Coagulation performance and mechanism analysis of humic acid by using covalently bonded coagulants: effect of pH and matching mechanism of humic acid functional groups.

Conventional inorganic coagulants (Al, Fe) and Al/Fe-based covalently bonded flocculants (CAFMs) had different hydrolysis species at different pHs, which subsequently led to differences in their binding sites and complexation ability with humic acid (HA). Studying the binding sites and interactions between CAFMs, AlCl3 (Al), and FeCl3 (Fe) hydrolysates and HA molecules is critical to understanding the coagulation mechanism. The results found that CAFM 0.6, Al, and AlCl3 combined FeCl3 (Al/Fe) removed more than 90% of HA at pH 6, and CAFMs showed higher HA removal rate than that of Al, Fe, and Al/Fe under the same reaction conditions. The flocs of CAFMs contained abundant -NH2/OH as well as the large particle size, compact structure, and excellent settling performance. The hydrolyzed species of Al and Fe were predominantly Alb and Feb at pH 6, but the hydrolyzed species of CAFMs were primarily (Al + Fe)c. Moreover, the hydrolyzed species of Al and Al/Fe were found to complex with HA functional groups such as -COOH, C = O, C-H/C-C, C = C, and C-OH to form ligand bonds, while the hydrolyzed species (Al + Fe)c of CAFMs could deeply interact with HA functional groups including C-O, -COOH, C = O, C-H/C-C, C = C, and C-OH by the adsorption and sweeping.

Recycling waste iron-rich algal flocs as cost-effective biochar activator for heterogeneous Fenton-like reaction towards tetracycline degradation: Important role of iron species and moderately defective structures.

Harvesting aquatic harmful algal blooms (HABs) and reusing them is a promising way for antibiotic degradation. Herein, a novel iron-rich biochar (Fe-ABC), derived from algal biomass harvested by magnetic coagulation, was successfully designed and fabricated as activator for heterogeneous Fenton-like reaction. The modification methods and pyrolysis temperatures (400-800 °C) were optimized to enhance the formation of rich iron species and moderately defective structure, yielding Fe-ABC-600 with enhanced electron transfer and H2O2 activation capability. Thus, Fe-ABC-600 exhibited superior removal efficiency (95.33%) on tetracycline (TC), where the presence of multiple iron species (Fe3+, Fe2+ and Fe4+) and moderately defective structure accelerating the Fenton-like oxidation. The concentration of leaching Fe after each reaction was all below 0.74 mg/L in five cycles, ensuring the sustained degradation. And •OH was proved to be the major radical contributing to the degradation of TC, as well as the direct electron transfer mechanism together, in which the CO acted as electron regulator and electron donor. Fe-ABC as a cost-effective catalyst has notable application potentials in TC removal from wastewater owing to its remarkable advantages of high resource utilization, enhanced catalytic property, high ecological safe, notable TC degradation efficiency, low cost and environmental-friendliness.

Hydrochloric acid-modified fungi-microalgae biochar for adsorption of tetracycline hydrochloride: Performance and mechanism.

Novel biochar (BC) was prepared by pyrolysis using Aspergillus oryzae-Microcystis aeruginosa (AOMA) flocs as raw materials. It has been used for tetracycline hydrochloride (TC) adsorption along with acid (HBC) and alkali modification (OHBC). Compared with BC (114.5 m2 g-1) and OHBC (283.9 m2 g-1), HBC had a larger specific surface area (SBET = 338.6 m2 g-1). Meanwhile, the Elovich kinetic and Sip isotherm models adequately fit the adsorption data, and intraparticle diffusion is the controlling factor for TC adsorption diffusion on HBC. Furthermore, the thermodynamic data indicated that this adsorption was endothermic and spontaneous. The experimental results demonstrated that there are multiple interactions during the adsorption reaction process, including pore filling, H-bonds, π-π interaction, hydrophobic affinity, and van der Waals forces. In general, biochar prepared from flocs of AOMA can be used to remediate tetracycline-contaminated water, and it is of great significance in improving resource utilization.

Enhancement of 15% calcium oxide doped nano zero-valent iron on arsenic removal from high-arsenic acid wastewater.

Nano zero-valent iron (nZVI) has a great potential for arsenic removal, but it would form aggregates easily and consume largely by H+ in the strongly acidic solution. In this work, 15%CaO doped with nZVI (15%CaO-nZVI) was successfully synthesized from a simplified ball milling mixture combined with a hydrogen reduction method, which had a high adsorption capacity for As(V) removal from high-arsenic acid wastewater. More than 97% As(V) was removed by 15%CaO-nZVI under the optimum reaction conditions of pH 1.34, initial As(V) concentration 16.21 g/L, and molar ratio of Fe/As (nFe/nAs) 2.5:1. The effluent pH solution was weakly acidic 6.72, and the secondary arsenic removal treatment reduced the solid waste and improved arsenic grade in slag from the mass fraction of 20.02% to 29.07%. Multiple mechanisms including Ca2+ enhanced effect, adsorption, reduction, and co-precipitation coexisted for As(V) removal from high-arsenic acid wastewater. Doping of CaO might lead to improving cracking channels which was benefit for electronic transmission and the confusion of atomic distribution. The in situ weak alkaline environment generated on the surface of 15%CaO-nZVI would increase the content of γ-Fe2O3/Fe3O4, which was in favor for As(V) adsorption. In addition, H+ in the strongly acidic solution could accelerate corrosion of 15%CaO-nZVI and abundant fresh and reactive iron oxides continuously generated, which would provide plenty specific reactive site and fast charge transfer and ionic mobility for arsenic removal.

Enhanced removal of aqueous Cr(VI) by the in situ iron loaded activated carbon through a facile impregnation with Fe(II) and Fe(VI) two step method: Mechanism study.

In this study, a novel in situ iron-loaded activated carbon (AFPAC) was prepared by a FeSO4/K2FeO4 impregnation and oxidation combination two-step supported on activated carbon for enhanced removal of Cr(VI) from aqueous solutions. Cr(VI) removal efficiency greatly increased by AFPAC more than 70% than that of fresh activated carbon (AC), which is due to rich iron oxides formed in situ and the synergistic effect between iron oxides and activated carbon. Cr(VI) adsorption behaviors on AFPAC under different water quality parameters were investigated. The maximum monolayer adsorption capacities for Cr(VI) by AFPAC are as high as 26.24 mg/g, 28.65 mg/g, and 32.05 mg/g at 25 °C, 35 °C and 45 °C at pH 4, respectively. Density functional theory (DFT) results showed that the adsorption energy of K2Cr2O7 on the surface of FeOOH was - 2.52 eV, which was greater than that on the surface of bare AC, and more charge transfer occurred during the adsorption of K2Cr2O7 on the surface of FeOOH, greatly promoting the formation of Cr = O-Fe. Cr(VI) removal by AFPAC included electrostatic attraction, redox reaction, coordinate complexation, and co-precipitation. Cr(VI) adsorption process on AFPAC consisted of the three reaction steps: (1) AFPAC was fast protonation and Cr2O72- would electrostatically attract to the positively charged AFPAC surface. (2) Cr2O72- was reduced into Cr2O3 by the carbons bond to the oxygen functionalities on activated carbon and the redox reaction process of FeSO4 and K2FeO4. (3) The inner-sphere complexes were formed, and adsorbed on AFPAC by iron oxides and then co-precipitation.

Biodegradability enhancement of phenolic wastewater using hydrothermal pretreatment.

A novel hydrothermal pretreatment was applied for the biochemical treatment of phenolic wastewater with high concentrations of phenolic substances. The results demonstrated that 250 °C was the reaction temperature dividing point for complete oxidation, hydrothermal gasification, and amino release from carbonaceous organics in phenolic wastewater. Before the dividing point reached, some of the large molecules were hydrolyzed into small molecules of volatile phenolic substances that were easily adsorbed by the activated sludge. After the integrated hydrothermal pretreatment and anaerobic/aeration process, the removal rate of volatile phenolswas respectively reached by 97 % and 88 % with hydrothermal temperature of 250 °C and without pretreatment. Functional microorganisms (i.e., Chloroflexi) responsible for aromatic compounds degradation were enriched, thus the dioxygenases, dehydrogenase reactions, and meta-cleavage of catechol were enhanced. This work provided an innovative approach to remove phenolic substances from phenolic wastewater, and in-depth understandings of microbial responses in biochemical systems.

Characteristics and mechanisms of As(III) removal by potassium ferrate coupled with Al-based coagulants: Analysis of aluminum speciation distribution and transformation.

This study was carried out to investigate the enhanced removal of arsenite (As(III)) by potassium ferrate (K2FeO4) coupled with three Al-based coagulants, which focused innovatively on the distribution and transformation of hydrolyzed aluminum species as well as the mechanism of K2FeO4 interacted with different aluminum hydrolyzed polymers during As(III) removal. Results demonstrated that As(III) removal efficiency could be substantially elevated by K2FeO4 coupled with three Al-based coagulants treatment and the optimum As(III) removal effect was occurred at pH 6 with more than 97%. K2FeO4 showed a great effect on the distribution and transformation of aluminum hydrolyzed polymers and then coupled with a variety of aluminum species produced by the hydrolysis of aluminum coagulants for arsenic removal. During enhanced coagulation, arsenic removal by AlCl3 was main through the charge neutralization of in situ Al13 and the sweep flocculation of Al(OH)3, while PACl1 mainly depended on the charge neutralization of preformed Al13 and the bridging adsorption of Al13 aggregates, whereas PACl2 mainly relied on the sweep flocculation of Al(OH)3. This study provided a new insight into the distribution and transformation of aluminum species for the mechanism of As(III) removal by K2FeO4 coupled with different Al-based coagulants.

Expression profile of CYP402C1 and its role in resistance to imidacloprid in the whitefly, Bemisia tabaci.

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cosmopolitan insect pest causing serious damage to crop production. Cytochromes P450 (CYPs) of B. tabaci are widely known to be involved in the metabolic resistance to a variety of insecticides, continuously increasing the difficulty in controlling this pest. In this study, four P450 genes (CYP6CM1, CYP6CX1, CYP6CX3, and CYP402C1) in B. tabaci exhibited correlations with the resistance to imidacloprid. We have focused on trying to understand the function and metabolism capacity of CYP402C1. The expression profiles of CYP402C1 were examined by reverse transcription quantitative real-time PCR and fluorescence in situ hybridizations. Its role in resistance to imidacloprid was investigated by RNA interference, transgenic Drosophila melanogaster, and heterologous expression. The results showed that CYP402C1 was highly expressed in the active feeding stages of B. tabaci, such as nymphs and female adults. CYP402C1 was mainly expressed in midguts of nymphs and adults, especially in the filter chamber. Knockdown of CYP402C1 significantly decreased the resistance of B. tabaci to imidacloprid by 3.96-fold (50% lethal concentration: 186.46 versus 47.08 mg/L). Overexpression of CYP402C1 in a transgenic D. melanogaster line (Gal4 > UAS-CYP402C1) significantly increased the resistance to imidacloprid from 12.68- to 14.92-fold (129.01 and 151.80 mg/L versus 1925.14 mg/L). The heterologous expression of CYP402C1 showed a metabolism ability of imidacloprid (imidacloprid decreased by 12.51% within 2 h). This study provides new insights for CYP402C1 function in B. tabaci and will help develop new strategies in B. tabaci control and its insecticide resistance.

Highly efficient removal of arsenate and arsenite with potassium ferrate: role of in situ formed ferric nanoparticle.

It is well known the capacity of potassium ferrate (Fe(VI)) for the oxidation of pollutants or co-precipitation and adsorption of hazardous species. However, little information has been paid on the adsorption and co-precipitation contribution of the Fe(VI) resultant nanoparticles, the in situ hydrolytic ferric iron oxides. Here, the removal of arsenate (As(V)) and arsenite (As(III)) by Fe(VI) was investigated, which focused on the interaction mechanisms of Fe(VI) with arsenic, especially in the contribution of the co-precipitation and adsorption of its hydrolytic ferric iron oxides. pH and Fe(VI) played significant roles on arsenic removal; over 97.8% and 98.1% of As(V) and As(III) removal were observed when Fe(VI):As(V) and Fe(VI):As(III) were 24:1 and 16:1 at pH 4, respectively. The removal of As(V) and As(III) by in situ and ex situ formed hydrolytic ferric iron oxides was examined respectively. The results revealed that As(III) was oxidized by Fe(VI) to As(V), and then was removed though co-precipitation and adsorption by the hydrolytic ferric iron oxides with the contribution content was about 1:3. For As(V), it could be removed directly by the in situ formed particles from Fe(VI) through co-precipitation and adsorption with the contribution content was about 1:1.5. By comparison, As(III) and As(V) were mainly removed through adsorption by the 30-min hydrolytic ferric iron oxides during the ex situ process. The hydrolytic ferric iron oxides size was obviously different in the process of in situ and ex situ, possessing abundant and multiple morphological structures ferric oxides, which was conducive for the efficient removal of arsenic. This study would provide a new perspective for understanding the potential of Fe(VI) treatment on arsenic control.

Efficient removal of cadmium by salts modified-biochar: Performance assessment, theoretical calculation, and quantitative mechanism analysis.

Modified biochar is a feasible adsorbent to solve cadmium pollution in water. However, few studies could elucidate the mechanism of cadmium adsorption by biochar from a molecular perspective. Furthermore, traditional modification methods are costly and have the risk of secondary contamination. Hence, several environmentally friendly sodium salts were used to modify the water chestnut shell-based biochar and employ it in the Cd2+ adsorption in this work. The modification of sodium salt could effectively improve the specific surface area and aromaticity of biochar. Na3PO4 modified biochar exhibited the highest Cd2+ adsorption capacity (112.78 mg/g). The adsorption of Cd2+ onto biochar was an endothermic, monolayer, chemisorption process accompanied by intraparticle diffusion. Microscopically, the enhancement of aromatization after modification made Cd2+ more likely to interact with the regions rich in π electrons and lone pair electrons. This study provided a new research perspective and application guidance for heavy metal adsorption on biochar.

Bio-flocculation of Microcystis aeruginosa by using fungal pellets of Aspergillus oryzae: Performance and mechanism.

Algal blooms caused by eutrophication are global phenomena that seriously threaten the sustainable use of freshwater resources. Traditional water treatment chemicals often typically lead to high levels of residue and cause damage to the morphology of algal cells. This study investigated an eco-friendly fungal bio-flocculant, Aspergillus oryzae, to remove the representative microalgae (Microcystis aeruginosa). Furthermore, it explored crucial flocculation parameters, adsorption kinetics, and thermodynamics of microalgae using A. oryzae. Accordingly, a flocculation efficiency of >95% was achieved when the fungus was cultured for six days, flocculant dosage was 11 g/L, rotation speed was 100 rpm, temperature was 25 °C, flocculation time was 5 h, and pH ranged between 4.0 and 9.0. KEGG analysis based on the genomic data, and chemical composition analysis revealed that proteins and polysaccharides were the major components of metabolites. Zeta potential analysis, scanning electron microscopy, three-dimensional fluorescence, X-ray spectroscopy, and infrared spectroscopy, electrostatic attraction revealed that electrostatic attraction promoted the destabilization and aggregation of microalgae. Additionally, hyphal surface adsorption and chemisorption from extracellular proteins and exopolysaccharides aided in the removal of microalgae. Therefore, fungi-based bio-flocculants have the potential to remove microalgae in a simple, effective, and eco-friendly manner without the complex extraction of extracellular metabolites.

Agricultural waste-derived biochars from co-hydrothermal gasification of rice husk and chicken manure and their adsorption performance for dimethoate.

This study aimed to combine energy utilisation of agricultural wastes with the dimethoate (DT) adsorption from agricultural wastewater via hydrogen and biochar production using co-hydrothermal gasification (CHTG). The gasification behaviour after CHTG of five ratios of rice husk (RH) and chicken manure (CM) and the corresponding adsorption performance of biochars on DT were evaluated. The results demonstrated that the feedstock of 3RH+ 1CM achieved the maximum gas yield and hydrogen gasification efficiency (HGE), and the highest adsorption capacity of the derived biochars was 3.57 mg g-1. Surface characterisation and elemental analysis showed that the biochar derived under different C/N ratios varied considerably. The results of the isotherm and kinetic simulation showed that the Langmuir model and pseudo-first-order model best fitted the experimental data. The superior performance of agricultural waste-derived biochars (AWB) over five cycles of regeneration and adsorption indicated that AWB is a green and stable adsorption material for farmland tailwater. In addition, the degradation pathway of DT during hydrothermal gasification (HTG) regeneration of the spent adsorbent was comprehensively discussed. The CHTG treatment enhanced the yield of gaseous products from RH and CM and produced AWBs with high adsorption capacities for DT. This provides a green and efficient technology for resource utilisation of agricultural waste and treatment of agricultural wastewater using pesticide residues.

Chitin-biocalcium as a novel superior composite for ciprofloxacin removal: Synergism of adsorption and flocculation.

The ubiquitous present antibiotics in aquatic environment is attracting increasing concern due to the dual problems of bioaccumulation toxicity and antibiotic resistance. In this study, a low-cost chitin-biocalcium (CC) composite was developed by a facile alkali activation process from shell waste for typical antibiotics ciprofloxacin (CIP) removal. Response surface methodology (RSM) was utilized to optimize synthesis methodology. The optimized CC products featured superior CIP removal capacity of 2432 mg/g at 25 °C (adsorption combined with flocculation), rapid adsorption kinetics, high removal efficiency (95.58%) and wide pH adaptability (under pH range 4.0-10.0). The functional groups in chitin and high content of biocalcium (Ca2+) endowed CC abundant active sites. The kinetic experimental data was fitted well by pseudo-second-order and intraparticle diffusion model at different concentrations, revealing the removal was controlled by chemisorption and mass transport step. From the macroscopic aspect, flocs were produced with the increase of CIP concentration during the reaction, adsorption combined with flocculation were related to the CIP removal. From the microcosmic aspect, the superior removal performance was attributed to cation bridging, cation complexation among biocalcium-CIP and hydrogen bond between functional groups of chitin and CIP.

Low-pressure UV-initiated synthesis of cationic starch-based flocculant with high flocculation performance.

A kind of starch-based flocculant (starch-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride], denoted St-g-PDMC-LPUV) has been synthesized by low-pressure ultraviolet initiation and was employed to remove humic acid (HA) for water purification. The physicochemical characteristics of starch and St-g-PDMC-LPUV were characterized by FT-IR, 1H NMR, XRD, TGA, SEM and BET to confirmed the successful grafting DMC onto starch. Effects of flocculant dosage, pH, the adding amount of Fe3O4, initial HA concentration and stirring speed were investigated systematically. The prepared St-g-PDMC-LPUV flocculant with non-toxic, biodegradability and environmental friendliness exhibited effective performance for removing HA from water in a wide pH range (5-10). The flocculation mechanism was attributed to the effective collision between function groups of the St-g-PDMC-LPUV flocculant and HA by charge neutralization, adsorption, bridging and patching.

Removal of emulsified oil from water by using recyclable chitosan based covalently bonded composite magnetic flocculant: Performance and mechanism.

In this work, a novel recyclable covalently bonded magnetic flocculant (FS-MC) was successfully prepared by combining chitosan-based modified polymers (MCS) with Fe3O4@SiO2 through a silane coupling agent. The covalent bond Fe-O-Si-O-C and the core-shell structure of FS-MC were confirmed through several characterization methods. The emulsified oily wastewater flocculation performance and mechanism by using FS-MC were evaluated and studied. Results showed that 94.47%, 93.95%, and 92.98% of emulsified oil could be removed by using FS-MC1, FS-MC2 and FS-MC3 at dosages of 2.0, 2.5, and 2.0 mg/L, respectively. Furthermore, FS-MC exhibited an excellent behavior on the removal of organic compounds with molecular weight > 10 kDa, including long chain alkanes, cycloalkanes, and aromatic hydrocarbon compounds. In addition, triple-phase separation of oil, water and flocculants was achieved by using magnetic FS-MC. Due to the introduction of cationic and hydrophobic groups in FS-MC, charge neutralization, compression double electric-layer action, hydrophobic interaction, interfacial adsorption bridging and sweep-flocculation synergistically contributed and enhanced the removal of emulsified oil. Recycling experiments also showed that no obvious decrease of oil removal rate was observed by using magnetic FS-MC flocculants in five cycles.

Novel sodium bicarbonate activation of cassava ethanol sludge derived biochar for removing tetracycline from aqueous solution: Performance assessment and mechanism insight.

NaHCO3 was used as a novel activator to produce cassava ethanol sludge-based biochar. The NaHCO3-activated biochar showed superior adsorption capacity for tetracycline (154.45 mg/g) than raw biochar (34.04 mg/g). Orthogonal experiments confirmed the optimal preparation conditions of biochar. Increasing adsorbent dosage and temperature facilitated tetracycline removal. The maximum removal was 92.60% at pH = 3.0. Calcium ions and alkalinity decreased tetracycline removal. The time for attaining equilibrium was extended with increasing tetracycline concentration, but the equilibrium could be completed within 24 h. Langmuir model fitted the equilibrium data well. Kinetics process followed the Elovich model. The adsorption rate was controlled by both intraparticle and liquid film diffusion and the process was endothermic and spontaneous. The electrostatic attraction, hydrogen bonding, π-π interactions, and pore-filling were involved in the adsorption mechanism. The findings may provide an underlying guide for sludge disposal and removal of tetracycline from wastewater in practical application.

Flocculation of emulsified oily wastewater by using functional grafting modified chitosan: The effect of cationic and hydrophobic structure.

In this work, modified chitosan flocculants (MCS) was synthesized by using chitosan (CS), acrylamide, cationic monomers and hydrophobic monomers via low-pressure UV-initiated copolymerization. The flocculation performance of MCS was evaluated in emulsified oily wastewater treatment. The effect of cationic and hydrophobic structure on oil removal was studied, and the interactions between these functional groups and the components in oil were also analyzed. Results suggested that MCS flocculants exhibited excellent oil removal efficiency in a wide pH range (2.0‒10). The flocculation efficiency of 91 % was achieved at the dosages of 0.6 mL/L (6 mg/L). During pH of 2.0-10, the optimal cationic and hydrophobic monomer was DMC and VT, respectively. Silane groups were favorable for oil removal than the other hydrophobic structures. The cationic groups expanded the optimal pH range of MCS in flocculation, whereas hydrophobic groups considerably reduced the dosage of MCS. The experimental results showed that alkane, cyclic aromatic hydrocarbon compounds in oil can be easily removed by using MC4, whereas cycloalkanes compounds was effectively removed by MC6 and MC7 because of preferable demulsification capacity, and the hydrophobic interaction, interfacial adsorption and electrostatic attraction played the dominant in flocculation. Thus, the synthesized MCS is favorable for emulsified oily wastewater treatment.

Adsorptive removal of gallic acid from aqueous solution onto magnetic ion exchange resin.

Finding an appropriate adsorbent with high adsorption capacity, quick adsorption kinetics and easy regeneration was crucial to the removal of gallic acid (GA) from water and wastewater. Our aims were to investigate whether a magnetic ion exchange (MIEX) resin had the three merits mentioned above, and investigate the feasibility of GA adsorption on MIEX resin, and the adsorption kinetics, equilibrium, thermodynamics, regeneration and mechanism using batch tests. The uptake of GA increased with increasing GA concentration. The GA concentration influenced the time needed to reach equilibrium, but the adsorption could be completed within 120 min. Elevating temperature facilitated the GA removal. The removal percent remained above 95.0% at pH 5.0-11.0. Carbonate and bicarbonate promoted the GA removal; conversely chloride, sulfate and nitrate restrained the GA removal significantly. The adsorption kinetics could be fitted well with the pseudo second-order model, and the film diffusion governed the whole adsorption rate. The equilibrium data followed the Redlich-Peterson isotherm model. The adsorption was a spontaneous, endothermic and entropy driven process. The ion exchange dominated the removal mechanism. The spent MIEX resin was well regenerated by sodium chloride. Therefore, MIEX resin is a potential adsorbent for removing GA quickly and efficiently from water and wastewater.

Role of moderately hydrophobic chitosan flocculants in the removal of trace antibiotics from water and membrane fouling control.

In this paper we describe the preparation and testing of a new class of chitosan-based flocculants for the treatment of surface waters containing antibiotic compounds. Three forms of moderately hydrophobic chitosan flocculants (MHCs) were prepared by chemically grafting hydrophobic branches with different lengths onto hydrophilic chitosan and these were evaluated by jar tests and a bench-scale continuous flow ultrafiltration (UF) membrane process with coagulation/sedimentation pre-treatment. Tests were conducted using both synthetic and real surface water in which norfloxacin and tylosin were added as representative antibiotics at an initial concentration of 0.1 µg/L. In jar tests, the MHCs achieved similar high removal efficiencies (REs) of turbidity and UV254 absorbance, but much higher REs of the two antibiotics (71.7-84.7% and 68.7-76.6% for synthetic and river waters, respectively), compared to several commercial flocculants; the superior performance was attributed to an enhanced hydrophobic interaction and H-bonding between the flocculants and antibiotics. The presence of suspended kaolin particles and humic acid enhanced the antibiotic removal, speculated to be through MHC bridging of the kaolin/humic acid and antibiotic molecules. In the continuous flow tests involving flocculation/sedimentation-UF for 40 days, an optimal MHC achieved a much greater performance than polyaluminium chloride in terms of the overall removal of antibiotics (RE (norfloxacin) of ∼90% and RE (tylosin) of ∼80%) and a greatly reduced rate of membrane fouling; the latter resulting from a more porous and looser structure of cake layer, caused by a surface-modification-like effect of residual MHC on the hydrophobic PVDF membrane. The results of this study have shown that MHCs offer a significant advance over the use of existing flocculants for the treatment of surface water.

Magnetic flocculants synthesized by Fe3O4 coated with cationic polyacrylamide for high turbid water flocculation.

A novel magnetic flocculant (CPAMF) was synthesized by using Fe3O4 coated with cationic polyacrylamide (CPAM) for flocculation of high turbid water. The surface morphology and chemical structures of CPAMF were confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) was employed to verify the crystal structure of CPAMF. The magnetic property of CPAMF was compared with Fe3O4 in this study. The flocculation performance by using flocculants CPAMF was evaluated in high turbid water treatment. The maximum transmittance 92.4% of kaolin suspension was achieved at corresponding optimal flocculation conditions. The result indicated that CPAMF was efficient in high turbid water flocculation. Analysis of FTIR, XRD of flocs, and zeta potential (ZP) of supernatant were accomplished for flocculation mechanism investigation. Because of low recovery factor in reflocculation under the effect of shear force on flocs, the bridging effect was found to be dominant in both acidic and alkaline conditions. Sedimentation experiments under the role of permanent magnet indicated that nano-Fe3O4 could effectively improve the settling property of CPAM. Graphical abstract ᅟ.