In today’s rapidly developing economy and increasingly progressive society, pollution has become a global concern and solving environmental pollution is an issue that must be considered in today’s society. In recent years, the economy of each region has its own characteristics, and the dye industry has developed rapidly, with a variety of dyestuffs and a growing number of dyestuffs.
Textile wastewater exhibits the following characteristics:
- Complex and high concentration of organic components in wastewater: The dye production process involves various unit operations, such as digestion, reduction, oxidation, and coupling, leading to the generation of numerous by-products and raw materials, including oil agents, auxiliaries, and dye slurry. Consequently, the composition of wastewater becomes complex, containing high levels of salts and organic matter. The COD (Chemical Oxygen Demand) value of high-concentration dye wastewater can reach up to 105mg/L.
- High volume of wastewater, high chromaticity, and high toxicity: As the solvent in the dyeing and finishing industry is water, each process, including pretreatment, dyeing, and washing, results in the discharge of substantial volumes of wastewater. The wastewater contains both organic and inorganic toxic substances, which contribute to its high toxicity. Additionally, the presence of numerous color-forming groups leads to a relatively high chromaticity.
- Intermittent and changeable wastewater discharge: The dyeing and finishing industry operates intermittently, producing multiple products throughout the year. Consequently, the discharge of production wastewater also occurs intermittently, resulting in fluctuations in both water quality and quantity. This variability poses challenges in selecting an appropriate wastewater treatment process and managing and maintaining the treatment system.
- Difficult wastewater treatment: Due to the wide range of dyestuff varieties produced, which tend to have anti-photolytic, anti-oxidation, and anti-bio-oxidation properties, dyeing wastewater and similar effluents exhibit higher concentrations, increased chromaticity, and challenging biochemical properties. Conventional treatment methods such as neutralization, coagulation, and activated carbon adsorption are often employed but may be expensive, ineffective, and insufficient in meeting national emission standards. Therefore, dye wastewater represents a particularly challenging category of industrial wastewater to treat.
Xinmi City is 40 kilometers from the provincial capital. The total area is 1001 square kilometers, with 13 townships and 4 local governmental areas, with an average temperature of 14.3°C, the average annual pressure is 1005.0~1023.5hPa, the average annual precipitation is 635.6 mm
In this project, Boromond built a wastewater treatment system to treat wastewater from a textile factory in Xinmi City, and the wastewater was mainly dyeing wastewater, which was a complex organic wastewater with organic pollution.
According to the requirements of environmental protection department, discharge water quality from the manufacturing facility should reach the standard of discharge as stipulated in the DB32/670-2004.
4 Principles of Selecting Textile Wastewater Treatment Process
The selection of a suitable wastewater treatment process for textile wastewater is crucial in ensuring compliance with relevant effluent quality standards. It directly impacts the stability of wastewater treatment plant operations, management and maintenance efficiency, and then comprehensive operational and investment costs. The following principles guide the careful selection of a treatment process in the design of wastewater treatment systems:
- Considering the characteristics of textile and dyeing wastewater, opt for a suitable and well-established process route that is technically reliable, ensuring that the treated effluent meets the required discharge standards. Simplicity in structure, ease of operation, and convenient maintenance and management should also be considered.
- In designing the wastewater treatment system, take into account the available urban land, aiming to minimize the required floor space, reduce construction costs, and optimize daily operational expenses.
- Plan the layout and engineering design to achieve a reasonable and smooth arrangement, adhering to engineering construction standards, and minimizing energy consumption and treatment costs.
- Utilize advanced, mature, and easily manageable design solutions from the wastewater treatment industry, facilitating efficient and stable operation, minimizing energy consumption, ensuring reasonable costs, and enabling convenient management and maintenance.
Usually, textile wastewater is treated using various methods, including physical, chemical, and biological methods. Among these methods, the physical method is less effective, while the chemical method requires a large dose of chemicals but offers space-saving advantages. The biological method is a commonly employed treatment approach.
Pretreatment Due to the intermittent nature of textile wastewater, its high chromaticity, serious pollution, and complex composition, pretreatment is necessary to ensure optimal treatment results.
- Regulation (homogenization of water quality and quantity) Textile wastewater has intermittent water flow, so a regulating pool is used to balance the water quantity. The pool is typically equipped with mechanical stirring to prevent debris from settling at the bottom. The hydraulic retention time is generally set at 8 hours.
- Neutralization A conditioning tank is used to balance the acidity and alkalinity of the wastewater. Since the pH of textile wastewater is often high, a neutralization tank is employed to adjust the pH to meet the process requirements.
- Waste liquid treatment During the printing process, substances like potassium dichromate are used, resulting in chromium pollution. Wastewater containing heavy metals needs separate treatment to eliminate their harmful effects.
- Pretreatment of dye bath effluents When dyeing processes change or are completed, small but highly concentrated dye bath effluents are generated. These effluents have high COD concentrations, often reaching tens of thousands or even hundreds of thousands. Separate pretreatment of these wastewater streams helps reduce the overall COD concentration, which is especially crucial for small-scale and multi-species production enterprises.
Electrolysis of Wastewater
Electrolysis is the process of converting electrical energy into chemical energy through chemical reactions induced by an applied electric current. Electrolytic treatment of wastewater, or electrolysis, involves removing harmful impurities from wastewater by converting them into chemical energy.
Electrolysis exhibits the following characteristics:
Rapid reaction speed, high decolorization rate, and minimal sludge production.
It can be operated at room temperature and pressure, making it easy to automate the management.
The voltage and current can be adjusted to maintain effluent stability when the pollutant concentration in the influent water fluctuates.
Short processing time, compact equipment, and a small carbon footprint.
Electrolysis requires direct current (DC), and it consumes a significant amount of electricity and electrode materials.
Boron doped diamond is introduced in this project to treat textile wastewater.
The testing result of influent to the wastewater treatment plant recorded SS>300, COD >1000 mg/L, BOD>200 mg/L, PH 10-12, Chromaticity is 400
Effluent parameters at SS<70, COD<100, BODs <25, PH 6-9, and Chromaticity 40.
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