Textile Industry Wastewater Impact & Textile Industry Wastewater Treatment
Impacts on Environment
Wastewater from the Textile Industry
The textiles and clothing industry is widely recognized as one of the most environmentally damaging sectors due to its significant ecological footprint. This footprint is mainly attributed to the industry’s excessive consumption of energy, water, and chemicals, as well as the generation of textile waste and the release of microfibers into the environment during the washing process. With complex supply chains and energy-intensive production methods, the apparel and footwear industries alone contribute a staggering 8-10% of global carbon emissions, surpassing the combined emissions of both aviation and shipping industries. Moreover, textile dyeing and finishing activities have been estimated to account for approximately 20% of pollution in industrial wastewater. The amount of water used as a solvent is the main concern since over 7 × 10^5 tons of salty effluents are being discharged in the environment every year.
The increasing public concern regarding the environmental contamination that arises from hazardous pollutants present in a wide variety of industrial effluents has brought about stricter legislation and lower disposal limits. Although no precise data are available in literature on the total world production of dyes, the textile industry releases several million tons annually.
Textile Industry Wastewater Parameters
Code/Number Parameters Value
1 PH 6-11
2 Temperature 34–46 °C
3 Biochemical oxygen demand 80–6,100 mg/L
4 Chemical oxygen demand 150–13,000 mg/L
5 Oil and grease 9–35 mg/L
6 Total suspended solids 15–8000 mg/L
7 Chloride 1,020–1,830 mg/L
8 Total dissolved solids 2,870–3,210 mg/L
9 Sodium 72 mg/L
10 Trace elements <11 mg/L
11 Silica <16 mg/L
12 Total Kjeldahl nitrogen 70-80 mg/L
13 Color (Pt-Co) 50–2,500
Dyeing Process & Wastewater
Several different activities are involved in the dyeing process, such as pretreatment, staining, inking and finishing of the textile materials. Textile dyeing activities are energy consuming and water guzzling, as well as highly polluting. Typically, the dyeing process of 1 kg of cotton fabric requires some 150 liter of water, 0.6 kilogram of salts, and 0.04 kilgram of dyes, but a majority of various other inorganic constituents such as H2O2,NaOH, etc.
Auxiliary organic chemicals such as softening, fixing, dispersing and detergents agents) are also involved. During the dyeing process, about 20–25% of the initial dye content is lost and ends up in the waste stream of the industrial plant. The presence of dyes in the waste effluents constitutes an important problem not only regarding the aesthetic aspect of the receiving water bodies but also because their presence interferes with the oxygen solubility and the photosynthetic activity of aquatic floras, thus modifying the biological cycles.
Textile Wastewater Treatment Methods
Conventional Wastewater Treatment Methods VS Electrochemical Oxidation Process
Several methods, including biological oxidation, coagulation–flocculation, and adsorption, have extensively been investigated for the treatment of textile effluents, and although they exhibit certain advantages, they cannot achieve complete decontamination typically due to the large variability in the composition of the effluent. As environmental legislation becomes much more strict, therefore the wastewater treatment industry and manufacturing plants are looking for cost effective treatment technology. In this context, advanced electrochemical oxidation process, such as electrochemical oxidation process (EOP), ozonation process and photocatalysis, have been evaluated for the destruction of synthetic and, to a lesser extent, actual textile effluents.
Electrochemical Oxidation Wastewater Treatment of Textile Wastewater
Electrochemical treatment has attracted a great deal of attention recently as it presents some advantages such as versatility and energy efficiency, ease of operation, and cost-effectiveness. The current efficiency of electrochemical oxidation depends strongly on the anode material. In this context, various types of anodes have been tested as a means to improve the effectiveness of oxidation and current efficiency, such as graphite, Pt, TiO2, IrO2, PbO2, and several Ti-based alloys in the presence of a supporting electrolyte.
Boron Doped Diamond Electrode Anode Material
In recent years, however, the boron-doped diamond (BDD) has emerged as a very promising electrode anode material. It possesses several advantageous properties such as an extremely wide potential window for water discharge, robust oxidation capacity, corrosion stability in very aggressive media, an inert surface with low adsorption, and corrosion resistance. Using BDD anode at high potential, highly reactive OH radicals generated on its surface lead to the combustion of the organic compounds.
Field Test via Boromond’s Electrochemical BDD System
The present study aims to assess the feasibility of an electrochemical BDD system for the treatment of both synthetic and actual textile effluent. The influence of diverse process parameters such as applied current density, electrolyte concentrations, temperatures, and PH on the efficiency of the process has been investigated for the treatment of the synthetic textile effluent. Optimal operating conditions were then employed for the treatment of the real effluent. Process efficiency has been evaluated in terms of colour removal, chemical oxygen demand reduction, mineralization, and energy consumption. The synthetic textile effluent used in the present study is a mixture of seventeen commercial dyes with a total dye concentration of 361 mg/L.
Field Test Data
All of the dyes were provided by KF Textile, a textile manufacturer located in southern Guangdong Province. In order to simulate the actual effluent, appropriate amounts of inorganic salts (e.g. Na2SO4 and Na2CO3) and NaOH were also added. The contribution of each dye to the total dye content was determined according to information provided by the textile manufacturer and given in previous work. The resulting synthetic wastewater has an intense blue–black color and is highly alkaline. The effluent has a light grey–blue color, low content of suspended solids, alkaline PH, and a COD content of 470 mg/L.
All experiments were performed in a batch type, laboratory-scale electrochemical reactor. This single-compartment cell comprised a BDD anode with an active working area of 15 cm2 and a zirconium cathode enclosed in a porous porcelain pot, while a magnetic bar provided continuous stirring. The actual wastewater was filtered. prior to each run in order to remove any suspended particles present. In a typical run, the effluent was mixed with the appropriate amount of HClO4, the current intensity was then set to the preferred character, and voltage was automatically regulated to match the current value.
HClO4 was chosen as the supporting electrolyte because no oxidizing species liable to react with organics are generated as occurs in the case of Cl− and SO4 media (i.e. production of Cl 2 and S2O8 respectively). Effluent mineralization was assessed following the decay of dissolved total organic carbon (TOC) on a TOC analyzer and COD according to the dichromate method.
Results and Discussion
The degradation of the organic pollutants in an electrochemical system occurs through two different mechanisms: (a) direct anodic oxidation, where the pollutants are adsorbed onto the anode sur-face and then destroyed through electron transfer reactions, and (b) indirect oxidation,where electrochemically generated oxidants(i.e. hydroxyl radicals, chlorine, hydrogen peroxide, hypochlorite, ozone and peroxodisulfate)oxidize the pollutants in the liquid bulk.The latter mechanism is dominant in the degradation of organics on a BDD anode, where water discharge leads to the for-mation of OH near the anode surface and, eventually to mineralizing of the organic matter. higher charges are required to obtain the same removalefficiency at increased current densities. The best efficiency is achieved at4–8 mA/cm2 since, compared to other current densities, higher degrees of mineralization are obtained at significantly lower electrical charges; this could be ascribed to the fact that current densities of 4–8mA/cm2 are close to the limiting current density where high efficiencies are expected.
Conclusions
The findings of this study can be summarized as follows:
- Electrochemical oxidation on the boron-doped diamond (BDD) anode proves to be effective in rapidly destroying the chromophore groups present in the dyes used in this study, while consuming relatively low amounts of energy. The treatment process achieves significant mineralization of the synthetic textile effluent, ranging between 60% and 85%, under the employed current densities. However, it is crucial to select the appropriate operating current as high current densities (e.g., 50 mA/cm2) can promote side reactions, such as oxygen evolution, leading to decreased efficiency and increased energy consumption (for instance, COD up to 1813 kWh/kg). The optimal conditions for electrochemical oxidation of the synthetic textile effluent were determined to be a current density of 8 mA/cm2, strongly acidic conditions (pH 1), and a 0.25 M HClO4 electrolyte.
- The performance of the treatment process, in terms of mineralization and chemical oxygen demand (COD) reduction, is influenced by operating parameters such as electrolyte concentration and effluent pH. However, the impact of temperature (in the range of 22-43°C) appears to be minimal, allowing for operation under ambient conditions.
- The composition of the water matrix can also influence the effectiveness of electrochemical treatment on the BDD anode, particularly in the case of actual effluents that often contain high concentrations of various auxiliary organic and inorganic species. These interfering components can significantly affect the efficiency of the process.
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