Responses of Chlorella vulgaris to the native bacteria in real wastewater: Improvement in wastewater treatment and lipid production.

Alga-bacterium interaction can improve wastewater treatment efficiency. To unravel the mystery of the interaction between microalgae and bacteria in wastewater, mono-cultures and co-cultures of Chlorella vulgaris and native bacteria in pretreated biochemical wastewater from landfill leachate were investigated. The results showed that the microalgae selected dominant commensal bacteria, creating a further reduction in species richness for the co-culture, which in turn aids in the dominant commensal bacteria's survival, thereby enhancing algal and bacterial metabolic activity. Strikingly, the lipid productivity of Chlorella in co-culture - namely 41.5 mg/L·d - was 1.4 times higher than in algal monoculture. Additionally, pollutant removal was enhanced in co-cultures, attributed to the bacterial community associated with pollutants' degradation. Furthermore, this study provides an important advance towards observations on the migration and transformation pathways of nutrients and metals, and bridges the gap in algal-bacterial synergistic mechanisms in real wastewater, laying the theoretical foundation for improving wastewater treatment.

Activation of peroxymonosulfate with biochar-supported CuO (CuO@BC) for natural organic matter removal and membrane fouling control.

To achieve excellent activation efficiency of peroxymonosulfate (PMS), this work prepared a biochar-supported CuO (CuO@BC) catalyst, and the CuO@BC/PMS system was proposed to remove the organic matter in natural surface water and reduce the fouling of ultrafiltration membrane. The successful synthesis of CuO@BC was demonstrated through characterization of its microscopic morphology and chemical composition by various techniques. The prepared heterogeneous catalyst showed a strong catalytic effect on PMS, which significantly removed natural organic matter through the production of active substances (•OH, SO4•-, O2•- and 1O2) from water. With respective degradation rates of 39.4% and 59.4%, the concentrations of DOC and UV254 dropped to 1.702 mg/L and 0.026 cm-1, respectively. Additionally, the CuO@BC/PMS oxidation displayed potent oxidation capabilities for contaminants and fluorescent organics with various molecular weights. The system effectively decreased the amount of organic matter that caused reversible and irreversible fouling of polyethersulfone membranes in natural water by 85.8% and 56.3%, respectively. The main fouling mechanisms changed as well, with standard and complete blocking dominating the entire filtration process. The results demonstrated the capacity of the CuO@BC/PMS system to remove contaminants in natural water and mitigate membrane fouling.

Improving ultrafiltration of algae-laden water with chitosan quaternary ammonium salt enhanced by sodium percarbonate.

Ultrafiltration (UF) is extensively used for algae removal because of its ability to retain algal cells with high efficiency, but it still faces the problem of membrane fouling and low retention capacity of dissolved organics. Hence, a strategy of coagulation with chitosan quaternary ammonium salt (HTCC) enhanced by sodium percarbonate (SPC) pre-oxidation was proposed to improve the UF performance. The fouling resistances were calculated by a resistance-in-series model based on Darcy's formula, and the membrane fouling mechanism was evaluated using a pore plugging-cake filtration model. The effect of SPC-HTCC treatment on the properties of algal foulants was explored, and the result showed that the water quality was improved with the maximum removal rates of 78.8 %, 52.4 % and 79.5 % for algal cells, dissolved organic carbon and turbidity, respectively. The SPC could achieve a mild oxidation effect that degraded the electronegative organics attached to algal cells without destroying the cell integrity, making the algal pollutants easier to agglomerate through subsequent HTCC coagulation by forming larger flocs. In terms of membrane filtration, the terminal normalized flux was increased from 0.25 to 0.71, with the reversible and irreversible resistances reduced by 90.8 % and 40.2 %, individually. The synergistic treatment reduced the accumulation of algal cells and algae-derived organics on the membrane surface as inferred from the interface fouling characteristics. The interfacial free energy analysis showed that the synergistic treatment reduced the adhesion of contaminants to the membrane surface, as well as the attraction among pollutants. Overall, the proposed process has high application prospects for algae-laden water purification.

Calcium sulfite oxidation activated by ferrous iron integrated with membrane filtration for removal of typical algal contaminants.

Oxidation treatment of algae-laden water may cause cells rupture and emission of intracellular organics, thus restricting its further popularization. As a moderate oxidant, calcium sulfite could be slowly released in the liquid phase, thus exhibiting a potential to maintain the cells integrity. To this end, calcium sulfite oxidation activated by ferrous iron was proposed integrated with ultrafiltration (UF) for removal of Microcystis aeruginosa, Chlorella vulgaris and Scenedesmus quadricauda. The organic pollutants were significantly eliminated, and the repulsion between algal cells was obviously weakened. Through fluorescent components extraction and molecular weights distribution analyses, the degradation of fluorescent substances and the generation of micromolecular organics were verified. Moreover, the algal cells were dramatically agglomerated and formed larger flocs under the premise of maintaining high cell integrity. The terminal normalized flux was ascended from 0.048-0.072 to 0.711-0.956, and the fouling resistances were extraordinarily decreased. Due to the distinctive spiny structure and minimal electrostatic repulsion, Scenedesmus quadricauda was easier to form flocs, and its fouling was more readily mitigated. The fouling mechanism was remarkably altered through postponing the formation of cake filtration. The membrane interface characteristics including microstructures and functional groups firmly proved the fouling control efficiency. The reactive oxygen species (i.e., SO4•- and 1O2) generated through the principal reactions and Fe-Ca composite flocs played dominant roles in alleviating membrane fouling. Overall, the proposed pretreatment exhibits a brilliant application potential for enhancing UF in algal removal.

Effect of ferrous-activated calcium peroxide oxidation on forward osmosis treatment of algae-laden water: Membrane fouling mitigation and mechanism.

Forward osmosis (FO) is a high-efficiency and low-energy consumption way for algae-laden water treatment, whereas membrane fouling is still an unavoidable problem in its practical application. In this work, a strategy of ferrous-activated calcium peroxide (Fe(II)/CaO2) was proposed to control FO membrane fouling in the purification of algae-laden water. With the treatment of Fe(II)/CaO2, the aggregation of algal contaminants was promoted, the cell viability and integrity were well preserved, and the fluorescent organics were efficiently removed. With respect to the fouling of FO membrane, the flux decline was generally alleviated, and the flux recovery was promoted to varying degrees under different process conditions. It could be revealed through the extended Derjaguin-Landau-Verwey-Overbeek theory that the adhesion of contaminants and membrane surfaces was reduced by Fe(II)/CaO2 treatment. The interface morphologies and functional groups of membrane verified that Fe(II)/CaO2 could mitigate the fouling by reducing the amount of algal contaminants adhering to the FO membrane. The co-coagulation of in-situ Fe(III) together with Ca(OH)2, as well as the oxidation of •OH were the main mechanisms for fouling mitigation. In sum, the Fe(II)/CaO2 process could effectively improve the efficiency of FO for algae-laden water treatment, and has broad application prospects.

Mutual activation between ferrate and calcium sulfite for surface water pre-treatment and ultrafiltration membrane fouling control.

In this work, ferrate (Fe(VI)) and calcium sulfite (CaSO3) were combined to treat surface water for improving ultrafiltration (UF) performance. During the pre-treatment process, the Fe(VI) and CaSO3 activated each other and a variety of active species (Fe(V), Fe(IV), OH, SO4-, 1O2, etc.) were generated. All of the five fluorescent components were effectively eliminated to different extents. With Fe(VI)/CaSO3 = 0.05/0.15 mM, the dissolved organic carbon and UV254 reduced by 44.33 % and 50.56 %, respectively. After UF, these values were further decreased with the removal rate of 50.27 % and 70.79 %. In the UF stage, the terminal J/J0 increased to 0.42 from 0.17, with the reversible and irreversible fouling decreased by 67.08 % and 79.45 % at most. The membrane pore blocking was significantly mitigated, as well as the foulants deposition on membrane surfaces was decreased to some extent. The complete blocking was altered to standard blocking and intermediate blocking, the volume when entering cake filtration was also delayed slightly. The extended Derjaguin-Landau-Verwey-Overbeek theory was employed to judge the interface fouling behavior, and the results indicated that the foulants became more hydrophilic, as well as the adhesion trend between foulants and membrane surface was weakened. Overall, these results provide a theoretical foundation for the practical application of the combined Fe(VI)/CaSO3-UF process in surface water purification.

Secondary pollution of microplastic hetero-aggregates after chlorination: Released contaminants rarely re-adsorbed by the second-formed hetero-aggregates.

In urban waters, microplastics (MPs) usually form hetero-aggregates through adsorption of organics and microbes. However, the effects of hetero-aggregates on water quality are rarely reported. In this study we found that the hetero-aggregates, which accumulated contaminants, were like a "time bomb". Chlorination was able to trigger the "time bomb" through destruction of hetero-aggregates, lysis of microbial cells and elevation of the concentration of low-molecular-mass organics. Thereupon previously adhered organics desorbed from MPs, intracellular metabolites were released from lysed cells, and re-formation of hetero-aggregates was limited. This process rapidly increased the concentration of organics but prevented the re-adsorption of organics, which leads to secondary pollution. Thus, to alleviate the risks of secondary pollution caused by hetero-aggregates, the choice of oxidant species and dose should be optimized based on the characteristics of existent hetero-aggregates when purifying urban waters containing MPs.

The synergistic mechanism of ß-lactam antibiotic removal between ammonia-oxidizing microorganisms and heterotrophs.

Nitrifying system is an effective strategy to remove numerous antibiotics, however, the contribution of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and heterotrophs for antibiotic removal are still unclear. In this study, the mechanism of ß-lactam antibiotic (cefalexin, CFX) removal was studied in a nitrifying sludge system. Results showed that CFX was synergistically removed by AOB (Nitrosomonas, played a major role) and AOA (Candidatus_Nitrososphaera) through ammonia monooxygenase-mediated co-metabolism, and by heterotrophs (Pseudofulvimonas, Hydrogenophaga, RB41, Thauera, UTCFX1, Plasticicumulans, Phaeodactylibacter) through antibiotic resistance genes (ARGs)-encoded ß-lactamases-mediated hydrolysis. Regardless of increased archaeal and heterotrophic CFX removal with the upregulation of amoA in AOA and ARGs, the system exhibited poorer CFX removal performance at 10 mg/L, mainly due to the inhibition of AOB. This study provides new reference for the important roles of heterotrophs and ARGs, opening the possibilities for the application of ARGs in antibiotic biodegradation.

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.

CuO@carbon nanofiber as an efficient peroxymonosulfate catalyst for mitigation of organic matter fouling in the ultrafiltration process.

Persulfate oxidation has been increasingly integrated with membrane separation for water purification, whereas the oxidizing ability of persulfate is relatively limited, and appropriate activation methods are urgently required. In this work, a novel catalyst of carbon nanofiber (CNF) supported CuO (CuO@CNF) was synthesized for peroxymonosulfate (PMS) activation. The micro-morphology showed that CuO nanoparticles were well dispersed on the CNF support, which solved the agglomeration problem of nanoparticles and improved the catalytic ability. Furtherly, PMS oxidation activated by CuO@CNF was proposed as a pre-processing means for improving ultrafiltration (UF) water purification efficiency and mitigating membrane fouling. The prepared CuO@CNF was more efficient than individual CNF and CuO in activating PMS for the reduction of various typical natural organic matter, improving permeation flux, and mitigating membrane fouling. The fouling control efficiencies were also verified by characterizing the membrane surface functional groups. The CuO@CNF catalyst could signally promote the oxidative capacity by generating a series of reactive oxygen species, thus enhancing the removal of organics with varying species and molecular weight ranges in surface water. With respect to the fouling condition, the specific permeation flux after filtration was improved from 0.25 to 0.61, with the removal rate of reversible fouling resistance reached 89.6%. The fouling mechanism was apparently altered, with both standard and complete blocking dominated throughout the filtration process. The findings are beneficial for the development of new strategies to improve membrane-based water purification efficiency.

Degradation of iopamidol by UV365/NaClO: Roles of reactive species, degradation mechanism, and toxicology.

The degradation of iopamidol (IPM) was investigated using a UV365/NaClO system. The reactive species (HO·, ClO·, ozone, Cl·, and Cl2-·) in the system were identified, and the changing trends of the percentage contributions of these reactive species to IPM removal under various conditions were systematically evaluated. The results showed that ClO· and HO· played the most significant roles in the apparent pseudo-first-order rate constants of IPM degradation (kobs, min-1) in the control experiment, and their percentage contributions to kobs were 41.31% and 34.45%, respectively. In addition, Cl· and Cl2-· together contributed 22% to the kobs. Furthermore, the contribution of ozone to the IPM removal could be neglected. The concentrations of these species increased significantly when the concentration of NaClO was increased from 50 µM to 200 µM, while the percentage contribution of ClO· to kobs was greatly increased. The concentrations and percentage contributions of HO· and ClO· decreased significantly as the solution pH increased from 5 to 9, with Cl2-· playing a greater role in the degradation of IPM under alkaline conditions. While Cl- or HCO3-/CO32- significantly promoted the generation of Cl2-· or CO3-·, neither had an obvious effect on kobs, suggesting that Cl2-· and CO3-· should have a certain reactivity with IPM. Compared with that of Cl2-·, the percentage contribution of ClO· and Cl· to kobs was more likely to be inhibited by NOM. In addition, the organic and inorganic oxidation products of IPM were detected. The oxidation mechanisms of IPM degradation in the UV365/NaClO system, such as the H-extraction reaction, deiodination, substitution reaction, amide hydrolysis, and amine oxidation, were proposed according to the obtained 15 organic products. No effect on acute toxicity towards Vibrio fischeri and Photobacterium phosphoreum was detected during the oxidation of IPM by the UV365/NaClO system. Furthermore, the engineering feasibility of the oxidation system was demonstrated, by the effective degradation of IPM in actual water. However, HOI rapidly accumulated during the removal of IPM in the UV365/NaClO system, which poses certain environmental risks and will needs to be investigated.

In Situ Chemical Modification with Zwitterionic Copolymers of Nanofiltration Membranes: Cure for the Trade-Off between Filtration and Antifouling Performance.

Breaking the trade-off between filtration performance and antifouling property is critical to enabling a thin-film nanocomposite (TFC) nanofiltration (NF) membrane for a wide range of feed streams. We proposed a novel design route for TFC NF membranes by grafting well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and 2-aminoethyl methacrylate hydrochloride (AEMA) on the polyamide surfaces via an in situ surface chemical modification process. The successful grafting of a zwitterionic copolymer imparted the modified NF membranes with better surface hydrophilicity, a larger actual surface area (i.e., nodular structures), and a thinner polyamide layer. As a result, the water permeability of the modified membrane (i.e., TFC-10) was triple that of the pristine TFC membrane while maintaining high Na2SO4 rejection. We further demonstrated that the TFC-10 membrane possessed exceptional antifouling properties in both static adsorption tests and three cycles of dynamic protein and humic acid fouling tests. To recap, this work provides valuable insights and strategies for the fabrication of TFC NF membranes with simultaneously enhanced filtration performance and antifouling property.

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.

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.

Assessment of organic contamination along the coast of Laizhou Bay, China: chemical analysis and integrated biomarker responses in the clam Ruditapes philippinarum.

An investigative biomonitoring study was conducted along the coastal area of Laizhou Bay (China) to evaluate the impact of organic pollution on the clam Ruditapes philippinarum using bioaccumulation and multi-biomarker measurements. In addition, the polychlorinated biphenyls (PCBs), total petroleum hydrocarbons (TPHs) and nonylphenol (NP) content in surface sediment at the study sites were also analyzed. Concentrations of PCBs, TPHs and NP in the sediments of the study area were 1.90 ± 0.10 µg kg-1, 39.55 ± 2.42 mg kg-1, 9.23 ± 0.41 µg kg-1 dry weight, respectively, while the organic contaminants in the soft tissues of R. philippinarum were 14.81 ± 0.96 µg kg-1 for PCBs, 165.87 ± 5.03 mg kg-1 for TPHs and 86.16 ± 5.29 µg kg-1 for NP. Linear regression analysis on the levels of organic pollutants accumulated in R. philippinarum and in sediments showed no significant correlation. Multi-biomarkers including superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, total glutathione and lipid peroxidation were assayed in gills and digestive glands of R. philippinarum. Finally, the biomarkers in gills were selected to calculate the Integrated Biomarker Response (IBR) index and to evaluate the impact of the three organic contaminants on R. philippinarum collected from different sites. According to IBR results, the western coast and eastern coast exhibited higher environmental stress than the sampling sites along the southern coast of Laizhou Bay. Significant correlation was found between the level of organic contaminants in the sediments and IBR whereas no dependence was found between pollutants' concentrations in sediments and separate biomarker responses. The results showed that PCBs and NP were the main organic pollutants among the three studied which have caused pollution pressure on R. philippinarum in Laizhou Bay coastal area.

Toward Enhancing Desalination and Heavy Metal Removal of TFC Nanofiltration Membranes: A Cost-Effective Interface Temperature-Regulated Interfacial Polymerization.

Polyamide (PA) chemistry-based nanofiltration (NF) membranes have an important role in the field of seawater desalination and wastewater reclamation. Achieving an ultrathin and defect-free active layer via precisely controlled interfacial polymerization (IP) is an effective routine to improve the separation efficiencies of NF membranes. Herein, the morphologies and chemical structures of the thin-film composite (TFC) NF membranes were accurately regulated by tailoring the interfacial reaction temperature during the IP process. This strategy was achieved by controlling the temperature (-15, 5, 20, 35, and 50°) of the oil-phase solutions. The structural compositions, morphological variations, and separation features of the fabricated NF membranes were studied in detail. In addition, the formation mechanisms of the NF membranes featuring different PAs were also proposed and discussed. The temperature-assisted IP (TAIP) method greatly changed the compositions of the resultant PA membranes. A very smooth and thin PA film was obtained for the NF membranes fabricated at a low interfacial temperature; thus, a high 19.2 L m-2 h-1 bar-1 of water permeance and 97.7% of Na2SO4 rejection were observed. With regard to the NF membranes obtained at a high interfacial temperature, a lower water permeance and higher salt rejection with fewer membrane defects were achieved. Impressively, the high interfacial temperature-assisted NF membranes exhibited uniform coffee-ring-like surface morphologies. The special surface-featured NF membrane showed superior separation for selected heavy metals. Rejections of 93.9%, 97.9%, and 87.7% for Cu2+, Mn2+, and Cd2+ were observed with the optimized membrane. Three cycles of fouling tests indicated that NF membranes fabricated at low temperatures exhibited excellent antifouling behavior, whereas a high interface temperature contributed to the formation of NF membranes with high fouling tendency. This study provides an economical, facile, and universal TAIP strategy for tailoring the performances of TFC PA membranes for environmental water treatment.

Contribution of vitamin B12 to biogas upgrading and nutrient removal by different microalgae-based technology.

The algae-based technology has a positive effect on the treatment of biogas slurry and the purification of biogas, while vitamin B12 (VB12) is one of the important regulatory substances in the algae-based cultivation system. In this study, different concentrations of VB12 were used in three microalgal treatment technologies to assess their effect on simultaneous removal of nutrients from biogas slurry and removal of CO2 from raw biogas. Results showed that Chlorella vulgaris exhibited higher growth rate, mean daily productivity, chlorophyll a content, carbonic anhydrase activity and better photosynthetic properties when co-cultivated with Ganoderma lucidum, rather than when co-cultivated with activated sludge or under mono-cultivation. Maximum mean chemical oxygen demand, total nitrogen, total phosphorus and CO2 removal efficiencies were found to be 84.29 ± 8.28%, 83.27 ± 8.14%, 85.27 ± 8.46% and 65.71 ± 6.35%, respectively when microalgae were co-cultivated with Ganoderma lucidum under 100 ng L-1 of VB12. This study shows the potential of microalgae and fungi co-cultivation supplemented with VB12 for the simultaneous upgradation of biogas production as well as for the purification of biogas slurry.

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.

The role of PAC adsorption-catalytic oxidation in the ultrafiltration performance for treating natural water: Efficiency improvement, fouling mitigation and mechanisms.

Powdered activated carbon (PAC) has turned out to be an efficient adsorbent in drinking water treatment, whereas its application integrated with membrane filtration is still controversial because of the combined fouling effect between organic pollutants and PAC. To this end, an integrated process of combining PAC adsorption-catalytic oxidation and membrane filtration was proposed for natural surface water treatment. The synergistic effect of PAC and peroxymonosulfate (PMS) was confirmed through the generation of reactive oxidation species, and both radical oxidative pathways (•OH, SO4•- and O2•-) and nonradical (1O2 and PMS) pathways involved in the process. The removal efficiency of DOC and UV254 was significantly strengthened by PAC/PMS, with removal rates of 56.1% and 64.9%, respectively. The integration of PAC and PMS could significantly enhance the reduction of fluorescent organics, and pollutants with varying molecular weights. The fouling condition of membrane was dramatically alleviated, with the flux increased by 38.9%, and the reversible and irreversible resistances declined by 79.7% and 48.3%, respectively. The major fouling mechanism was significantly changed, and complete pore blocking always played a dominant role, rather than cake filtration. The effectiveness of PAC/PMS was further verified by the characterization of membrane surface morphologies and functional groups. Moreover, the attractive interactions between foulants and membrane were converted to repulsive interactions with the pretreatment of PAC/PMS. The proposed synergistic process was efficient and convenient, which could significantly improve the purification efficiency of conventional PAC-UF system in drinking water treatment.

Biochemical wastewater from landfill leachate pretreated by microalgae achieving algae's self-reliant cultivation in full wastewater-recycling chain with desirable lipid productivity.

Heightened awareness of additional pretreatment for wastewater, has driven studies towards building a full wastewater-recycling chain wherein the wastewater pretreatment is performed by microalgae themselves. We applied biochemical wastewater from landfill leachate with added K2HPO4 (BWLL + P) directly to microalgal cultivation. The results showed that the pretreatment provided by the 1st cultivation reduced suspended solids by nearly half, greatly boosting microalgal growth, which thus yielded 1.06 g/L of dry mass and 87.06 mg/L·d of biomass productivity. From the 2nd to the 4th cultivation, lipid accumulation in BWLL + P was 1.12-1.27 times and 1.95-2.36 times higher than in BG11 and BWLL, respectively, mainly attributed to the comfortable environment engendered by the microalgal pretreatment and the organic carbon in the wastewater. Strikingly, the biodiesel production fed with BWLL + P could save 99% of the cost compared with in BG11. In combination, our pioneering full wastewater-recycling chain achieved microalgae's self-reliant cultivation, with wastewater nourishment.