Search Results (287)

A highly efficient ZnO/biochar (ZnO/BC) composite was synthesised from phytoremediation residue and evaluated for the advanced sonocatalytic degradation of malachite green in aqueous solutions. The structural, chemical, and morphological properties of the composite were characterised using physicochemical techniques, confirming the successful impregnation of zinc oxide (ZnO) onto the biochar matrix. The catalytic performance of the synthesised composite in treating malachite green was systematically evaluated and optimised using response surface methodology (RSM), specifically a central composite design (CCD), to analyse the interactive effects of initial dye concentration, catalyst loading, and ultrasonic irradiation time. The developed model exhibited a high coefficient of determination (R²) of 0.996 and an adequate precision of 62.67, confirming the model’s significance. Optimal degradation was observed at an initial malachite green concentration of 73.71 mg/L, a catalyst loading of 0.527 g/L, and a sonocatalytic treatment duration of 18.7 min. Furthermore, the ZnO/biochar composite demonstrated excellent mineralisation capabilities, with chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies reaching 89.79% and 68.43%, respectively, after 60 min of treatment. These findings establish ZnO/BC as a highly active sonocatalyst, offering a promising approach for the remediation of organic dyes in industrial wastewater treatment. Full article

The persistence of azo dyes in industrial effluents poses significant environmental risks; therefore, there is a need to develop effective adsorbents. This study investigates the efficiency of a Cu₂O/CuO nanocomposite as an adsorbent for the removal of a model dye, methyl orange (MO), from aqueous solutions. The material was characterized by XRD, SEM and BET analyses, revealing a dominant Cu₂O phase (96 wt%) with CuO fractions, and an average particle size of ~18 nm paired with a specific surface area of 19.54 m² g⁻¹. FTIR and TOC assays revealed the adsorption and degradation of MO by action of the nanocomposite. Operational parameters such as adsorbent dosage, initial dye concentration, pH, and the point of zero charge (PZC) were investigated. Under the optimized conditions, the nanocomposite achieved a dye removal efficiency of 97.0%. The kinetic results showed a strong correlation with the pseudo-second-order model. Furthermore, isotherm analysis revealed that the adsorption process is best described by the Langmuir–Freundlich model, demonstrating an outstanding maximum theoretical adsorption capacity (q_max) of 254.76 mg g⁻¹, which closely aligns with the experimental value (249.48 mg g⁻¹). The findings demonstrated that the synthesized Cu₂O/CuO nanocomposite acts as an efficient and promising adsorbent for the remediation of dye-contaminated waters. Full article

The efficient removal of low-concentration antibiotics from wastewater is a persistent challenge. In this work, we enhance the performance of a W-BiVO₄ photoanode by modifying it with CoNi-based metal–organic framework nanosheets (CoNi-MOF), constructing a W-BiVO₄@CoNi-MOFN composite. This integration markedly improves the separation and migration of photogenerated charge carriers. Consequently, the modified photoanode delivers a substantially higher photocurrent density of 3.92 mA cm⁻² at 1.23 V_RHE, representing a 2.3-fold enhancement over the pristine W-BiVO₄ (1.74 mA cm⁻²). Furthermore, the photoelectrocatalytic (PEC) system employing the W-BiVO₄@CoNi-MOFN photoanode demonstrates significantly superior degradation efficiency for low-concentration tetracycline compared to the system based on unmodified W-BiVO₄. The performance enhancement is attributed to a dual mechanism. First, the CoNi-MOF modification optimizes the PEC performance of W-BiVO₄, facilitating the generation of photogenerated holes and active oxidants. Second, the composite photoanode exhibits enhanced tetracycline adsorption via π–π stacking and hydrogen bonding, thereby promoting degradation kinetics. The photoanode also shows excellent reusability. Total organic carbon (TOC) analysis and biotoxicity tests confirm effective mineralization and reduced environmental toxicity. Furthermore, the system demonstrates promising concurrent cathodic hydrogen evolution. This work highlights the potential of the W-BiVO₄@CoNi-MOFN-based PEC system for integrated wastewater treatment and hydrogen production. Full article

Pharmaceuticals and personal care products (PPCPs), as persistent organic pollutants, are widely present in various aquatic environments. Their long-term presence in aquatic environments poses a potential threat to ecosystems and human health. This study established an efficient, green, and cost-effective photocatalytic method using P25 titanium dioxide (P25TiO₂) to simultaneously degrade five representative PPCPs (methyl paraben (MeP), carbamazepine (CBZ), bisphenol A (BPA), diclofenac (DFC), and triclosan (TCS), while elucidating the reaction mechanisms. Under sunlight irradiation, degradation rates for all five PPCPs reached 100%, achieving near-complete mineralization with total organic carbon (TOC) removal rates exceeding 95%. This demonstrates the system’s exceptional capability to not only degrade the parent compounds but to thoroughly convert them into benign inorganic substances. We systematically investigated the effects of catalyst concentration, initial pollutant concentration, light intensity, pH, and various common inorganic anions (chloride, sulfate, bicarbonate, phosphate) and humic acid (HA) on the degradation process. Additionally, mechanistic studies indicated that hydroxyl radicals (·OH) are the primary active species in the system. The degradation rate differences among various persistent organic pollutants (DFC > BPA > TCS > CBZ > MeP) primarily stem from variations in the reactivity of different functional groups within their molecular structures toward ·OH. In summary, this study provides a promising and practical solution for treating complex medical wastewater containing five typical PPCPs. Full article

Chelating agents can extend the operational pH range of iron-based advanced oxidation processes, yet comprehensive studies on chelated Fe-activated persulfate systems for textile dye degradation remain scarce. This study establishes an integrated framework for optimizing Fe(II)/persulfate (PS) systems using chelating ligands and hybrid energy inputs under near-neutral conditions. Among the tested systems, Fe(II)/PS complexed with citric acid (CA) exhibited superior performance, achieving ~91% dye removal within 20 min at pH 6.5 under optimized conditions (1.25 mM Fe(II), 10 mM PS, 0.1 mM CA). Chelation stabilized Fe redox cycling and prevented precipitation, enabling effective catalysis across pH 3–10. Optimal CA/Fe and Fe/PS ratios (0.1:1.25 and 1.25:10) yielded ~96% decolorization and 67.65% TOC removal in 60 min, while excessive chelation reduced activity. Transition metal screening (Mn(II), Zn(II), Cu(II), Co(II), and Ni(II) confirmed Fe(II) as the most effective activator, providing removal efficiencies up to 3.2-fold higher than competing metals. Mixed-dye experiments showed competitive degradation, with >37% color removal after 60 min for ternary dye mixtures. Mineralization reached ~92% TOC reduction after 120 min, indicating deep oxidation beyond chromophore cleavage. Reactive species quenching revealed a mixed oxidation mechanism involving ^•OH radicals and high-valent Fe(IV) species. Hybrid assistance improved mineralization, with UVC increasing TOC removal by 15.6%, while solar irradiation provided moderate enhancement under low-energy input. In contrast, low-power ultrasound (40 kHz, 60 W) delivered only 17.6 W acoustic power to the solution and did not improve performance due to limited cavitation and mixing. This work thus contributes a robust platform for advancing chelated iron-persulfate oxidation systems toward practical, effective treatment of recalcitrant dye-contaminated wastewaters under near-neutral conditions. Full article

The removal of nitrogen and phosphorus from wastewater with low organic carbon content requires the addition of an external carbon source. The objective of this study was to assess the influence of hydraulic retention time (HRT) on the efficiency of external carbon source utilization and on nitrogen and phosphorus removal in a Rotating Electro-Biological Disc Contactor (REBDC). The energy demand was evaluated based on energy consumption (E) and current efficiency (CE). Hydroponic tomato wastewater was treated in the REBDC at a constant current density of 2.5 A/m². Sodium acetate was used as the carbon source. Two C/N ratios were tested, 2.0 and 3.0, under HRT conditions of 24 h and 48 h. For both C/N ratios, extending the HRT resulted in decreased nitrogen removal efficiency. At HRT = 48 h and C/N = 3.0, the nitrogen concentration in the effluent was more than three times lower compared with C/N = 2.0. The highest phosphorus removal efficiency was achieved at C/N = 3.0 and HRT = 48 h (98.8%). Increasing the HRT led to reduced TOC utilization for both C/N ratios. As a consequence of extended HRT, lower CE values and higher E values were observed, indicating increased energy demand for nutrient removal. Full article

Soluble cutting fluids (SCFs) from metalworking processes pose significant treatment challenges. Here, SCFs were treated using a monopolar electrochemical (EC) system, using turning scrap generated from metalworking operations as the anode. The system was operated for 60 min under various conditions, including different anode materials, electrolyte addition, aeration, and initial pH. Treatment performance was evaluated in terms of chemical oxygen demand (COD_Cr) and total organic carbon (TOC) removal efficiencies and specific energy consumption (SEC) for COD_Cr removal. The Al scrap (20 g/L) showed the optimal overall performance, achieving COD_Cr and TOC removal efficiencies of 29.28% and 25.62%, respectively, with an SEC comparable to that of the Al electrode. Electrolyte addition improved the energy efficiency under all conditions, with NaNO₃ 10 mM yielding the lowest SEC (0.57 kWh/kg-COD_Cr), and aeration negatively affected both removal efficiency and energy consumption. Although acidic conditions (pH 2) resulted in high apparent removal, most of the reduction occurred during pre-treatment pH adjustment, and the highest energy efficiency was achieved at pH 7 (0.47 kWh/kg-COD_Cr). These results demonstrate that Al turning scrap is a promising alternative anode material for electrochemical treatment of SCFs with optimized electrolyte addition and operating pH enabling improved energy efficiency. Full article

A novel catalyst, Tm₂FeSbO₇, was synthesized by employing the solid-phase high-temperature sintering method, and, for the first time, it was utilized to create a Z-type heterojunction with BiYO₃. A direct Z-scheme Tm₂FeSbO₇/BiYO₃ heterojunction photocatalyst (TBHP) was successfully produced by employing the ball-milling technique. X-ray diffraction analysis results indicated that Tm₂FeSbO₇ crystallized in a cubic pyrochlorestructure which owned the Fd-3m space group, with a unit cell parameter of 10.1769 Å, whereas BiYO₃ displayed a fluorite structure in the Fm-3m space group, with a unit cell parameter of 5.4222 Å. The Mossbauer spectrum of Tm₂FeSbO₇ showed that Fe³⁺ ions might locate at octahedral sites. The measured bandgap widths for the TBHP, Tm₂FeSbO_7, and BiYO₃ were 2.14 eV, 2.21 eV, and 2.30 eV, respectively. Multiple experimental results demonstrated that the TBHP exhibited a higher valence band ionization potential, a narrower band gap width, and a higher removal efficiency of the sulfamethoxazole (SMX) compared with the Dy₂TmSbO₇/BiHoO₃ heterojunction photocatalyst. Under visible-light irradiation (VISLI) of 115 min, the TBHP showcased exceptional photocatalytic elimination performance; therefore, the elimination rate of the SMX and the total organic carbon (TOC) mineralization rate reached 99.51% and 98.10%, respectively. In contrast to single-component Tm₂FeSbO₇, BiYO_3, or conventional nitrogen-doped titanium dioxide (N-TiO₂) catalyst, the TBHP exhibited removal efficiency enhancement for degrading the SMX by 1.17 times, 1.31 times, or 4.06 times. Simultaneously, the matching mineralization rate for removing the TOC density by employing the TBHP was 1.20 times, 1.34 times, or 4.73 times higher than that by employing Tm₂FeSbO₇, BiYO₃, or conventional N-TiO₂. Above experimental results indicated that the mineralization efficiency for removing TOC density by employing the TBHP was higher than that by employing Tm₂FeSbO₇, BiYO₃, or N-TiO₂. Radicals trapping experiments and the electron paramagnetic resonance spectroscopy results revealed that hydroxyl radicals, superoxide anions, and photoinduced holes were the primary active species during the catalytic elimination course of the SMX by employing the TBHP under VISLI. The results demonstrated that the direct Z-scheme TBHP, which was developed in this study, exhibited the maximal removal efficiency for degrading the SMX in contrast to Tm₂FeSbO₇, BiYO₃, or N-TiO₂. Additionally, the possible elimination routes and elimination mechanisms of the SMX were proposed. Therefore, an important scientific foundation for developing high-performance heterojunction catalysts was established. Full article

This study examines the application of mining effluents as feed solutions in a bench scale pressure retarded osmosis (PRO) system for energy generation and the prospect of water recycling or safe discharge to the environment. Effluents were characterized and pretreated by ultrafiltration (UF) and nanofiltration (NF) prior to PRO. The PRO process was then conducted over 6 h in a cross flow flat plate cell with an effective membrane area of 34 cm², a hydraulic pressure of 12.4 bar and a 3M ammonium carbonate (NH₄)₂CO₃ as draw solution. Effluent 1 contained ions such as Cl⁻ (539 mg/L), NO₃⁻ (585 mg/L), SO₄²⁻ (3000 mg/L), Na⁺ (560 mg/L), and Mg²⁺ (656 mg/L), with a total dissolved solids (TDS) concentration of 5400 mg/L, chemical oxygen demand (COD) of 136 mg/L, total organic carbon (TOC) concentration of 3.5 mg/L, and acidic pH of 3.8, while effluent 2 was highly dominated by Cl⁻ (32,100 mg/L), NO₃⁻ (9720 mg/L), SO₄²⁻ (6512 mg/L), Na⁺ (14,306 mg/L), and Mg²⁺ (5336 mg/L), had a TDS concentration of 73,315 mg/L, COD of 8100 mg/L, TOC concentration of 10.2 mg/L, and pH of 7.4. These physiochemical properties indicated a significant potential of fouling and scaling which necessitated the appropriate pretreatments. It was shown that integrating UF and NF pretreatments was highly effective in refining the quality of effluents with a significant removal efficiency of above 90% for ions and heavy metals by NF, led to fouling mitigation, higher and more stable power density as well as potential water reuse or safe environmental discharge. The achieved water fluxes and power densities were 54 L/m²h and 18.6 W/m², for effluent 1, and 38 L/m²h and 13 W/m², for effluent 2, respectively. The outcome of this study is applicable for the mining sector especially in remote areas with the potential for water and energy recoveries to contribute to more sustainable mining operations. Full article

Leachates generated in sanitary landfills are a mixture of contaminants harmful to adjacent ecosystems. Coagulation and flocculation are common treatment methods; however, their efficiency depends on the type of coagulant–flocculant and the operating conditions. This study addressed leachate treatment using two natural biocoagulants, Nostoc sphaericum (CNS) and Opuntia ficus-indica mucilage (CMN), in combination with aluminum sulfate (CSA). Optimization was performed using response surface methodology, employing a Box–Behnken design with five factors, namely CNS, CMN, and CSA doses, as well as agitation time and agitation speed, evaluated at three levels, on turbidity reduction. Fourier transform infrared spectroscopy (FTIR) showed that the biocoagulants possess anionic surfaces with carboxyl and hydroxyl groups. The particle size of CNS exhibited a bimodal distribution with a zeta potential of −28.74 mV, while CMN showed a unimodal distribution with a zeta potential of −21.95 mV. Under optimal conditions (88.97 mg/L CNS, 105.60 mg/L CMN, 9.13 mg/L CSA, a mixing time of 25.96 min, and an agitation speed of 24.21 rpm), a turbidity reduction to 48.15 NTU was predicted. During the experimental validation of these optimal conditions, turbidity was reduced to 49.02 NTU, achieving a removal efficiency of 70%. Total organic carbon (TOC) was reduced by 65%, and metals such as arsenic were reduced by 56%. Reductions in phosphates and Biochemical Oxygen Demand (BOD₅) were moderate, while the removal of Chemical Oxygen Demand (COD), surfactants, and ammoniacal nitrogen was limited. These results indicate that the combination of CNS and CMN is a viable alternative for leachate pretreatment. Full article

Coagulation significantly alters molecular characteristics and oxidizability of dissolved organic matters (DOM), while the linkage between DOM molecular characteristics and fragmentation pathways were unclear for the following processes. Here, four typical coagulation processes were employed to improve DOM molecular properties in leachate, and their subsequent impact on oxidizability in ozonation was identified. The results indicate that Polyaluminum chloride (PAC), Polyferric sulfate (PFS), Polyaluminium ferric chloride (PAFC) and Polymerized aluminum ferric silicate (PSAF) can all reduce the COD and TOC levels of the leachate concentrate through coagulation and precipitation, with PAC achieving the highest removal efficiency. PAC-ozonation effectively removes aromatic and unsaturated compounds, significantly improving DOM composition and enhancing conditions for subsequent oxidation. In contrast, PFS shows the poorest removal of aromatics (2.92%) and polycyclic aromatics (9.81%), along with the highest NOSC (−0.5036) and lowest (DBE-O)/C (−0.0051), indicating greater oxidation resistance. Only 11% of COD was further removed by ozonation after PFS treatment, suggesting limited reactivity of the residual DOM. Machine learning analysis of molecular transformation networks further confirmed that PFS treatment produced the fewest conversion pathways following ozonation. This indicates the choice rules and relationship between coagulation and ozonation for landfill leachate. This work provides an effective strategy to enhance leachate treatability and reduce energy and reagent consumption in subsequent processes, thereby contributing to more sustainable and cost-effective landfill leachate management. Full article

The meat industry generates wastewater with high organic matter loads, posing a significant environmental risk if not properly treated. The present study evaluated the performance of a horizontal subsurface flow constructed wetland (HSSF-CW) treating slaughterhouse effluents characterized by high-strength influent concentrations of 3570.51 ± 153.82 mg/L COD, 2114.33 ± 104.58 mg/L BOD₅, and 1173.77 ± 96.95 mg/L TOC. Furthermore, Response Surface Methodology (RSM) was employed to model and optimize the operational parameters. The independent variables considered were hydraulic retention time (HRT: 3, 5, and 10 days) and vegetation type (Heliconia latispatha, Typha latifolia, and polyculture). The results demonstrated a statistically significant improvement in treatment efficiency, achieving maximum removal efficiencies of 86.5% for COD, 89.4% for BOD₅, and 91.5% for TOC. The statistical models exhibited high accuracy (R² ≥ 0.996, p < 0.001). Adjusted response surface equations identified the polyculture with a 5-day HRT as the most favorable operational scenario. These findings confirm that properly designed and operated constructed wetlands represent a viable and sustainable alternative for treating high-load agro-industrial effluents, contributing to the protection of receiving water bodies. Future research should focus on full-scale studies and the inclusion of critical parameters such as nutrients and pathogens for a more comprehensive system characterization. Full article

Landfill leachate (LL) is a complex wastewater characterized by high concentrations of organic matter and heavy metals, posing significant challenges to conventional treatment technologies. Electrochemical methods, particularly electrocoagulation (ECG), have shown promise for LL treatment; however, issues related to operational optimization and electrode durability remain insufficiently addressed. In this study, a novel electrocoagulation-based approach is proposed that systematically integrates process optimization with an explicit assessment of iron electrode reusability, which is an aspect that has been rarely explored in previous ECG studies on LL. Key operational parameters—current density, pH, inter-electrode distance, electrode surface area, and electrode material—were optimized to enhance treatment performance. Optimal conditions were achieved using iron electrodes at a current density of 256 A/m², pH 8, an inter-electrode distance of 1 cm, and an effective electrode surface area of 19.5 cm²/L. Under these conditions, removal efficiencies of 100% for zinc, 94.9% for copper, and 54.5% for total organic carbon (TOC) were obtained, demonstrating effective simultaneous removal of inorganic and organic contaminants. The electrode reusability tests showed stable removal efficiencies over ten consecutive operational cycles, highlighting the potential for reduced operational costs and improved process sustainability. Additionally, the treated effluent exhibited reduced phytotoxicity, as evidenced by lower germination inhibition (GI), reduced root growth inhibition (RGI), and enhanced removal of humic substances. Overall, the results demonstrate that the proposed ECG approach is a robust, flexible, and environmentally sustainable solution for LL treatment, with clear advantages over conventional EC systems in terms of long-term performance and resource efficiency. Full article

This study optimized a homogeneous photo-Fenton process for the simultaneous degradation of the emerging pesticides atrazine and methomyl in water using Response Surface Methodology (RSM). A synthetic agricultural effluent containing 2.0 mg L⁻¹ of each pesticide (COD = 103.2 mg O₂ L⁻¹; TOC = 26.1 mg C L⁻¹; BOD₅ = 45.8 mg O₂ L⁻¹) was treated in a recirculating UV–H₂O₂/Fe²⁺ reactor. A 2³ factorial design with replication and five central points identified the H₂O₂/Fe²⁺ ratio and irradiation time as the main factors controlling mineralization, achieving up to 88.9% COD removal in the best screening run. Steepest-ascent experiments were then performed to approach the region of maximum response, followed by a rotatable Central Composite Design (20 runs). The resulting quadratic model explained 98.14% of the COD variance (R² = 0.9814; adjusted R² = 0.9646; predicted R² = 0.8591; CV = 0.2736%) and predicted a maximum COD removal of 94.5% at a volumetric flow rate of 0.466 L min⁻¹, a Fenton ratio of 12.713 mg mg⁻¹, and a treatment time of 71.0 min. Experimental validation under these optimized conditions yielded highly reproducible removals of 94.2 ± 0.04% COD and 81% TOC, confirming the predictive capability of the RSM model and demonstrating a high degree of organic mineralization. The response surfaces revealed that increasing the Fenton ratio enhances oxidation up to an optimum, beyond which hydroxyl-radical self-scavenging slightly decreases efficiency. Overall, the integration of multivariable experimental design and RSM provided a robust framework to maximize photo-Fenton performance with moderate reagent consumption and operating time, consolidating this process as a viable alternative for the mitigation of pesticide-laden agricultural wastewaters. Full article

This study investigated the efficacy of electrochemical treatment of a water-soluble cutting fluid (SCF) solution using Al, Fe, and stainless steel (SUS304) scraps as three-dimensional (3D) electrode packing materials. The SCF solution had an initial COD_Cr of approximately 109,000 mg·L⁻¹, a TOC of approximately 25,000 mg·L⁻¹, and an initial pH of 9.65. During treatment, the pH remained in the alkaline range (9.99–10.67), and the solution conductivity was approximately 1000 μS·cm⁻¹. Using a conventional two-dimensional (2D) configuration, Al exhibited the highest removal efficiencies (TOC: 58.55%; COD_Cr: 57.12%). An applied current of 0.8 A, corresponding to a current density of 5.00 mA·cm⁻² based on the geometric electrode area, and an inter-electrode distance of 40 mm provided an optimal balance between treatment performance and energy consumption. Under these optimized conditions, the introduction of metal scraps as 3D packing media significantly enhanced treatment efficiency. Al scrap (20 g) achieved the highest TOC removal (69.55%), while Fe scrap showed superior COD_Cr removal (87.42% at 40 g) with the lowest specific energy consumption (0.27 kWh·kg⁻¹ COD_removed). The energy consumption of the baseline D system was 0.46 kWh·kg⁻¹ COD_removed(cage O) and 0.72 kWh·kg⁻¹ COD_removed(cage X). Overall, scrap-based 3D electrodes effectively improved organic removal and energy performance, demonstrating their potential as low-cost and sustainable electrode materials for the electrochemical pre-treatment of high-strength oily wastewater. Full article