Ferrous-activated sodium percarbonate pre-oxidation for membrane fouling control during ultrafiltration of algae-laden water

Promoted production of Fe(IV)/Fe(V) intermediates in the calcium peroxide/ferrate(VI) process for low-damage removal of algal contaminants and membrane fouling control

Ultrafiltration (UF) is widely employed for harmful algae rejection, whereas severe membrane fouling hampers its long-term operation. Herein, calcium peroxide (CaO2) and ferrate (Fe(VI)) were innovatively coupled for low-damage removal of algal contaminants and fouling control in the UF process. As a result, the terminal J/J0 increased from 0.13 to 0.66, with Rr and Rir respectively decreased by 96.74 % and 48.47 %. The cake layer filtration was significantly postponed, and pore blocking was reduced. The ζ-potential of algal foulants was weakened from -34.4 mV to -18.7 mV, and algal cells of 86.15 % were removed with flocs of 300 µm generated. The cell integrity was better remained in comparison to the Fe(VI) treatment, and Fe(IV)/Fe(V) was verified to be the dominant reactive species. The membrane fouling alleviation mechanisms could be attributed to the reduction of the fouling loads and the changes in the interfacial free energies. A membrane fouling prediction model was built based on a long short-term memory deep learning network, which predicted that the filtration volume at J/J0= 0.2 increased from 288 to 1400 mL. The results provide a new routine for controlling algal membrane fouling from the perspective of promoting the generation of Fe(IV)/Fe(V) intermediates.

Role of reactive manganese and oxygen species in the KMnO4/Na2SO3 process for purification of algal-rich water and membrane fouling alleviation

Ultrafiltration (UF) is a highly efficient technique for algal-rich water purification, but it is heavily contaminated due to the complex water characteristics. To solve this problem, potassium permanganate (KMnO4) oxidation enhanced with sodium sulfite (Na2SO3) was proposed as a pretreatment means. The results showed that the end-normalized flux was elevated from 0.10 to 0.91, and the reversible fouling resistance was reduced by 99.95%. The membrane fouling mechanism also changed obviously, without the generation of cake filtration. Regarding the properties of algal-rich water, the zeta potential was decreased from -29.50 to -5.87 mV after KMnO4/Na2SO3 pretreatment, suggesting that the electrostatic repulsion was significantly reduced. Meanwhile, the fluorescent components in algal-rich water were significantly eliminated, and the removal of dissolved organic carbon was increased to 67.46%. In the KMnO4/Na2SO3 process, reactive manganese species (i.e., Mn(V), Mn(III) and MnO2) and reactive oxygen species (i.e., SO4•- and •OH) played major roles in purifying algal-rich water. Specifically, SO4•-, •OH, Mn(V) and Mn(III) could effectively oxidize algal pollutants. Simultaneously, the in-situ adsorption and coagulation of MnO2 could accelerate the formation of flocs by decreasing the electrostatic repulsion between cells, and protect the algal cells from being excessive oxidized. Overall, the KMnO4/Na2SO3 process showed significant potential for membrane fouling alleviation in purifying algal-rich water.

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines-specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)-within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0-9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Improving membrane distillation performance by Fe(II) activated sodium percarbonate oxidation during the treatment of shale gas produced water

Membrane distillation (MD) offers promise for recycling shale gas produced water (SGPW), while membrane fouling is still a major obstacle in standalone MD. Herein, sodium percarbonate (SPC) oxidation was proposed as MD pretreatment, and the performance of the single MD, SPC-MD hybrid process and Fe(II)/SPC-MD hybrid process for SGPW treatment were systematically evaluated. Results showed that compared to raw SGPW, the application of SPC and Fe(II)/SPC led to the decrease of the fluorescent organics by 28.54 % and 54.52 %, respectively. The hydrophobic fraction decreased from 52.75 % in raw SGPW to 37.70 % and 27.20 % for SPC and Fe(II)/SPC, respectively, and the MD normalized flux increased from 0.19 in treating raw SGPW to 0.65 and 0.81, respectively. The superiority of SPC oxidation in reducing the deposited membrane foulants and restoring membrane properties was further confirmed through scanning electron microscopy observation, attenuated total reflection fourier transform infrared, water contact angle and surface tension analyses of fouled membranes. Correlation analysis revealed that hydrophobic/hydrophilic matters and fluorescent organics in SGPW took a crucial role in MD fouling. The mechanism of MD fouling mitigation by Fe(II)/SPC oxidation was attributed to the decrease in concentrations and hydrophobicity of organic by synergistic oxidation, coagulation and adsorption.

Enhancing microfiltration membrane performance by sodium percarbonate-based oxidation for hydraulic fracturing wastewater treatment

Low pressure membrane takes a great role in hydraulic fracturing wastewater (HFW), while membrane fouling is a critical issue for the stable operation of microfiltration (MF). This study focused on fouling mitigation by sodium percarbonate (SPC) oxidation, activated by ultraviolet (UV) and ferrous ion (Fe(II)). The higher the concentration of oxidizer, the better the anti-fouling performance of MF membrane. Unlike severe MF fouling without oxidation (17.26 L/(m2·h)), UV/SPC and Fe(II)/SPC under optimized dosage improved the final flux to 740 and 1553 L/(m2·h), respectively, and the latter generated Fe(III) which acted as a coagulant. Fe(II)/SPC oxidation enabled a shift in fouling mechanism from complete blocking to cake filtration, while UV/SPC oxidation changed it to standard blockage. UV/SPC oxidation was stronger than Fe(II)/SPC oxidation in removing UV254 and fluorescent organics for higher oxidizing capacity, but the opposite was noted for DOC removal. The deposited foulants on membrane surface after oxidation decreased by at least 88% compared to untreated HFW. Correlation analysis showed that UV254, DOC and organic fraction were key parameters responsible for membrane fouling (correlation coefficient＞0.80), oxidizing capacity and turbidity after oxidation were also important parameters. These results provide new insights for fouling control during the HFW treatment.

Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)-activated ferrate (Fe(vi)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(vi) could generate active species (Fe(v), Fe(iv), ˙OH and O2˙-) to degrade pollutants, while the in situ produced Fe(iii) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(vi) system, dissolved organic carbon was reduced by 49.38%, while UV254 was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J0 was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(vi) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.

Novel calcium hypochlorite/ferrous iron as an ultrafiltration membrane pretreatment process for purifying algae-laden water

Algal fouling has become one of the most critical factors hindering the large-scale development of membrane processes in algae-laden water treatment. Herein, novel calcium hypochlorite (Ca(ClO)2)/ferrous iron (Fe(II)) process was proposed as an ultrafiltration (UF) membrane pretreatment technology, and its effects on membrane fouling and water properties were systematically studied. Results showed that the terminal specific fluxes were significantly elevated to 0.925 and 0.933, with the maximum removal ratios of reversible resistance reaching 99.65% and 96.99% for algae-laden water and extracellular organic matter (EOM), respectively. The formation of cake filtration was dramatically delayed, accompanied by a significant reduction of the adhesion free energy, and the contaminants attached to the membrane surface were effectively decomposed. With respect to water quality, the removal ratios of OD685 and turbidity achieved 81.25-95.31% and 90.16-97.72%, individually. The maximum removal rates of DOC, UV254 and fluorescent organics in influent water reached 46.14%, 55.17% and 75.77%, respectively. Furthermore, the generated reactive species (e.g., •OH, Cl•, Cl2•- and ClO•) could efficiently degrade EOM, which appreciably reduced the electrostatic repulsion between the algal foulants while ensuring the integrity of algal cells. At the Ca(ClO)2/Fe(II) dosage of 0.04/0.24 mM, the zeta potential changed from -32.9 mV to -10.8 mV, and a large range of aggregates was formed. The macromolecules in the algal solution were significantly removed, and the proportion of micromolecular organics was increased to some extent. Coagulation of in-situ formed Fe(III) dominated the membrane fouling mitigation, and the reactive species also contributed to the improvement of filtration performance. Overall, Ca(ClO)2/Fe(II) pretreatment has an exceptional prospect for efficient degradation of algal pollutants and enhancement of UF capability.

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.

Hydroxyl radical dominated ibuprofen degradation by UV/percarbonate process: Response surface methodology optimization, toxicity, and cost evaluation

Ibuprofen (IBP) is a typical nonsteroidal anti-inflammatory drug with a wide range of applications, large dosages, and environmental durability. Therefore, ultraviolet-activated sodium percarbonate (UV/SPC) technology was developed for IBP degradation. The results showed that IBP could be efficiently removed using UV/SPC. The IBP degradation was enhanced with prolonged UV irradiation time, with the decreasing IBP concentration and the increasing SPC dosage. The UV/SPC degradation of IBP was highly adaptable to pH ranging from 4.05 to 8.03. The degradation rate of IBP reached 100% within 30 min. The optimal experimental conditions for IBP degradation were further optimized using response surface methodology. IBP degradation rate reached 97.3% under the optimal experimental conditions: 5 μM of IBP, 40 μM of SPC, 7.60 pH, and UV irradiation for 20 min. Humic acid, fulvic acid, inorganic anions, and natural water matrix inhibited the IBP degradation to varying degrees. Scavenging experiments of reactive oxygen species indicated that hydroxyl radical played a major role in the UV/SPC degradation of IBP, while carbonate radical played a minor role. Six IBP degradation intermediates were detected, and hydroxylation and decarboxylation were proposed as the primary degradation pathways. An acute toxicity test, based on the inhibition of luminescence in Vibrio fischeri, indicated that the toxicity of IBP during UV/SPC degradation decreased by 11%. An electrical energy per order value of 3.57 kWh m^-3 indicated that the UV/SPC process was cost-effective in IBP decomposition. These results provide new insights into the degradation performance and mechanisms of the UV/SPC process, which can potentially be used for practical water treatment in the future.

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.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Enhancing ultrafiltration of algal-rich water using ferrate activated with sodium percarbonate: Foulants variation, membrane fouling alleviation, and collaborative mechanism

Ultrafiltration (UF) is a reliable method to treat algal-rich water, whereas severe membrane fouling has impeded its actual application. To improve UF performance and alleviate membrane fouling resulted by algal foulants, a novel strategy coupling ferrate (Fe(VI)) and sodium percarbonate (SPC) was proposed. During the coupling process, Fe(VI) was activated by SPC to generate high-valent Fe intermediates (Fe(V) and Fe(IV)), which played a crucial role in high-efficiency oxidation for algal foulants, and the in-situ formed Fe(III) particles decomposed by Fe(VI) also enhanced the coagulation and adsorption capacity to the coupling system. Under the triple effects of coagulation, adsorption and oxidation, the algal foulants were efficiently eliminated. The zeta potential increased from -32.70 mV to -6.56 mV at most, the particle size was significantly enlarged, and the generated flocs possessed a great settleability. The morphology, viability, and integrity of algae cells were effectively maintained. The dissolved organic matters and fluorescent organics were efficiently removed, as well as macromolecular organics were reduced into lower molecular weight components. With the collaborative effect of Fe(VI) and SPC, the terminal specific flux was increased from 0.29 to 0.92, and the reversible and irreversible fouling resistances were reduced by 98.5% and 69.4%, individually. The surface functional groups were changed, and the dominant mechanisms were also converted to pore blocking from cake layer filtration. Overall, the experimental results would provide some new thoughts in actual production for algal-rich water treatment and UF membrane fouling alleviation.

Oxidation and coagulation/adsorption dual effects of ferrate (VI) pretreatment on organics removal and membrane fouling alleviation in UF process during secondary effluent treatment

Ultrafiltration (UF) has been widely used in water and advanced sewage treatment. Unfortunately, membrane fouling is still the main obstacle to further improvement in the system. Fe (III) salt, a type of traditional coagulant, is often applied to mitigate UF membrane fouling. However, low molecule organic weight cannot be effectively removed, thus the water quality after single coagulation treatment does not effectively meet the standard of subsequent water reuse during secondary effluent treatment. Recently, it has been found that potassium ferrate (Fe (VI)) has multiple functions of oxidation, sterilization and coagulation, with other studies proving its good performance in organics removal and membrane fouling mitigation. However, the respective contributions of oxidation and coagulation/adsorption have not yet been fully understood. The oxidation and coagulation/adsorption effects of Fe (VI) during membrane fouling mitigation were investigated here. The oxidation effect of Fe (VI) was the main reason for organics with the MW of 8-20 kDa removal, and its coagulation/adsorption mainly accounted for the smaller amounts of molecular organics removed. The oxidation of Fe (VI) was the main method for overcoming membrane fouling in the initial filtration; it largely alleviated the standard blockage. The formation of a cake layer transformed the main membrane fouling alleviation mechanism from oxidation to coagulation/adsorption and further removed smaller amounts of molecule organics with the increase of filtration cycles and Fe (VI) dosages. The main fouling mechanism altered from standard blocking and cake filtration to only cake filtration after Fe (VI) treatment. Overall, the mechanism of the oxidation and coagulation/adsorption of Fe (VI) were differentiated, and would provide a reference for future Fe (VI) pretreatment in UF membrane fouling control during water and wastewater treatments.

Effect of peroxydisulfate oxidation catalyzed with ordered mesoporous carbons on controlling ultrafiltration membrane fouling by algal organic matter

As typical ordered mesoporous carbons (OMCs) materials, CMK-3 and CMK-8 were proposed for catalyzing peroxydisulfate (PDS), and the OMCs/PDS process was combined with membrane filtration to remove algal extracellular organic matter and mitigate membrane fouling. The CMK-3/PDS process achieved substantial reduction of dissolved organic carbon and UV₂₅₄, followed by CMK-8/PDS. The degradation behavior of fluorescent organics demonstrated the superior performance of OMCs/PDS, while the decomposition of high molecular weight (MW) compounds and generation of lower MW organics were observed. Generally, CMK-3 possessed higher catalytic activity on PDS compared with CMK-8 and powdered activated carbon. The CMK-3/PDS process distinctly decreased the fouling resistances for polyether sulfone and polyvinylidene fluoride membranes, with the reversible resistance reduced by 59.5-83.2% and irreversible resistance declined by 71.7-73.0%. In the meanwhile, CMK-3/PDS prolonged the volumes to the transition period, and postponed the cake layer's generation. The characterization of the membrane morphologies and chemical compositions also showed effective alleviation of fouling. The generated SO₄^-, OH, O₂^- and ¹O₂ as major active oxidation species provided radical as well as non-radical reaction ways for pollutants removal. Overall, our study provides some new ideas for membrane-based combined water purification processes.

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

In this work, peracetic acid (PAA), ultraviolet (UV)/PAA and ultrasonic (US)/PAA pre-oxidation were applied to enhance ultrafiltration (UF) performance during algae-laden water treatment. The results showed that 10 mg/L PAA, exhibiting an optimal performance with membrane fouling resistance reduced by 76.26%. Low dosage of UV/PAA can effectively control fouling by enhancing the degradation of dissolved organics. Though more radicals were generated with the increasing dosage of PAA during the UV/PAA process, flux deterioration was occurred when PAA dosage over 10 mg/L, owing to a negative correlation between fouling resistance and algal integrity loss. Compared with UV, US exhibited a worse activation effect on PAA with less reactive radicals produced. Even worse, US can stimulate the stress metabolism of algal cells with slightly integrity loss, which then resulted in an exacerbation of permeate quality. Fouling mechanism analysis revealed that the delay formation of cake layer with membrane fouling alleviation mainly through efficient degradation of macromolecular organics. The investigation of synergistic and individual effect of EOM degradation, algae rupture and IOM release on the filtration performance revealed that EOM degradation was the primary mechanism for fouling control while algae rupture rather than IOM release was crucial for membrane fouling aggravation. This indicates that moderate oxidation, with property of high organic degradation and low cell rupture, was the working principal and objectives for algae-laden water treatment. Additionally, it was found that the ·OH radicals produced during UV/PAA process can efficiently degrade representative odors. In general, pretreatments of PAA and low dosages of UV/PAA showed promising prospects in improving the UF performance of algae-laden water and treating algal secretions.

Synergistic process using calcium peroxide and ferrous iron for enhanced ultrafiltration of Microcystis aeruginosa-laden water

Algal blooms and eutrophication in natural surface water not only pose a threat to human health, but also adversely affect the water purification process. Ultrafiltration (UF) has been proved to be effective for the retention of algal cells, but its further application is still restricted by the relatively limited removal of algal organics and membrane fouling. To enhance the UF performance, a synergistic process using calcium peroxide and ferrous sulfate (CaO₂/FeSO₄) was proposed for the treatment of Microcystis aeruginosa-laden water. The results suggested that the removal of algal cells and organics, fluorescent components were effectively increased with the synergism of CaO₂ and FeSO₄. The particle size distribution and morphology revealed that the size of algal pollutants apparently increased due to the formation of algal flocs. With CaO₂/FeSO₄ pretreatment, the terminal specific flux of polyethersulfone and polyvinylidene fluoride membranes were increased by 75.0% and 56.5%, individually. The fouling resistances were significantly reduced, and the fouling mechanism transition to cake filtration was delayed. The membrane interface properties including morphologies and functional groups were characterized, further verifying the effectiveness. The in-situ formed Fe³⁺ integrated with Ca(OH)₂ showed excellent coagulation effect, thus promoting the agglomeration of algal foulants. Simultaneously, the generated hydroxyl radical could improve the oxidative degradation of algal organics. In conclusion, the CaO₂/FeSO₄ strategy has great advantages and application prospects in enhancing UF performance for Microcystis aeruginosa-laden water treatment.

Forward osmosis treatment of algal-rich water: Characteristics and mechanism of membrane fouling

Membrane fouling is an inevitable problem in forward osmosis (FO) treatment of algal-rich water (ARW). Natural ARW has a complex composition. Therefore, the coexisting components (Ca²⁺, natural organic humic acid [HA], and inorganic particulate kaolinite) in the influence of ARW on FO membrane fouling were studied. The analysis of extended Derjaguin-Landau-Verwey-Overbeek theory and the confocal laser scanning microscopy revealed that the addition of coexisting components increased the attraction between pollutants and membranes, as well as among pollutants to varying degrees, and promoted the development of membrane fouling. Furthermore, Ca²⁺ and HA aggravated irreversible membrane fouling. All coexisting components changed the distribution and thickness of the fouling layer, and the addition of Ca²⁺ increased the content of extracellular organic matter (proteins and polysaccharides). The present results enhance the understanding of the mechanism through which natural ingredients affect microalgal membrane fouling and provide a basis for membrane fouling control to treat ARW.

Preparation of a newly synthesized biopolymer binder and its application to reduce the erosion of tailings

A new type of binder was developed by grafting casein and β-glucan to investigate its effect on tailings erosion and plant growth. 6% casein and 2% β-glucan were recommended as the best ratio of the new biopolymer binder, which had the best effect on the soil utilization of iron tailings. The infrared analysis of the new binder demonstrated that casein and β-glucan reacted adequately as raw materials. The results of physichemical properties and loss prevention of iron tailings showed that the binder-treated soils demonstrated lower erodibility compared with untreated iron tailings. The particle size of the tailings was increased after the addition of the binder. In treated soil, the content of soil organic matter increased significantly, which provided sufficient nutrients for the plants growing. Compared with natural tailings without binder, plant height, fresh weight, chlorophyll content, and enzyme activity (POD and SOD) were also significantly increased. This study overcame the current defects of biopolymer in soil improvement and provided an environmentally friendly method to prevent the loss of iron tailings and promote its soil utilization efficiency.

Coupling sodium percarbonate (SPC) oxidation and coagulation for membrane fouling mitigation in algae-laden water treatment

To alleviate algal fouling in membrane water treatment processes, conventional technologies such as coagulation with poly aluminum chloride (PACl) has been widely adopted by many drinking water treatment plants. However, coagulation alone exhibited relatively weak removal effect for algal pollutants, and the coagulant residues due to the excess dosage also raised concerns. Thus, a novel process of coupling sodium percarbonate (SPC) oxidation and PACl coagulation was proposed, integrated with membrane filtration for algae-laden water treatment. The dosages of PACl and SPC were optimized, and the SPC dosing strategies were systematically compared. The changes in the characteristics of algal pollutants were investigated, and the results revealed that the resistance of algal foulants to aggregation was decreased, and the particle size of algal foulants became larger. With the synergism of coagulation and oxidation, the degradation of fluorescent organics was strengthened, and macromolecular biopolymers were decomposed into low molecular weight organics. The fouling control efficiency was further explored, and the results indicated that both irreversible and reversible fouling were effectively controlled, among which PACl/SPC (simultaneous treatment) performed best with the irreversible fouling reduced by 90.5%, while the efficiency of SPC-PACl (SPC followed by PACl) was relatively lower (57.3%). The fouling mechanism was altered by slowing the formation of cake filtration, and the reduction of algal cells played a more important role for the fouling alleviation. The interface properties of contaminated membranes (i.e., functional groups, images, and micromorphology) were characterized, and the efficiency of the proposed strategy was further verified. The proposed strategy exhibits great application values for improving membrane performance during algae-laden water treatment.

Simultaneous mitigation of disinfection by-product formation and odor compounds by peroxide/Fe(II)-based process: Combination of oxidation and coagulation

To remove disinfection by-product (DBP) precursors and mitigate odor compounds, peroxide (peroxymonosulfate and persulfate)/Fe(II)-based process was applied as a combination of coagulation and oxidation. Compared with traditional Fe-based salt coagulation (FeSO₄ and FeCl₃), peroxide/Fe(II)-based process was more efficient in dissolved organic carbon, UV₂₅₄ and turbidity removal, and peroxymonosulfate showed better performance than persulfate. The better coagulation performance arose from a combination of enhanced neutralization and different characteristics of flocs. Even though the combined process would increase the bromine substitution factor of DBPs, DBP formation and DBP-associated toxicity after peroxide/Fe(II)-based process were 9.2-38.8% and 5.2-27.2% lower than that after conventional Fe(III) coagulation. Both enhanced dissolved organic matter removal and oxidation of DBP precursors played vital roles in DBP control. Conventional Fe-based salt coagulation could hardly remove odor compounds (less than 10%, generally), whereas 28.2-84.9% of odor compounds were degraded during peroxide/Fe(II)-based process, due to free radical formation. This study demonstrated that PMS/Fe(II)-based process might be a promising treatment process for simultaneous DBP control and odor removal in source water.

Membrane Fouling in Algal Separation Processes: A Review of Influencing Factors and Mechanisms

The use of algal biotechnologies in the production of biofuels, food, and valuable products has gained momentum in recent years, owing to its distinctive rapid growth and compatibility to be coupled to wastewater treatment in membrane photobioreactors. However, membrane fouling is considered a main drawback that offsets the benefits of algal applications by heavily impacting the operation cost. Several fouling control strategies have been proposed, addressing aspects related to characteristics in the feed water and membranes, operational conditions, and biomass properties. However, the lack of understanding of the mechanisms behind algal biofouling and control challenges the development of cost-effective strategies needed for the long-term operation of membrane photobioreactors. This paper reviews the progress on algal membrane fouling and control strategies. Herein, we summarize information in the composition and characteristics of algal foulants, namely algal organic matter, cells, and transparent exopolymer particles; and review their dynamic responses to modifications in the feedwater, membrane surface, hydrodynamics, and cleaning methods. This review comparatively analyzes (i) efficiency in fouling control or mitigation, (ii) advantages and drawbacks, (iii) technological performance, and (iv) challenges and knowledge gaps. Ultimately, the article provides a primary reference of algal biofouling in membrane-based applications.

Effects of oxidation on humic-acid-enhanced gypsum scaling in different nanofiltration phases: Performance, mechanisms and prediction by differential log-transformed absorbance spectroscopy

The aim of this study was to evaluate the effects of oxidation on humic-acid-enhanced gypsum scaling in different nanofiltration phases, including the short-term membrane flux behaviors and the long-term ones. On the basic of correlation analysis between the changing physicochemical properties of feed solution and membrane fouling, the inner mechanisms were revealed from aspects of bulk crystallization (interaction between humic acid and inorganic ions) and surface crystallization (compositions and morphologies of surface crystallization). Furthermore, the reliability of applicating differential log-transformed absorbance spectroscopy for predicting membrane fouling was also systematically evaluated. There was an upward trend in short-term membrane fouling with increasing dosage of NaClO, while long-term membrane fouling decreased after an initial increase. During short-term filtration, the enhanced combination between inorganic ions and the humic acid with stronger density of carboxyl groups, which was generated more easily under stronger oxidation conditions, favored the earlier appearance of flux decline. During long-term filtration, the size of bulk crystallization depended on the total content of carboxyl groups in feed solution. Both of them increased firstly and then decreased with increasing oxidation. The terminal fouling layer resistance also shared a similar tendency with them, because the deposition of bulk crystallization on membranes and the formation of dense scaling layer were the direct reasons for the long-term membrane fouling. Furthermore, the differential log-transformed absorbance spectroscopy was proven to be an efficient approach to predict short-term membrane fouling, especially in the wavelength range of 260 to 280 nm. This research could not only provide guidance on alleviating oxidation-enhanced membrane fouling in nanofiltration but also propose an efficient way to predict the membrane fouling which was influenced by the interaction between organic matters and inorganic ions.

A sodium percarbonate/ultraviolet system generated free radicals for degrading capsaicin to alleviate inhibition of methane production during anaerobic digestion of lipids and food waste

To alleviate inhibition of anaerobic digestion caused by capsaicin, which is easily soluble in the lipid components of food waste (FW), an advanced oxidation process with sodium percarbonate/ultraviolet (SPC/UV) was used to generate free radicals for degrading capsaicin and recovering methane production. Free radical sweeping showed that the free radicals OH, O₂^- and CO₃^- worked together to degrade capsaicin. Gas chromatography-mass spectrometry showed that capsaicin likely had four degradation pathways via conversion into benzoquinone, and finally into carbon dioxide and water. The degradation rate of capsaicin in lipids increased from 62.2% to 96.0% when the SPC concentration increased from 2 mmol/L to 32 mmol/L (UV intensity = 20.66 mW/cm²). The degradation rate increased from 70.9% to 94.6% when the UV intensity increased from 20.66 mW/cm² to 46.86 mW/cm² (SPC concentration = 4 mmol/L). The subsequent products after capsaicin degradation were subjected to anaerobic digestion either directly or by adding FW. The reduced intracellular oxidative kinases of anaerobic digestion microorganisms recovered the CH₄ yield from 27.2 mL/g-total volatile solids (TVS) with capsaicin to 311.2 mL/g-TVS with degraded capsaicin, which was 40.7% that of the control group (765.3 mL/g-TVS without capsaicin). After adding FW, the CH₄ yield of SPC/UV degradation effluent was 504.1 mL/g-TVS, which was 82.6% that of the control group (610.4 mL/g-TVS).