Optimized parameters of the electrocoagulation process using a novel reactor with rotating anode for saline water treatment

Application of electrocoagulation process for the disposal of COD, NH3-N and turbidity from the intermediate sanitary landfill leachate

This study aims to determine the COD, NH3-N and turbidity disposal efficiencies from leachate in the Bingöl landfill and highlight the electrocoagulation (EC) process's performance in removing these pollutants. After establishing that landfill leachate was intermediate aged, its characteristics were identified using physical, chemical and elemental analyses. Six parallel-connected electrode plates with stainless steel as the cathode and aluminium as the anode were used to construct an electrocoagulation cell. After a 40-min treatment interval, the optimal disposal efficiencies for COD and turbidity from the leachate were determined to be 87% and 62%, respectively, at pH 5. Following a 40-min reaction, BOD5 concentration and BOD5/COD ratio were determined to be 85.75 mg O2/L and 0.64, respectively, at pH 5. At a NaCl concentration of 10 mM, the optimum disposal efficiency for NH3-N was determined to be 33%. The reaction kinetics matched pseudo-first-order (PFO) kinetics due to high correlation coefficients (R2 = 0.93-0.99) in removing COD, NH3-N and turbidity under different experimental conditions. The optimal reaction rate constants were determined as 2.93 × 10-2 min-1, 1.92 × 10-2 min-1 and 7.3 × 10-3 min-1 for the disposal of COD, NH3-N and turbidity, respectively. Energy consumption, unit energy consumption and total consumption cost rose in the EC process when the current density was augmented from 15 to 25 mA/cm2.

Study on the treatment of oily wastewater by evaluating the growth process of aggregates in an electrocoagulation reactor

Electrocoagulation has been widely studied in oily wastewater treatment because of its high demulsification efficiency and no secondary reagent is required. Oil removal largely depends on the properties of the aggregates. This study aimed to explore the growth process of aggregates and oil removal near the anode by electrocoagulation. Four factors, current density, solution temperature, initial pH value, and electrode structure, were investigated. According to the findings, the current density and temperature have the most significant influence on the growth process of aggregates. The oil removal rate depends more on the average particle size than the fractal dimension. The results showed that the current density and solution temperature have the most significant influence on the parameters of the electrocoagulation process. With increasing current density, the aggregate growth rate and average particle size entering the stable period were accelerated, and the oil removal efficiency was promoted. The growth of aggregates was retarded at high temperatures. The change in the scope of the fractal dimension was minor, ranging from 1.65 to 1.84, during the growth process of the aggregates. Foamed aluminium electrodes were beneficial for accelerating aggregate growth instead of aluminium plates, but the energy consumption was obviously increased. The relationship between the mean particle size and mean fractal dimension of aggregates is consistent with the power function. From the point of view of aggregate growth, this study forms the basis for an in-depth understanding of the demulsification mechanism.

Synthesis of highly fluorescent carbon quantum dots from rubber seed shells for the adsorption and photocatalytic degradation of dyes

The potentials of biomass-based carbon quantum dot (CQD) as an adsorbent for batch adsorption of dyes and its photocatalytic degradation capacity for dyes which are congo red (CR) and methylene blue (MB) have been conducted in this study. The CQDs properties, performance, behaviour, and photoluminescence characteristics were assessed using batch adsorption experiments which were carried out under operating conditions including, temperature, pH and dosage. The morphological analysis revealed that CQDs are highly porous, uniform, closely aligned and multi-layered. The presence of hydroxyl, carboxyl and carbonyl functional groups indicated the significance of the oxygenated functional groups. Spectral analysis of photoluminescence for CQDs confirmed their photoluminescent quality by exhibiting high excitation intensity and possessing greenish-blue fluorescence under UV radiation. The removal percentage of the dyes adsorbed for both CR and MB dyes was 77% and 75%. Langmuir isotherm and pseudo-second-order models closely fitted the adsorption results. Thermodynamics analysis indicated that the adsorption process was exothermic and spontaneous, with excellent reusability and stability. The degradation efficiency of CQDs on both dyes was more than 90% under sunlight irradiation and obeyed the first-order kinetic model. These results demonstrated CQDs to be an excellent adsorbent and outstanding photocatalyst for organic dye degradation.

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

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl^- ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Removal of inorganic pollutants using electrocoagulation technology: A review of emerging applications and mechanisms

Electrocoagulation (ECoag) technique has shown considerable potential as an effective method in separating different types of pollutants (including inorganic pollutants) from various sources of water at a lower cost, and that is environmentally friendly. The EC method's performance depends on several significant parameters, including current density, reactor geometry, pH, operation time, the gap between electrodes, and agitation speed. There are some challenges related to the ECoag technique, for example, energy consumption, and electrode passivation as well as its implementation at a larger scale. This review highlights the recent studies published about ECoag capacity to remove inorganic pollutants (including salts), the emerging reactors, and the effect of reactor geometry designs. In addition, this paper highlights the integration of the ECoag technique with other advanced technologies such as microwave and ultrasonic to achieve higher removal efficiencies. This paper also presents a critical discussion of the major and minor reactions of the electrocoagulation technique with several significant operational parameters, emerging designs of the ECoag cell, operating conditions, and techno-economic analysis. Our review concluded that optimizing the operating parameters significantly enhanced the efficiency of the ECoag technique and reduced overall operating costs. Electrodes geometry has been recommended to minimize the passivation phenomenon, promote the conductivity of the cell, and reduce energy consumption. In this review, several challenges and gaps were identified, and insights for future development were discussed. We recommend that future studies investigate the effect of other emerging parameters like perforated and ball electrodes on the ECoag technique.

Fabrication of Polyelectrolyte Membranes of Pectin Graft-Copolymers with PVA and Their Composites with Phosphomolybdic Acid for Drug Delivery, Toxic Metal Ion Removal, and Fuel Cell Applications

In this study, a simple method for the fabrication of highly diffusive, adsorptive and conductive eco-friendly polyelectrolyte membranes (PEMs) with sulfonate functionalized pectin and poly(vinyl alcohol)(PVA) was established. The graft-copolymers were synthesized by employing the use of potassium persulfate as a free radical initiator from pectin (PC), a carbohydrate polymer with 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS) and sodium 4-vinylbenzene sulphonate (SVBS). The PEMs were fabricated from the blends of pectin graft-copolymers (PC-g-AMPS and PC-g-SVBS) and PVA by using a solution casting method, followed by chemical crosslinking with glutaraldehyde. The composite PEMs were fabricated by mixing phosphomolybdic acid with the aforementioned blends. The PEMs were successfully characterized by FTIR, XRD, SEM, and EDAX studies. They were assessed for the controlled release of an anti-cancer drug (5-fluorouracil) and the removal of toxic metal ions (Cu²⁺) from aqueous media. Furthermore, the composite PEMs were evaluated for fuel cell application. The 5-fluorouracil release capacity of the PEMs was found to be 93% and 99.1% at 300 min in a phosphate buffer solution (pH = 7.4). The highest Cu²⁺ removal was observed at 206.7 and 190.1 mg/g. The phosphomolybdic acid-embedded PEMs showed superior methanol permeability, i.e., 6.83 × 10⁻⁵, and 5.94 × 10^−5, compared to the pristine PEMs. Furthermore, the same trend was observed for the proton conductivities, i.e., 13.77 × 10⁻³, and 18.6 × 10⁻³ S/cm at 30 °C.

Fabrication of Eco-Friendly Polyelectrolyte Membranes Based on Sulfonate Grafted Sodium Alginate for Drug Delivery, Toxic Metal Ion Removal and Fuel Cell Applications

Polyelectrolyte membranes (PEMs) are a novel type of material that is in high demand in health, energy and environmental sectors. If environmentally benign materials are created with biodegradable ones, PEMs can evolve into practical technology. In this work, we have fabricated environmentally safe and economic PEMs based on sulfonate grafted sodium alginate (SA) and poly(vinyl alcohol) (PVA). In the first step, 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS) and sodium 4-vinylbenzene sulfonate (SVBS) are grafted on to SA by utilizing the simple free radical polymerization technique. Graft copolymers (SA-g-AMPS and SA-g-SVBS) were characterized by ¹H NMR, FTIR, XRD and DSC. In the second step, sulfonated SA was successfully blended with PVA to fabricate PEMs for the in vitro controlled release of 5-fluorouracil (anti-cancer drug) at pH 1.2 and 7.4 and to remove copper (II) ions from aqueous media. Moreover, phosphomolybdic acids (PMAs) incorporated with composite PEMs were developed to evaluate fuel cell characteristics, i.e., ion exchange capacity, oxidative stability, proton conductivity and methanol permeability. Fabricated PEMs are characterized by the FTIR, ATR-FTIR, XRD, SEM and EDAX. PMA was incorporated. PEMs demonstrated maximum encapsulation efficiency of 5FU, i.e., 78 ± 2.3%, and released the drug maximum in pH 7.4 buffer. The maximum Cu(II) removal was observed at 188.91 and 181.22 mg.g^–1. PMA incorporated with PEMs exhibited significant proton conductivity (59.23 and 45.66 mS/cm) and low methanol permeability (2.19 and 2.04 × 10⁻⁶ cm²/s).

The removal of anionic and cationic dyes from an aqueous solution using biomass-based activated carbon

In this study, two biomass-based adsorbents were used as new precursors for optimizing synthesis conditions of a cost-effective powdered activated carbon (PAC). The PAC removed dyes from an aqueous solution using carbonization and activation by KOH, NaOH, and H₂SO₄. The optimum synthesis, activation temperature, time and impregnation ratio, removal rate, and uptake capacity were determined. The optimum PAC was analyzed and characterized using Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), Zeta potential, and Raman spectroscopy. Morphological studies showed single-layered planes with highly porous surfaces, especially PAC activated by NaOH and H₂SO₄. The results showed that the experimental data were well-fitted with a pseudo-second-order model. Based on Langmuir isotherm, the maximum adsorption capacity for removing methylene blue (MB) was 769.23 mg g⁻¹ and 458.43 mg g⁻¹ for congo red (CR). Based on the isotherm models, more than one mechanism was involved in the adsorption process, monolayer for the anionic dye and multilayer for the cationic dye. Elovich and intraparticle diffusion kinetic models showed that rubber seed shells (RSS) has higher α values with a greater tendency to adsorb dyes compared to rubber seed (RS). A thermodynamic study showed that both dyes’ adsorption process was spontaneous and exothermic due to the negative values of the enthalpy (ΔH) and Gibbs free energy (ΔG). The change in removal efficiency of adsorbent for regeneration study was observed in the seventh cycles, with a 3% decline in the CR and 2% decline in MB removal performance. This study showed that the presence of functional groups and active sites on the produced adsorbent (hydroxyl, alkoxy, carboxyl, and π − π) contributed to its considerable affinity for adsorption in dye removal. Therefore, the optimum PAC can serve as efficient and cost-effective adsorbents to remove dyes from industrial wastewater.

Electrocoagulation treatment of industrial tannery wastewater employing a modified rotating cylinder electrode reactor

The removal of highly concentrated pollutants, presented in a wastewater mixture from industrial tannery effluents by electrocoagulation, was examined. All experiments were carried out in a rotating cylinder electrode reactor with six aluminum anodes and two sedimentation tanks. The influence of the applied current density and rotational speed on the removal efficiency of an electrocoagulation reactor was studied. Chemical oxygen demand was diminished at 70%, while total suspended solids, chromium (III) and turbidity were almost eliminated (>90%) with 6 mA cm^-2 of the applied current density. Additionally, a homogeneous cathodic deposit was obtained at the end of each test. Those cathodic deposits and flocs were analyzed by SEM-EDS. Calculations of the cell energy consumption and the produced aluminum cost were estimated for 6 mA cm^-2 and 100 rpm, obtaining 1.98 kWh m^-3 and $0.7 USD m^-3, respectively.

Application of life cycle assessment for desalination: Progress, challenges and future directions

The sustainability performance of the desalination processes has received increasing attention in recent years. In this study, the current progress and future perspective of a life cycle assessment (LCA) of desalination technology in 62 previous studies have been reviewed for the period 2004-2019. It was found that the number of LCA studies related to seawater reverse osmosis has gained popularity compared to other types of desalination technologies. The review emphasized the application of LCA to desalination by means of research objective, scope of study, life stages, and impact assessment. Although previous LCA studies were conducted to assess the environmental performance of the desalination technology, little attention was given to evaluating the impact of other sustainability aspects (i.e., economic and social). The latter part of this study discusses the challenges, feasibility, and recommendations for future LCA studies on desalination technology. The integration of the LCA approach with other approaches allows a comprehensive assessment of the sustainability performance of desalination technology. Thus, the combined approaches should be explored in future studies to gain insight into the sensitivity and uncertainty of the data to make an assessment that can be useful in policy-making.

Phytoremediation of TSS, NH3-N and COD from Sewage Wastewater by Lemna minor L., Salvinia minima, Ipomea aquatica and Centella asiatica

The rapid growth of industries has resulted in wastewater generation containing different organic and chemical substances channeled into the water body. This causes the arising of water pollution issues in many regions. The phytoremediation method was introduced in the process of treating water pollution as it is low cost and environmentally friendly. Lemna minor, Salvinia minima, Ipomoea aquatica and Centella asiatica were chosen in this study because they have tolerance to various pollution conditions and are able to remove organic pollutants and heavy metals. The objectives of this study were to determine the water quality before and after treatment, to determine the rate of reduction in total suspended solids (TSS), ammoniacal nitrogen (NH3-N), and chemical oxygen demand (COD) in sewage water through the phytoremediation method and to assess the effectiveness of the plants in the phytoremediation of sewage wastewater. It was found that, Lemna minor, Salvinia minima, Ipomoea aquatica and Centella asiatica were able to reduce TSS by 50.8%, 77.6%, 85.6% and 67.6%, respectively; NH3-N by 80.4%, 89.9, 97.3% and 79.1%, respectively; and COD by 75%, 82%, 44.8% and 36.46%, respectively. In this study, it was found that sewage wastewater treatment using Ipomoea aquatica was more efficient in reducing NH3-N and Salvinia minima was more efficient in reducing TSS and COD values.

Hydrogen-free hydrogenation of nitrobenzene via direct coupling with cyclohexanol dehydrogenation over ordered mesoporous MgO/SBA-15 supported Cu nanoparticles

Direct catalytic coupling of nitrobenzene hydrogenation and cyclohexanol dehydrogenation was studied in the gas phase over mesoporous MgO-SBA15 supported Cu nanoparticles. This approach avoids an external supply of H₂ and utilizes the in situ liberated H₂ from the dehydrogenation step of the first reactant for the hydrogenation reaction of the second reactant. A catalyst series consisting of four Cu/MgO-SBA15 mesoporous solids with varying Cu loadings (5–20 wt%) were prepared and systematically characterized by BET, ICP, XRD, TPR, TPD, FT-IR, SEM, XPS, and TEM. Among the series, the 15 wt% Cu catalyst exhibited the best performance with ≥82% conversion of nitrobenzene along with ≥89% cyclohexanol conversion. In addition, significantly higher yields of cyclohexanone (83%) and aniline (75%) could be achieved successfully over the same catalyst. Furthermore, the catalyst exhibited almost stable activity during 30 h time-on-stream with slow deactivation. The highly ordered mesoporous silica increases the metal–support interaction with smaller particles of Cu on the surface, and the synergism between acid–base sites is responsible for the improved catalytic activity.

Coupling of nitrobenzene and cyclohexanol over mesoporous Cu/MgO-SBA15 exhibited better conversion of 89% cyclohexanol, 82% nitrobenzene with remarkable yields of cyclohexanone (83%) and aniline (75%). The catalyst has stable activity up to 30 h.