national environmental protection policy strict requirements of enterprises to increase investment in environmental protection, overcapacity, sales decline, and higher prices of many reasons, the speed of industrial development has been affected to varying degrees. In the initial stage of transformation, the phenomenon of industrial development fluctuations is normal, we must adhere to the transformation. Continuous improvement.

2. Research status of industrial wastewater treatment

2.1 Process and principle of wastewater pretreatment The process treatment before biochemical treatment is called pretreatment. The biochemical system runs smoothly and the investment cost and operation cost are relatively small. However, it is not possible to treat wastewater by biochemical treatment alone, because industrial wastewater contains some active substances that can damage the ecosystem: Microorganisms and fungi have the presence of inhibiting and destructive substances, so in order to ensure the healthy operation of the biochemical system, a series of pretreatment must be carried out before the sewage enters the physicochemical section to adjust the biodegradability of the water quality and ensure the healthy operation of biochemical treatment.

There are two specific purposes of pretreatment: first, the organic or inorganic substances contained in the wastewater that have an impact on the active substances of the sludge in the biochemical tank are separated and removed to a certain extent or transformed into other harmless forms to protect the growth environment of the active substances of the sludge; The second is to reduce the chroma, salinity and suspended particles of the water before the biochemical section, adjust the COD load, and reduce the operating pressure of the biochemical section. Impurities in wastewater can be divided into suspended matter, colloids and dissolved matter according to particle size, and other large particles with particle size greater than 100 μm generally will naturally precipitate or separate from the water body. Colloids and fine particles and suspended matter need condensation, flocculation and coagulation methods to convert small particles into large particles, precipitate and separate from the water body.

1.1.1 Coagulation method and flocculation method Add coagulation agents containing positive ions or groups in wastewater. Using the principle of electrostatic induction, when adding a large number of positive ions or groups into colloids, a large number of positive ions will form a large number of colloidal particles between colloidal particles to coagulate and adsorb together to form macromolecular groups. It is easy to separate from the water body to achieve the purpose of water purification. The most used coagulants are aluminum sulfate, ferrous sulfate, alum, ferric chloride and so on. Flocculation method is the use of polymer coagulant in sewage to form a linear polymer polymer, polymer structure between the particles adsorption combination to form a relatively stable bridging effect, in this subunit between the continuous formation of bridging accumulation, condensation polymer material continues to grow, and finally reached saturation to form large particles of flocculant condensation together. Commonly used flocculants are polyacrylamide (PAM), polyiron (PE) and so on.

1.1.2 Coagulation method As the name suggests, the coagulation method is a method that combines coagulation and flocculation. Coagulation method is often applied in the process of industrial sewage pretreatment, the basic process is roughly the first to add coagulant (alum, ferrous sulfate and other agents) to the sewage, eliminate the electrostatic repulsion between colloidal particles, and then add flocculant (PAM, PE and other agents), so that the radius of the particles in the water increases, forming precipitation.

1.1.3 After the removal and treatment of sewage impurity particles into the iron carbon micro-electrolysis section Iron carbon treatment method is also called iron carbon micro-electrolysis method or iron carbon internal electrolysis method. Iron carbon micro-electrolysis uses the REDOX reaction of Fe2 + /Fe3 + in iron carbon micro-electrolysis. Iron carbon micro-electrolysis will form countless tiny units of iron carbon galvanic cells. The activity of active electrons is generated, which promotes the reactivity of organic matter in the sewage, makes the toxic and unsaturated substances in the sewage decompose and transform into other forms, reduces the load of chemical oxygen demand COD and biological oxygen demand BOD5, and lays the foundation for the normal operation of the subsequent treatment section. Iron carbon micro-electrolysis is an important means of industrial wastewater treatment. The iron carbon method has a remarkable effect on the treatment of industrial wastewater with toxic and high COD concentration. The reaction principle of the iron-carbon method is recognized as follows: under acidic conditions, iron-carbon fillers are added to water, forming a galvanic reaction between iron and carbon, forming a local unit of a large number of micro-current reaction areas, and promoting the reduction and oxidation of inorganic substances in sewage under the action of micro-current. The treatment effect of iron carbon micro-electrolysis is good in the actual sewage treatment, and the treatment effect has been recognized. The shortcomings of iron carbon method analysis: ① the price of iron carbon filler is not cheap, in the acidic conditions are decomposed, part of the incomplete reaction of iron filings and carbon will remain in the water, increasing the amount of sewage solid waste, blocking the instrument pipeline; ② Iron forms black iron sulfide in sulfur-containing wastewater under acidic conditions, which increases the color of the water, and a large number of iron ions enter the water to increase the salt content of the water.

1.1.4 Neutralization of pH Industrial wastewater generally uses sodium hydroxide and sulfuric acid to regulate pH.

1.1.5 Fenton oxidation wastewater flows into Fenton reaction, and hydrogen peroxide H2O2 is added. H2O2 and Fe2 + brought by electrolytic reaction form strong oxidizing Fenton reagent, which can produce ·OH radical with strong oxidizing ability. Under catalysis, The free radical can destroy the polymer aromatic ring, which is difficult to be removed by biochemical removal, so as to degrade and remove. The biodegradability of wastewater is greatly improved, and the B /C ratio is increased. In addition to the above process, the pretreatment of wastewater also includes membrane separation, air flotation, filtration, disinfection ion exchange and adsorption and other physical and chemical sections. According to the actual situation of factory sewage, different process requirements are selected for wastewater pretreatment.

1.1 Biochemical Treatment process and Principle of Industrial wastewater At present, most industrial wastewater treatment is bioactivated sludge process. The use of biological activated sludge process has evolved A large number of treatment techniques, industrial park secondary sewage treatment plants commonly used treatment processes are: A /O phosphorus removal process, A /O nitrogen removal process, AB process, A2 /O phosphorus removal and nitrogen removal process, UASB process, oxidation ditch series process. The different distribution and combination of treatment facilities make the processing focus and operation debugging of different treatment processes different. With the continuous development and progress of sewage treatment has been formed: A /O process, UASB process, ion exchange resin, reverse osmosis water treatment technology, biofilm method and other typical biochemical treatment processes. The following will be an in-depth introduction to these several widely used processing processes.

2.2.1 A /O(A2 /O) process A /O is the abbreviation of Anoxic /Oxic(anaerobic/aerobic) or Anerabic /Oxic(anaerobic/aerobic) technology, which is an important treatment process for the biological treatment of sewage to remove phosphorus and nitrogen. In the process of biological nitrogen removal, as denitrifying bacteria are anaerobic bacteria, they need a large amount of carbon sources to maintain metabolism and achieve denitrification process. However, after the aerobic nitrification reaction, the concentration of organic matter (carbon source) in polluted water is low, which cannot provide sufficient demand for denitrification. In the traditional biological dephosphorization and nitrogen removal section, methanol is added in front of the anoxic unit to supplement the content of organic carbon sources. The anaerobic section is placed before the aerobic section, and the organic matter contained in the water is used as the carbon source. This method is called pre-denitrification process. Nitrate and nitrite are introduced into the anoxic reaction section through the mixed liquid reflux.

AB process AB process is a new two-stage biological treatment process, that is, adsorption biodegradation method for short. AB process is A high-load method and two stages of activated sludge method combined treatment method, A, B two sections are strictly separated, so that different characteristics of bacteria are separated, played a complementary, complementary role. Therefore, AB process has higher removal rates of BOD5, COD, SS, TP and ammonia nitrogen than traditional activated sludge process. However, the AB process cannot achieve the effect of deep phosphorus and nitrogen removal, because the limit of phosphorus and nitrogen removal is restricted, and there are still a large number of nutrients in the sewage, which is easy to lead to eutrophication of the water body. Principle: The main role of AB process in the removal of pollutants in sewage is reflected in the adsorption flocculation effect of section A. The sewage is directly connected to Section A through the pipeline, and the suspended matter in the wastewater is mixed with bacteria to form A copolymer with relatively stable structure, and at the same time, it provides abundant microorganisms for Section A. It increases the growth rate of the microbial community in section A under sewage treatment, shortens the microbial metabolic cycle, and decomposes a large number of viscous substances. This part of viscous substances interacts with suspended substances, large particles and free bacteria in the wastewater to form adsorption condensation, produce flocculant groups, and finally separate from the water through screen or precipitation. Stage B is similar to the ordinary activated sludge process.

2.2.3 UASB process The Chinese name of UASB is upflow anaerobic sludge bed, which includes the double-sided characteristics of anaerobic activated sludge method and anaerobic filtration method. Born in 1971 in Henan Agricultural University, researchers used the difference in the nature of substances with different densities under the action of gravity to create a three-phase separator, which created favorable conditions for the advent and upgrade of upflow anaerobic sludge beds. The UASB process has the advantages of simple structure, low operation, maintenance and operation difficulty, and is suitable for different kinds of industrial sewage treatment requirements. After long-term development and innovation, it has mature technical support and has been widely promoted and used. Principle: The composition of UASB is divided into sludge reaction zone, gas-liquid-solid three-phase separation and gas chamber. There is a large amount of anaerobic active sludge at the bottom of the reactor tower. Due to the condensation and suspension of this part of sludge, a suspended layer of sludge in good condition is formed at the bottom of the anaerobic tower. In the suspended state, the metabolism of microorganisms, bacteria and fungi is active. When the waste water enters from the bottom of the anaerobic tower, the organic matter will be fully catabolized by the active sludge components into biogas and produce bubbles. The bubbles continue to merge and float up under the action of water pressure, driving part of the sludge to float up into the three-phase separator on the upper part of the anaerobic tower, and the gas burst from the water surface into the biogas processing unit, where it is collected and derived from the UASB reaction tower. The other part of the floating sludge mixture enters the three-phase separator area, and the solid-liquid-gas mixture in the region is formed into large particle groups through the flocculation and coagulation of chemicals added in the three-phase separator. The density becomes larger and sinks to the bottom to continue to participate in the biochemical reaction of the activated sludge at the bottom. The metabolites of the activated sludge substances will continue to separate the sludge bed from the water outlet with the buoyancy. It is collected outside the tower and then processed into solid waste by a mud press.