Efficient treatment of saline recalcitrant petrochemical wastewater using heterogeneous UV-assisted sono-Fenton process

Unlocking the potential of Eichhornia crassipes for wastewater treatment: phytoremediation of aquatic pollutants, a strategy for advancing Sustainable Development Goal-06 clean water

The 2030 Agenda, established in 2015, contains seventeen Sustainable Development Goals (SDGs) aimed at addressing global challenges. SDG-06, focused on clean water, drives the increase in basic sanitation coverage, the management of wastewater discharges, and water quality. Wastewater treatment could contribute to achieving 11 of the 17 SDGs. For this purpose, phytoremediation is a low-cost and adaptable alternative to the reduction and control of aquatic pollutants. The objective of this study is to highlight the role of macrophytes in the removal and degradation of these compounds, focusing on Eichhornia crassipes (Mart.) Solms, commonly known as water hyacinth. The reported values indicate that this plant has a removal capacity of over 70% for metals such as copper, aluminum, lead, mercury, cadmium, and metalloids such as arsenic. Additionally, it significantly improves water quality parameters such as turbidity, suspended solids, pH, dissolved oxygen, and color. It also reduces the presence of phosphates, and nitrogen compounds to values below 50%. It also plays a significant role in the removal of organic contaminants such as pesticides, pharmaceuticals, and dyes. This study describes several valuable by-products from the biomass of the water hyacinth, including animal and fish feed, energy generation (such as briquettes), ethanol, biogas, and composting. According to the analysis carried out, E. crassipes has a great capacity for phytoremediation, which makes it a viable solution for wastewater management, with great potential for water ecosystem restoration.

Removal of Azo Dyes from Water Using Natural Luffa cylindrica as a Non-Conventional Adsorbent

Reducing high concentrations of pollutants such as heavy metals, pesticides, drugs, and dyes from water is an emerging necessity. We evaluated the use of Luffa cylindrica (Lc) as a natural non-conventional adsorbent to remove azo dye mixture (ADM) from water. The capacity of Lc at three different doses (2.5, 5.0, and 10.0 g/L) was evaluated using three concentrations of azo dyes (0.125, 0.250, and 0.500 g/L). The removal percent (R%), maximum adsorption capacity (Qm), isotherm and kinetics adsorption models, and pH influence were evaluated, and Fourier-transform infrared spectroscopy and scanning electron microscopy were performed. The maximum R% was 70.8% for 10.0 g L-1Lc and 0.125 g L-1 ADM. The Qm of Lc was 161.29 mg g-1. Adsorption by Lc obeys a Langmuir isotherm and occurs through the pseudo-second-order kinetic model. Statistical analysis showed that the adsorbent dose, the azo dye concentration, and contact time significantly influenced R% and the adsorption capacity. These findings indicate that Lc could be used as a natural non-conventional adsorbent to reduce ADM in water, and it has a potential application in the pretreatment of wastewaters.

Wastewater Characterization: Chemical Oxygen Demand or Total Organic Carbon Content Measurement?

The long time (2 h) required for measurement, expensive chemicals (Ag2SO4), and toxic reagents (K2Cr2O7, HgSO4) limit the application of the standard method for measuring the oxygen equivalent of organic content in wastewater (chemical oxygen demand, COD). In recent years, the COD has increasingly been replaced by the total organic carbon (TOC) parameter. Since the limit values of the pollution levels are usually given in terms of the COD, efforts are being made to find the correlation between these parameters. Several papers have published correlation analyses of COD and TOC for industrial and municipal wastewater, but the relationship has not been discussed for individual chemicals. Here, this relationship was investigated using 70 contaminants (laboratory chemicals, pharmaceuticals, and pesticides). The calculated COD values, in most cases, agreed, within ~10%, with the experimental ones; for tetracyclines and some chloroaromatic molecules, the measured values were 20-50% lower than the calculated values. The COD/TOC ratios were between 2 and 3: for macrolides, they were ~3; for fluoroquinolones and tetracyclines, they were ~2. The molecular structure dependence of the ratio necessitates the establishing of the correlation on an individual basis. In advanced oxidation processes (AOPs), the ratio changes during degradation, limiting the application of TOC instead of COD.

Electrochemical-based approaches for the treatment of pharmaceuticals and personal care products in wastewater

In recent times, emerging contaminants (ECs) like pharmaceuticals and personal care products (PPCPs) in water and wastewater have become a major concern in the environment. Electrochemical treatment technologies proved to be more efficient to degrade or remove PPCPs present in the wastewater. Electrochemical treatment technologies have been the subject of intense research for the past few years. Attention has been given to electro-oxidation and electro-coagulation by industries and researchers, indicating their potential to remediate PPCPs and mineralization of organic and inorganic contaminants present in wastewater. However, difficulties arise in the successful operation of scaled-up systems. Hence, researchers have identified the need to integrate electrochemical technology with other treatment technologies, particularly advanced oxidation processes (AOPs). Integration of technologies addresses the limitation of indiviual technologies. The major drawbacks like formation of undesired or toxic intermediates, s, energy expenses, and process efficacy influenced by the type of wastewater etc., can be reduced in the combined processes. The review discusses the integration of electrochemical technology with various AOPs, like photo-Fenton, ozonation, UV/H2O2, O3/UV/H2O2, etc., as an efficient way to generate powerful radicals and augment the degradation of organic and inorganic pollutants. The processes are targeted for PPCPs such as ibuprofen, paracetamol, polyparaben and carbamezapine. The discussion concerns itself with the various advantages/disadvantages, reaction mechanisms, factors involved, and cost estimation of the individual and integrated technologies. The synergistic effect of the integrated technology is discussed in detail and remarks concerning the prospects subject to the investigation are also stated.

Ultrasound-based advanced oxidation processes for landfill leachate treatment: Energy consumption, influences, mechanisms and perspectives

Advanced oxidation processes (AOPs) based on ultrasound (US) have attracted considerable attention in recent years due to its advantages in the degradation of landfill leachate. The review summarizes the existing treatment methods of leachate from lab-scale, compares their advantages and disadvantages by focusing on the degradation of emerging contaminants (ECs) in the leachate. Then the US-based AOPs are introduced emphatically, including their degradation mechanisms, influencing factors, energy consumption, further optimization methods as well as the possibility of field-scale application are systematically described. Moreover, this review also expounds on the advantages of dual-frequency US (DFUS) technology compared with single-frequency US, and a theoretically feasible DFUS process is proposed to treat ECs in the leachate. Finally, suggestions and prospects for US technologies in treating landfill leachate are put forward to aid future research on landfill leachate treatment. Meaningfully, this manuscript will provide reference values of US-based technologies in landfill leachate treatment for the practical use, facilitating the development of US-based AOPs in landfill leachate management and disposal.

Synergetic Photocatalytic Peroxymonosulfate Oxidation of Benzotriazole by Copper Ferrite Spinel: Factors and Mechanism Analysis

The development of oxidation processes with the efficient generation of powerful radicals is the most interesting and thought-provoking dimension of peroxymonosulfate (PMS) activation. This study reports the successful preparation of a magnetic spinel of CuFe₂O₄ using a facile, non-toxic, and cost-efficient co-precipitation method. The prepared material exhibited a synergetic effect with photocatalytic PMS oxidation, which was effective in degrading the recalcitrant benzotriazole (BTA). Moreover, central composite design (CCD) analysis confirmed that the highest BTA degradation rate reached 81.4% after 70 min of irradiation time under the optimum operating conditions of CuFe₂O₄ = 0.4 g L^-1, PMS = 2 mM, and BTA = 20 mg L^-1. Furthermore, the active species capture experiments conducted in this study revealed the influence of various species, including ^•OH, SO₄^•-, O₂^•-, and h⁺ in the CuFe₂O₄/UV/PMS system. The results showed that SO₄^•- played a predominant role in BTA photodegradation. The combination of photocatalysis and PMS activation enhanced the consumption of metal ions in the redox cycle reactions, thus minimizing metal ion leaching. Additionally, this maintained the reusability of the catalyst with reasonable mineralization efficiency, which reached more than 40% total organic carbon removal after four batch experiments. The presence of common inorganic anions was found to have a retardant effect on BTA oxidation, with the order of retardation following: HCO₃^- > Cl^- > NO₃^- > SO₄^2-. Overall, this work demonstrated a simple and environmentally benign strategy to exploit the synergy between the photocatalytic activity of CuFe₂O₄ and PMS activation for the treatment of wastewater contaminated with widely used industrial chemicals such as BTA.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe2+ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80 mM, the Fe2+ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20-25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Carbon Nanofibers-Sheathed Graphite Rod Anode and Hydrophobic Cathode for Improved Performance Industrial Wastewater-Driven Microbial Fuel Cells

Carbon nanofiber-decorated graphite rods are introduced as effective and low-cost anodes for industrial wastewater-driven microbial fuel cells. Carbon nanofiber deposition on the surface of the graphite rods could be performed by the electrospinning of polyacrylonitrile/N,N-Dimethylformamide solution using the rod as nanofiber collector, which was calcined under inert atmosphere. The experimental results indicated that at 10 min electrospinning time, the proposed graphite anode demonstrates very good performance compared to the commercial anodes. Typically, the generated power density from sugarcane industry wastewater-driven air cathode microbial fuel cells were 13 ± 0.3, 23 ± 0.7, 43 ± 1.3, and 185 ± 7.4 mW/m² using carbon paper, carbon felt, carbon cloth, and graphite rod coated by 10-min electrospinning time carbon nanofibers anodes, respectively. The distinct performance of the proposed anode came from creating 3D carbon nanofiber layer filled with the biocatalyst. Moreover, to annihilate the internal cell resistance, a membrane-less cell was assembled by utilizing a poly(vinylidene fluoride) electrospun nanofiber layer-coated cathode. This novel strategy inspired a highly hydrophobic layer on the cathode surface, preventing water leakage to avoid utilizing the membrane. However, in both anode and cathode modifications, the electrospinning time should be optimized. The best results were obtained at 5 and 10 min for the cathode and anode, respectively.

Valorisation of residual iron dust as Fenton catalyst for pulp and paper wastewater treatment

In this work, the performance of residual iron dust (RID) from metallurgic industry was assessed as Fenton catalyst for the treatment of real pulp bleaching wastewater. The focus was on the removal of recalcitrant pollutants AOX (adsorbable organic halides), by a novel, cleaner, and cost-effective circular solution based on a waste-derived catalyst. The behaviour of RID as iron source was firstly assessed by performing leaching tests at different RID:wastewater w/v ratios and contact time. Afterwards, RID-catalysed homogeneous and heterogeneous Fenton processes were conducted to maximise AOX removal from the pulp bleaching wastewater. Reusability of RID was assessed by a simple collect-and-reuse methodology, without any modification. Similar AOX removal under less consumption of chemicals was achieved with the novel heterogeneous Fenton process. Reaction in the bulk solution was the main pathway of AOX removal, given that the low surface area and porosity of the material did not allow for a high contribution of surface reaction to the overall performance. Moreover, AOX removal was similar over two consecutive treatment cycles, with Fenton process being responsible for 56.7-62.1% removal of AOX from the wastewater, and the leaching step adding 11.4-13.2%. At the end of treatment, COD either decreased (1^st cycle) or remained unchanged (2^nd and 3^rd cycle). The operating cost of the optimised heterogeneous Fenton was 3-11% lower than under conventional Fenton process. This work presented a novel, circular solution based on a low-cost waste-derived catalyst, advancing the knowledge needed to foster industrial application of such technologies to increase industrial environmental performance and efficiency.

Comparison of Fenton and Ozone Oxidation for Pretreatment of Petrochemical Wastewater: COD Removal and Biodegradability Improvement Mechanism

Cost-effective pretreatment of highly concentrated and bio-refractory petrochemical wastewater to improve biodegradability is of significant importance, but remains challenging. This study compared the pretreatment of petrochemical wastewater by two commonly used chemical advanced oxidation technologies (Fenton and ozone oxidation), and the mechanisms of biodegradability improvement of pretreated wastewater were explored. The obtained results showed that in the Fenton oxidation system, the COD removal of petrochemical wastewater was 89.8%, BOD5 decreased from 303.66 mg/L to 155.49 mg/L, and BOD5/COD (B/C) increased from 0.052 to 0.62 after 60 min under the condition of 120 mg/L Fe2+ and 500 mg/L H2O2, with a treatment cost of about 1.78 $/kgCOD. In the ozone oxidation system, the COD removal of petrochemical wastewater was 59.4%, BOD5 increased from 127.86 mg/L to 409.28 mg/L, and B/C increased from 0.052 to 0.41 after 60 min at an ozone flow rate of 80 mL/min with a treatment cost of approximately 1.96 $/kgCOD. The petrochemical wastewater treated by both processes meets biodegradable standards. The GC–MS analysis suggested that some refractory pollutants could be effectively removed by ozone oxidation, but these pollutants could be effectively degraded by hydroxyl radicals (•OH) produced by the Fenton reaction. In summary, compared with ozone oxidation, petrochemical wastewater pretreated with Fenton oxidation had high COD removal efficiency and biodegradability, and the treatment cost of Fenton oxidation was also lower than that of ozone oxidation.

Investigations on influences of MWCNT composite membranes in oil refineries waste water treatment with Taguchi route

Most of the 'oil refineries' severally pollutes the water resources by depleting their untreated waste water like cooling water, storm water and unsanitary sewage water. These wastewaters are to be treated with high care to protect the human, pebbles, plants, fish and other water animals and from harmful effects. The present study focused to treat the oil refinery wastewater by means of Multi wall carbon nanotube (MWCNT) coated Polyvinylidene Fluoride (PVDF) membrane. The main objectives are: to increases the life of filter, reduce the percolation flux and reduce the formation of antifouling in the filter by using MWCNT composite membrane in it. Different process parameters of the proposed water treatment process, like diameter of MWCNT (15 nm, 20 nm, 25 nm and 30 nm), operating pressure (3 bar, 4 bar, 5 bar and 6 bar), pH value (3, 5, 7 and 9) and temperature (25 °C, 30 °C, 35 °C and 40 °C) temperature. Taguchi statistical technique is employed for designing experiments and for optimizing the process parameters of wastewater treatment process of an oil refinery. The proposed filter for wastewater treatment exhibited appreciable performance in removal rate of Percolation flux, percentage of chemical oxygen demand removal and percentage of total carbolic rejection as 27.2 kg/m²h, 78.51% and 95.33% respectively.

The comparison of Fenton and photo-Fenton oxidation as a primary unit process for the treatment of raw textile wastewaters

The Fenton and photo-Fenton oxidation processes (FOP and PFOP) are usually applied as a secondary unit process, and direct usage of both processes is critical in textile wastewater treatment. There is seldom study on the direct application of the FOP or PFOP showing the treatment of raw textile industry wastewaters. This study demonstrates the application and comparison of both FOP and PFOP as single units separately for the treatment of wastewater in a textile industry producing woven fabrics. In both processes, the highest treatment efficiency was achieved at pH 3. Chemical oxygen demand (COD), suspended solids (SS), and color parameters in FOP reduced from 1341 to 254 mg/L, 99.5 to 19.9 mg/L, and 1396 to 97.7 Pt-Co, respectively. Separately, in the PFOP, 365-nm wavelength UV radiation sources have been used. In PFOP, the same parameters were reduced from 715 to 42.9 mg/L, 90 to 9 mg/L, and 2080 to 83.2 Pt-Co, respectively. These results were obtained at 0.7 g Fe2+/L and 2 mM H2O2 concentrations in both studies. PFOP can meet the textile industry receiving environment discharge standards of many countries, especially in Turkey. The use of PFOP as a single unit is possible in the treatment of textile industry wastewater without primary precipitation. The findings in this study may be practical for the adaptation of the processes on the field scale. PRACTITIONER POINTS: There is seldom study on the direct application of Fenton or photo-Fenton processes as a single unit to raw textile wastewaters This study shows the application of the Fenton or photo-Fenton processes as single units for the treatment of raw wastewater in a textile industry Results of both processes in this study meet the discharge standards of many countries Evaluations of efficiencies of both processes were achieved This study may be the focus of attention of treatment plant operators and researchers.

Peroxymonosulfate activation by Fe3O4-MnO2/CNT nanohybrid electroactive filter towards ultrafast micropollutants decontamination: Performance and mechanism

Electrocatalytic peroxymonosulfate (PMS) activation is a promising advanced oxidation process for the degradation of micropollutants. Herein, we developed an electroactive carbon nanotube (CNT) filter functionalized with Fe₃O₄-MnO₂ hybrid (Fe₃O₄-MnO₂/CNT) to activate PMS towards ultrafast degradation of sulfamethoxazole (SMX). SMX was completely degraded via a single-pass through the nanohybrid filter (τ < 2 s). The ultrafast degradation kinetics were maintained across a wide pH range (from 3.0 to 8.0), in complicated matrices (e.g., tap water, lake water, WWTP effluent and pharmaceutical wastewater), and for the degradation of various persistent micropollutants. Compared with a conventional batch reactor, the flow-through operation provides an 9.2-fold higher SMX degradation kinetics by virtue of the convection-enhanced mass transport (1.47 vs. 0.16 min^-1). The efficient redox cycle of Fe²⁺/Fe³⁺ and Mn²⁺/Mn⁴⁺ facilitate the PMS activation to generate SO₄^•- under electric field. Meanwhile, the ketonic groups on the CNT provide active sites for the generation of ¹O₂. Both experimental and theoretical results revealed the superior activity of nanohybrid filter associated with the synergistic effects among Fe, Mn, CNT and electric field. Therefore, the electrocatalytic filter based PMS activation system provides a green strategy for the remediation of micropollutants in a sustainable manner.

Encapsulation of spinel CuCo2O4 hollow sphere in V2O5-decorated graphitic carbon nitride as high-efficiency double Z-type nanocomposite for levofloxacin photodegradation

In this study, spinel CuCo₂O₄ (CCO) with a hierarchical hollow sphere morphology was encapsulated in V₂O₅-decorated ultra-wrinkled graphitic carbon-nitride (VO-UCN) for the first time via a facile glycerol-assisted solvothermal method in the interest of developing a novel high-efficiency double Z-type nano-photocatalyst (denoted as VO-UCN@CCO). The remarkable physicochemical features of the as-prepared nano-photocatalysts were verified using diverse characterization techniques including TGA, XRD, FT-IR, FE-SEM, TEM, BET, UV-vis DRS, PL, EIS, and transient photocurrent techniques. Herein, VO-UCN@CCO nanocomposite was employed for the photodisintegration of levofloxacin (LVOF) antibiotic under visible-light irradiation and the impact of certain operative reaction system variables was explored in an effort to optimize the photocatalytic capability. The 40% loading of CCO in VO-UCN@CCO nanocomposite was found to display maximum photocatalytic performance (about 95%) for LVOF photodecomposition, which was 9.3, 6.6, and 13.8 times greater when compared with pristine VO, UCN, and CCO, respectively. A high capability was observed for as-prepared photocatalyst during reusability tests and near 90% degradation efficiency was obtained in the sixth run. The complete mineralization of LVOF was achieved by the VO-UCN@CCO photocatalyst process after 300 min of reaction. An excellent synergy factor towards the degradation of LVOF was obtained for VO-UCN@CCO compared to each of its components alone. This peculiar design is envisaged to provide new inspirations for ameliorating the photocatalytic decontamination of tenacious and non-biodegradable species present in real wastewater.

Iron nanoparticles supported on N-doped carbon foam with honeycomb microstructure: An efficient potassium peroxymonosulfate activator for the degradation of fluoranthene in water and soil

A promising technology was developed for the remediation of fluoranthene (FLT) contaminated water and soil. Specifically, iron nanoparticles supported on N-doped carbon foam (Fe@CF-N) was synthesized by in-situ impregnation and a unique calcination process using pine cone as the precursor. The obtained Fe@CF-N was used as an activator of potassium peroxymonosulfate (PMS) to degrade FLT in water and soil. According to experimental results, Fe@CF-N had a three-dimensional network structure with a large specific surface area of 249.0 m² g^-1, displaying excellent catalytic performance. The maximum removal efficiency of FLT in water and soil reached 81.83% and 78.12% within 180 min, respectively. After four consecutive degradation cycles, the removal efficiency of FLT in water was still 55%. Electron spin resonance (ESR) measurements showed that hydroxyl radicals (·OH), sulfate radical (SO₄^-·) and ¹O₂ were the major reactive oxygen species (ROS). A series of low molecular weight intermediates were generated during the FLT degradation progress, such as C₆H₆O₃ and C₃H₈O₂. The effect of Fe@CF-N/PMS system on the phytotoxicity was evaluated via bioassay based on peas. The results indicated that seed germination rate and root shoot elongation of remediated soil by Fe@CF-N/PMS system were not significantly different from those of noncontaminated soil. This study provided a cost-effective remediation option for PAHs contaminated water and soil.

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.

Bisphenol A degradation by peroxymonosulfate photo-activation coupled with carbon-based cobalt ferrite nanocomposite: Performance, upgrading synergy and mechanistic pathway

Cobalt ferrite (CoFe₂O₄, CF) nanoparticles were anchored on the multiwalled carbon nanotube (MWCNT) for synthesis of CF@MWCNT nanocomposite and enhancing the catalytic activity of CF. After well characterization, it was applied as a catalyst towards photo-activation peroxymonosulfate (PMS) for degradation of bisphenol A (BPA). Based on the identified intermediates, a possible degradation pathway was proposed for BPA. CF@MWCNT coupled with PMS and UV (i.e., CF@MWCNT/PMS/UV) exhibited a better performance than homogeneous UV-assisted PMS processes under Fe and Co ions. A significant synergy on the degradation of BPA was observed in the simultaneous application of catalyst, UV light and PMS. Under optimum conditions, the removal efficiencies of 100 and 72.6% were attained respectively for BPA and TOC by CF@MWCNT/PMS/UV within 60 min reaction. These efficiencies were decreased to 88 and 61% after five times use of catalyst, respectively. The leaching of metal ions dissolved from the catalyst was slight during cyclic utilization of catalyst, confirming high stability of CF@MWCNT. In this process, the participation of radical mechanisms was approximately 60%, which SO₄^•- and HO^• species contributed as predominant oxidizing reactive species. It also showed the excellent catalytic performance towards decomposition of persulfate and hydrogen peroxide. Overall, UV-assisted PMS catalyzed by CF@MWCNT exhibited a good catalytic performance and so it can be potentially introduced as a promising method for efficient treatment of water contaminated by BPA.

Fast preparation of Fe3O4@polydopamine/Au for highly efficient degradation of tetracycline

This work reported the fast synthesis of magnetic polydopamine Au-Fenton catalyst (Fe₃O₄@PDA/Au) under UV irradiation at 365 nm. The microstructure of prepared nanocomposites was characterized by various techniques. The effects of several key factors (pH values, H₂O₂ content and TC concentration) of tetracycline (TC) degradation were evaluated. The results revealed that the TC and total organic carbon (TOC) removal rate reached up to 98.16% and 93.14% within 300 min under optimal conditions (pH 3, H₂O₂ 80 μL, TC concentration 20 mg/L). Besides, HO radicals were generated during the Fenton-like degradation process and the plausible degradation mechanism was discussed. Moreover, Fe₃O₄@PDA/Au catalyst retained excellent catalytic capacity (TC removal rate 96.94% and TOC removal rate 87.69%) and exhibited fantastic stability after six cycles. Moreover, metal ions leaching was evaluated (0.023 mg/L). Altogether, the novel Fe₃O₄@PDA/Au Fenton-like catalyst is highly promising for wastewater management.

Magnetic copper smelter slag as heterogeneous catalyst for tetracycline degradation: Process variables, kinetics, and characterizations

The treatment of solid wastes and wastewater for sustainable development has been a hot topic. This work proposes a novel process of "waste treating waste" using magnetic copper smelter slag (CSS) as heterogeneous catalyst. The effect of process variables and water matrix was studied on catalytic performance. Under conditions of CSS 10 g/L, H₂O₂ 100 mM, pH 4.4, and temperature 25 °C, tetracycline can be effectively degraded within 30 min. The apparent rate constant is comparable to or higher than previous reports, and the activation energy is 37 kJ/mol. The broad operation pH, slight effect of water matrix, and magnetic property of CSS are favorable for potential application. CSS was characterized by N₂ adsorption-desorption isotherm, SEM-EDS, XRD, XPS, ICP and zeta potential. The dominant components of CSS are fayalite and magnetite, and the major metals of Fe and Cu provide active sites for H₂O₂ activation. Hydroxyl radical generated by H₂O₂ activation is dominant oxidative specie for tetracycline degradation. The plausible mechanism of tetracycline degradation in the solution and on catalyst surface is proposed.

l-cysteine-modified Fe3 O4 nanoparticles as a novel heterogeneous catalyst for persulfate activation on BTEX removal

l-cysteine-modified Fe₃ O₄ nanoparticles (l-cys@nFe₃ O₄ ) were synthesized successfully and used as catalyst to activate persulfate (PS) for benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation. The composite was fully characterized, and the l-cys@nFe₃ O₄ had more protrusions and l-cys was combined on the surface of nFe₃ O₄ . The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/l-cys@nFe₃ O₄ system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe₃ O₄ chelated with l-cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/l-cys@nFe₃ O₄ system. The synergistic mechanisms of BTEX degradation in PS/l-cys@nFe₃ O₄ system were investigated by electron paramagnetic resonance (EPR), benzoic acid (BA) probe and X-ray photoelectron spectroscopy (XPS) tests. SFe bond in l-cys-Fe complexes promoted the electron transfer between nFe₃ O₄ core and the solution, iron and iron at the interface, thereby promoting the Fe³⁺ /Fe²⁺ cycle and the catalytic capacity of nFe₃ O₄ . The optimal pH of PS/l-cys@nFe₃ O₄ system was 3, while HCO₃ ^- and Cl^- exhibited negative influences on BTEX degradation. Only 14.2%, 15.5%, 15.9%, and 15.6% BTEX had been removed in the presence of 0.12-M PS and 8.0 g/L l-cys@nFe₃ O₄ under the actual groundwater condition. However, expanding the dosage of PS and l-cys@nFe₃ O₄ was an effective strategy to overcome the adverse effect. PRACTITIONER POINTS: L-cys@nFe₃ O₄ were synthesized successfully and used as catalyst to activate PS for BTEX degradation. Four successive cycles of BTEX degradation were completed in PS/L-cys@nFe₃ O₄ system. lS-Fe bond in L-cys@nFe₃ O₄ promoted the electron transfer between PS and nFe₃ O₄ core.

Enhanced oxidative removal of NO by UV/in situ Fenton: Factors, kinetics and simulation

A series of experiments on the oxidative removal of NO from flue gas using a novel in situ Fenton (IF) system was performed in the presence of ultraviolet light (UV). The comparison tests revealed that the in situ Fenton system facilitated by UV (UV/IF) has a better oxidation ability of NO than that of the IF system due to the photochemical effect on the generation of oxidative species like (OH). Both of the aforementioned oxidation efficiencies were higher than that of the conventional Fenton system (CF) depending on the premix of Fe²⁺ and H₂O₂ solutions, which attribute to the improvement of (OH) yield and valid utilization with continuous addition of fresh reagents and UV radiation. In follow-up experiments, the effects of UV power, gas flow rate, reagent temperature, Fe²⁺/H₂O₂ molar ratio, initial pH, initial concentration of NO and SO₂ and volume fraction O₂ and CO₂ on the oxidative removal of NO by UV/IF method were investigated respectively. Moreover, the results of kinetic analysis indicated that NO oxidation was confirmed to have a pseudo-first-order kinetics pattern. The rate constants decreased slightly with increasing liquid temperature, and then the apparent activation energy of NO oxidation reactions in the UV/IF system was calculated as -5.62 kJ/mol by the Arrhenius equation. Furthermore, the reaction mechanism and application prospects concerning NO oxidative removal by using the UV/IF system was speculated in brief. Finally, the computational fluid dynamics (CFD) simulations revealed that the improvement of axial and radial gas hold-up would enhance the gas-liquid contact and accelerate the oxidation reactions on the interface. In addition to reasonable control of process parameters, the optimization of reactor interior structure needs to be carried out via CFD simulation and experimental validation in future research, both are favourable to promote the NO oxidation efficiency and large-scale development of this technology.

A critical review on metal complexes removal from water using methods based on Fenton-like reactions: Analysis and comparison of methods and mechanisms

Metals mainly exist in the form of complexes in urban wastewater, fresh water and even drinking water, which are difficult to remove and further harm human health. Fenton-like reaction has been used for the removal of metal complexes. Effective removal of metal complexes using Fenton-like reaction requires the removal of both metals and organic ligands, meanwhile, the fate of metals and organic pollutions must be clearly understood. Thus, this review summarizes the relevant research on metal complex removal from using Fenton-like reactions in the past ten years, with the detailed removal approaches and mechanisms analyzed. Electro-, photo-, microwave/ultrasound-Fenton reactions or the synergistic Fenton reaction have been shown to exhibit excellent metal complex treatment capabilities. Furthermore, various catalysts, such as transition metals, bimetals and metal-free catalytic systems can expand the potential applications of Fenton-like reactions. Novel Fenton reaction methods without the addition of metals or H₂O₂, with construction of a dual active center catalyst, or with the introduction of other free radicals, are all worthy of further investigation. Due to increasing levels of environmental metal and organic pollutions remediation requirements, more research is required for the development of economical and efficient novel Fenton-like processes.

Recent trends and developments in Fenton processes for industrial wastewater treatment - A critical review

This study reviews the recent developments in the application of Fenton processes in real industrial wastewater treatment, focusing on heterogeneous catalysts and catalyst regeneration/reuse. This article presents the features, inherent advantages or drawbacks, and primary experimental results obtained on established and emerging Fenton processes, highlighting the course of innovations and current scenario in a research field that has recently undergone rapid transition. Therefore, a comprehensive literature survey was conducted to review studies published over the last decade dealing with application of Fenton processes to industrial wastewater treatment. The research in this field is primarily focused on discovering or synthesizing new materials to substitute conventional iron salt Fenton catalysts and/or regenerate and reuse the spent catalyst, in contrast to optimizing the application of existing materials. Hence, the emphasis is on producing reusable materials, transitioning from linear to circular economy. Some of the major challenges identified herein include analyzing or improving heterogeneous catalyst lifetime, determining the predominant pathway of heterogeneous and homogeneous catalysis to pollutant degradation, and defining the best layout to incorporate Fenton processes into full-scale treatment plants, particularly its coupling with biological treatment.

Application of polyamide thin-film composite layered on polysulfone-GO/TiO2 mixed matrix membranes for removal of nitrotoluene derivatives from petrochemical wastewaters

Release of harmful organic intermediates or byproducts during the manufacture of petrochemical compounds is a serious problem in petrochemical plants. In this work, polysulfone membranes blended with GO/TiO₂ nanocomposite were synthesized by phase inversion method and coated with a polyamide layer formed by interfacial polymerization to prepare a thin-film composite (TFC) sample. Analysis and characterization of the sample were carried out by XRD, FE-SEM, BET, FTIR/ATR, AFM, TGA, and zeta potential. Results indicated that incorporation of GO/TiO₂ into the membrane structure enhanced porosity, surface roughness, and macrovoid formation along the cross-section of the sublayer and permeability of the membrane. The TFC membranes were applied to remove mononitrotoluene (MNT) and dinitrotoluene (DNT) as the basic intermediates of toluene diisocyanate (TDI). The membranes demonstrated high efficiency (> 90%) for the removal of MNT and DNT according to the charge exclusion mechanism and Donnan effect. Application of the TFC membrane for treatment of wastewater in the TDI plant showed that the removal of pollutants is variable in the range of 45-65% and 53-69% for the membrane with the highest flux and highest rejection in different transmembrane pressure, respectively.

Photoinduced degradation of indigo carmine: insights from a computational investigation

In this work, we present a computational investigation on the photoexcitation of indigo carmine (IC). Physical insights regarding IC photoexcitation and photolysis were obtained from a fundamental perspective through quantum chemistry computations. Density functional theory (DFT) was used to investigate the ground state while its time-dependent formalism (TD-DFT) was used for probing excited state properties, such as vertical excitation energies, generalized oscillator strengths (GOS), and structures. All the computations were undertaken using two different approaches: M06-2X/6-311+G(d,p) and CAM-B3LYP/6-311+G(d,p), in water. Results determined using both methods are in systematic agreement. For instance, the first singlet excited state was found at 2.28 eV (with GOS = 0.4730) and 2.19 eV (GOS = 0.4695) at the TD-DFT/CAM-B3LYP/6-311+G(d,p) and TD-DFT/M06-2X/6-311+G(d,p) levels of theory, respectively. Excellent agreement was observed between the computed and the corresponding experimental UV-Vis spectra. Moreover, results suggest IC undergoes photodecomposition through excited state chemical reaction rather than via a direct photolysis path. To the best of our knowledge, this work is the first to tackle the photoexcitation, and its potential connections to photodegradation, of IC from a fundamental chemical perspective, being presented with expectations to motivate further studies.

Petrochemical wastewater and produced water: Treatment technology and resource recovery

Petrochemical wastewater and produced water from oil and gas operations typically contain an array of organic and inorganic contaminants. The complexity of the wastewater, stringent environmental regulations, and the need for sustainable solutions have driven many research efforts in studying and developing advanced technology or combined treatment processes. On the other hand, the wastewater itself can be resources for water, energy, and other valuable product if appropriate technology is developed to recover them in a cost-effective fashion. The research advances in wastewater treatment and resource recovery technology are reviewed and summarized. For petrochemical wastewater, progresses were made in advanced oxidation, biological processes, and recovery of energy and water from wastewater. For produced water, many efforts were focused on membrane processes, combined systems, and biological treatment. PRACTITIONER POINTS: Significant progress continued to be made on petrochemical wastewater and produced water treatment. Recent technological advances in various treatment processes were summarized. Technologies focusing on resource recovery (e.g., water or energy) were presented.

Nanomaterials application in greenhouse structures, crop processing machinery, packaging materials and agro-biomass conversion

The discovery of nanomaterials has flagged off crucial research and innovations in science and engineering. Its unique properties and diverse applications present it as the material for the future. The aim of this study is to presents the relative applications of nanomaterial in some aspects of agriculture production. The study discussed nanotechnology applicability in climate control and photosynthesis in the greenhouse farming, hydroponic systems, solar drying, fabrication of crop processing machine components, oxygen scavengers in crop packaging, and micro-organism stimulant in anaerobic digestion for agro biomass conversion. Some highlights from the review revealed that Nanotechnology can be applied to increase water surface area to volume ratio and heat transfer in the air moving into a greenhouse farming. Water cluster can be changed when treated with nanoparticles through ultraviolet absorption spectrum and nuclear magnetic resonance (NMR) spectroscopy resulting in lower micelles to manipulate water delivery in green house farming. Nano-fluids or Nano-composites can be used to recombine the reactive parts of thermal storage materials after broken at elevated temperature to recover the stored heat for drying purpose during the off-sunshine periods in solar drying of crops. Nanomaterials can be a source of electroluminescence light in hydroponic system and act as coatings and surface hardener in crop processing machinery for post-harvest machines. The reviewed work showed that nanotechnologies has good prospect in adding value in agricultural production in the aspects discussed.

Sono-photocatalytic degradation of tetracycline and pharmaceutical wastewater using WO3/CNT heterojunction nanocomposite under US and visible light irradiations: A novel hybrid system

In this paper, in-situ fabrication of tungsten oxide (WO₃) on carbon nano-tube (CNT) was performed via sol-gel/hydrothermal method to prepare WO₃/CNT nanocomposites and then coupled with visible light and ultrasound (US) irradiations for sono-photocatalytic removal of tetracycline (TTC) and pharmaceutical wastewater treatment. The as-prepared catalysts were characterized by FT-IR, XRD, TEM, UV-VIS DRS, FESEM, EDS, TGA, BET, BJH, EIS, and EDX techniques. The characterization tests, indicated successful incorporation of CTNs into the WO₃ framework and efficient reduction of charge carries recombination rate after modifying with CNT. The investigation of experimental parameters verified that 60 mg/L TTC could be perfectly degraded at optimum operational parameters (WO₃/CNT: 0.7 g/L, pH: 9.0, US power: 250 W/m², and light intensity: 120 W/m² over 60 min treatment. Trapping experiments results verified that HO radicals and h⁺ were the main oxidative species in degradation of TTC. The as-prepared photocatalysts could be reused after six successive cycles with an approximately 8.8 % reduction in removal efficiency. Investigation of the effect of real pharmaceutical wastewater revealed that this system is able to eliminate 83.7 and 90.6 % of TOC and COD, respectively after 220 min of reaction time. Some compounds with lower toxic impact and molecular weight, compared to raw pharmaceutical wastewater, were detected after treatment by sono-photocatalysis process. The biodegradability of real pharmaceutical wastewater was improved significantly after treatment by WO₃/CNT sono-photocatalysis.

Use of Ultrasound as an Advanced Oxidation Process for the Degradation of Emerging Pollutants in Water

Emerging pollutants are compounds of increased environmental importance and, as such there is interest among researchers in the evaluation of their presence, continuity and elimination in different environmental matrices. The present work reviews the available scientific data on the degradation of emerging pollutants, mainly pharmaceuticals, through ultrasound, as an advanced oxidation process (AOP). This study analyzes the influence of several parameters, such as the nature of the pollutant, the ultrasonic frequency, the electrical power, the pH, the constituents of the matrix and the temperature of the solution on the efficiency of this AOP through researches previously reported in the literature. Additionally, it informs on the application of the referred process alone and/or in combination with other AOPs focusing on the treatment of domestic and industrial wastewaters containing emerging pollutants, mainly pharmaceuticals, as well as on the economic costs associated with and the future perspectives that make ultrasound a possible candidate to solve the problem of water pollution by these emerging pollutants..

Comparison of four test methods for toxicity evaluation of typical toxicants in petrochemical wastewater on activated sludge

The shock impact of toxic pollutants in petrochemical wastewater on the activated sludge in biological treatment system is a key factor restricting the treatment efficiency. It is necessary to evaluate the toxicity of these pollutants by appropriate methods. In this study, four test methods were used to evaluate the toxicity of characteristic organic pollutants in petrochemical wastewater including 2,4-dichlorophenol, formaldehyde and pyridine, as well as one frequently-used reference toxicant 3,5-dichlorophenol. The sensitivity, accuracy and response time were compared among these methods: the oxygen consumption rate inhibition method (OCRIM), the dehydrogenase activity inhibition method (DAIM), the nitrification rate inhibition method (NRIM) and the growth rate inhibition method (GRIM). Principal component analysis was used to evaluate the correlation among the results of different methods. The OCRIM was comprehensively outstanding with the highest correlation between concentration and inhibition ratio (R² values were all higher than 0.9854), good sensitivity, best accuracy (error value of the effective concentrations below 0.15 mg/l) and fastest response (<40 min). The sensitivity of the NRIM was found to be the highest in this study (10% effective inhibition concentration (EC₁₀) value of 3,5-dichlorophenol was only 0.03 mg/l). Therefore, combined tests of OCRIM and NRIM were suggested.