In recent years, with the rapid development of China's glass fiber industry, environmental pollution has become increasingly serious.
The organic wastewater discharged from glass fiber production will pollute river water bodies and destroy water sources. China is a developing country with a large population, relatively insufficient water resources, and ecologically fragile. The intensified water pollution and the deteriorating water ecology of cities and towns have become one of the major factors affecting China's sustainable development. Most of the fiberglass factories in China have gradually improved their sewage treatment to varying degrees. It is imperative to solve the pollution problem of glass fiber wastewater thoroughly.
Some developed countries in foreign countries have conducted fiberglass wastewater treatment earlier. For example, fiberglass plants in the United States, the United Kingdom, Germany, and Japan have completely conducted wastewater treatment and formed complete technology and equipment. Domestically, from the 1970s onwards, R&D and introduction of fiberglass wastewater treatment processes have been explored, so its governance is entirely feasible.
1. Water quality analysis of glass fiber drawing wastewater
Drawing wastewater is an organic waste water whose properties are related to the type of sizing agent contained. Generally, infiltrants can be divided into three major categories: starch type, reinforced type, and paraffin type. The chemical composition of these three types of infiltrants differ greatly. Even the same type of infiltrant has very different chemical composition formulas due to different uses of the products. Comprehensive chemical composition of various infiltration formulations, drawing wastewater components are mainly lipids, emulsifiers, water-soluble organic compounds, toxic substances, a small amount of glass fiber and residue. The above types of substances are the pollutants of glass fiber drawing wastewater, in which solid organic matter and water-soluble organic matter are the main pollutants. Formaldehyde is also one of the main pollutants in paraffin-infiltrating wastewater.
2. Biochemical characteristics of glass fiber wastewater
From the above analysis of water quality, it can be known that glass fiber drawing wastewater is an organic wastewater, but due to the different types of sizing agents, the characteristics exhibited vary greatly. In general, the biodegradability of glass fiber organic wastewater can be determined by the BOD5/CODcr value.
3. Main treatment process of glass fiber waste water
We have adopted the most widely used physical chemistry + biological treatment + physical treatment process, commonly known as "three steps."
The wastewater treatment capacity is 10 tons/day·tonne ~13 tons/day·tonne. Some individual companies are 2 ton/day ton yarns to 5 ton/day ton yarns.
From the indicators of water quality treatment, BOD5 and CODcr are the main treatment indicators. In addition, since the waste water is emulsified, the transparency is low and the appearance is milky white. Therefore, the color and turbidity of the waste water are also the objects to be treated.
The entire process can be divided into three stages from performance: pretreatment, secondary treatment, and tertiary treatment.
Wastewater passes through the grid to intercept large inorganic substances (such as waste glass fiber, residues, etc.) and then enters a regulating tank, which is metered by a helium-type flowmeter and enters the reaction tank. Alkaline aluminum chloride was added to the reaction tank to break the emulsion, and NaOH was added to adjust the pH between 6.8 and 7.4. After the wastewater has been broken, fine floc forms and enters the flocculation tank. Polymer flocculants are added in the flocculation tank to form solid flocks in the wastewater, and enter the first sedimentation tank for precipitation and separation.
After pretreatment by chemical flocculation, most of the solid organic matter was separated. The supernatant of the sedimentation tank enters the biochemical treatment system to further remove the soluble organic matter in the water.
First enter the first aeration tank. The first and second aeration tanks are connected in series and biological contact oxidation is used to blow aeration. The N and P nutrients were added in the aeration tank. After aerobic aeration, most of the soluble organics were biodegraded and removed, and then entered the second sedimentation tank to separate the activated sludge. The supernatant enters the second flocculation tank. Depending on the water quality, PAC and PAM may be added as appropriate, and the remaining solid organic matter may be further removed to enter the third sedimentation tank, and the sludge and water separation may be performed again. The supernatant fluid enters the treatment tank and is then treated with sand filtration to the reuse pool. Most of them are reused and discharged in small portions.
The sludge in the first sedimentation tank is mainly chemical sludge. Part of the activated sludge in the second sedimentation tank is returned to the first aeration tank. The remaining part is pumped to the sludge concentration tank together with the chemical sludge in the first sedimentation tank. , Then to the sludge pool, then pumped from the sludge pool to the dewatering machine for dehydration, and bags are shipped for landfill.
After this complete set of processing, the BOD5 removal rate is about 80%, and the external drainage can reach the national first-level or second-level standards.
4. Technical and economic analysis
The baseline water treatment capacity is 2000m3/day, and the CODcr concentration is 1500mg/L, that is, 3,000kg of organic matter is processed per day. The operating expenses only analyze the electricity and pharmaceutical expenses, excluding depreciation and labor costs.
Comprehensive chemical flocculation tank sedimentation, biochemical, and other auxiliary power costs, the total cost of processing per ton of water is 1.69 yuan/m3.
The influent CODcr is calculated on the average 1500 mg/L, and the total CODcr removal rate is calculated as 97%. The CODcr removed is 2,910 kg/day per day, 1047.6 tons per year, and the annual CODcr is 32.4 tons.
5. Optimized operating conditions and engineering design parameters
As previously mentioned, glass fiber drawing waste water is a highly emulsified organic waste water. The chemical composition is mainly based on polyvinyl acetate emulsion, and there are also some organic coupling agents and emulsifiers. The organic solid particles in the waste water are fine. Below 1 micron, most of the organic solids can be removed by chemical demulsification and flocculation. At the same time, because the flocculate formed by flocculation has a large area, it can still adsorb a part of soluble organic molecules.
Therefore, chemical flocculation is an important unit operation for such organic wastewater treatment.
The chemicals added to this treatment process are basic aluminum chloride (PAC) and polyacrylamide (PAM). PAC is both an inorganic flocculant and a demulsifier. Adding a certain amount of PAC to the waste water will produce a visible flocculent solid in the water and clarify the water. Dosing PAM is to make the organic solids in the de-emulsified wastewater condense into large flocs and accelerate the precipitation effect. The dosage has a direct effect on the floe effect. Grasping the best dosage can not only improve the treatment effect but also reduce unnecessary waste. It is an essential parameter for operation and design.
6. Advanced Treatment and Reuse of Glass Fiber Wastewater
From the perspective of the tertiary treatment process, the purification function can meet the national emission standards, but the effluent still contains a considerable amount of pollutants. This part of the water will still affect the water and it is even more unsuitable for reuse. Further in-depth processing. The objects and targets of advanced treatment are: removing suspended matters (including activated sludge particles) remaining in the treated water: decolorization and deodorization to further clarify the water; further reduce BOD5, CODcr and other indicators to further stabilize the water; disinfection and sterilization, Remove toxic and harmful substances from water.
The in-depth treated water can discharge any water body including high economic value water bodies and gentle flowing water, and supplement the surface water source; it can be used for irrigation of farmland, municipal miscellaneous use, such as watering urban green areas, washing streets, vehicles, and landscapes. Water, etc.; can also be used to flush toilets and even used to make demineralized water and pure water.
Water is the only irreplaceable nature in nature and the only resource that can be regenerated. Wastewater recycling is the most cost-effective water-saving measure and the most effective way to control water pollution.
At present, China's glass fiber industry is facing an arduous adjustment of its industrial structure and technical structure. With the rapid development of the drawing technology of the kiln and kilns, new research and development of sewage treatment processes, technologies, and pharmaceuticals are also increasing. The simple and practical, highly efficient, reliable, and low-cost water reuse deep treatment processes and technologies will continue to be the trend of development.
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