Research Progress Of Dry Acrylic Fiber Wastewater Treatment Technology

world

1 physicochemical treatment of dry spun acrylic fiber wastewater

Dry spun acrylic fiber

1.1 coagulation

According to the characteristics of suspended solids and the nature of charge in dry acrylic fiber wastewater, coagulation has been widely used in pretreatment of acrylic fiber wastewater.

According to the test results, [2] showed that the mixture of inorganic and organic coagulants had better effect than single addition. After adding Magnesium Sulfate, the removal rate of chemical oxygen demand (COD) was improved. The best combination was polyaluminum ferric chloride (PFS) + cationic polyacrylamide (PAM) +MgSO4, and the removal rate of COD was 32.5%.

Other scholars, [3], will combine coagulation with advanced "over potential three dimensional electrolysis technology" and "high efficiency and complex microbial strain" to form a "coagulation overpotential three dimensional electrolysis anaerobic aerobic process" process to treat dry acrylic fiber wastewater. The results showed that COD decreased from 1585mg/L to 95mg/L, NH3-N (ammonia nitrogen) decreased from 65mg/L to 2mg/L, and the biodegradability of treated wastewater increased to 0.4.

But the combined process is only a laboratory study.

In addition to using PFS, PAM and other chemicals to remove suspended solids, and also using lime coagulation and bentonite adsorption capacity to treat acrylic fiber wastewater, [4] was studied. The results showed that the highest removal rate of COD was 34% after the treatment of 1%~5% lime and bentonite, and the effect of this method on subsequent biochemical treatment was also not investigated.

1.2 ozone oxidation

Some researchers also compared the oxidation effects of ozone (O3), ozone activated carbon and ozone manganese dioxide in 3 ways. The results showed that ozone and manganese dioxide had the highest removal rate of organic matter in wastewater, and the removal of COD was 40% after treatment of 20min. The removal rate of [5] was the highest.

The experimental data show that ozonation is not effective in improving the biodegradability of wastewater.

The results of foreign studies also show that although the oxidation capacity of ozone is stronger than that of chlorine, it has no effect on complex compounds containing CN-. Moreover, catalytic ozonation can produce hydroxyl radicals or other enhanced ozonation methods, although it can improve the treatment effect of wastewater. However, ozone oxidation is difficult to completely mineralized pollutants, and only oxidizes it to intermediate product CNO- for CN-.

1.3 Fenton (Fenton) reagent oxidation method

The oxidation of Fenton reagent is essentially the hydroxyl radical produced by hydrogen peroxide catalyzed by two iron ions.

It has been reported that the organic matter that can not be removed by traditional wastewater treatment technology can also be oxidized by Fenton reagent and effectively remove [6,7], such as desizing wastewater and textile waste water.

In 2006, Xu Zhibing, Kong Xuejun and others used the enhanced Fenton reagent oxidation process to treat acrylic fiber wastewater. The results showed that ultrasonic +Fenton reagent could treat the raw water with COD value of 1432mg/L to COD for 400mg/L, and CN- also greatly reduced.

However, the cost of this method is too high. 1t wastewater needs 30L hydrogen peroxide [8][. Currently, anthraquinone (anthraquinone) is widely used in industry to produce hydrogen peroxide with high cost. Moreover, the ultrasonic water treatment technology is not mature. Therefore, this method has only research value for treating acrylic fiber wastewater.

There are also some researches on Fenton reagent recombination and other technologies in the laboratory research stage [9,10].

If Fenton composite micro electrolysis -UV (UV) catalytic oxidation was used to treat dry spinning acrylic fiber wastewater [11], the COD of treated effluent was less than 500mg/L.

Foreign studies also showed that the Fenton reagent oxidation method alone used to treat CN- was very effective.

M.Sarla[12] has studied the oxidation of CN- wastewater by Fenton reagent. The result also shows that the effect of UV enhanced +Fenton reagent oxidation is much better than that of single Fenton reagent oxidation.

1.4 iron scrap internal electrolysis

Lu Bin and Wei Heping [13] carried out laboratory and field studies on the pretreatment of acrylonitrile wastewater by iron chip internal electrolysis process. The results showed that iron scrap internal electrolysis was suitable for treating acidic high temperature wastewater with pH value of 3~4. After internal electrolysis, the average removal rate of COD was 16% (lower than 27.7% ~ 45% of laboratory value), and the biodegradability of wastewater treated by internal electrolysis was slightly improved.

Wei Shouqiang and Liu Ying [14] further studied the treatment of dry spun acrylic fiber wastewater by iron scrap activated carbon internal electrolysis. The beaker test data showed that iron carbon ratio was 10: 1, pH value 4.5 (that is, keeping the pH value of raw water), 1H and COD were removed 60%. However, the researchers ignored the active carbon as a component of the treatment agent.

There are also some researches on iron chip internal electrolysis combined with other processes, such as [15], such as Fushun acrylic fiber plant, which has been carrying out industrial experiment [16]. However, due to the existence of many problems, it has been discontinued.

Because of the low cost of iron chip internal electrolysis, the technology has been reported abroad in recent years, and has been reported in the application of pesticide wastewater, dyestuff wastewater, textile wastewater and polyester wastewater.

In general, iron chip internal electrolysis is used as a pretreatment method, followed by other biochemical treatment technologies. For example, the iron chip internal electrolysis anaerobic aerobic process can be used to treat COD4000mg/L polyester wastewater to 100mg/L.

As a pretreatment technology for acrylic fiber wastewater, this method is still of great significance.

1.5 membrane method

"Membrane" from laboratory to large-scale industrial applications for only 50 years, domestic research on membrane is currently limited to the application of mature membrane products.

Some scholars used polysulfone ultrafiltration membrane to treat acrylonitrile wastewater (hot stretch wastewater and washing machine wastewater), and used ultrafiltration membrane and reverse osmosis membrane to treat the wastewater from acrylic fiber plant. The results showed that the COD of the hot drawn water after ultrafiltration treatment was greatly reduced, and it could be reused; the washing machine wastewater after ultrafiltration can be directly used as water for washing machine, and the super concentrated liquid was precipitated and recycled to the polyacrylonitrile polymer [17].

However, the adhesion of polyacrylonitrile powder on the surface of ultrafiltration membrane is serious.

Ultrafiltration and reverse osmosis membrane treatment of ultrafiltration water, if there is ultrafiltration membrane pretreatment, a short period of time, reverse osmosis membrane flux unchanged.

Polysulfone ultrafiltration membranes, reverse osmosis membranes and nanofiltration membranes are all organic polymer membranes. The feasibility of applying them to organic wastewater with high suspended solids is still to be investigated.

In addition, the proportion of thermal stretch waste water and washing machine waste water in acrylic fiber plant is relatively small, and the maintenance cost of membrane is high, so its economy needs to be investigated.

Treatment of polyacrylonitrile wastewater by nanofiltration membrane has also been studied by [18]: FT-50 nanofiltration membrane, two stage treatment, effluent COD can be reduced to 83mg/L, turbidity 2NTU, conductivity 50 u s/cm, SS (suspended solids) can not be detected.

Although the treatment can be used for washing water in acrylonitrile production process and achieve the purpose of waste water recycling, the author has not considered the service life of nanofiltration membrane.

Another scholar [19] uses laminated filter + ultrafiltration + reverse osmosis membrane integration technology to treat acrylic washing water. It is found that COD after reverse osmosis treatment is about 60mg/L, and does not change with the influent.

Due to the influence of residual organic solvents on membrane life in organic wastewater, there are few reports on organic film used for organic wastewater treatment. Especially, a large number of suspended solids in acrylic fiber wastewater can quickly cause the concentration polarization of microfiltration ultrafiltration membrane.

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2 biochemical treatment of dry spun acrylic fiber wastewater

Biochemical treatment is an effective way to degrade small organic compounds. In recent years, scholars have made some explorations in the cultivation of highly efficient engineering bacteria, membrane bioreactors and optimization of anaerobic reaction.

2.1 efficient microbial treatment

The effect of single activated sludge treatment on dry spun acrylic fiber wastewater is not good. Therefore, some scholars have enriched and domesticated a highly efficient nitrifying bacteria for dry spinning acrylic fiber wastewater, and tested the dry treated acrylic fiber production wastewater after biochemical treatment. The results show that the bacteria can adapt to the refractory biodegradable substances in dry nitrile production wastewater and effectively remove NH3-N from wastewater.

The start-up period of DO (dissolved oxygen) showed a "high low to high" change. The sludge growth rate in operation period showed a "S" type change. When the influent NH3-N load increased, the NH3-N of water could be maintained below 5mg/L, and the removal rate of NH3-N could always be higher than 96% when the influent COD load increased.

The researchers suggested that the nitrification reaction device should be used at the end of biochemical treatment of dry acrylic fiber wastewater.

However, there are few reports on this direction.

2.2 membrane bioreactor

Membrane bioreactor (MBR) is a biological treatment technology developed in recent years, which is replaced by membrane filtration instead of traditional biochemical treatment in the two sedimentation tank and sand filter.

Some scholars [21] used packing anoxic aerobic membrane bioreactor technology to treat dry acrylic fiber wastewater. The results showed that the effluent quality of MBR treated dry acrylic fiber wastewater was stable, and had strong impact resistance to influent water quality and water volume changes.

However, due to the poor biodegradability and high NH3-N of dry spinning acrylic fiber wastewater, there is a lack of carbon source and alkalinity in the anoxic stage denitrification and aerobic nitrification.

It is also reported that the sequencing batch membrane bioreactor combined with internal electrolysis -Fenton oxidation treatment of dry acrylic fiber wastewater is reported. The results show that the internal electrolysis -Fenton combined process reduces the COD from 1328mg/L to 369mg/L, and the effluent COD can be reduced to 61mg/L after the treatment of the membrane bioreactor ([22]).

The research in this area did not consider economic feasibility, and the related work is also in the laboratory research stage.

2.3 optimization of anaerobic reaction

Anaerobic reaction is suitable for the treatment of high concentration organic wastewater. Some scholars have studied the optimization of single phase and two-phase anaerobic reaction for dry acrylic fiber wastewater.

A scholar [23] investigated the effect of monophasic and two-phase anaerobic treatment on dry acrylic fiber wastewater containing sulfate and refractory biodegradable materials. The results showed that the two-phase anaerobic phase had higher removal rate than single phase anaerobic COD, stable operation and little interference from sulfate radical, and could significantly improve the biodegradability of wastewater.

Another scholar, [24], treated the wastewater after flocculation by single-phase and two-phase anaerobic treatment respectively. The results showed that the removal rate of single-phase anaerobic COD was between 7.5%~35.0% and fluctuated greatly, and the two-phase anaerobic removal rate was between 31.5% and 41%, and the removal rate was relatively stable.

In industrial applications, only the current anaerobic parallel treatment system can be changed to a series connection mode, so that it is convenient to implement.

In order to solve the adverse effects of sulfate radical on anaerobic digestion, a scholar [25] investigated the effects of direct air oxidation and air catalytic oxidation (adding different manganese metal ions) on the removal rate of SO32- in dry spun acrylic fiber wastewater.

The effect of air catalytic oxidation on sulfite is better than that of direct air oxidation. The removal rate of sulfite can reach 90%. Most of the manganese metal ion catalyst is oxidized to manganese dioxide insoluble when it catalyzes, and the insoluble matter is intercepted with the organic suspended matter in the water with the subsequent filtering facilities, which will not affect the subsequent treatment process and effluent index.

In conclusion, the polymers in acrylic fiber wastewater are compounds containing CN-. The biodegradation of cyanide in most literatures indicates that cyanide can be degraded, and this is an environmentally benign pformation process.

For example, in the process of biological treatment of metal cyanide, microbes convert the CN- linked to metal to carbon dioxide and ammonia, while free metal ions are adsorbed by biofilms or precipitated from aqueous solutions.

However, microbes can not use and decompose large molecular substances, so the polymers in acrylic wastewater are not directly degraded.

Only by maximizing the removal of polymers from waste water can the anaerobic aerobic biological activated carbon process combination of dry acrylic fiber production plant play a role.

3 other methods

In recent years, some scholars have explored the microwave method [26] and photocatalytic oxidation of [27]. It is believed that microwave and photocatalytic oxidation can improve the biodegradability of dry spun acrylic fiber wastewater. There are also some patented technologies, [28-31], some of which belong to the pilot study, and some of them are not effective after industrialization.

For example, the sewage treatment process of China Petroleum Fushun Petrochemical Co acrylic fiber plant was pformed from the biological anaerobic (A) - biological aerobic (O) process in 1990 to chemical oxidation (iron carbon internal electrolysis) - coagulation sedimentation - anoxic - Biological fluidization - nitrification - biological carbon treatment, but the operation effect was still poor.

The technology of dry spinning acrylic fiber has seriously polluted the environment. Developed countries have pferred it to developing countries. No matter whether the technology itself is pformed or the treatment of related waste water has not been reported.

DuPont Co, the inventor of the technology, focused on developing functional, environment-friendly and high-tech products after 90s, and withdrew from dry acrylic fiber production. So far, it has not solved the trend of environmental protection.

Like China, other developing countries, such as India, Burma and Russia, are also facing the problem of dry spinning acrylic fiber wastewater treatment. Countries can only reduce emission standards and losses at present.

For example, the new brux POLYMIC plant in Belarus has 3 production processes, including DMF dry method, NaSCN method and modified acrylic fiber three routes. In order to reduce environmental pollution, strictly control material consumption and energy consumption, especially the actual consumption of DMF is only 28kg/t products. The upper part of the machine, such as spinning machine, washing machine and tractor, is equipped with suction hood, and concentrates and scour the air for recycling DMF.

China has revised the discharge standard of dry spun acrylic fiber wastewater to maintain the development of enterprises.

4 Conclusion

As for the problem of dry acrylic fiber wastewater treatment, the developed countries are in a state of stagnation, and the developing countries that use this technology have not yet solved the relevant technology.

We must find new breakthroughs to solve this problem.

The author recommends: first, we need to further analyze the composition characteristics of pollutants in the special waste water and determine the target pollutants; then we will carry out the optimal combination research of various processing technologies and the development of other new technologies; reduce pollutants into the water at the source of production, so as to reduce the difficulty of terminal treatment.