Recently, biochemistry process is the most frequently used method by polyester mills to treat organic matters in polyester production wastewater which include EG, acetaldehyde, 2,2-DIMETHYL-1,3-DIOXOLANE, etc. With the production capacity of global polyester industry increasing With the production capacity of global polyester industry increasing year after year especially in China, and improvements on recycle technology of EG and acetaldehyde, there is a big market margin.
Polyester is an important raw material for chemical fiber industry, which is made of diol or polyol and acetaldehyde. Polyester is an important raw material for the chemical fiber industry, and is a general term for a class of polymer compounds formed by the polymerization of diols or polyols and dibasic acids or polyacids. Polyester can usually be divided into saturated polyester and unsaturated polyester two categories, saturated polyester products mainly include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), etc., and unsaturated polyester products are mainly polyester fiberglass reinforced plastics. At present, the world's polyester fiber enterprises are mainly concentrated in China, the British consulting firm PCI Fibers predicted that the world's top ten polyester fiber producers in 2010, the capacity of the situation, and filament and staple fiber production is also analyzed, specifically as shown in Table 1.
Polyester production wastewater refers to the polyester production of esterification reaction process by-products containing organic wastewater, wastewater COD value is generally in the 10,000 ~ 30,000mg / L between. Wastewater usually contains a small amount of ethylene glycol (EG), acetaldehyde, dimethyl ? 1,3? Dioxolane and other organic substances, according to the polyester plant technology sources and management level of different levels, the content of the above three major organic substances is usually between 0.2% ~ 2.0%.
According to statistics, as of the end of 2009, the global polyester production capacity has reached 58 million tons, only China is more than 25 million t. The world polyester industry is huge, according to theoretical calculations, every production of 1 t PET, its wastewater emissions of 0.187 t, so that the global 58 million tons of polyester wastewater emissions of 1,084.6 million tons of the content of the three main organic matter in the 2.17 million ~ 21.7 million tons, China's 25 million tons of polyester factory wastewater discharge is 467.5 million tons, three kinds of major organic content in 0.935 million ~ 9.35 million tons, it can be seen that the polyester production wastewater emissions are quite large, such as left untreated, discharged into the river will be a serious harm to the receiving body of water and the surrounding environment. On the contrary, if these are considered to be polluted organic matter extracted, waste into treasure, not only reduces the impact on the environment around the polyester plant, but also to increase the profits of the polyester plant. Now briefly introduce the domestic and foreign polyester industrial production of wastewater treatment methods.
1 domestic and foreign polyester esterification wastewater treatment method
1.1 foreign polyester industrial wastewater treatment
Many foreign polyester enterprises are huge, has been built in the largest single-line capacity of 1,800 t/d, a polyester production enterprises in Spain on the production process of the two major wastewater (esterification wastewater and spinning wastewater) using anaerobic intermittent The COD (chemical oxygen demand, generally referred to the potassium dichromate index) removal rate of 90% and 75%; at the same time, the use of laboratory-scale continuous upflow anaerobic sludge bed (UASB) reactor to study the effect of esterification wastewater and 1:1 mixing (v/v) of esterification and spinning wastewater treatment. The methanogenic activity of the UASB reactor was 0.71 g COD per gram of volatile solids (VSS) per day, and the initial COD was 2 900, 6 750, and 17 870 mg/L. The results showed that the organic loading of COD > 12 g/(L?d) (0.3 g COD per gram of VSS per day), and the removal of COD was stable at more than 90%. Moreover, the commissioning period is very short and the recovery is fast.
Turkey, a polyester production enterprises *** produced glass polyester resin (COD 180 g / L, pH = 2.3), unsaturated polyester (COD 210 g / L, pH = 2.3) and saturated polyester (COD 230 g / L, pH = 2.3) three esterification wastewater. S. Meric et al. first distillation process will be used to reduce the COD of raw water from 200 g / L to 40%. S. Meric et al. first reduced the COD of the raw water from 200 g/L to 40 g/L by distillation process, and then compared the treatment effect of ordinary activated sludge and Fenton oxidation method. The results showed that: the biological treatment of distilled polyester wastewater and domestic sewage mixture, diluted with a longer retention time (10 days), lower sludge load (each gram of VSS produces 0.1 g of COD) in order to achieve 70% COD removal; while the use of Fenton oxidation treatment of wastewater in a shorter period of time (1 day), COD removal can reach 66%; the use of chemical oxidation method COD can be reduced by 56% by using chemical oxidation method to treat wastewater after biological treatment. However, chemical oxidation is expensive and can be used for pre-treatment of wastewater, deep treatment of wastewater or emergency treatment after biological treatment.
Poo Jin Yong, Korea, the use of ceramic catalytic oxidation + activated sludge method of treatment of esterification wastewater (COD 10 g / L, pH = 12 ~ 14), in order to reduce the influent COD, BOD (Biochemical Oxygen Demand (BOD), generally refers to the 5-day BOD) load, esterification of wastewater and traditional printing and dyeing wastewater were mixed with 1:6, 1:12 (mass ratio). Then the ceramic catalyst is added to the sodium hypochlorite or calcium hypochlorite solution to formulate the oxidized water, and then oxidize the mixed water samples with it, and finally treat them with aerobic activated sludge method.
Toray Industries, Ltd. of Japan added alkaline compounds to polyester production wastewater to convert acetaldehyde in the wastewater to other compounds, thus reducing the acetaldehyde content in the wastewater.
1.2 domestic polyester industrial wastewater treatment
China's polyester production in the introduction of foreign polyester plant technology on the basis of the gradual development of localized technology is becoming more mature. Enterprise device size has reached a maximum of 1 200 t / d, and 600, 900 t / d scale polyester device countless.
At present, the domestic polyester esterification wastewater treatment in a more representative enterprises, including Yizheng Chemical Fiber Corporation (referred to as "Yizheng Chemical Fiber"), Liaoyang Petrochemical Company (referred to as "Liaoyang Petrochemical"), Shanghai Petrochemical Corporation (referred to as "Shanghai Petrochemical"), Shanghai Petrochemical Corporation (referred to as "Shanghai Petrochemical"), Shanghai Petrochemical Corporation (referred to as "Shanghai Petrochemical"), Shanghai Petroleum & Chemical Industry Co. ("Shanghai Petrochemical"), Tianjin Petrochemical Company ("Tianjin Petrochemical"), Luoyang Petrochemical Engineering Company ("Luoyang Petrochemical"), etc. As some of the engineers and technicians of the above five enterprises have lost their skills in the market economy, they have been forced to leave the company. Because some engineers and technicians of the above five enterprises have moved to most of the domestic polyester enterprises in the market economy, the wastewater treatment technologies of other enterprises are basically included in the technologies of these companies.
1.2.1 Yizheng Chemical Fiber
Yizheng Chemical Fiber production wastewater discharged in the glycol and PTA and other organic substances, the organic load varies greatly. The company adopts "composite biological aeration" process to treat the production wastewater. The process in the influent COD load is relatively low, ordinary activated sludge and composite biological aeration method of organic matter in wastewater removal effect (up to 80% of the left stone) are relatively good, and the difference is not significant; in the influent COD is relatively high, composite bioreactor biochemical system biomass concentration increased by more than 50 percent, HRT (hydraulic retention time) for 8 h, the age of the mud is 5 days, COD, ammonia nitrogen removal rate, respectively. and ammonia nitrogen were increased by 20% and 9.6%, respectively, and the process had a better control of sludge expansion.
1.2.2 Liaoyang Petrochemical
Liaoyang Petrochemical polyester plant adopts the "Flotation ? Biofiltration Ozone catalytic oxidation (OCOR) ? (FBOF) process for deep treatment of polyester wastewater effluent from the secondary sedimentation tank.
The results show that the effluent from the biochemical secondary sedimentation tank can be reduced to 13 mg/L COD, 0.4 mg/L turbidity, 0.27 mg/L oil content, 0.03 mg/L total iron ions after treatment with the pilot plant of FBOF, which fully meets the requirements of the circulating cooling water. In addition, Liaoyang Petrochemical also in 0.3 MPa pressure on polyester plant polyester production of esterification wastewater vaporization treatment, vaporization of waste gas sent to the hot coal furnace incineration, after treatment of wastewater sent to the olefin plant sewage treatment station.
1.2.3 Shanghai Petrochemical
Shanghai Petrochemical Plant uses activated sludge process to treat polyester production wastewater. The shortcomings of this process are sensitive to changes in water quality and quantity, not resistant to the impact of organic loads, large sludge production and high energy consumption, residual sludge production, increasing the investment in sludge treatment equipment and operating costs. Later, it was changed to biological contact oxidation method. Using ordinary activated sludge or biological contact oxidation method, COD removal rate can generally reach 82% ~ 92%. However, if the requirements of the effluent up to the national level discharge standards (COD
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