Optimization of the electrochemical oxidation of textile wastewater by graphite electrodes by response surface methodology and artificial neural network

Hybrid process combining ultrafiltration and electro-oxidation for COD and nonylphenol ethoxylate removal from industrial laundry wastewater

Laundry wastewater is a significant source of nonylphenol ethoxylate (NPEO) at wastewater treatment plants, where its breakdown forms persistent nonylphenol (NP). NP poses risks as an endocrine disruptor in wildlife and humans. This study investigates the degradation of NPEO and COD in industrial laundry wastewater (LWW) using a two-stage process combining ultrafiltration (UF) and electro-oxidation (EO). UF was used to remove suspended solids, while soluble COD (COD0 = 239 ± 6 mg.L-1) and NPEO (NPEO0 = 341 ± 8 μg.L-1) were oxidized by the EO process. Different operating parameters were studied such as current density, electrolysis time, type of cathode and supporting electrolyte concentration. Using an experimental design methodology, the optimal conditions for COD and NPEO3-17 degradation were recorded. This included achieving 97% degradation of NPEO3-17 and 61% degradation of COD, with a total operating cost of 3.65 USD·m-3. These optimal conditions were recorded at a current density of 15 mA cm-2 for a 120-min reaction period in the presence of 4 g·Na2SO4 L-1 using a graphite cathode. The EO process allowed for reaching the guidelines required for water reuse (NPEO <200 μg.L-1, COD <100 mg.L-1) in the initial laundry washing cycles. Furthermore, our results demonstrate that both NP and NPEO compounds, including higher and shorter ethoxylate chains (NPEO3-17), were effectively degraded during the EO process, with removal efficiencies between 94% and 98%. This confirms the EO process's capability to effectively degrade NP, the by-product of NPEO breakdown.

Electrochemical treatment of malachite green dye wastewater by pulse three-dimensional electrode method

Water pollution is becoming more and more serious nowadays, and water resources are in shortage. As an environmentally friendly wastewater treatment technology without secondary pollution, the three-dimensional electrode method has received more and more attention. However, the conventional direct current (DC) three-dimensional electrode method has the disadvantages of high energy consumption and low current efficiency. Based on this, this work investigated the treatment of malachite green (MG) dye wastewater by pulse three-dimensional electrode method. The influences of pulse duty cycle, pulse period, electrolysis voltage, initial pH, aeration rate and Na2SO4 concentration on MG degradation were investigated. The results showed that under the optimal operating conditions of pulse duty cycle of 0.4, pulse period of 15 s, electrolysis voltage of 15 V, initial pH of 5, aeration rate of 0.5 L/min, Na2SO4 concentration of 0.10 mol/L, the removal rates of MG and COD reached 96.2% and 80.5%, respectively, the current efficiency reached 93.4%, and the energy consumption was 24.2 kWh/kg COD after 150 min. Compared with DC power supply mode, the MG removal rate, COD removal rate and current efficiency were enhanced, and the energy consumption was reduced by 83.9%. Moreover, the generation capacity of ·OH was increased under pulse power supply mode. Finally, a possible degradation pathway of MG in pulse power supply mode was inferred using UV-vis and GC-MS analysis. This study indicates that the pulse three-dimensional electrode method is an efficient and low-energy-consumption wastewater treatment method with stable degradation performance for MG dye wastewater.

Fabric dyeing wastewater treatment and salt recovery using a pilot scale system consisted of graphite electrodes based on electrooxidation and nanofiltration

In this study, color removal, suspended solids removal, and salt recovery were investigated from different fabric dyeing wastewaters using a pilot scale treatment system. A pilot scale system was installed in the wastewater outlet area of five different textile companies. Experiments were planned for pollutant removal and salt recovery from wastewater. First, the wastewater was treated by electrooxidation (EO) using graphite electrodes. After a reaction time of 1 h, the wastewater was passed throughout the granular activated carbon (AC) coloumn. The pre-treated wastewater was passed through the membrane (NF) system to recover the salt in the wastewater. Finally, the recovered salt water was used for fabric dyeing. In the pilot scale treatment system (EO + AC + NF), 100% of suspended solids (SS) and an average of 99.37% of color were removed from fabric dyeing wastewaters. At the same time, a high amount of salt water was recovered and reused. Optimum conditions were determined as 4 V current, 1000 A power, wastewater's own pH values and 60 min of reaction time. The energy and operating cost for treatment of 1 m3 of wastewater were determined as 40.0 kWh/m3 and 2.2 US$/m3, respectively. In addition to the prevention of environmental pollution by the treatment of wastewater using the pilot-scale treatment system, the reuse of the recovered water will contribute to the protection of our valuable water resources. In addition, using the NF membrane process after the EO system, it will be possible to recover salt from wastewater with high salt content such as textile wastewater.

Optimization of the anaerobic fermentation process for phosphate release using food waste

Phosphorus (P) problem worries the whole world due to the increasing demand for finite and non-renewable natural phosphate resources and the inadequacy of sustainable phosphate production technologies. In this study, bio-acidification processes using waste sludge and food waste for simultaneous sustainable phosphate release and biogas production were investigated. Response surface methodology (RSM) was used for bio-acidification optimization. High performance was achieved with the addition of 10% FW and a temperature of 45 °C, which provided 5.30 pH and 371 mg/L P release for 10 days. A total of 196 mL of cumulative biogas was produced. Using food waste potentially reduces operating costs, eliminating the need for external chemical additions for pH control. Also, this approach offers benefits such as waste management, recovery of valuable resources, cost reduction, and environmental friendly.

Water and wastewater quality prediction: current trends and challenges in the implementation of artificial neural network

Traditional freshwater supplies have been over-abstracted in the current global problem of water scarcity. Through the analysis of complex experimental and real-time data, to improve the activity of water and wastewater treatment (WWT) systems, an artificial neural network (ANN), a computational model inspired by the human brain, and its variants were created. This review paper focuses on recent trends and advances in modeling and simulating different water and wastewater systems using ANN. This study uses ANN in watershed management, impurity removal from wastewater, and wastewater treatment plants. According to the literature review, ANN can predict nonlinear, linear, and complex systems with high accuracy and well control. Finally, the limitations and future scope of ANNs were discussed. ANN proved itself in the prediction of various water and WWT processes. Still, implementation has practical challenges, which include a lack of data availability, poorly built models, timely updates in developed models, and low repeatability. The use of a proper toolbox, faster computing power, and proper domain knowledge makes the practical implementation of ANN successful. As a result, ANN can build a solid foundation for attracting and motivating investigators to work in this region in the forthcoming.

Electrocoagulation of Corrugated Box Industrial Effluents and Optimization by Response Surface Methodology

The electrocoagulation method using stainless steel anodes was applied to a corrugated cardboard box manufacturing plant's wastewater with high COD content. The effects of current density, processing time and stirring speed on response functions were studied using the Response Surface Methodology (RSM). The removal efficiency of chemical oxygen demand (COD) and energy consumption were selected as response functions. The Central Composite Design (CCD) was chosen to explain the single and combined effects of independent variables on response functions. The COD concentration of the real industrial wastewater used in the experiments was 9130 mg L^-1. The maximum COD removal efficiency of 91.6% is obtained with 19.78 Wh g^-1 energy consumption. Current density and treatment time were effective parameters for both COD removal and energy consumption. Optimization for maximum COD removal with minimum energy consumption showed 80.9% of COD removal with 6.7 Wh g^-1 of energy consumption at 15 mA cm^-2, 700 rpm, and 28 min treatment time. The variables are optimized with a few experiments using the response surface method.

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Catalytic efficiency of raw and hydrolyzed eggshell in the oxidation of crystal violet and dye bathing wastewater by thermally activated peroxide oxidation method

In this study, hydrochar-based-eggshell was prepared via the subcritical water medium (SCWM) and used as a catalyst in the thermally activated peroxide oxidation (TAPO) approach for crystal violet and dye bathing wastewater degradation. The catalytic activities for the raw eggshell (RES) and hydrochar-based-eggshell (HES) were compared. RES and HES were characterized using a scanning electron microscope (SEM),energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transforms infrared spectroscopy (FT-IR). The affecting parameters on the degradation process were optimized using response surface methodology (RSM). The effects of temperature (293-333 K), amount of catalyst (5-25 mg/50 mL), the concentration of H₂O₂ (0-8 mM), and treatment time (10-70 min) on the TAPO method were investigated using central composite design (CCD). For the crystal violet removal, two models were developed. Both models were significant and can be used to describe the design space. Also, the dye bathing wastewater degradation was described by another developed model, which had a high correlation coefficient (R² = 0.97). In general, catalytic activity for HES was higher than RES. The degradation of crystal violet reached 98.10% when a 20 mg HES catalyst and 6 mM H₂O₂ at 323 K for 55 min were used. While 97% of the color of dye bathing wastewater was removed in 55 min at 323 K using 25 mg of HES and 4 mM H₂O₂. This study showed that the hydrolyzed eggshells could be used in the oxidation of crystal violet and dye bathing wastewater by the thermally activated peroxide oxidation method.

Three-Phase Three-Dimensional Electrochemical Process for Efficient Treatment of Greywater

Water shortages around the world have intensified the search for substitute sources. Greywater can serve as a solution for water requirements. Compared to two-dimensional electrochemical processes for water treatment, the addition of particle activated carbon enhances the conductivity and mass transfer or the adsorption of pollutants in a three-dimensional (3D) electrochemical process. The large specific surface areas of these particles can provide more reactive sites, resulting in a higher removal efficiency. In this study, the treatment of greywater by the electro-Fenton (E-Fenton) method was carried out in a 3D electrolytic reactor. The effects of the operating conditions, such as electrode spacing, applied voltage, treatment time, and activated carbon loading, on the efficacy of the E-Fenton process were investigated, and the corresponding optimum conditions were found to be 7 cm, 9 V, 2 h, and 10 g. The results showed that CODCr removal of greywater treated using the 3D electrochemical process was 85%. With the help of the Box–Behnken experiment design and the response surface methodology, the parameters were optimized to determine the optimal conditions. The results of the response surface analysis were consistent with the experimental results. The above findings illustrate that the proposed three-phase 3D electrochemical process is feasible for the efficient treatment of greywater.

Water recovery from yarn fabric dyeing wastewater using electrochemical oxidation and membrane processes

This study intended to evaluate and compare the efficiency of electrochemical oxidation (EO), nanofiltration (NF), and reverse osmosis (RO) membranes processes in the treatment of yarn fabric dyeing wastewater (YFDW) in terms of chemical oxygen demand (COD) removal, color removal, salinity reduction, and conductivity removal. EO tests of the textile effluent were conducted under various current densities and solution pH conditions employing a graphite electrode. Membrane filtration experiments were conducted using two different NF membranes: NP010 and NP030 and two distinct RO membranes: BW30 and SW30 flat-sheet membranes. The experimental results showed that NF membrane process is not suitable for yarn fabric wastewater treatment showing low removal efficiencies for COD, color, and conductivity. However, both EO and RO membranes could reduce COD and color to high removal performances. EO results showed more than 99% of color removal and 80% of COD elimination at pH = 6 and current density of 50 mA/cm² after 180 min of reaction. Using RO membrane for yarn fabric wastewater treatment demonstrated relatively complete removal of color concentration and 98% of COD elimination. However, EO process showed less performance in conductivity removal efficiency compared to the RO membranes. EO treatment of YFDW decreased conductivity by 31.2%, whereas RO membrane process reduced conductivity to a greater extent and recorded 97.1% of removal elimination percentage. Therefore, the treated water by RO membrane could be recycled back to the process such as washing and dyeing, in that way offering economic profits by decreasing water consumption and wastewater treatment cost. PRACTITIONER POINTS: Electrochemical oxidation and membrane filtration processes were combined for the treatment of yarn fabric dyeing wastewater (YFDW). A 100% color removal of color and 98.5% COD elimination efficiencies were obtained for the electrochemical oxidation (EO) + RO combined process. EO treatment of YFDW decreased conductivity by 32.7%, whereas the RO membrane process reduced conductivity to a greater extent and recorded 97.7% of removal elimination percentage.