Mechanism study on the effect of peracetic acid (PAA), UV/PAA and ultrasonic/PAA oxidation on ultrafiltration performance during algae-laden water treatment

Establishing electro-functionalized gravity-driven ceramic membrane filtration (EGDCM) for decentralized treatment of algae-laden brackish water: Comparison of in-situ electro-oxidation and ex-situ electro-coagulation

Algae-laden brackish water (ABW) has remarkably threatened drinking water safety in warm coastal areas. Although gravity-driven ceramic membrane filtration (GDCM) exhibits high potential in ABW treatment during decentralized water supply, membrane fouling is still a critical problem. Herein, GDCM was skillfully electro-functionalized (EGDCM) by in-situ electro-oxidation (ISEO) based on self-fabricated Ti/SnO2-Sb dimensionally stable anode (DSA) (EO-EGDCM) and ex-situ electro-coagulation (ESEC) based on iron anode (EC-EGDCM) in this study. EO-EGDCM with KMnO4 augment (MnEO-EGDCM) was also established for comparison. Results show that ISEO increased GDCM membrane permeability by 22 %, while EC-EGDCM membrane flux was nearly 4.8 times that of GDCM. ISEO enhanced the early removal of organic pollution, and KMnO4 facilitated the active chlorine oxidization of ammonia and algal toxins on electrified Ti/SnO2-Sb DSA by suppressing the transformation of free chlorine to less reactive chloramines. Both algae cell permeabilization and intracellular organic matter release were enhanced by ISEO. But SEM-EDS, CLSM and biomass analysis evidenced that membrane biological process, which was improved by 32 %∼323 % by electrical stimulation, developed porous structures in the fouling layer in EO-EGDCM/MnEO-EGDCM. According to energy consumption and carbon emissions evaluation, GDCM was confirmed as an energy-saving system for treating ABW with the consumption of only 3.47 × 10-3 kWh/m3. Electricity demand was increased for EGDCM but still considerably lower than that for other algae-laden water treatment processes. EC-EGDCM reduced energy consumption and carbon emission by around 80 % compared to EC-EGDCM/MnEO-EGDCM. Electro-functionalization was a promising option to improve GDCM treatment of ABW via multiple mechanisms but further optimization was still required.

Revealing the essence of anion ligands in regulating amorphous MnOx to activate peracetic acid for micropollutant removal

How the anion ligands of manganese precursors affect the catalytic activity of amorphous manganese oxides (MnOx) in Fenton-like process is poorly understood. Here, five amorphous MnOx synthesized by Mn(II) precursors with different ligands were characterized and adopted to activate peracetic acid (PAA) for bisphenol A (BPA) degradation. Although > 90 % BPA removal was achieved in the five MnOx/PAA processes via both adsorption and oxidation, the oxidation kobs greatly differentiates by the ligands types with the order of MnOx-N > MnOx-S > MnOx-Cl > MnOx-AA > MnOx-OA. Ligands types would affect the specific surface area of MnOx and their ability to adsorb BPA, however which is not the decisive factor in determining the contaminant oxidation efficiency. Multiple experimental results indicate that the generation of oxygen vacancies induced by the ligands alters the Mn(III)/Mn(IV) ratio, ultimately contributing to the different efficiency of BPA oxidation driven by the direct electron transfer mechanism. Moreover, amorphous MnOx holds the promise of practical applications in catalytic PAA of various micropollutants with good stability. This study advances the fundamental understanding of ligand-regulated amorphous MnOx-catalyzed PAA process.

Pre-exposure to peracetic acid followed by UV treatment for deactivating vancomycin-resistant Enterococcus faecalis through intracellular attack

Antimicrobial resistance (AMR) poses a global health threat to aquatic environments and its propagation is a hot topic. Therefore, deactivating antibiotic-resistant bacteria (ARB) and removing antibiotic resistance genes (ARGs) from water is crucial for controlling AMR transmission. Peracetic acid (PAA), which is known for its potent oxidizing properties and limited by-product formation, is emerging as a favorable disinfectant for water treatment. In this study, we aimed to assess the efficacy of pre-exposure to PAA followed by UV treatment (PAA-UV/PAA) compared with the simultaneous application of UV and PAA (UV/PAA). The focus was on deactivating vancomycin-resistant Enterococcus faecalis (VREfs), a typical ARB in water. Pre-exposure to PAA significantly enhanced the efficacy of subsequent UV/PAA treatment. At a UV fluence of 7.2 mJ cm-2, the PAA-UV/PAA method achieved a 6.21 log reduction in VREfs, surpassing the 1.29 log reduction observed with UV/PAA. Moreover, compared to UV/PAA, PAA-UV/PAA showed increased efficacy with longer pre-exposure times and higher PAA concentrations, maintaining superior performance across a broad pH range and in the presence of humic acid. Flow cytometry analysis indicated minimal cellular membrane damage using both methods. However, the assessments of superoxide dismutase (SOD) activity and adenosine triphosphate content revealed that PAA-UV/PAA induced greater oxidative stress under similar UV irradiation conditions, leading to slower bacterial regrowth. Specifically, SOD activity in PAA-UV/PAA surged to 3.06 times its baseline, exceeding the 1.73-fold increase under UV/PAA conditions. Additionally, pre-exposure to PAA amplified ARGs degradation and reduced resistance gene leakage, effectively mitigating the spread of AMR. Pre-exposure to 200 μM PAA for 10 and 20 min enhanced vanB gene removal efficiency by 0.14 log and 1.29 log, respectively. Our study provides a feasible approach for optimizing UV/PAA disinfection for efficient removal of ARB and ARGs.

Treatment of sludge hydrothermal carbonization wastewater by ferrous/sodium percarbonate system: Effect of wastewater composition and role of coagulation and oxidation

It is crucial to explore the effect of complex wastewater compositions on the ferrous/sodium percarbonate (Fe(Ⅱ)/SPC) system and the role of oxidation-coagulation in designing water treatment processes. This study employed redundancy analysis to investigate the effects of wastewater constituents on oxidation and coagulation. Raman analysis, X-ray Photoelectron Spectroscopy, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry were used to determine the roles of oxidation and coagulation in the system. The results showed that sulfates and phosphates formed amorphous complexes with iron species via coprecipitation, thereby promoting coagulation to remove organics. Some heavy metals can also be removed by coagulation. The co-activation of SPC by pre-existing transition metals and the added Fe(Ⅱ) facilitated the oxidative removal of organics, while chloride and arsenic were the main inhibitory inorganic substances in the system. Aromatic compounds mainly promoted coagulation, polysaccharides promoted oxidation, humic acid promoted oxidation and coagulation, and C=C/C=O inhibited the Fe(Ⅱ)/SPC system. The oxidation process removed graphitic structures and unsaturated organic matter in the region of (O/C, H/C) = (0.2-0.4, 0.9-2.0) through free radicals and generated amorphous carbon structures and saturated organic matter in the region of (O/C, H/C) = (0.3-0.7, 1.2-1.9). The coagulation process removed aromatic organics with 2-5 rings and unsaturated organics in the region of (O/C, H/C) = (0.2-0.6, 0.7-1.6) with oxygen-containing organics. The combined effects of coagulation and oxidation enhanced the removal efficiency of organic carbon by approximately 40%. This study facilitates the optimization of hydrothermal carbonization wastewater treatment and advanced oxidation processes.

A membrane fouling control strategy based on a combination of pre-treatment mitigation and in-situ membrane surface regulation using a composite coagulant

Ultrafiltration technology (UF) is efficient in surface water treatment, but its development and widespread application are limited by membrane fouling. Herein, an efficient and stable polymerized ferric titanium coagulant (PFTC) was synthesized and used as a UF pretreatment agent in actual lake water treatment. The control mechanism of PFTC on membrane fouling was investigated from the perspective of organic removal efficiency and in-situ membrane surface regulation. PFTC demonstrated a remarkable affinity for soluble metabolic intermediates and hydrophilic proteins through complexation and hydrogen bonding force, achieving removal efficiencies of 66.4 % for UV254 and 81.3 % for DOC, respectively. The hydrophilic pollutants with high molecular weight and non-saturated structure could be preferentially removed by PFTC due to its diverse hydrolysates including positively charged Fe-based hydrolysates, amorphous Ti-based hydrolysates, and highly polymerized Fe-Ti copolymers. The flocs generated by PFTC exhibited strong hydrophilicity, allowing for the formation of a loose porous cake layer on the ultrafiltration membrane, which acted as a hydrophilic layer to enhance the anti-fouling performance of ultrafiltration membrane. With its dual function of contaminant removal and in-situ membrane surface regulation, PFTC alleviated 98.9 % of membrane fouling. This study provides new insights into membrane fouling control by coagulation pretreatment and efficient treatment of surface water.

Revealing the vital role of sulfur site on the surface of pyrite in 1O2 formation for promoting ciprofloxacin degradation via peracetic acid activation

Pyrite has been widely utilized to activate oxidants for water treatment, yet the regulation of reactive oxygen species (ROS) by sulfur sites on its surface has been overlooked. In this study, the surface sulfur sites were regulated by thermal modification of natural pyrite in the N2 atmosphere (denoted as P-X, where X represented pyrolysis temperatures ranging from 400 to 700 °C), and these modified pyrites were employed to activate peracetic acid (PAA) for ciprofloxacin (CIP) degradation. The results revealed that the degradation rate of CIP increased as the reduced sulfur content increased, with the P600/PAA system achieving the highest apparent degradation rate (kobs = 0.0999 min-1). Quenching experiments and electron paramagnetic resonance (EPR) analysis identified various ROS involved in the P-X/PAA system, with hydroxyl radical (·OH) and singlet oxygen (1O2) identified as dominant reactive species responsible for CIP degradation. The reduced sulfur sites served as the primary active sites facilitating the conversion of organic radicals (·CH3C(O)OO) into superoxide radicals (·O2-) and 1O2. Furthermore, the P600/PAA system demonstrated robust adaptability under both acidic and neutral pH conditions, efficiently degrading CIP even in the presence of complex matrices such as Cl-, NO3-, SO42-, NH4+, or humic acid (HA) in water bodies, although HCO3- was found to inhibit CIP degradation. This study significantly enhances our understanding of the interaction between reduced sulfur sites and ROS in PAA-based advanced oxidation processes (AOPs), offering a promising technology for efficient antibiotic treatment in water purification.

The reactivity of organic radicals in the performic, peracetic, perpropionic acids-based advanced oxidation process: A case study of sulfamethoxazole

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) displayed great potential in removing emerging contaminants by generating HO• and organic radicals. Performic and perpropionic acids (PFA and PPA) also act as disinfectants, but their application potential has not been investigated yet. Here, we investigated the degradation mechanism and kinetics of sulfamethoxazole (SMX) by HO•, RC(O)O• species (including HC(O)O•, CH3C(O)O• and CH3CH2C(O)O•) and RC(O)OO• species (including HC(O)OO•, CH3C(O)OO• and CH3CH2C(O)OO•). The results show that the calculated reaction rate constants of SMX follow the order of HC(O)O• > CH3C(O)O• > CH3CH2C(O)O• > HO• > HC(O)OO• > CH3C(O)OO• > CH3CH2C(O)OO•. The reactivity towards SMX is strongly correlated with the redox potentials of reactive radicals. Hence, the RCOO• species play dominant roles in the purification of SMX in PFA/PAA/PPA-based AOPs. The degradation of SMX mainly proceeds via addition at the benzene ring, the hydrogen abstraction from the -NH2 group as well as the single electron transfer reaction. This study highlights the fundamental aspects of PFA, PAA, and PPA in the purification of sulfamethoxazole and enhances the role of organic radicals in the AOPs based on organic peracetic acids.

Protocatechuic acid enhanced the selective degradation of sulfonamide antibiotics in Fe(III)/peracetic acid process under actually neutral pH conditions

The practical application of the Fe-catalyzed peracetic acid (PAA) processes is seriously restricted due to the need for narrow pH working range and poor anti-interference capacity. This study demonstrates that protocatechuic acid (PCA), a natural and eco-environmental phenolic acid, significantly enhanced the removal of sulfonamide antibiotics in Fe(III)/PAA process under actually neutral pH conditions (6.0-8.0) by complexing Fe(III). With sulfamethoxazole (SMX) as the model contaminant, the pseudo-first-order rate constant of SMX elimination in PCA/Fe(III)/PAA process was 63.5 times higher than that in Fe(III)/PAA process at pH 7.0, surpassing most of the previously reported strategies-enhanced Fe-catalyzed PAA processes (i.e., picolinic acid and hydroxylamine etc.). Excluding the primary contribution of reactive species commonly found in Fe-catalyzed PAA processes (e.g., •OH, R-O•, Fe(IV)/Fe(V) and 1O2) to SMX removal, the Fe(III)-peroxy complex intermediate (CH3C(O)OO-Fe(III)-PCA) was proposed as the primary reactive species in PCA/Fe(III)/PAA process. DFT theoretical calculations indicate that CH3C(O)OO-Fe(III)-PCA exhibited stronger oxidation potential than CH3C(O)OO-Fe(III), thereby enhancing SMX removal. Four potential removal pathways of SMX were proposed and the toxicity of reaction solution decreased with the removal of SMX. Furthermore, PCA/Fe(III)/PAA process exhibited strong anti-interference capacity to common natural anions (HCO3-, Cl-and NO3-) and humic acid. More importantly, the PCA/Fe(III)/PAA process demonstrated high efficiency for SMX elimination in actual samples, even at a trace Fe(III) dosage (i.e., 5 μM). Overall, this study provided a highly-efficient and eco-environmental strategy to remove sulfonamide antibiotics in Fe(III)/PAA process under actually neutral pH conditions and to strengthen its anti-interference capacity, underscoring its potential application in water treatment.

Oxidation of Microcystis aeruginosa and Microcystins with Peracetic Acid

Peracetic acid (PAA) shows potential for use in drinking water treatment as an alternative to prechlorination, such as for mussel control and disinfection by-product precursor destruction, though its impact as a preoxidant during cyanobacterial blooms remains underexplored. Here, Microcystis aeruginosa inactivation and microcystin-LR and -RR release and degradation using PAA were explored. The toxin degradation rates were found to be higher in alkaline conditions than in neutral and acidic conditions. However, all rates were significantly smaller than comparable rates when using free chlorine. The inactivation of M. aeruginosa cells using PAA was faster at acidic pH, showing immediate cell damage and subsequent cell death after 15-60 min of exposure to 10 mg/L PAA. In neutral and alkaline conditions, cell death occurred after a longer lag phase (3-6 h). During cell inactivation, microcystin-LR was released slowly, with <35% of the initial intracellular toxins measured in solution after 12 h of exposure to 10 mg/L PAA. Overall, PAA appears impractically slow for M. aeruginosa cell inactivation or microcystin-LR and -RR destruction in drinking water treatment, but this slow reactivity may also allow it to continue to be applied as a preoxidant for other purposes during cyanobacterial blooms without the risk of toxin release.

Moderate oxidation of algae-laden water: Principals and challenges

The occurrence of seasonal algae blooms represents a huge dilemma for water resource management and has garnered widespread attention. Therefore, finding methods to control algae pollution and improve water quality is urgently needed. Moderate oxidation has emerged as a feasible way of algae-laden water treatment and is an economical and prospective strategy for controlling algae and endogenous and exogenous pollutants. Despite this, a comprehensive understanding of algae-laden water treatment by moderate oxidation, particularly principles and summary of advanced strategies, as well as challenges in moderate oxidation application, is still lacking. This review outlines the properties and characterization of algae-laden water, which serve as a prerequisite for assessing the treatment efficiency of moderate oxidation. Biomass, cell viability, and organic matter are key components to assessing moderate oxidation performance. More importantly, the recent advancements in employing moderate oxidation as a treatment or pretreatment procedure were examined, and the suitability of different techniques was evaluated. Generally, moderate oxidation is more promising for improving the solid-liquid separation process by the reduction of cell surface charge (stability) and removal/degradation of the soluble algae secretions. Furthermore, this review presents an outlook on future research directions aimed at overcoming the challenges encountered by existing moderate oxidation technologies. This comprehensive examination aims to provide new and valuable insights into the moderate oxidation process.

Catalytic activation of peracetic acid for pelargonic acid vanillylamide degradation by Co3O4 nanoparticles in-situ anchored carbon-coated MXene nanosheets: Performance and mechanism insight

Pelargonic acid vanillylamide (PAVA), a capsaicin-type dacryagogue agent utilized for counter-terrorism and riot control, possesses a low stimulus threshold. This characteristic can lead to environmental contamination following its application and may easily result in secondary stimulation to personnel. Cobalt-doped Ti3C2-MXene nanosheets (Co3O4/Ti3C2@C) were synthesized for the purpose of activating peracetic acid (PAA) and degrading PAVA. A carbon layer was coated on the surface of Ti3C2-MXene nanosheets to address the challenge of poor oxygen resistance in MXenes, thus preventing a significant decline in surface reactivity. The BET surface area of Co3O4/Ti3C2@C was expanded to 149.6 m2/g, significantly exceeding that of Ti3C2 (13.0 m2/g) and Co3O4 (56.4 m2/g). With 0.5 mg/mL of Co3O4/Ti3C2@C and 0.35 mM of PAA, 100 mg/L of PAVA was completely degraded within 60 min. The augmented BET surface area and the presence of more active sites confer remarkable PAA activation and catalytic degradation properties toward PAVA. Parameters such as initial pH, PAVA concentration, catalyst dosage, and PAA concentration on PAVA degradation were systematically assessed. Furthermore, the reusability and stability of the nanocomposite were substantiated through recycling tests. Radical quenching experiments and electron paramagnetic resonance analysis demonstrated the acetylperoxy radical (CH3CO3) as the primary species responsible for PAVA degradation. This research serves as an illustration of the utilization of MXene and transition metal activated PAA in wastewater treatment.

Investigating synergism and mechanism during sequential inactivation of Staphylococcus aureus with ultrasound followed by UV/peracetic acid

This study explored the inactivation of Staphylococcus aureus (S. aureus) by ultrasound (US) and peracetic acid (PAA) coupling with UV simultaneously (US/PAA/UV) or sequentially (US→PAA/UV) for the strengthened disinfection. The result showed that US→PAA/UV system had excellent inactivation performance with 5.05-log in a short time. Besides US, UV, PAA and free radicals, the contribution of the synergy of all components to the entire disinfection were obvious under US→PAA/UV system. The inactivation performance of S. aureus significantly decreased with the increase of humic acid (HA) concentration and pH; however, the rising temperature contributes to the enhancement of the inactivation efficiency under the US→PAA/UV system. The disinfection mechanism includes a decrease of cell agglomeration, a loss of intracellular substance, and changes of cell structure and membrane permeability, as evidenced through a nanoparticle size analyzer, scanning electron microscope (SEM), transmission electron microscope (TEM) and laser confocal microscopy (LSCM). Furthermore, the inactivation efficiency of the US→PAA/UV system for the total bacteria from actual sewage (the untreated inflow) was high, which reached 3.86-log. In general, the pretreatment of US combined with UV/PAA showed a promising application in the rapid disinfection of sewage.

A comparison of micro-flocculation and ozonation as pretreatments for ultrafiltration: organic removal and membrane fouling

Micro-flocculation and ozone were applied as pretreatments of ultrafiltration to treat sodium alginate (SA) and humic acid (HA) simulated water, respectively, to investigate the effects of different pretreatments of ultrafiltration (UF) on filtration flux and removal of organic matters. Regarding the SA simulated water, micro-flocculation helped to improve the dissolved organic carbon (DOC) removal efficiency highly, maximum DOC removal efficiency reached to 79.77%, due to the rejection of gel layer introduced by the alginate-aluminum complexes, but the gel layer had a negative impact on membrane flux. Compared with micro-flocculation, ozone as pretreatments had better ability to enhance the membrane specific flux, the maximum final specific flux remained as 0.786, larger than that of MF-UF process (0.574). Ozonation oxidizing SA into small organic molecules significantly reduced membrane fouling and filtration resistance, but also produced some dissolved organic matters hindering DOC removal of effluent. As for HA simulated water, both the micro-flocculation and ozone could effectively improve the specific flux, the final specific flux of MF-UF and ozone-UF were about 0.930, but MF-UF exhibited better DOC removal than ozone-UF, which avoided the introduction of additional dissolved organic matters.

Mechanistic insight into single-atom Fe loaded catalytic membrane with peracetic acid and visible light activation

Advanced oxidation is an effective method for removing hard-to-degrade organic pollutants from water. In this paper, a novel structure of a single atom Fe anchored g-C3N4 (FeCN) membrane was proposed to remove pollutants from water by coupling membrane technology with photocatalytic and peroxyacetic acid oxidation. The presence of zero-dimensional Fe atoms in FeCN membranes allows for the removal of acetaminophen (APAP) in mobile membrane filtration systems without compromising permeation performance by simultaneously possessing visible photocatalytic capability and peroxyacetic acid (PAA) activation. Existence of inter-membrane domain-limiting conditions led to 100 % degradation of APAP within 10.5 ms, which is 5 orders of magnitude faster than conventional catalytic systems. Notably, photo-generated electrons/holes generated by light and HClO generated by Cl- promote the conversion of Fe(V) and the removal of pollutants during the catalytic process. The spatial separation ability of the membrane catalytic layer surface mitigates the catalyst's passivation by macromolecular organics. Furthermore, surface photocatalysis of the membrane and interlayer catalysis generated by PAA mitigate the surface and interlayer pollutants of the membrane, respectively. This study explores a novel approach for the development of highly efficient atom-catalyzed membrane systems with multiple purposes.

Using Fe(II)/Fe(VI) activated peracetic acid as pretreatment of ultrafiltration for secondary effluent treatment: Water quality improvement and membrane fouling mitigation

Ultrafiltration (UF) is a technology commonly used to treat secondary effluents in wastewater reuse; however, it faces two main challenges: 1) membrane fouling and 2) inadequate nitrogen (N), phosphorus (P), and organic micropollutants (OMPs) removal. To address these two issues, in this study, we applied peracetic acid (PAA), Fe(VI)/PAA, and Fe(II)/PAA as UF pretreatments. The results showed that the most effective pretreatment was Fe(II)/200 μM PAA, which reduced the total fouling resistance by 90.2%. In comparison, the reduction was only 29.7% with 200 μM PAA alone and 64.3% with Fe(VI)/200 μM PAA. Fe(II)/200 μM PAA could effectively remove fluorescent components and hydrophobic organics in effluent organic matter (EfOM), and enhance the repulsive force between foulants and membrane (according to XDLVO analysis), and consequently, mitigate pore blocking and delay cake layer formation. Regarding pollutant removal, Fe(II)/200 μM PAA effectively degraded OMPs (>85%) and improved P removal by 58.2% via in-situ Fe(Ⅲ) co-precipitation. The quencher and probe experiments indicated that FeIVO2+, •OH, and CH3C(O)OO•/CH3C(O)O• all played important roles in micropollutant degradation with Fe(II)/PAA. Interestingly, PAA oxidation produced highly biodegradable products such as acetic acid, which significantly elevated the BOD5 level and increased the BOD5/total nitrogen (BOD5/TN) ratio from 0.8 to 8.6, benefiting N removal with subsequent denitrification. Overall, the Fe(II)/PAA process exhibits great potential as a UF pretreatment to control membrane fouling and improve water quality during secondary effluent treatment.

Synergistic effect of potassium ferrate and ferrous iron for improving ultrafiltration performance in algae-laden water treatment

The application of ultrafiltration (UF) technology in algae-laden water is limited due to the serious membrane fouling caused by algal foulants. Herein, a Ferrate/FeSO4(Fe(VI)/Fe(II)) pretreatment was proposed aiming to improve the performance of UF. The results showed that the synergistic of Fe(VI) and Fe(II) significantly increased the zeta potential of Microcystis aeruginosa, which enhanced the agglomerative tendency of algal foulants, and the particle size of flocs remarkably increased due to the in-situ generated Fe(III). Results from dissolved organic carbon (DOC), UV254, K+, and fluorescent spectra indicated that the introduction of Fe(II) avoided the excessive oxidation of Fe(VI) to algal cells and reduced the production of intracellular organic matter (IOM), while the strong coagulation efficiency of in-situ Fe(III) further enhanced the removal effect of algal organics. Meanwhile, the molecular weight distribution showed that macromolecular organics were decomposed into low molecular matters under Fe(VI) oxidation, while the Fe(VI)/Fe(II) process reduced the formation of small molecular matters compared with single Fe(VI) pretreatment. The algal-source fouling was efficaciously mitigated under the optimal experimental condition, the terminal membrane flux could be increased from 0.16 to 0.62, while reversible and irreversible fouling decreased by 67.1% and 64.1%, respectively. Modeling analysis demonstrated that the Fe(VI)/Fe(II) process altered the fouling mechanism by delaying the formation of cake filtration. Membrane interface characterization further indicated that large size algal flocs form a loose cake layer and reduce the deposition of algal pollutants on the membrane surface. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory confirmed that the hydrophobic adsorption between the algal foulant and the membrane was weakened, thus relieving the membrane fouling. Overall, this strategy can be considered for application in improving the UF performance and mitigating algal-source membrane fouling.

Enhancement of KMnO4 treatment on cyanobacteria laden-water via 1000 kHz ultrasound at a moderate intensity

1000 kHz high-frequency ultrasound at 0.12 and 0.39 W/mL intensity was used to enhance the inactivation of suspensions of Microcystis aeruginosa cells using KMnO₄. With 10 mg/L of KMnO₄, ultrasound at 0.12 W/mL intensity was found to be effective in inactivating the cyanobacteria within 10 min. A Weibull model was found to describes the inactivation well. Its concave shape shows that some cells have a certain resistance to this treatment. Cytometry and microscopic analysis confirm that the treatment damages cell integrity. Despite that the extracellular organic matter in the water was not significantly increased. The concentration of extracellular cyanobacterial toxins even decreased. The filtered suspension of inactivated cyanobacteria was used to cultivate mung beans, and the suspension did not hinder their germination. This provides a new idea for using cyanobacteria-laden wastewater. These findings suggest a technique for speeding up the oxidation of Microcystis cells using KMnO₄ with ultrasound at moderate intensity, which provide new insights into the biological effects of ultrasound.

UV/Fe(II)/S(IV) Pretreatment for Ultrafiltration of Microcystis aeruginosa-Laden Water: Fe(II)/Fe(III) Triggered Synergistic Oxidation and Coagulation

Ultrafiltration (UF) has been proven effective in removing algae during seasonal algal blooms, but the algal cells and the metabolites can induce severe membrane fouling, which undermines the performance and stability of the UF. Ultraviolet-activated sulfite with iron (UV/Fe(II)/S(IV)) could enable an oxidation-reduction coupling circulation and exert synergistic effects of moderate oxidation and coagulation, which would be highly preferred in fouling control. For the first time, the UV/Fe(II)/S(IV) was systematically investigated as a pretreatment of UF for treating Microcystis aeruginosa-laden water. The results showed that the UV/Fe(II)/S(IV) pretreatment significantly improved the removal of organic matter and alleviated membrane fouling. Specifically, the organic matter removal increased by 32.1% and 66.6% with UV/Fe(II)/S(IV) pretreatment for UF of extracellular organic matter (EOM) solution and algae-laden water, respectively, while the final normalized flux increased by 12.0-29.0%, and reversible fouling was mitigated by 35.3-72.5%. The oxysulfur radicals generated in the UV/S(IV) degraded the organic matter and ruptured the algal cells, and the low-molecular-weight organic matter generated in the oxidation penetrated the UF and deteriorated the effluent. The over-oxidation did not happen in the UV/Fe(II)/S(IV) pretreatment, which may be attributed to the cyclic redox Fe(II)/Fe(III) coagulation triggered by the Fe(II). The UV-activated sulfate radicals in the UV/Fe(II)/S(IV) enabled satisfactory organic removal and fouling control without over-oxidation and effluent deterioration. The UV/Fe(II)/S(IV) promoted the aggregation of algal foulants and postponed the shift of the fouling mechanisms from standard pore blocking to cake filtration. The UV/Fe(II)/S(IV) pretreatment proved effective in enhancing the UF for algae-laden water treatment.

Treatment of sewage sludge hydrothermal carbonization aqueous phase by Fe(II)/CaO2 system: Oxidation behaviors and mechanism of organic compounds

The Fe(II)/CaO₂ system with a stable oxidant and a low-cost homogeneous activating agent has been considered as a prospective process for the disposal of wastewater. The system was constructed to treat sewage sludge hydrothermal carbonization aqueous phase (HTC-AP) in this study. As the hydrothermal temperature increased, the organics in the HTC-AP were first decomposed and then cyclized, while the Maillard reaction occurs throughout the stage. The oxidation efficiency of the Fe(II)/CaO₂ system was related to the composition of organics in HTC-AP, and the removal of dissolved organic carbon (DOC) by the system was 38.56 % in the HTC-AP obtained by hydrothermal treatment at 220 °C. Redundancy analysis showed that the low molecular weight organics, hydrophobic acids, and hydrophobic neutral components were beneficial to DOC removal, while Maillard products and cyclization products were hard to be oxidized to CO₂ and H₂O. The CN functional group of the protein facilitated DOC removal, and some organics in HTC-AP were oxidized to acids and phenols. The energy input to remove DOC in Fe(II)/CaO₂ system was 27.74 MJ per kg carbon. This study provides a low-energy consumption Fe(II)/CaO₂ system for the post-treatment of HTC-APs and explores the applicability of the system.

Aging of polyvinylidene fluoride (PVDF) ultrafiltration membrane due to ozone exposure in water treatment: Evolution of membrane properties and performance

Pre-ozonation is an effective pretreatment tactic for mitigating fouling of ultrafiltration (UF) membrane in water and wastewater treatment, but the compatibility of polymeric UF membranes with residual ozone remains unclear. In this study, effects of long-term ozone exposure on properties and performance of polyvinylidene fluoride (PVDF) UF membrane reinforced by polyethylene terephthalate (PET) layer were systematically investigated. The exposure intensities were designed to simulate ozone exposure at 0.1 mg/L for 0.5-5 years. Chemical composition analysis suggested that the hydrophilic additives, such as possibly polyvinyl pyrrolidone (PVP), was gradually degraded and released from the membrane, whereas the PVDF matrix exhibited fairly good ozone resistance. Ozonation resulted in increase of pore size and decrease of surface hydrophilicity, which can be attributed to oxidation and dislodgement of hydrophilic additives. Accordingly, long-term ozonation led to moderate changes in performance factors, including increase of membrane permeability by 34%, decrease of retention ability by 21.8%, increase of organic fouling propensity. It is worth noting that membrane tensile strength suffered substantial decrease after ozonation, probably due to ozonation of the PET support layer. Overall, it seems that the PVDF functional layer exhibited good ozone resistance, but the PET support layer was the Achilles' heel of the reinforced PVDF membrane for integrating with pre-ozonation.

Introduction of oxygen vacancy to manganese ferrite by Co substitution for enhanced peracetic acid activation and 1O2 dominated tetracycline hydrochloride degradation under microwave irradiation

High microwave-response cobalt-substituted manganese ferrite (CMFO-0.5) was successfully synthesized as a heterogeneous catalyst for efficient peracetic acid (PAA) activation and tetracycline hydrochloride (TCH) degradation with singlet oxygen (¹O₂) as the dominated reactive oxidized species (ROS). The removal efficiency of TCH could reach 98.16% within 6 min under microwave irradiation when the CMFO-0.5 was added at 20 mg/L. It's found that the Co substitution could produce the oxygen vacancies (OVs), improve the microwave (MW) absorbing performance and enhance the internal electron transfer efficiency of materials. The phenomenon why ¹O₂ as the dominated ROS rather than hydroxyl radical (•OH) and organic radicals (R-O•) would be explained by the following aspects: the oxygen adsorbed on the OVs can accept the electron transformed from PAA to form superoxide radical (•O₂^-), which will disproportionate to form ¹O₂; the energy generated by the non-thermal effect of MW can dissociate PAA to generate peroxy-group for ¹O₂ generation. Furthermore, the possible TCH degradation pathways were proposed based on DFT theory calculations and product identification, and the toxicity predictions of the degradation products were also performed by the Ecological Structure-Activity Relationship Model (ECOSAR) software. Additionally, the decrease of acute toxicity of treated TCH, excellent stability and strong resistance towards water matrix fully demonstrate the superiority of the proposed system for practical application in wastewater treatment.