The role of in situ Fenton coagulation on the removal of benzoic acid

Fenton-coagulation process for simultaneous abatement of micropollutants and dissolved organic carbon in treated wastewater

This study demonstrates the integration of the Fenton reaction into the flocculation process at circumneutral pH (6-7), offering a practical approach for simultaneous micropollutant and organic matter removal in wastewater treatment. Unlike conventional Fenton oxidation, which requires acidic conditions, this approach allows Fe(II) to react with hydrogen peroxide at near-neutral pH, forming Fe(III) flocs that enhance flocculation while also generating reactive species for pollutant degradation. At pH 6, hydroxyl radicals were the dominant oxidants, whereas at pH 7, additional reactive species likely contributed to micropollutant removal. Bisphenol A and benzoic acid were removed by approximately 90% at 1 mM peroxide and 2 mM iron. In addition to micropollutant degradation, the Fenton-coagulation process achieved substantial dissolved organic carbon (DOC) removal, which was not observed with Fenton oxidation alone or ozonation. DOC removal was up to 51% in Suwannee River Natural Organic Matter solutions, whereas only 30% of DOC was removed from municipal wastewater effluent, likely due to differences in organic matter composition. These findings highlight the potential of Fenton-coagulation as an effective and scalable treatment strategy for wastewater reuse, improving both pollutant degradation and organic matter removal under practical conditions.

Removal of Microplastics from Laundry Wastewater Using Coagulation and Membrane Combination: A Laboratory-Scale Study

Microplastic (MP) pollution has recently emerged as a critical global environmental issue. Laundry wastewater is a significant contributor to MP pollution, containing high concentrations of MPs. Although coagulation has recently been widely applied to remove MPs from such wastewater, its efficiency remains poor, and the removal mechanisms are not yet fully elucidated. In this study, the occurrence and characteristics of MPs in raw domestic laundry wastewater were investigated. The coagulation process was combined with ultrafiltration (UF) membrane filtration to enhance MP removal. The results showed that the concentrations of MPs in laundry wastewater ranged from 9000 to 11,000 particles/L, with fibrous particles constituting the majority (42.6%) and polyester accounting for 68.2% of detected MPs. Using aluminium chloride and ferric chloride as coagulants, maximum removal efficiencies of 91.7 and 98.3% were achieved, respectively. Mechanistic analysis revealed that charge neutralization played a dominant role during coagulation. Fourier transform infrared spectroscopy further demonstrated the formation of new functional groups, substituted benzene rings, and the presence of Fe-O and Al-O bonds, indicating the interaction between MPs and coagulants. Furthermore, the UF membrane was used to remove fibrous MPs and MPs with low densities. These MPs had not been removed with pre-coagulation. The removal efficiency of these MPs reached 96 ± 2%, reducing their concentration to only 60 particles/L in the UF permeate. These findings highlight the synergistic potential of coagulation and UF membrane filtration for effective MP removal and provide a valuable reference for advancing wastewater treatment technologies targeting MP pollution.

Two-dimensional black phosphorus/platinum catalase-like nanozyme-based Fenton reaction-mediated dual-mode immunoassays for the detection of enrofloxacin

Hydrogen peroxide-based Fenton reaction can effectively degrade many small-molecule fluorescent dyes, leading to notable alterations in fluorescence signals. Additionally, the two-dimensional black phosphorus/platinum nanocomposite (BP/Pt) demonstrates exceptional catalase (CAT) characteristics. Based on these, a colorimetric-fluorescence dual-mode signal output pattern based on BP/Pt-Fenton reaction-rhodamine B tandem reaction system is reported. The physical adsorption property of the BP/Pt nanozymes was utilized to couple with antibodies, thus constructing a novel dual-mode nanozyme-based immuno-sensing assay (NISA). By using the migratory antibiotic enrofloxacin (ENR) as the target, the NISA provided highly sensitive detection with the detection limits of 0.058 ng/mL for colorimetric-mode and 0.025 ng/mL for fluorescence-mode and achieved accurate quantitative detection in environmental water and crucian carp samples. This work provides an innovative design for monitoring antibiotics in the environment and broadens the idea for the application of nanozymes and Fenton systems in immunosensing assays.

Enhancing the coagulation process for the removal of microplastics from water by anionic polyacrylamide and natural-based Moringaoleifera

The existence of microplastics (MPs) in water is a significant global concern since they have the potential to pose a threat to human health. Therefore, there is a need to develop a sustainable treatment technology for MPs removal, as the conventional methods are inadequate to address this problem. Coagulation is a typical process in treatment plants that can capture MPs before releasing them into the environment. In this work, the removal behaviors of polyamide (PA), polystyrene (PS), and polyethylene (PE) MPs were systematically investigated through coagulation processes using aluminum sulfate (Al2(SO4)3) and Moringa oleifera (MO) seeds extract. Subsequently, the coagulation performance of Al2(SO4)3 was improved by the separate addition of anionic polyacrylamide (APAM) and naturally derived MO. Results showed that Al2(SO4)3 in combination with APAM had better performance than Al2(SO4)3 or MO alone. In the Al2(SO4)3+APAM system, the removal efficiencies were 93.47%, 81.25%, and 29.48% for PA, PS, and PE MPs, respectively. Furthermore, the effectiveness of the Al2(SO4)3 and MO blended system was approximately similar to the Al2(SO4)3+APAM system. However, the required amount of Al2(SO4)3 was decreased to 50% in the Al2(SO4)3+MO system compared to the optimal dosage in the Al2(SO4)3 system alone. The combination of 40 mg/L of Al2(SO4)3 and 60 mg/L of MO resulted in removal efficiencies of 92.99%, 80.48%, and 28.94% for PA, PS, and PE MPs, respectively. The high efficacy of these enhanced methods was due to the synergic effects of charge neutralization and agglomeration adsorption, which were validated through zeta potential assessments and visual analysis using scanning electron microscopy (SEM) images. In the case of experimental conditions, initial pH had little impact on removal efficiency, while NaCl salinity and stirring speed directly affected MPs removal. Consequently, this research took a step toward finding a green strategy to remove MPs from water systems.

Coagulative removal of polystyrene microplastics from aqueous matrices using FeCl3-chitosan system: Experimental and artificial neural network modeling

Effluent from sewage treatment plants (STPs) is a significant source of microplastics (MPs) re-entry into the environment. Coagulation-flocculation-sedimentation (CFS) process as an initial tertiary treatment step requires investigation for coagulative MPs removal from secondary-treated sewage effluents. In this study, experiments were conducted on synthetic water containing 25 mg/L polystyrene (PS) MPs using varying dosages of FeCl3 (1-10 mg/L) and chitosan (0.25-9 mg/L) to assess the effect of process parameters, such as pH (4-8), stirring speed (0-200 rpm), and settling time (10-40 min). Results revealed that ∼89.3% and 21.4% of PS removal were achieved by FeCl3 and chitosan, respectively. Further, their combination resulted in a maximum of 99.8% removal at favorable conditions: FeCl3: 2 mg/L, chitosan: 7 mg/L, pH: 6.3, stirring speed: 100 rpm, and settling time: 30 min, with a statistically significant (p < 0.05) effect. Artificial neural network (ANN) validated the experimental results with RMSE = 1.0643 and R2 = 0.9997. Charge neutralization, confirmed by zeta potential, and adsorption, ascertained by field-emission scanning electron microscope (FESEM) and Fourier-transform infrared spectroscopy (FTIR), were primary mechanisms for efficient PS removal. For practical considerations, the application of the FeCl3-chitosan system on the effluents from moving bed biofilm reactor (MBBR) and sequencing batch reactor (SBR)-based STPs, spiked with PS microbeads, showed > 98% removal at favorable conditions.

An innovative method to degrade xanthate from flotation tailings wastewater in acid mine drainage (AMD) system: Performance, degradation mechanism and pathways

This study objective is to degrade xanthate from flotation tailings wastewater by using a coagulation-flocculation co-Fenton oxidation process in an acid mine drainage (AMD)-H2O2 system. More than 98% sodium butyl xanthate (SBX) removal rate was achieved by the method under optimal conditions. The acids and Fe2+ in AMD were sufficient to initiate a Fenton reaction at the aid of H2O2. Furthermore, iron ions were reduced to an extremely low level (0.19 mg/L) by participating in an oxidation process. Meanwhile, the Cu2+ ions in AMD facilitated the coagulation-flocculation process. Comparison experiments confirmed that the method was superior to the AMD alone (54.26%) and H2O2 alone (32.23%) in terms of performance in degrading SBX. The kinetic results showed that SBX degradation followed a pseudo first-order kinetic model. Additionally, the electron paramagnetic resonance (EPR) and quenching results suggested that hydroxyl radicals (•OH) were the main active species in AMD-H2O2 system. Degradation products were analyzed, and two possible pathways of SBX degradation were proposed. One pathway displayed that the SBX was first transformed into butyl xanthate peroxide (BPX), CO32- and S2O32-, and then further decomposed into CO2, H2O and SO42- under the ongoing •OH attack. Another pathway showed that precipitates consisting of butyl copper xanthate and iron oxide species were generated during the SBX degradation. This study provides a novel perspective on the innovative application of AMD in Fenton oxidation and provides a strong basis for the green and sustainable treatment of xanthate wastewater in tailings.

Electro-Fenton and Induced Electro-Fenton as Versatile Wastewater Treatment Processes for Decontamination and Nutrient Removal without Byproduct Formation

It is a long-pursued goal to develop electrified water treatment technology that can remove contaminants without byproduct formation. This study unveiled the overlooked multifunctionality of electro-Fenton (EF) and induced EF (I-EF) processes to remove organics, pathogens, and phosphate in one step without halogenated byproduct formation. The EF and I-EF processes used a sacrificial anode or an induced electrode to generate Fe2+ to activate H2O2 produced from a gas diffusion cathode fed by naturally diffused air. We used experimental and kinetic modeling approaches to illustrate that the •OH generation and radical speciation during EF were not impacted by chloride. More importantly, reactive chlorine species were quenched by H2O2, which eliminated the formation of halogenated byproducts. When applied in treating septic wastewater, the EF process removed >80% COD, >50% carbamazepine (as representative trace organics), and >99% phosphate at a low energy consumption of 0.37 Wh/L. The EF process also demonstrated broad-spectrum disinfection activities in removing and inactivating Escherichia coli, Enterococcus durans, and model viruses MS2 and Phi6. In contrast to electrochemical oxidation (EO) that yielded mg/L level byproducts to achieve the same degree of treatment, EF did not generate byproducts (chlorate, perchlorate, trihalomethanes, and haloacetic acids). The I-EF carried over all the advantages of EF and exhibited even faster kinetics in disinfection and carbamazepine removal with 50-80% less sludge production. Last, using septic wastewater treatment as a technical niche, we demonstrated that iron sludge formation is predictable and manageable, clearing roadblocks toward on-site water treatment applications.

Enhanced degradation of emerging contaminants by percarbonate/Fe(II)-ZVI process: case study with nizatidine

Pharmaceuticals have recently emerged as a significant environmental concern due to the growth of population, expansion of industry, and the shift in modern lifestyles. Herein, we present a Fe(II)/percarbonate (SPC) process with dramatically enhanced efficiency by the introduction of zerovalent iron (ZVI). After the addition of ZVI, the removal rate of nizatidine (NZTD) went up from 71.7 to 84.2%. The removal rate of NZTD decreases with rising pH and speeds up with increasing temperature. It was found that under the condition of pH = 7 and T = 25 °C, the molar ratio of the optimal concentration of NZTD degradation in the system was [NZTD]₀:[SPC]₀:[Fe(II)]₀:[ZVI]₀ = 1:8:24:16, with a degradation rate of 99.8%. At the same time, target pollutants can also be successfully eliminated from actual water bodies. Moreover, we test for toxicity using luminescent bacteria, and the results demonstrate that the system is capable of effectively decreasing the toxicity of NZTD. The research findings can contribute to the clarification of the migration and transformation law of NZTD in the oxidation process, thereby providing a scientific basis and technical support for the removal of NZTD in the tertiary water treatment for a water source.

Optimization of a compact on-site stormwater runoff treatment system: Process performance and reactor design

Stormwater runoff has become a major anthropogenic urban pollution source that threatens water quality. In this study, coagulation-sedimentation, and ammonium ion exchange and regeneration (AIR) modules were coupled as a CAIR system to efficiently treat stormwater runoff. In the coagulation module, 99.3%, 91.7%, and 97.0% of turbidity, total phosphorus, and chemical oxygen demand could be removed at an optimized poly-aluminum ferric chloride dosage of 30 mg/L, and the continuous experiment confirmed that the full load mode was more suitable for its rapid start-up. In the AIR module, dynamic ammonium removal indicated that the breakthrough time decreased with the rising initial concentration and superficial velocity. The Modified Dose Response (MDR) model described the ammonium exchange behavior better than the Thomas and the Bohart-Adams models. Then, a design flow of the ion exchange reactor was constructed by correlating constants in the MDR model with engineering parameters, and the ion exchange reactor was designed for continuous operation of the CAIR system. The average concentrations of chemical oxygen demand, total phosphorus, ammonium nitrogen, and total nitrogen in the effluent of the CAIR system were 7.22 ± 2.26, 0.17 ± 0.05, 1.49 ± 0.01, and 1.62 ± 0.02 mg/L, respectively. The almost unchanged exchange capacity and physicochemical properties after the multicycle operation confirmed the durability of zeolite for ion exchange. Techno-economic analysis suggested that the CAIR system is practically promising for stormwater management with efficient pollutants removal, small footprint, and acceptable operating cost.

Renewable cellulose aerogel embedded with nano-HFO for preferable phosphate capture from aqueous solution

Excess phosphate in water can cause eutrophication, which must be addressed. Despite many efforts devoted to the adsorptive removal of phosphate from water, the development of new adsorbents with high adsorption capacity is highly desirable. Herein, a novel nanocomposite was proposed for phosphate removal by confining hydrated ferric oxide (HFO) nanoparticles into a cellulose aerogel (CA) network named as HFO@CA. Benefiting from the characteristics of the low density and porous structure of CA, the internal surface of the nanocomposite is more accessible and thus improves the utilization of the HFO nanoparticles. Batch adsorption experiments were carried out to evaluate the phosphate uptake by the prepared adsorbent. The maximum adsorption capacity of HFO@CA occurs at near-acidic pH. With increasing temperature, the composite adsorbent is more favorable for phosphate adsorption. Moreover, the hybrid aerogel exhibited fast kinetic behavior for phosphate removal, which could be accurately depicted by pseudo-second-order model. HFO@CA shows excellent adsorption selectivity in solutions containing competitive anions at higher levels. In addition, five cycles of the phosphate adsorption experiments without obvious capacity loss indicated that HFO@CA has great regenerability. These results demonstrate that HFO@CA has a wide field of application with good prospects in phosphate removal from wastewater, which also provides a new strategy to prepare adsorbents with excellent performance using renewable cellulose resources.

Efficient removal of nano- and micro- sized plastics using a starch-based coagulant in conjunction with polysilicic acid

Microplastic (MP) pollution has increasingly become an enormous global challenge due to the ubiquity and uncertain environmental performance, especially for nano- and micro- sized MPs. In this work, the performance and mechanisms in coagulation of 100 nm-5.0 μm sized polystyrene particles using an etherified starch-based coagulant (St-CTA) assisted by polysilicic acid (PSA) were systematically studied on the basis of the changes in MPs removal rates under various pH levels and in the presence of different coexisting inorganic and organic substances, zeta potentials of supernatants, and floc properties. St-CTA in conjunction with PSA had a high performance in coagulation of nano- and micro- sized MPs from water with a lower optimal dose and larger and compacter flocs. Besides, the MPs removal rate can be improved in acidic and coexisting salt conditions. The efficient performance in removal of MPs by this enhanced coagulation was owing to the synergic effect, that is, the effective aggregation of MPs through the charge neutralization of St-CTA followed by the efficient netting-bridging effect of PSA. The effectiveness of this enhanced coagulation was further confirmed by removal of two other typical nano-sized MPs, such as poly(methyl methacrylate) and poly(vinyl chloride), from different water sources including tap water, river water, and sludge supernatant from a sewage treatment plant. This work provided a novel enhanced coagulation technique that can effectively remove nano- and micro- sized MPs from water.

Photo-persulfate oxidation and mineralization of benzoic acid: Kinetics and optimization under UVC irradiation

The strong oxidant, persulfate (PS, S₂O₈^2-), was applied to treat the synthetic wastewater of benzoic acid (BA) under UV irradiation. UVC light initiated a chain reaction that derived the sulfate radical (SO₄•^-) and hydroxyl radical (HO•) from S₂O₈^2- ion. The experiment parameters, including light irradiation (UVA and UVC), pH, dose ratio ([PS]₀/[BA]₀), initial concentration ([BA]₀, mg/L), was optimized based on degradation efficiency and total organic carbon (TOC) removal of BA, which reached up to 100% and 96%, respectively, under pH 3.0. The best dose ratio was close to equivalent stoichiometry (and [PS]₀/[BA]₀ = 15) for the treatment of 100 mg-BA/L, suggesting that UV/S₂O₈^2- was able to completely convert BA to carbon dioxide and water. The scavenging test showed that SO₄•^- contributed to about 60% of degradation rate, which the HO• predominated the mineralization rate, i.e., TOC removal. A consecutive kinetic model was proposed to clarify the reaction sequence and rate-determining factor of photo-persulfate oxidation for benzoic acid.

Decontamination of real urban sewage-comparison between Fenton and electrochemical oxidation

Advanced oxidation processes have been used for wastewater treatment due to their capacity to reduce the organic loading and for their fast reactions. In this paper, we explore the viability of isolated and sequential use of electrochemical oxidation and Fenton processes into treatment of real raw urban sewage. The electrochemical process was carried out using DSA®-Cl₂ electrodes and factorial planning in order to investigate the influence of pH, current density, and electrolyte. Fenton reaction was also used and H₂O₂ and Fe²⁺ concentration effects were investigated. The efficiency was estimated by chemical oxygen demand (COD) removal and in the optimized conditions the effluent was characterized by turbidity, suspended/dissolved/total solids, ammonia, chloride ions, free chlorine, nitrite, and potassium analysis and bioassays with Artemia ssp. and Lactuca sativa. The study demonstrated that the use of electrochemical technique followed by Fenton allowed an improvement in the degradation of organic matter and reduction of turbidity and solid content, reaching reductions of 86.8, 96.4, 99.4, 56.1, and 66.7% for COD, turbidity, SS, DS, and TS, respectively. The associated treatment also contributed to the reduction of energy consumption by 74.9%, from the 23.9 kWh m^-3 observed during the electrochemical treatment isolated to the 6 kWh m^-3 during the associated process. All the treatments presented toxicity reduction, with the electrochemical process achieving the best results.

Cu-coupled Fe/Fe3C covered with thin carbon as stable win-win catalysts to boost electro-Fenton reaction for brewing leachate treatment

The electro-Fenton oxidation is one of the powerful approaches for achieving the complete mineralization of organic pollutants in water. The key dilemma for efficient industrial application of electro-Fenton oxidation is the complicated post-processing of iron sludge, and the cost and risk associated with H₂O₂ transportation and storage. Herein, Cu-coupled Fe/Fe₃C covered with carbon layer on carbon felt (Cu-Fe/Fe₃C@C), engineered by a hydrothermal reaction followed by the consequent thermal-treatment in N₂ atmosphere, as a self-supported integrated cathode were used for an onsite oxygen reduction reaction and a Fenton oxidation reaction. Experimental evidences demonstrate that, at the operating potential of -1.1 V, Fe₃C can selectively catalyze O₂ into H₂O₂ by 2e reduction pathways with assistance of metal Cu. Meanwhile, metal Fe and Cu incorporated into Cu-Fe/Fe₃C@C simultaneously motivate the onsite Fenton oxidation arose by H₂O₂. Such a win-win catalyst presented high activity in the electro-Fenton process. In acidic environment, the efficient mineralization rate of methylene blue, nitrobenzene, phenol, and bisphenol A can reach more than 70% in 60 min, as well as the excellent stability and durability due to the protection of graphited carbon layer. Compared with tradition electrochemical degrade system, the prepared Cu-Fe/Fe₃C@C electrode as cathode for practical refractory brewing leachate treatment reveal more efficient decolorization and mineralization, saving 14.3% of electricity.

Synergistic effects of oxidation, coagulation and adsorption in the integrated fenton-based process for wastewater treatment: A review

Fenton process is the most popular for wastewater treatment among all available advanced oxidation processes (AOPs). Numerous endeavors have been devoted to improving the oxidation efficiency of Fenton reaction in terms of promoting ·OH generation, accelerating iron redox cycle and extending applicable pH range. However, in addition to oxidation, coagulation and adsorption also simultaneously occur in the Fenton process, which play important role in the removal of pollutants. Rapid progress has revealed the synergistic effects of oxidation, coagulation and adsorption in the Fenton process, providing new ideas for the treatment of complex and refractory wastewater. Based on available studies, this review is the first to systematically summarize the research progress regarding the synergistic effects of oxidation, coagulation and adsorption in the integrated Fenton-based processes for wastewater treatment. The involved mechanism of the synergistic effects in different Fenton processes (homogeneous Fenton, heterogeneous Fenton and physical field-assistant Fenton coupling process) are critically reviewed. Furthermore, special attention has been paid to the representative applications of the synergistic effects in wastewater treatment (such as industrial organic wastewater, landfill leachate and heavy metal-organic complexes, etc.), particularly focusing on the operation parameters and removal performance. Finally, a conclusion of the review and subsequently, perspectives are given for possible research directions. We believe this review can provide useful information for researchers and end-users involved in the development and application of the Fenton process in wastewater treatment.

Enhanced nutrient removal from stormwater runoff by a compact on-site treatment system

Efficient and space-saving technologies for on-site treatment of stormwater runoff are required to control water pollution in the urban surface. The intermittent nature of stormwater runoff and extremely limited land available greatly hindered the application of current wastewater treatment technologies, and thus synchronous removal of multiple contaminants (especially for nutrient) efficiently was failed by current processes. In this study, a new compact CFFA treatment system, consisting of coagulation, flocculation, filtration and ammonium ion exchange units, was constructed for on-site treatment of stormwater runoff based on batch test optimization and pilot-scale test verification. The coagulation process effectively aggregated particles and precipitated phosphorus by dosing Al₂(SO₄)₃, while flocculation using anionic polyacrylamide further enlarged particle size for efficient micromesh filtration. The dynamic micromesh filtration obtained turbidity and phosphorus removal efficiencies comparable to 30 min gravity settling with greatly smaller footprint. Ion exchange by zeolite showed higher exchange capacity owing to lower initial ammonium nitrogen concentration in the stormwater runoff. The pilot-scale experiments with treatment capacity of 1 L/s showed that the CFFA treatment system achieved synchronous removal of particles (97.2%), nitrogen (79.7%), phosphorus (95.0%) and organic matters (83.3%) efficiently within short hydraulic retention time of 0.35 h, yielding effluent with chemical oxygen demand, suspended solids, total phosphorus and total nitrogen of 38.7, 7.80, 0.22 and 2.80 mg/L, respectively. The CFFA treatment system had the highest pollutant removal loads compared to reported runoff treatment processes in literatures, and was well suited to on-site treatment of stormwater runoff with high space utilization efficiency.

Enhanced complexation of humic acids: Homogenization of protonated groups in the hybrid ozonation-coagulation process

In this study, we compared dissolved organic carbon (DOC) and UV₂₅₄ removal efficiencies of the hybrid ozonation-coagulation (HOC) and pre-ozonation-coagulation (POC) processes for humic acid (HA) at pH 5 with AlCl₃•6H₂O as the coagulant. The DOC and UV₂₅₄ removal efficiencies of the HOC process were higher than those of the POC process at ozone dosages less than 2.0 mg O₃ (mg DOC)^-1. The ozone dosage was optimized at 0.3 and 0.1 mg O₃ (mg DOC)^-1 for the HOC and POC processes, respectively, implying a more rigorous ozone dosage for the POC process. During the POC process, pre-ozonation was observed to increase the binding sites of HA (e.g., hydroxyl and carboxyl groups), improving the complexation of dissolved organic matter. For the HOC process, in addition to its role in the oxidation of organic matter, ozone also reacted with coagulants. The reaction between ozone and coagulants can facilitate the formation of Al₁₃. Moreover, the oxidation of •OH and ozone can increase the charge density of the HA binding sites, homogenizing the binding sites of HA and enhancing the complexation with Al₁₃.

Characteristics of refractory organics in industrial wastewater treated using a Fenton-coagulation process

It is a challenging environmental issue to develop a cost-efficient approach for the removal of low-concentration refractory organics in industrial wastewater. In this study, the Fenton-coagulation process was utilised to remove the organics from the industrial effluent. The operational conditions of the Fenton-coagulation process were optimised, and then, the molecular weight (MW) and resin fraction distribution of dissolved organic matter (DOM) were investigated before and after the Fenton-coagulation process. The results showed that the efficiency of organic matter removal was affected by the Fe²⁺/H₂O₂ molar ratio, pH, and reaction time. The removal rate of chemical oxygen demand (COD) by Fenton-coagulation process reached 37.8% under the following conditions: pH = 4.0 - 5.0, H₂O₂ concentration = 34 mg/L, Fe²⁺/H₂O₂ molar ratio = 1.5, and reaction time = 120 min. The resin fraction distribution results showed that hydrophobic bases (HoB) were almost completely removed, and the removal rate of hydrophobic acids (HoA) reached 58%, while hydrophilic matter (HiM) became the dominant form in the final effluent after the Fenton-coagulation process due to the appearance of hydrophilic charged fractions (HiC). The results were explained by a two-step mechanism (Fenton oxidation and Fe³⁺ coagulation). According to the molecular weight (MW), 35.7% removal of the main fractions of organic matter with MW < 1 kDa was achieved. Furthermore, a pilot test proved that the final effluent quality after the Fenton-coagulation process conformed to the first class of the A discharge standard of pollutants for municipal wastewater treatment plants in Tianjin.

Removal of polystyrene and polyethylene microplastics using PAC and FeCl3 coagulation: Performance and mechanism

As a new type of potentially threatening pollutant, microplastics are widely distributed in water and may come into contact with the humans through tap water. The removal behaviors of microplastics in water treatment plants coagulation are not completely clear. In this paper, the removal performance and mechanism of polystyrene (PS) and polyethylene (PE) microplastics using PAC and FeCl3 coagulation were studied. Results showed that PAC was better than FeCl3 in removal efficiency of PS and PE microplastics. Charge neutralization occurred in the coagulation process. The figures of scanning electron microscope (SEM) illustrate that agglomeration adsorption occurred in PS system, and the Fourier transform infrared spectroscope (FTIR) spectra demonstrates that new bonds were formed during the interaction between PS microplastics and coagulants. In addition, the hydrolysis products of coagulants played a major role rather than the hydrolysis process in both PS system and PE system. The removal efficiency of microplastics in alkaline conditions was higher than that in acidic conditions. Cl- had little effect on the removal efficiency of microplastics, while SO42- and CO32- had inhibitory and promoting effects respectively. The increase of stirring speed could improve the removal efficiency of microplastics. This paper can provide a reference for the study of microplastics treated by coagulation.

Decomposition performance of hypochlorite on bead-type NiOx(OH)y catalyst: improving applicability of catalysts

An easy-to-use, pollution-free and reusable beaded NiO_x(OH)_y catalyst for improving hypochlorite oxidation was prepared by impregnating the mixture of persulfate and alkali over alumina and then reduced it with Ni²⁺. The effects of catalyst preparation conditions and reaction parameters on NaClO conversion rate and Ni²⁺ dissolution rate were studied. Impregnating the γ-Al₂O₃ beads in PS/OH^- mixed solution with 0.59 M PS and PS/OH^- molar ratio of 1.1, and then reducing with 0.8 M Ni²⁺ solution is the best condition for preparing catalyst. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The best catalytic layer is characterized by high content of chemisorbed oxygen which can be converted into atomic oxygen. The hypochlorite conversion rate increased with the catalyst dosage and reuse times, and decreased with available chlorine, while pH of hypochlorite solution had little effect on the conversion rate. After running stably for 120 h in continuous flow test, the chemisorbed oxygen content in the optimal catalytic layer decreased slightly. Atomic oxygen plays an important role in the decolorization of dye solution by NaClO/NiO_x(OH)_y system. The oxidant consumption cost of this process is much cheaper than Fenton reagent. The prepared catalyst has great potential in hypochlorite decomposition and wastewater treatment.