A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal

Removal of lead ions from aqueous solution by modified nanocellulose

Heavy metals significantly impact the environment due to their non-biodegradable, toxic, and carcinogenic behaviors. Lead contaminants impose severe health impacts on humans and the water environment. Therefore, eco-friendly and efficient lead ion removal practices such as nanotechnology are an urgent requirement for the abatement of lead pollution. In the present study, nanocellulose was synthesized from the cotton straw residue using chemical methods and modified with titanium dioxide to form a nanocomposite. The nanocomposite synthesized was characterized by using FTIR, XRD, FESEM, and BET. FTIR results noticed peaks at 1648.43 and 1443.57 cm-1 for cellulose and Ti-O-Ti bonding at 505.02 cm-1. The nanocomposite was noticed to be disordered and irregular in shape. The nanocomposite has particle sizes of 83 nm. The nanocomposite crystalline particle had 65% anatase and 32% rutile phases observed from the XRD result. BET results show that the surface area of nanocellulose increases after surface modification from 25.692 to 42.510 m2/g. The adsorption capacity of the nanocomposite was 0.552 mg/g was noticed. The Elovich kinetic and Baudu isotherms are the best-fitted models for lead ion adsorption. Thermodynamic parameters resulted in Gibbs free energy decreasing with temperature. This study revealed that modified cellulosic adsorbents efficiently absorbed lead ions derived from cotton straws.

Integrating of electrocoagulation process with submerged membrane bioreactor for wastewater treatment under low voltage gradients

Treating and reusing wastewater has become an essential aspect of water management worldwide. However, the increase in emerging pollutants such as polycyclic aromatic hydrocarbons (PAHs), which are presented in wastewater from various sources like industry, roads, and household waste, makes their removal difficult due to their low concentration, stability, and ability to combine with other organic substances. Therefore, treating a low load of wastewater is an attractive option. The study aimed to address membrane fouling in the submerged membrane bioreactor (SMBR) used for wastewater treatment. An aluminum electrocoagulation (EC) device was combined with SMBR as a pre-treatment to reduce fouling. The EC-SMBR process was compared with a conventional SMBR without EC, fed with real grey water. To prevent impeding biological growth, low voltage gradients were utilized in the EC deviceThe comparison was conducted over 60 days with constant transmembrane pressure and infinite solid retention time (SRT). In phase I, when the EC device was operated at a low voltage gradient (0.64 V/cm), no significant improvement in the pollutants removal was observed in terms of color, turbidity, and chemical oxygen demand (COD). Nevertheless, during phase II, a voltage gradient of 1.26 V/cm achieved up to 100%, 99.7%, 92%, 94.1%, and 96.5% removals in the EC-SMBR process in comparison with 95.1%, 95.4%, 85%, 91.7% and 74.2% removals in the SMBR process for turbidity, color, COD, ammonia nitrogen (NH3-N), total phosphorus (TP), respectively. SMBR showed better anionic surfactant (AS) removal than EC-SMBR. A voltage gradient of 0.64 V/cm in the EC unit significantly reduced fouling by 23.7%, while 1.26 V/cm showed inconsistent results. Accumulation of Al ions negatively affected membrane performance. Low voltage gradients in EC can control SMBR fouling if Al concentration is controlled. Future research should investigate EC-SMBR with constant membrane flux for large-scale applications, considering energy consumption and operating costs.

Z. AL-bonsrulah H. Optimization of oil industry wastewater treatment system and proposing empirical correlations for chemical oxygen demand removal using electrocoagulation and predicting the system's performance by artificial neural network

The alarming pace of environmental degradation necessitates the treatment of wastewater from the oil industry in order to ensure the long-term sustainability of human civilization. Electrocoagulation has emerged as a promising method for optimizing the removal of chemical oxygen demand (COD) from wastewater obtained from oil refineries. Therefore, in this study, electrocoagulation was experimentally investigated, and a single-factorial approach was employed to identify the optimal conditions, taking into account various parameters such as current density, pH, COD concentration, electrode surface area, and NaCl concentration. The experimental findings revealed that the most favorable conditions for COD removal were determined to be 24 mA/cm2 for current density, pH 8, a COD concentration of 500 mg/l, an electrode surface area of 25.26 cm2, and a NaCl concentration of 0.5 g/l. Correlation equations were proposed to describe the relationship between COD removal and the aforementioned parameters, and double-factorial models were examined to analyze the impact of COD removal over time. The most favorable outcomes were observed after a reaction time of 20 min. Furthermore, an artificial neural network model was developed based on the experimental data to predict COD removal from wastewater generated by the oil industry. The model exhibited a mean absolute error (MAE) of 1.12% and a coefficient of determination (R2) of 0.99, indicating its high accuracy. These findings suggest that machine learning-based models have the potential to effectively predict COD removal and may even serve as viable alternatives to traditional experimental and numerical techniques.

Chitosan cross-linked and grafted with epichlorohydrin and 2,4-dichlorobenzaldehyde as an efficient adsorbent for removal of Pb(II) ions from aqueous solution

Epichlorohydrin-modified chitosan-Schiff base composite (CS/24Cl/ECH) prepared via the one-pot reaction as characterized by Fourier transform Infra-Red spectroscopy (FT-IR), X-ray powder diffraction (XRD), Differential scanning calorimetry (DSC) and Scanning electron microscope (SEM). Its removal ability of Pb(II) ions from aqueous solution was investigated. The adsorption of Pb(II) ions carried out at different initial pH, dose of CS/24-Cl/ECH, contact time and co-existing ions. The maximum adsorption capacity of Pb(II) ions was 170 mg/g. Finally, based on the absorption results, the adsorption of Pb(II) ions was fitted by single-layer Langmuir isotherm model and the pseudo-second-order (PSO) kinetics model. The absorption mechanism of Pb(II) ions was controlled by chemical coordination Pb(II) ions with the active sites on the surface of CS/24Cl/ECH composite. Also, CS/24Cl/ECH showed excellent recyclable efficiency up to 5 cycle and potential sorbent for other heavy metal ions.

Electrocoagulation treatment of furniture industry wastewater

Electrocoagulation was investigated as a method for treating wastewater containing polyvinyl acetate (PVAc) from the furniture industry. The study evaluated the evolution of iron concentration and passivation during the treatment process. Laboratory-scale experiments were conducted to evaluate the effects of inter-electrode distance (d), current density, and mode on treatment performance. Three values of d (0.3, 0.6, and 0.9 cm) were studied and found to have no significant effect on performance. However, lower d values resulted in reduced energy consumption due to a decrease in applied voltage. Three values of current density (132, 158, and 197 A m^-2) were studied under two current modes, Direct Current (DC) and Alternating Pulsed Current (APC). The best treatment performance for DC occurred under 158 A m^-2 (the treated wastewater was characterized by pH = 4.59 ± 0.02, conductivity = 996 ± 21 μS cm^-1, COD = 1940 ± 55 mgO₂ L^-1, TSS = 105 ± 14 mg L^-1, and Fe = 50.39 ± 1.87 mgFe L^-1). For APC, the best performance was achieved under 197 A m^-2 (the treated wastewater was characterized by pH = 6.33 ± 0.06, conductivity = 988 ± 17 μS cm^-1, COD = 1942 ± 312 mgO₂ L^-1, TSS = 199 ± 55 mg L^-1, and Fe = 44.68 ± 4.60 mgFe L^-1). Despite the promising results, treatment performance was insufficient to meet the legal requirements for water discharge. APC was found to be a more economically viable approach, as it reduced anode wear, electrode passivation, and energy consumption. The quantity of iron released increased with d, and the effect of current density on iron concentration was found to be non-linear. However, applying APC reduced the iron content for all tested current densities. The tests showed that EC was effective in removing chemical oxygen demand (COD) and total suspended solids (TSS), achieving removal efficiencies above 92% and 99%, respectively. However, the studied treatment procedures were insufficient to meet the EU legal requirements for water discharge. Therefore, the obtained wastewater should undergo a post-treatment process.

Using deep eutectic solvent dissolved low-value cotton linter based efficient magnetic adsorbents for heavy metal removal

In this study, a novel magnetic bio-adsorbent was synthesized by modifying cotton linter (CL) cellulose with deep eutectic solvents (DESs) and Fe₃O₄ magnetic nanoparticles. The adsorption capacity of CL, Fe₃O₄/CL, Fe₃O₄/CL-oxidation, and Fe₃O₄/CL-DES for Cu²⁺ was 11.0, 66.1, 85.7, and 93.1 mg g^-1, respectively, under the optimal adsorption conditions of an initial pH value of 6.0, stirring rate of 300 rpm, and a temperature of 30 °C. The presence of Fe₃O₄ nanoparticles increased the proportion of hydroxyl groups and thus improved the ion-exchange ability of Cu²⁺. The dissolution of DES significantly decreased fiber crystallinity and increased the number of hydroxyl group (amorphous regions increased), thus improving the chelation reaction of Cu²⁺, which was favorable for surface adsorption. In addition, we used the Langmuir and Freundlich isothermal models to simulate the adsorption behavior of Fe₃O₄/CL-DES, and the results indicated that Cu²⁺ follows a Freundlich isotherm model of multilayer adsorption. The fitting of the adsorption kinetics model indicated that the adsorption process involves multiple adsorption mechanisms and can be described by a quasi-second-order model. These results provide a potential method for the preparation of high-efficiency adsorbents from low-value cotton linter, which has broad application prospects in wastewater treatment.

Sustainable green conversion of coal gangue waste into cost-effective porous multimetallic silicate adsorbent enables superefficient removal of Cd(II) and dye

Converting solid wastes into new materials for wastewater decontamination is a feasible "one stone, three birds" strategy to achieve sustainable value-added utilization of resources and minimize waste emissions, but significant challenges remain. In response to this, we proposed an efficient "mineral gene reconstruction" method to synchronously transform coal gangue (CG) into a green porous silicate adsorbent without using any harmful chemicals (i.e., surfactants, organic solvents). The one of the synthesized adsorbents with a high specific surface area (582.28 m²/g) and multimetallic active centres shows outstanding adsorption performance (adsorption capacities: 168.92 mg/g for Cd(II), 234.19 mg/g for methylene blue (MB); removal rate: 99.04% for Cd(II) and 99.9% for MB). The adsorbent can also reach a high removal rate of 99.05%∼99.46% and 89.23%∼99.32% for MB and Cd(II) in real water samples (i.e., Yangtze River, Yellow River, seawater and tap water), respectively. After 5 adsorption-desorption cycles, the adsorption efficiency remained above 90%. The adsorbents mainly adsorbed Cd(II) by electrostatic attraction, surface complexation and partial ion exchange and MB by electrostatic and hydrogen bonding interactions. This study provides a sustainable and promising platform for developing a new-generation cost-efficient adsorbent from waste for clean water production.

Hexavalent Chromium Removal from Water and Wastewaters by Electrochemical Processes: Review

Hexavalent chromium (Cr(VI)) is a toxic, mutagenic, teratogenic, and carcinogenic species. Its origin is in industrial activities. Therefore, its effective control is realized on a source basis. Although chemical methods proved effective in removing Cr(VI) from wastewaters, more economic solutions with a minimum sludge production have been sought. Among them, the use of electrochemical processes has emerged as a viable solution to the problem. Much research was conducted in this area. The aim of this review paper is to make a critical evaluation of the literature on Cr(VI) removal by electrochemical methods, particularly electrocoagulation with sacrificial electrodes, and to assess the present data as well as to point out the areas that need further elaboration. Following the review of the theoretical concepts of electrochemical processes, the literature on the electrochemical removal of Cr(VI) was evaluated on the basis of important elements of the system. Among them are initial pH, initial Cr(VI) concentration, current density, type and concentration of supporting electrolyte, and the material of electrodes and their operating characteristics and process kinetics. Dimensionally stable electrodes that realize the reduction process without producing any sludge were evaluated separately. Applications of electrochemical methods to a wide spectrum of industrial effluents were also assessed.

Functionalization of Sodium Magnesium Silicate Hydroxide/Sodium Magnesium Silicate Hydrate Nanostructures Using 2,3-Dihydroxybenzaldehyde as a Novel Nanocomposite for the Efficient Removal of Cd(II) and Cu(II) Ions from Aqueous Media

Cd(II) and Cu(II) ions cause many diseases in humans. Therefore, they should be removed from water sources using simple and cost-effective adsorbents. Consequently, sodium magnesium silicate hydroxide/sodium magnesium silicate hydrate nanostructures were synthesized and functionalized using 2,3-dihydroxybenzaldehyde as a novel nanocomposite. Several instruments were used to characterize the synthetic products, such as an X-ray diffractometer (XRD), a Fourier-transform infrared spectrophotometer (FT-IR), an N2 adsorption/desorption analyzer, a CHN elemental analyzer, an energy-dispersive X-ray spectrophotometer (EDS), and a field emission scanning electron microscope (FE-SEM). The functionalization of the nanostructures with 2,3-dihydroxybenzaldehyde led to the disappearance of the XRD peaks of the nanostructures and the presence of a broad XRD peak at 2θ = 32°. In addition, the FE-SEM images revealed that the nanostructures consisted of spheres, cubes, and irregular shapes with an average grain size of 115 nm, and the nanocomposite consisted of spherical conglomerates consisting of needle-like shapes. The anticipated morphology following the functionalization of the nanostructures with 2,3-dihydroxybenzaldehyde resulted from the presence of 2,3-dihydroxybenzaldehyde on the backbones of the nanostructures. The EDS results showed that the nanostructures were composed of O, Na, Mg, and Si with weight percentages equal to 38.59%, 5.95%, 16.60%, and 38.86%, respectively. Additionally, the nanocomposite was composed of C, N, O, Na, Mg, and Si with weight percentages equal to 55.31%, 2.23%, 30.09%, 6.56%, 2.98%, and 12.83%, respectively. The synthesized nanostructures and nanocomposite samples were utilized for the efficient removal of cadmium and copper ions from aqueous media using the ion exchange and chelation adsorption procedures, respectively. Optimum conditions for removing the cadmium and copper ions were achieved at a pH, time, and temperature equal to 7.5, 80 min, and 298 K, respectively. The maximum uptake capacities of the synthesized nanostructures and nanocomposite samples toward cadmium ions were 89.44 mg/g and 155.04 mg/g, respectively, and the maximum uptake capacities of the synthesized nanostructures and nanocomposite samples toward copper ions were 103.73 mg/g and 177.94 mg/g, respectively. Moreover, the adsorption processes were exothermic, chemical, and followed the pseudo-second-order model and Langmuir equilibrium isotherm model.