In recent years, with the rapid development of China's glass fiber industry, environmental pollution problems have become increasingly serious.
The organic wastewater discharged from the production of glass fiber will pollute the river water body and destroy the water source. China is a developing country with a large population, relatively insufficient water resources and fragile ecology. The intensification of water pollution and the degeneration of urban water ecology have become one of the main factors affecting China's sustainable development. Most of China's fiberglass plants have gradually treated the sewage they produced to varying degrees. It is imperative to completely solve the pollution problem of glass fiber wastewater, and it is imperative.
In some developed countries abroad, the treatment of glass fiber wastewater has been carried out relatively early. For example, the glass fiber plants in the United States, Britain, Germany and Japan have completely carried out sewage treatment and formed complete technology and equipment. Since the 1970s, China has also explored the development and introduction of glass fiber wastewater treatment processes, so it is completely feasible to control it.
1. Analysis of water quality of glass fiber drawing wastewater
Drawing wastewater is an organic wastewater whose properties are related to the type of infiltrant contained. Generally, sizing agents can be classified into three major categories: starch type, reinforced type, and paraffin type. The chemical composition of these three types of sizing agents varies greatly. Even for the same type of sizing agent, the formulation of chemical composition is quite different due to the different uses of the product. The chemical composition of various types of sizing agents is synthesized. The components of drawing wastewater are mainly lipids, emulsifiers, water-soluble organic substances, toxic substances, a small amount of glass fiber and residues. The above types of substances are 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 major pollutants in paraffin-type sizing wastewater.
2. Biochemical characteristics of glass fiber wastewater
From the above water quality analysis, it can be seen that the glass fiber drawing wastewater is an organic wastewater, but the characteristics exhibited by the sizing agent are different. Generally, the biodegradability of glass fiber organic wastewater can be judged by the BOD5/CODcr value.
3. The main treatment process of glass fiber wastewater
The process that we use the most is still the physical chemistry + biological treatment + physical processing process, commonly known as "three-step".
The wastewater treatment capacity is 10 tons/dayÂ·ton yarn to 13 tons/dayÂ·ton yarn. Some companies are 2 tons / day Â· tons of yarn ~ 5 tons / day Â· tons of yarn.
From the water quality treatment indicators, BOD5 and CODcr are the main treatment indicators. In addition, since the wastewater is emulsified, the transparency is low and the appearance is milky white. Therefore, the color and turbidity of the wastewater are also the objects to be treated.
The whole process can be divided into three segments in terms of performance: pre-processing, secondary processing, and tertiary processing.
The sewage intercepts the larger inorganic substances (such as waste glass fiber, residue, etc.) through the grille, enters the regulating tank, and is metered by the helium flow meter to enter the reaction tank. Alkali aluminum chloride is added to the reaction tank to break the wastewater, and NaOH is added to adjust the pH between 6.8 and 7.4. After the wastewater is demulsified, fine flocs are formed and then enter the flocculation tank. The high-molecular flocculant is added to the flocculation tank to form a solid floc in the solid organic matter in the wastewater, and is separated into the first sedimentation tank for precipitation.
After pretreatment by chemical flocculation, most of the solid organic matter is separated. The supernatant of the sedimentation tank enters the biochemical treatment system to further remove soluble organic matter from the water.
First enter the first aeration tank. The first and second aeration tanks are connected in series, using biological contact oxidation method and blast aeration. N and P nutrients are added to the aeration tank. After aerobic aeration treatment, most of the soluble organic matter is biodegraded and removed, and then enters the second sedimentation tank to separate the activated sludge. The supernatant enters the second flocculation tank, and depending on the water quality, PAC and PAM are added as appropriate, and the remaining solid organic matter is further removed and then enters the third sedimentation tank, and the mud water is separated again. The supernatant enters the treatment tank, and then passes through the sand filter treatment to the reuse pool, and most of it is reused, and a small portion is discharged.
The sludge in the first sedimentation tank is mainly chemical sludge, and a part of the activated sludge in the second sedimentation tank is returned to the first aeration tank, and the remaining part is pumped to the sludge concentration tank together with the chemical sludge of the first sedimentation tank. Then, to the sludge tank, and then dewatered by the sludge tank pump to the dewatering machine, the bag is shipped out and landfilled.
After this whole process, the BOD5 removal rate is about 80%, and the external drainage can reach the national first or second level standard.
4. Technical and economic analysis
The reference water treatment capacity is 2000 m3/day, and the CODcr concentration is 1500 mg/L, that is, the organic matter treated per day is 3000 kg. The operating costs are only analyzed for electricity and pharmacy fees, excluding depreciation and labor.
Comprehensive chemical flocculation tank sedimentation, biochemical, and other auxiliary equipment electricity costs, the total cost per ton of water treatment is 1.69 yuan / m3.
The influent CODcr is 1500mg/L on average, and the total CODcr removal rate is 97%. The CODcr removed per day is 2910 kg/day, 1047.6 tons per year, and the annual CODcr is 32.4 tons.
5. Optimize operating conditions and engineering design parameters
As mentioned above, glass fiber drawing wastewater is a highly emulsified organic wastewater. The chemical composition is mainly composed of polyvinyl acetate emulsion, and some organic coupling agents and emulsifiers. The organic solid particles in the wastewater are fine, below 1 micron, and most of the organic solids can be removed by chemical demulsification flocculation. At the same time, due to the large area of â€‹â€‹the floc formed by flocculation, a certain amount of soluble organic molecules can be adsorbed.
Therefore, chemical flocculation is an important unit operation for such organic wastewater treatment.
The chemicals to be added to this process are basic aluminum chloride (PAC) and polyacrylamide (PAM). PAC is both an inorganic flocculant and a demulsification effect. When a certain amount of PAC is added to the wastewater, the flocculent solid visible to the naked eye appears and the water is clarified. Adding PAM is to make the organic solid in the demulsified wastewater condense into a large floc and accelerate the precipitation. The dosage has a direct effect on the floc effect. Mastering the optimal dosage can not only improve processing but also reduce unnecessary waste, which 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, its purification function can meet the national emission standards, but the effluent will still contain a considerable amount of pollutants. This part of the water will still affect the water body, and it is not suitable for reuse. Further advanced processing. The objects and targets for deep treatment are: removing the suspended solids (including activated sludge particles) in the treated water: decolorizing and deodorizing, further clarifying the water; further reducing BOD5, CODcr and other indicators to further stabilize the water; disinfection, Remove toxic and hazardous substances from the water.
After deep treatment, the water can discharge any water body including high economic value water body and slow-flowing water body, supplement the surface water source; reuse it for farmland irrigation, municipal miscellaneous use, such as watering urban green space, washing streets, vehicles, landscape Water, etc.; can also be used to flush toilets, and even used to make softened water and pure water.
Water is the only irreplaceable and the only renewable resource in nature. The recycling of wastewater is the most economical 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 industrial structure and technical structure. With the rapid development of the drawing technology of the pool kiln, the research and development of new sewage treatment processes, technologies and pharmaceuticals generated by it are also increasing, in line with China. The process and technology of reclaimed water treatment with simple and practical national conditions, high efficiency and reliability, and low operating cost will continue to be the development trend.
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