Treatment of chemical acrylic fiber wastewater

        The dry-process acrylic fiber technology is a patented technique owned by the American company DuPont. The acrylic fiber products manufactured using this process are highly favored in the market due to their variety and superior quality. However, this method generates a large amount of pollutants and wastewater that is difficult to treat, causing significant harm to the environment. As a result, the world’s major acrylic fiber production facilities have shifted to developing countries.     　Due to the difficulty in treating wastewater from the dry-process acrylic fiber production, it is extremely challenging, with current technology levels, to reduce the COD level in the wastewater to the discharge standard of 100 mg/L at the biochemical treatment stage. Therefore, at the end of 1999, the **Environmental Protection Administration issued a notice titled \"Notice on Publishing the Amendment to the COD Standard for the petrochemical industry in the ‹Comprehensive Wastewater Discharge Standards› (GB8978-1996)\", adjusting the COD discharge standards for dry-process acrylic fiber wastewater as follows: the first-level discharge standard is 160 mg/L, the second-level standard is 250 mg/L, and the third-level standard is 500 mg/L. 　　The treatment of acrylic wastewater has drawn the attention of many environmental protection professionals in China. This paper summarizes the current research status on acrylic wastewater, providing feasible solutions and a basis for the operation of wastewater treatment plants for this type of waste. 　　Generation and Characteristics of Dry-process Acrylic Fiber Wastewater Acrylic fiber is produced using a two-step dry-spinning process, and the wastewater associated with this production comes from various stages of the manufacturing process. Due to the use of raw materials such as dimethylformamide (DMF), acrylonitrile (AN), EDTA, and nonylphenol polyethoxylate in this process, as well as the formation of polyacrylonitrile with different molecular weights during the polymerization reaction, the main pollutants present in acrylic fiber wastewater are sulfates, AN, DMF, EDTA, sodium cyanosulfonate, organic amines, oils, and polyacrylonitrile oligomers. 　　Based on the pollutants present in acrylic fiber wastewater, it can be summarized that such wastewater has the following four characteristics: First, more than 20 different raw materials are used in the production process, and during the polymerization reaction, polymers with various molecular weights as well as by-products are generated; as a result, the wastewater contains a large number of pollutants, including high-molecular-weight polymers that are difficult to biodegrade and to settle naturally ； Secondly, sulfuric acid is added during the production process, and the reaction byproduct, sodium propionitrile sulfonate, undergoes anaerobic hydrolysis to produce sulfate ions; as a result, high concentrations of sulfates also become the main pollutants in the wastewater ； Third, the wastewater contains organic amines and ammonia nitrogen, which requires the system to have the capability to remove ammonia nitrogen ； Fourth, the wastewater contains 100–150 ppm of EDTA and 50–70 ppm of nonylphenol polyethoxylate; both of these substances have long been considered difficult to biodegrade, which directly affects the achievement of the required discharge standards for acrylic fiber wastewater treatment. 　　Current wastewater treatment processes in acrylic fiber factories and existing problems At present, there are five dry-process acrylic fiber production facilities of this type across the country, namely the acrylic fiber factory of Fushun Petrochemical Company in Liaoning, Zhejiang Jinyong Acrylic Fiber Factory, Qinhuangdao Acrylic Fiber Factory in Hebei, Maoming Acrylic Fiber Factory in Guangdong, and the acrylic fiber factory of Shandong Qilu Petrochemical Company. The wastewater treatment systems of these five acrylic fiber factories all employ an anaerobic-aerobic-biological activated carbon treatment process, and all of them exhibit varying degrees of non-compliance with the required standards. 　　The main problem restricting the normal operation of wastewater treatment plants is: dry powder impact. Dry powder is a polymer, oligomer, or mixture of monomers; its molecules are large and difficult to be degraded by microorganisms. Moreover, these oligomers have strong adhesive properties that cover the soft fillers in the anaerobic and aerobic tanks, thereby damaging the microbial membrane and causing a sharp decline in the efficiency of wastewater treatment plants. 　　The adverse effects of sulfate on anaerobes. The competition for substrate between sulfate-reducing bacteria and methanogens reduces the microorganisms’ ability to degrade organic matter, thereby posing a challenge to anaerobic treatment. 　　The issue of sludge return. The wastewater treatment plant was not designed with ammonia nitrogen issues in mind; by returning the sludge from the secondary sedimentation tank to the anaerobic tank, it became impossible to ensure an adequate retention time for the sludge in the aerobic tank, resulting in the system losing its ability to remove ammonia nitrogen. 　　Separation of clean and wastewater is not considered. Domestic wastewater has good biodegradability; upon entering the anaerobic tank, it increases the wastewater load in that tank and, at the same time, reduces the ability of bacteria to degrade substances that are difficult to biodegrade. 　　Current Research Status on the Treatment of Dry-process Acrylic Waste Water Dry-process acrylic waste water, due to its presence of biodegradable substances and high concentrations of sulfates, has become a major challenge in environmental protection efforts. A domestic research institute conducted four years of research on acrylic fiber wastewater, using three different treatment processes: SBR, the conventional activated sludge method, and biological contact oxidation. At partial load, the COD level could be reduced to 280 mg/L, while at full load it could be lowered to around 400 mg/L. It was concluded that this wastewater contains substances that are not biodegradable and cannot be accumulated, hence it is impossible to determine a precise value. 　　In 1997, the Qilu Petrochemical Research Institute conducted biochemical experiments as well as various in-depth treatment tests using six different combinations of anaerobic, anoxic, and aerobic processes. Among these six processes, the anaerobic-aerobic biological treatment process proved to be the most effective, with the COD level of the treated wastewater ranging from 280 to 320 mg/L. It was concluded that dry acrylic fiber wastewater indeed contains substances that are difficult to biodegrade; such substances are mainly EDTA and organic sulfonates. Therefore, it is necessary to enhance pre-treatment steps in order to improve the efficiency of the biochemical treatment system. Some scholars have conducted experimental studies on the pretreatment of acrylic fiber production wastewater using coagulation, air flotation, ozone oxidation, and ultrafiltration, and have reached the following main conclusions: For the coagulation and sedimentation process, PAC and CP-937 are the best flocculants; the optimal dosage of PAC is 60–100 mg/L, while that of CP-937 is 1 mg/L. Under these conditions, the COD removal rate ranges from 10% to 20%, and the turbidity of the treated water is below 10 mg/L. 　　The optimal dosage of PAC in the pressure dissolved air flotation process is 20–50 mg/L, while the dosage of CP-937 is 1 mg/L. The COD removal rate ranges from 10% to 35%, and the turbidity of the effluent is below 10 mg/L. 　　   Ozone oxidation pretreatment: at ozone concentrations of 0.87 g/L, 1.73 g/L, and 2.6 g/L, the COD removal rates for acrylic fiber process wastewater were 2.12%, 3.13%, and 4.94% respectively. In terms of removal efficiency, ozone oxidation does not achieve a high level of COD reduction in acrylic fiber wastewater. The ultrafiltration pretreatment experiment was carried out using an ultrafiltration device, and the test results showed that the COD removal rate of ultrafiltration for acrylic fiber production wastewater was 9.9%, indicating low efficiency. 　　    Based on the results of the pretreatment studies, a coagulation-two-phase anaerobic-anoxic-aerobic process was determined. The test results showed that the COD of the effluent ranged from 220 to 260 mg/L, while the BOD5 ranged from 10 to 15 mg/L. 　　For acrylic wastewater containing large molecular, biodegradable substances, with a COD concentration of 1500–2000 mg/L, anaerobic biological treatment is theoretically the appropriate approach. However, in anaerobic processes, acrylic wastewater contains 300–1200 mg/L of sulfates, and due to the intermittent nature of production, the sulfate concentration in this wastewater fluctuates significantly, which prevents the anaerobic reactor from operating properly and stably. The use of two-phase anaerobic treatment can effectively mitigate the adverse effects of sulfates on anaerobic processes. 　　Due to the large fluctuations in the quality of acrylic wastewater and the presence of biodegradable substances, the secondary treatment employs an AB process (with Phase B using a two-phase anaerobic-anoxic-aerobic process). Section A consists of an aeration adsorption tank and a sedimentation tank. The wastewater enters section A, where the suspended solids and colloids in the wastewater, together with the backflow pollutants, form a suspension-microorganism complex. Flocculation and adsorption occur between these components. The activated sludge in this section has a strong adsorption capacity; the refractory organic substances in the wastewater, as well as plant nutrients such as nitrogen and phosphorus, are adsorbed by the sludge and are subsequently removed through the disposal of excess sludge. This segment possesses a high capacity to resist impact loads, as well as the ability to buffer against the effects of pH and toxic substances. The more thorough removal of suspended solids and colloidal organic matter in Section A results in an **increase** in the amount of COD removed through abiotic degradation throughout the process, thereby reducing operating and investment costs. 　　The test methods and results for the air flotation-AB process show that the COD concentration in the effluent is 150–180 mg/L. Ammonia nitrogen is undetectable in the effluent from the biochemical system, and the nitrate nitrogen concentration is less than 50 mg/L. 　　Current research findings indicate that there are biodegradably difficult substances in acrylic wastewater; the use of the air flotation-AB process can enable the treatment of such wastewater to meet the **first-class industry discharge standards. This post was last edited by johncom on 2009-2-18 10:05]

“Current research findings indicate that there are biodegradably difficult substances in acrylic wastewater; the use of the air flotation-AB process can enable the treatment of such wastewater to meet the **first-class industry discharge standards. ” The difficulty in treating acrylic wastewater lies in the presence of oligomers, which make biochemical degradation difficult. Air flotation is merely a pre-treatment method used to remove suspended solids and oil; it does not significantly help improve the biodegradability of the wastewater, and thus it is likely unable to meet the required discharge standards

For acrylic wastewater, specialized microorganisms have been developed abroad for its degradation, offering greater specificity compared to the biochemical methods currently in use. The United States has precedents for such applications, while our country does not yet.

For using specialized engineered bacteria to treat acrylic fiber wastewater, industrial application is not very feasible. Firstly, the quality of chemical wastewater varies greatly, and such engineered bacteria have poor resistance to such fluctuations. Secondly, there are many issues related to the cultivation and maintenance of these specialized engineered bacteria

In my opinion, it’s mainly the ammonia nitrogen issue. COD can be reduced to below 150 through physical and chemical methods after biochemical treatment. Furthermore, wastewater has poor biodegradability; the MBBR media I saw in Liaoning were all bare, so it is necessary to choose the media carefully.

Using a mixture of acrylonitrile and vinyl acetate as the main raw materials, a polymerization reaction takes place in a polymerization reactor under the action of prepared oxidants, reducers, water, etc., to produce a polyacrylonitrile polymer slurry. The filtrate generated during the washing and dewatering processes of this slurry is considered polymerization wastewater. The pre-treated polymerized wastewater, when mixed with the spinning and recycling wastewater (containing trace sodium hydrosulfide at ≤80 mg/L), becomes acrylic fiber wastewater. Following preliminary laboratory tests, evaporation and concentration were carried out under a vacuum level of -0.068/Mpa; the COD value of the condensed liquid was 109 mg/L, with a pH of 7. It is colorless and odorless. After evaporation and concentration using MVR, the amount of mother liquor remaining is small; it is a light yellow turbid liquid, which facilitates further incineration. Processing cost: Power consumption for evaporating each ton of water using the entire set of equipment is 35 kwh/t. If you have such wastewater, please contact me at TEL: 13651399966

Hello, the original poster. I have a question: where can I find the COD requirements for the wastewater entering different processes in acrylic fiber factories? Do you know this information? Such as polymerization washers and dehydrators, spinning setting machines and drawing machines, wastewater treatment towers for recycling, etc. I’m currently working on a report related to this area and hope my assistance can be useful. Thank you!