Organic Carbon Removal Research Articles

Modeling and Optimization of Electrochemical Advanced Oxidation of Clopidogrel Using the Doehlert Experimental Design Combined with an Improved Grey Wolf Algorithm

In this research, the optimization of the electrochemical advanced oxidation treatment for the degradation of Clopidogrel was investigated. This study examined the influence of various experimental parameters including applied current, initial Clopidogrel concentration, and ferrous ion concentration by the use of the Doehlert design within a response surface methodology framework. The improved grey wolf optimizer was applied in order to define the optimum operating conditions. The monitoring of clopidogrel concentration during treatment revealed that complete disappearance of clopidogrel was achieved under an initial clopidogrel concentration of 0.02 mM, current intensity of 0.55 A, Fe2+concentration of 0.7 mM, and a reaction time of 20 min in a solution containing 50 mM Na2SO4 at pH 3. A quadratic polynomial model was developed, and its statistical significance was confirmed through the analysis of variance, demonstrating a high level of confidence in the model (R2 = 0.98 and p-value < 0.05). Furthermore, following electrolysis treatment for 480 min, the synthetic clopidogrel solutions underwent mineralization, achieving a 70.4% removal rate of total organic carbon. Subsequently, the applicability of the optimized process was tested on real pharmaceutical wastewater, and mineralization was investigated under the identified optimal conditions, resulting in a total organic carbon removal rate of 87% after 480 min of electrolysis time. The energy consumption for this system was calculated to be 1.4 kWh·kg−1 of the total organic carbon removed. These findings underscore the effectiveness and potential applicability of the electrochemical advanced oxidation for industrial wastewater treatment.

Unravelling the impact of oxic-settling-anaerobic cycle implementation and solid retention time on sludge generation, membrane operation, and contaminant removal in membrane bioreactors

Sewage sludge production represents a critical issue nowadays. The oxic-settling-anaerobic (OSA) system is a promising strategy for reducing sludge production during biological wastewater treatment. However, the distinct effect of OSA process and solid retention time (SRT) on sludge production has not been clarified yet. Therefore, during this study, the impacts of OSA system implementation at different SRT on sludge generation, membrane operation, and contaminant removal were elucidated in two lab-scale membrane bioreactors working at 20 d (MBR20) and 60 d (MBR60). After OSA implementation, the MBR-OSA20 and MBR-OSA60 were operated at a hydraulic retention time in the sludge holding tank (HRTSHT) of 6–12 h and of 6–24 h, respectively. The estimated observed sludge yield (Yobs) showed a reduction of 38–48 % for the MBR-OSA20, but no beneficial effect was observed for MBR-OSA60 at 6 h of HRTSHT. At the HRTSHT of 24 h, Yobs decreased by 17 % due to hydrolysis and acidogenic biomass fermentation. OSA implementation and long SRT had no negative effects on organic carbon and ammonium removal (96(±3) % and 100 %, respectively) and improved total nitrogen (TN) reduction by 19–41 %. Membrane fouling and sludge filterability were not significantly affected, whereas sludge settleability worsened after the implementation of the OSA cycle. This activity provided additional insights about the distinct impact of the OSA process and SRT on sludge production and characteristics, confirming the OSA process as a valid solution for reducing sludge production under a moderate SRT, but revealing a negligible effect on Yobs under a prolonged SRT and a short HRTSHT.

Research on Ammonium Removal from Wastewater by Adsorption and Ozonation Processes

With the ongoing amendment of the European Union legislation on the treatment of municipal wastewater, stricter requirements for the removal of pollutants are expected, which calls for the need for innovative wastewater treatment technologies. Our research was focused on the removal of ammonium nitrogen from municipal wastewater by nontraditional processes based on the use of adsorption processes on zeolite (ZEO) and ozone. Adsorption, adsorption-regeneration, and adsorptive ozonation processes were applied. All processes were carried out in a completely stirred reactor (CSR) and a jet-loop reactor (JLR) with external recirculation of the reaction mixture. Experimental measurements were carried out with real municipal wastewater after mechanical treatment. The best results were achieved in the adsorption-regeneration process, which was implemented in a current loop reactor. An average ammonium nitrogen removal efficiency of 53.1% was obtained by adjusting the pH value to 10.0. Average values of 46.2% and 49.2% for chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies are an added value of the process. The values of ammonium nitrogen, COD, and TOC removal efficiencies in individual cycles confirm the high stability of the process.

Combined treatment of domestic wastewater with landfill leachate using aerobic moving bed bioreactor (AeMBBR)

In this study, the treatment of landfill leachate (LFL) and domestic wastewater using an aerobic moving bed biofilm reactor (AeMBBR) was investigated. AeMBBR was filled with 30 % (v:v) biocarrier material (Kaldnes K1). The effect of different hydraulic retention times (HRTs) (6- 24 h) at a constant dissolved oxygen (DO) of 3.2 mg/L was investigated for system optimization. AeMBBR was successfully operated for LFL and domestic wastewater treatment corresponding to 94 %, and 78 % ammonium nitrogen (NH4-N) and total organic carbon (TOC) removals, respectively. Additionally, Proteobacteria (66%) have been identified as the predominant culture in the biofilm layer, which plays an important role in the co-treatment of domestic wastewater and LFL. Considering the results obtained; it was found that a significant amount of NH4-N was successfully removed.

Examining how media age affects organic matter removal in activated carbon filtration

AbstractWater samples from Waiora Drinking Water Treatment Plant in New Zealand were analyzed using excitation‐emission matrix fluorescence spectroscopy (EEMS) and parallel factor (PARAFAC) analysis to evaluate organic matter removal across the plant. The assessment also included the individual granular activated carbon (GAC) filters since the filters had varying media ages due to partial media replacement over a 10‐month period, presenting a unique assessment opportunity. PARAFAC analysis identified humic‐like, tyrosine‐protein‐like, and tryptophan‐protein‐like components representing fluorescent dissolved organic matter groups. The humic‐like component strongly correlated with total organic carbon (TOC) concentration and removal was significantly influenced by filter media age. However, protein‐like components had minimal TOC correlation and were not effectively removed by the overall plant treatment irrespective of filter media age. These findings have implications for disinfection, taste and odor, and bacterial regrowth and require an improved media replacement strategy. Further study of the protein‐like components is required.

Synergizing MBR and MCDI systems as a sustainable solution for decentralized wastewater reclamation and reuse

Decentralized wastewater reclamation and reuse systems have drawn much attention due to their capability for reducing the energy demand for water conveyance and reclaiming wastewater for local re-use. While membrane bioreactor (MBR) stands as a mature technology offering comprehensive solid and liquid separation, membrane capacitive deionization (MCDI) presents a promising avenue for ion separation. Unfortunately, MCDI has seldom been incorporated into decentralized wastewater reclamation and reuse systems. This study aims to exemplify the design and the operation of the synergistic integration of MBR and MCDI system with a practical capacity of 1 m3 d− 1, showcasing its efficacy in reclaiming and reusing water at regional level. The integrated system demonstrated significant high removal of total organic carbon (from 97 to 2 mg L− 1) and chemical oxygen demand (COD, from 218 to < 3 mg L− 1). Meantime, nearly complete transformation (approximately 91%) of NH3 to NO3− within the MBR effluent was observed with a hydraulic retention time of 4.3–4.8 h and a food-to-microorganism of 0.15–0.20 kg COD kg− 1 MLSS d− 1 which can be further removed through the MCDI system (> 92% TN removal). A significant milestone of MCDI unit was reached with the remarkable removal efficiency of total ions (93%) and water recovery (80%) using a stop-flow regeneration approach coupled with an optimized voltage of 2.0 V. The MCDI unit not only proved its high stability but also featured low energy consumption (0.44 kWh m− 3). Overall, synergizing MBR and MCDI systems emerges as a sustainable and effective solution for decentralized wastewater reclamation and reuse, contributing to a more environmentally friendly and resource-efficient water management paradigm.

Mineralization of clofibric acid by persulfate-promoted catalytic subcritical water oxidation process using CoFe2O4@SiO2 catalyst

The design and use of innovative treatment processes are very important in preventing the possible toxic effects of organic pollutants in aquatic environments. One of these methods is the subcritical water oxidation method, which has been used recently. In the current study, the mineralization of clofibric acid (CFA) was carried out under more effective and mild conditions using persulfate (PS) as an oxidant and CoFe2O4@SiO2 catalyst by the subcritical water oxidation (sub-CWO) process. Characterization of the synthesized catalyst was performed through XRD, FTIR, TEM and SEM–EDS analyses. In the CFA oxidation with persulfate-promoted catalytic Sub-CWO process, optimum working conditions was determined as 15 mM PS, 40 min, 383 K, and 0.3 g L−1 catalyst dosage using the response surface method and Box–Behnken design. The catalyst's efficiency remained relatively stable after three cycles under optimal conditions, resulting in a 97% total organic carbon (TOC) removal. Decomposition products were determined and a degradation mechanism was proposed.

Photocatalytic and persulfate-facilitated tetracycline degradation using NiFe2O4/carbon/polymer membranes: Activity and stability during flow-through

We synthesized NiFe2O4/carbon composite nanoparticles through a straightforward co-precipitation method, and incorporated these particles into porous polyethersulfone (PES) membranes via casting solution blending and film casting cum phase separation. The resulting photocatalytic membranes were used for the oxidative degradation of tetracycline (TC) in flow–through. We could demonstrate a higher catalytic activity in acidic conditions, a photocatalytic enhancement under visible light irradiation, and a 3x higher TC removal by persulfate (PS) in comparison to H2O2. Moreover, we observed the leaching of all Ni from the incorporated NiFe2O4 after using a membrane for 30 h in the flow-through degradation of 5 ppm TC with PS. This was accompanied by a loss of the total organic carbon removal activity, suggesting that Ni plays an important role as mineralization promoter. However, no Fe leaching occurred and the in situ formed FexOy retained the high TC conversion activity of NiFe2O4 after 30 h contact to acidic conditions, highlighting an exceptional long-term stability. We further identified that substrate desorption, catalyst complexation, and metal leaching can be facilitated by the presence of radical scavengers. This significantly contributed to their inhibitory effects, illustrating that an altered substrate-catalyst interaction may frequently be overlooked during the detection of radical species.

Bergera koenigii stem-derived magnetic biochar nanocomposite for enhanced photocatalytic efficiency of Ce1-xZnxO2-δ NPs under UV light for the degradation of methyl orange

The production of mesoporous, nanocrystalline, Zn-doped CeO2 nanoparticles (NPs) at various concentrations of Zn, Magnetic biochar (MBC)-Zn-doped CeO2 nanocomposites (NC), their characterizations, and photocatalytic degradation analysis are presented in this study. The synthesis of MBC-Ce0.91Zn0.09O2-δ NC is based on the carbonization of an iron oxide precursor with powdered Bergera koenigii stem (curry leaf stem). XRD and TEM results confirm polycrystalline, spherical fluorite Ce1-xZnxO2-δ NPs and MBC-Ce0.91Zn0.09O2-δ NC formations. The crystallite size varies from 4–12 nm with an increase in the doping concentration of Zn and 8.55 nm for MBC-Ce0.91Zn0.09O2-δ NC. XPS analysis displays the valence states and surface chemical composition of the as-prepared MBC-Ce0.91Zn0.09O2-δ sample. BET analysis provides the surface area (17–32 m2/g for Ce1-xZnxO2-δ NPs and 142 m2/g for MBC-Ce0.91Zn0.09O2-δ NC) and pore size (25–45 Å for Ce1-xZnxO2-δ NPs and 17.35 Å for MBC-Ce0.91Zn0.09O2-δ NC) of all the samples. All the samples possess good UV absorption in the range of 200–400 nm, and the bandgap energy of the as-prepared samples decreased from 3.088 to 2.79 eV with increased dopant concentration and on-load magnetic biochar. The oxygen deficiencies and lattice deformations of the as-prepared samples are studied using Raman, FTIR, and photoluminescence (PL) spectra. The degradation efficiency of 5 ppm Methyl Orange (MO) is analyzed using 50 mg catalytic (Ce1-xZnxO2-δ NPs, MBC-Ce0.91Zn0.09O2-δ NC) dosage by maintaining the pH of the solution as 4. After 16 min of UV irradiation, the as-synthesized Ce0.91Zn0.09O2-δ NPs and MBC-Ce0.91Zn0.09O2-δ NC exhibit 91 % and 97 % decolorization and 90 % and 94 % total organic carbon (TOC) removal efficiency. Regression analysis is performed to evaluate each model's applicability to photocatalytic degradation. The regeneration experiments on Ce0.91Zn0.09O2-δ NPs and MBC-Ce0.91Zn0.09O2-δ NC prove the stability of these catalysts for activating MO.

Heterogeneous catalytic ozonation of ciprofloxacin in wastewater with red mud: Characterization and performance

As a kind of solid waste, red mud (RM) contains various metal oxides, which have been proven to be effective as catalysts in different reactions. This study investigates the impact of RM on the catalytic ozonation for degrading ciprofloxacin (CIP). Compared to the single O3 system, the RM/O3 system improved CIP and Total Organic Carbon (TOC) removal rates by 44.8 % and 21.6 %, respectively, under identical conditions, and exceeded catalytic ozonation by most oxides. The influence factors, CIP degradation products, and reaction mechanisms were discussed in detail. The redox pairs of Fe2+/Fe3+ promoted the formation of oxygen vacancies (Ovac), and the hydroxyl groups and Ovac on the surface of RM were the active sites, facilitating ozone decomposition to reactive oxygen species (ROS). The scavenging experiments confirmed the presence of hydroxyl radical (·OH), peroxyl radical(·O2−), and singlet oxygen (1O2) in the RM/O3 system. Furthermore, toxicity assessment indicated reduced toxicity of intermediate products compared to the parent compound CIP. The catalytic performance of RM remained relatively stable after 5 cycles of experiments, with CIP removal remaining at 100 % and TOC removal decreasing by 5.3 %. This study offers a novel perspective on utilizing RM as an efficient catalyst in CIP ozonation, beneficial for both RM treatment and antibiotic pollution mitigation.

Integrating AgFeO2 and Bi5O7I to establish an S-scheme heterojunction with significantly boosted norfloxacin photocatalytic degradation

Developing highly efficient heterojunction photocatalysts for high performance antibiotic removal is of immense importance but still remains a challenge. Herein, AgFeO2-Bi5O7I (AF-BI), a promising oxygen vacancies rich binary S-scheme heterojunction photocatalyst was synthseized via co-precipitation and hydrothermal treatment. The spherical AgFeO2 spheres were uniformly affixed on the nanorods of Bi5O7I via an intimate contact, as verified through electron microscopy. The photodegradation efficiency of optimized 15 %AgFeO2-Bi5O7I (15AF-BI) for norfloxacin (NFX) was 98.2 % (120 min) with apparent rate constant 0.022 min−1 which was 4 times pure AgFeO2. In municipal water, removal efficiency reached 90.4 % and a high 76.1 % and 65.2 % total organic carbon removal in 3 h in visible light and solar light respectively was achieved. The coupling of AgFeO2 and Bi5O7I triggers electron transfer, forming an internal electric field (leading to a directional charge transfer efficient separation of the photo-induced carriers as confirmed by PL, EIS, TPCR results. The validation of existence of S-scheme mechanism and oxygen vacancies was achieved by in-situ X-ray photoelectron spectroscopy (XPS) and EPR analysis. The free radical scavenging experiments and electron spin resonance (ESR) spectroscopy revealed ●OH and ●O2– radicals were the major reactive species involved in the photodegradation process. The heterojunction is magnetic and can be separated under guidance of magnetic field which makes reusability and separation easy. Based on ESR findings, band structure analysis and mass spectrometry NFX degradation route was predicted. This work provides effective potential solution for preparing new magnetic S-scheme heterojunctions for effective antibiotics degradation and further will expand to realm of clean energy storage and conversion.

Enhanced Mineralization of Organic Pollutants through Atomic Hydrogen-Mediated Alternative Transformation Pathways.

Electrocatalytic hydrogen atom-hydroxyl radical (H*-·OH) redox system is a promising approach for contaminant removal and mineralization. However, its working mechanism, especially the effect of H*, remains unclear, hindering its practical application. Herein, we constructed an electrochemical reactor equipped with our self-made Pd-loaded Ti/TiO2 nanotube cathode and a commercial boron-doped diamond anode. After fulfilling the electrode characterization and free radical detection, we employed coumarin and 7-azido-4-methylcoumarin as probes to confirm the participation of H* in the transformation of organic compounds. A comprehensive study on the degradation kinetics, reaction, and mineralization mechanisms using benzoic acid (BA) and 4-chlorophenol (4-CP) as model compounds was further conducted. The rate constants and total organic carbon removal of BA and 4-CP in the redox system increased compared with those of the individual oxidation and reduction processes. Theoretical calculations demonstrate that H* opens up alternative pathways for BA and 4-CP ring cleavage, forming quinones as reactive intermediates. Furthermore, H* facilitates the mineralization of the typical intermediates, maleic acid and fumaric acid, through C=C bond addition and H-abstraction from the 1,1-diol structure. The presence of H* provides alternative pathways for pollutant transformation, consequently reducing the treatment duration.

Integration of coagulation–flocculation and photolysis processes for treating reverse osmosis concentrate (ROC) of pharmaceutical wastewater management

ABSTRACT This study provides novel insights into optimizing the integral treatment process, contributing to ROC treatment strategies. A comprehensive treatment approach for reverse osmosis concentrate (ROC) from pharmaceutical wastewater was investigated using an integral system consisting of a coagulation-flocculation and photolysis process. Ferric chloride (FC) and poly-aluminum chloride (PAC) are examined as coagulants within the range (0.1–1) gL−1, focusing on turbidity, chemical oxygen demand (COD), and total organic carbon (TOC) removal. The findings show that the optimal FeCl3 dosage is 0.4 gL−1, achieving significant turbidity reduction to 1 NTU. PAC at 0.2 gL−1 is optimal, reducing turbidity to 1 NTU and exhibiting non-linear behavior in COD and TOC removal, introducing them as a starting point to the post-treatment. Photolysis of treated samples at pH 7 yields COD reductions of 60.5% for PAC and 79.5% for FC, with respective TOC reductions of 79.5% and 75.23% over 360 min. At (pH 3.5) showed a significant reduction in the COD and TOC of treated ROC. The FC coagulant could decrease the COD from 261 to 5 mgL−1 (98% COD removal) and the TOC from 143.9 to 5 mgL−1 (74.8% TOC removal). The FAC coagulant could decrease the COD from 675 to 39 mgL−1 (93% COD removal) and the TOC from 186 to 13.1 mgL−1 (69.7% TOC removal). The conventional oxidant (H2O2) at optimal dosages enhanced COD and TOC removal at pH 7, with treated PAC and FeCl3 achieving 81.8% and 97.2% COD reduction and 89% and 98% TOC reduction at 360 minutes. These results were supported by the cost analysis in which this system was cost effective manner. This system can offer a solution for the efficient treatment of other types of industrial wastewater and open the door to new applications for water reuse on a broad scale, contributing to global water sustainability.

The effect of temperature on fouling in anaerobic membrane bioreactor: SMP- and EPS-membrane interactions

Biofouling is the main challenge in the operation of anaerobic membrane bioreactors (AnMBRs). Biofouling strongly depends on temperature; therefore, we hypothesize that the interactions and viscoelastic properties of soluble microbial products (SMP) and extracellular polymeric substances (EPS) vary with temperature, consequently influencing membrane permeability. This study compares the performance of an AnMBR operated at a similar permeate flux at two temperatures. The transmembrane pressure (TMP) rose rapidly after 5 ± 2 days at 25 °C but only after 18 ± 2 days at 35 °C, although the reactor's biological performance was similar at both temperatures, in terms of the efficiency of dissolved organic carbon removal and biogas composition, which were obtained by changing the hydraulic retention time. Using confocal laser scanning microscopy (CLSM), a higher biofilm amount was detected at 25 °C than at 35 °C, while quartz crystal microbalance with dissipation (QCM-D) showed a more adhesive, but less viscous and elastic EPS layer. In situ optical coherence tomography (OCT) of an ultra-filtration membrane, fed with the mixed liquor suspended solids (MLSS) at the two temperatures, revealed that while a higher rate of TMP increase was obtained at 25 °C, the attachment of biomass from MLSS was markedly less. Increased EPS adhesion to the membrane can accelerate TMP increase during the operation of both the AnMBR and the OCT filtration cell. EPS's reduced viscoelasticity at 25 °C suggests reduced floc integrity and possible increased EPS penetration into the membrane pores. Analysis of the structures of the microbial communities constituting the AnMBR flocs and membrane biofilms reveals temperature's effects on microbial richness, diversity, and abundance, which likely influence the observed EPS properties and consequent AnMBR fouling.

A short-circuited photo-assisted electrochemical cell for wastewater treatment

An economically attractive and highly efficient electrochemical cell is fabricated by connecting a carbon felt (CF) and a steel plate (S). Using this configuration, a photo-stimulated (CF/S) arrangement promotes photo-assisted Fenton reactions that result in the degradation of recalcitrant pollutants in water. As opposed to electro-Fenton reports that describe systems with externally polarized electrodes or photo-Fenton systems that utilize iron modified carbon substrates, this work proposes a short-circuited CF/S arrangement that does not require an external potential source. By following the color removal of a dye solution and the chromatography analysis of an emergent contaminant (sulfamethoxazole (SMX)), it was found that the highest efficiencies for the production of oxidative species are observed for tests performed under O2 saturation and UV light irradiation. Under these conditions, the CF/S arrangement achieves 97 % degradation of SMX (after 60 min) and 40 % of total organic carbon (TOC) removal after 240 min. Interestingly however, the CF/S arrangement also revealed a notable efficiency when anoxic and dark conditions were employed. We postulate that in this case, •OH radicals are produced by means of Fenton-like reactions and in order to support this interpretation, cyclic voltammetry and scanning electronic microscopy (SEM) and X-ray diffraction spectroscopy (XRD) measurements were carried out. The resulting data confirmed a Fenton-like mechanism that was further supported by the detection of •OH radical species that was assessed using coumarin absorption data. This study demonstrates that the CF/S cell is a promising approach for a novel photo-assisted Fenton wastewater treatment.

CNT/Nafion functionalized Ti/SnO2-Sb/β-PbO2-CNT/Nafion composite electrode toward highly active and robust degradation of octadecylamine and 4-dodecylmorpholine in real high-salinity system

The efficient removal of recalcitrant organics in high-salinity systems, specifically brine, poses a significant challenge for electrochemically advanced oxidation processes in terms of both activity and stability. Herein, a composite electrode comprising of CNT/Nafion functionalized Ti/SnO2-Sb/β-PbO2-CNT/Nafion was developed for efficient and stable removal of octadecylamine (ODA) and 4-dodecylmorpholine (DMP) in a real high-salinity environment. The degradation efficiencies of ODA and DMP on the composite electrode can reach 100 % within 60 min, respectively. The total organic carbon (TOC) removal efficiency of ODA and DMP was significantly improved to 78 % and 66 % with remarkably low energy consumption (0.414 and 1.402 kWh/g TOC), respectively. The electrochemical characterizations demonstrate that the composite electrode exhibits improved electrochemical activity (oxygen evolution potentials = 1.791 V) and electrode surface area (ECSA = 20 cm2), while maintaining reduced charge transfer resistance (Rct = 18.21 Ω/cm2) and enhanced corrosion-resistant capacity (corrosion potential = 1.115 V). Based on recycling and accelerated lifespan testing, the composite electrode demonstrates exceptional stability and recyclability. Additionally revealed was the linked stability mechanism. The electrocatalytic degradation of ODA and DMP begins with the removal of amino and morpholine rings, and then the decomposition of the carbon chains. Gas chromatography-mass spectrometry (GC–MS) and theoretical calculations were used to identify intermediate products generated during the degradation of ODA and DMP, and possible degradation pathways were provided in high-salinity systems, respectively. This work offered a fresh perspective on electrocatalytic oxidation for a real high-salinity system that is more efficient and stable.

A hydrodynamic cavitation prototype reactor evaluation for decreasing cephalexin concentration in aqueous solution

A prototype of a hydrodynamic cavitation reactor was evaluated to determine the effectiveness of this system on the percentage decrease of cephalexin concentration present in an aqueous solution prepared with ultrapure water. The process variables or factors were pH [5 and 9], number of holes in the cavitation plate [5 and 7] and reaction time (30 min and 60 min). The results indicate that the percentage removal of Cephalexin (CFX) and total organic carbon (TOC) depends on the variables studied and the interaction between them. The highest yields were achieved at pH 5, 5 holes in the cavitation plate and 60 min of reaction reaching values of 24.16 % for CFX and 16.8 % for TOC. It was determined that, for the lowest number of holes in the cavitation plate and acid pH, the phenomenon that guides the process is the hydrodynamic cavitation, when increasing the number of holes and therefore decreasing the intensity of cavitation, the pH becomes more relevant and has incidence on the performance of the analyzed process. On the other hand, it was determined that, also in reaction times of 30 min, removal values very close to the maximum values obtained are achieved. The process can be intensified by the simultaneous application of other advanced oxidation processes to increase the effectiveness.

Electro-Fenton degradation of pefloxacin using MOFs derived Cu, N co-doped carbon as a nanocomposite catalyst

Electro-Fenton (EF) can in-situ produce H2O2 and effectively activate H2O2 to generate powerful reactive species for the destruction of contaminants under acidic conditions, however, the production of iron-containing sludge and requirement of low working pH significantly hinder its practical application. Herein, a novel Cu, N co-doped carbon (Cu–N@C) with metal organic framework (MOF) as a precursor was constructed and adopted for the elimination of pefloxacin (PEF) in the heterogeneous electro-Fenton (HEF) process. PEF could be almost completely removed within 1 h and total organic carbon (TOC) removal efficiency was 48.57% within 6 h. Meanwhile, Cu–N@C had good repeatability and environmental adaptability, it can still maintain excellent catalytic performance after 10 cycles, and it exhibited satisfactory remediation performance in simulated water matrix. In addition, the HEF process catalyzed by Cu–N@C also showed satisfactory degradation effect on other organic pollutants including atrazine, methylene blue, and chlorotetracycline. Under the action of impressed current, the HEF system could generate H2O2 in-situ, and the active species could be generated in the redox cycle of Cu0/Cu1+/Cu2+. Electron paramagnetic resonance and quenching experiments confirmed that •OH was the dominant active species in the degradation of organic compounds. The degradation process of PEF was studied by mass spectrometry analysis of intermediate products. This study provided a simple method to prepare MOF-based electrocatalyst, which exhibits promising application potential for treatment wastewater.

Integrated anoxic/oxic biofilm reactor and photocatalytic treatment for enhanced antibiotic removal from real wastewater matrices

The widespread occurrence of sulfamethoxazole (SMZ), one of the widely used antibiotics, in aqueous environments, poses a significant threat to ecosystem health. In this study, the combination of a biofilm-based treatment system and photocatalysis was explored for the effective removal of SMZ. Initially, sulfur-doped g-C3N4 (S-C3N4) was synthesized and then combined with Bi2O3 to improve the overall photocatalytic performance. Characterization of as-prepared photocatalysts was performed to understand the chemical structures, morphologies, and optical properties. Batch studies have shown that, at neutral pH, using 1 g/L of S-C3N4/Bi2O3 (CNBI) composite results in the removal of 87.2 % of SMZ with an initial concentration of 10 mg/L. In accordance with the scavenging study, O2–• was identified as the dominant reactive species for the degradation of SMZ. After that, the identification of SMZ degradation products was carried out, and possible degradation pathways were proposed. After obtaining the optimal dosage, continuous experimentation was conducted using a photocatalytic reactor coated with CNBI composite combined with anoxic/oxic moving bed biofilm reactor. The investigation of real municipal and hospital liquid wastes containing SMZ showed an overall total organic carbon removal of 87 % and 81 %, respectively. Economic assessment, including capital and operational expenditures and synthesis costs involved in photocatalyst material, was performed to check the feasibility of photocatalysis integrated with biological systems at large-scale treatment.

Aerobic Polishing of Liquid Digestate for Preparation of Hydroponic Fertiliser

Nutrient pollution—mainly nitrogen and phosphorus—caused by organic waste continues to impact the environment. The implementation of a circular economy is integral to alleviating these effects. Liquid digestate, which is a byproduct of anaerobic digestion (a waste-valorising process), is a nutrient-dense organic fertiliser with vast applications in agriculture. Using an aerobic polishing unit, this study developed a viable method for the preparation of a hydroponic fertiliser by investigating the effect of pH on the nutrient recycling capabilities of said system. The heterotrophic bacteria present in the biofilm, identified by 16S gene sequencing, are responsible for 90% of organic carbon (as TOC) removal with minimal ammonium loss. This is ideal for promoting optimal nitrification in hydroponic systems in the absence of organic carbon to ensure plant growth is not affected. Although pH 8 was found to be ideal for batch operation, this pH condition resulted in decreased microbial longevity and, therefore, increased ammonification due to microbial decay. Therefore, continuous operation at pH 7 proved to be a better option owing to the ammonium-rich effluent (&gt;220 mg/L) which was produced, which is on par with the nitrogen concentration of a Hoagland solution. The continuous carbon polishing of liquid digestate provides an efficient way of utilising organic fertilisers in hydroponic systems.