TEXTILE WASTEWATER TREATMENT USING ELECTROCHEMICAL AND PHOTOELECTROCHEMICAL PROCESSES.

Abstract

The textile industry is important for manufacturing an extensive range of fibers like cotton, jute, wool, silk (natural), polyester, viscose, nylon, etc. (synthetic). The textile industry utilizes chemicals ranging from solvents to resins and caustic soda to bleach in its production process, which has a harsh environmental impact. A large amount of colored dye in wastewater is released because the fabric cannot uptake these synthetic dyes completely, and the major part is released in wastewater. Heavy metals (non-biodegradable) and chlorine accumulate in organs of marine and terrestrial life, leading to various diseases. So, there is an urgent need to treat textile wastewater. The textile industry utilizes different fibers that demand various chemicals for dyes. The characteristics of woolen, cotton silk, and viscose fiber have been reviewed for the dyeing textile unit. Techno-economic analysis of the all the electrochemical processes have not been reviewed for the textile wastewater treatment. The mechanism of all the electrochemical processes has been explained in the literature review section. Highly toxic compounds cannot be treated by primary and secondary treatment methods. Therefore, tertiary treatment methods are applied. The focus of this study is on the tertiary treatment methods, mainly on electrochemical treatments, i.e., electrocoagulation (EC), electro- Fenton (EF), electrooxidation (EO), photoelectrochemical (PEC) process, and solar electro- Fenton (SPEF) process with their mechanism and the techno-economic analysis. The bibliometry of the most used dyes and the most used electrochemical method has been explained. It also focuses on electrodes used for electrochemical treatments, including dimensionally stable anodes (DSAs). In the first part of the study, textile wastewater was treated by an electrochemical process using Ti/RuO2 as anode and stainless steel as a cathode. Textile wastewater contains harmful dyes that can be broken down into simpler products like CO2 and H2O using the electro-oxidation process. For this process, a dimensional stable anode (Ti/RuO2) has been fabricated using sol-gel method. Apreo Field Emission Scanning Electron Microscopy (FE-SEM) with Energy Dispersed X-ray (EDX), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) has been done to study their characteristics. Design expert software was used to optimize the parameters using the Response surface methodology. Response parameters such as pH (2-10), current (0.5-2 A), initial concentration (50-200 mg/L), and time (2-15 min) were varied, and 30 sets of experiments were designed. The optimized value obtained for maximizing the dye degradation percentage and COD removal percentage is at initial pH of 3.3, current of 0.5 A, initial concentration of 50 mg/L, and time of 9.4 min for dye degradation of 99.82%, COD removal of 82.50% removal, and 1.81 kWh/m3 energy consumption (minimum) keeping 0.2 M NaCl electrolyte as constant. Kinetic study shows that the reaction is first order. The mechanism of the process was also studied using UPLC-QTOF. The Total Cost of the process was found to be 300.94 ₹ or 3.6108 $ using industrial prices. Characterization of the sludge was also done to check its reusability. To overcome the cost of the electrochemical process along with the green fuel production second part was studied on the photoelectrochemical (PEC) treatment, PEC possesses energyefficient wastewater treatment by harnessing solar energy. The cost-effective and eco-friendly PEC method reduces the reliability of conventional energy sources. This work established the approach for textile wastewater treatment (TWW) along with hydrogen production. The WO3/BiVO4/Ni-PbS photoanode was prepared by optimizing Ni atomic (at.) concentration by a new approach showing a good photocurrent of 5.56 mA cm-1 in 0.5 M Na2SO3+PBS electrolyte using an external bias of 1.23 V vs. RHE at 7 pH. 99.9% TOC removal with 52.2 μmol cm-2 hydrogen was produced. The presence of sulfate and chloride ions helps degrade the TWW in the presence of Na2SO3+PBS electrolyte. The contribution of RCS (Cl•, Cl2•, ClO•, ClO3•-, ClO- /HClO), SO4•2, and •OH in TOC removal was studied by the mechanism. Powdered BiVO4 has been utilized for testing photocatalytic degradation. Finally, better results were found with the EC-PEC process and PC-PEC process which is useful for chromium removal enhancement in the TWW. It was found that PEC treatment can be a better process in terms of efficiency and the economic perspective as it utilizes solar energy instead of electrical energy and the cost of the PEC can also be recovered by the generation of H2.