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Highlights • A novel cationic flocculant PDD was synthesized through ultraviolet initiation. • PDD constructed sludge aggregates through flocculation. • The main mechanisms for sludge conditioning were adsorption–bridging interaction and electrical neutralization. • Low pH was favorable for sludge dewatering by PDD. • PDD was efficient for enhancing sludge dewaterability. Abstract In this study, a novel flocculant called PDD was synthesized under ultraviolet irradiation using acrylamide (AM), methacryloyloxyethyl trimethylammonium chloride (DMC), and dimethyldiallylammonium chloride (DMDAAC) as monomers. The effects of monomer concentration, cationic degree, cationic monomer ratio, photo-initiation time, photo-initiator concentration, and pH value on the conversion rate and relative molecular mass of PDD were investigated through single-factor and orthogonal experiments. The microstructure of the synthesized product PDD was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry–differential thermal analysis, and proton nuclear magnetic resonance. The factors that ensure the optimal sludge dewatering performance of PDD obtained under the optimal synthesis conditions were as follows: flocculant dosage = 80 mg/L, pH value = 3, cationic degree = 60%, and relative molecular mass = 9.0 × 106. The solid content of the sludge filter cake, the residual turbidity of the filtrate, and the sludge specific resistance under the optimal synthesis conditions were 31.44%, 11.80 NTU, and 2.11 × 109 m/kg, respectively. Dewatering experimental results showed that PDD had significantly better sludge dewatering efficiency than the commercial flocculants. The main mechanisms for sludge conditioning were adsorption–bridging interaction and electrical neutralization after determining the zeta potential. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ni2+ rich wastewater has caused critical water contamination, a growing issue of environmental pollution as well as serious threat to aquatic organisms and human health. It is of great significance and urgent to develop a novel and efficient wastewater treatment technology for Ni2+ removal. The efficient removal of Ni2+ by flocculation has always become a hot and focus topic. In this study, a novel chitosan (CS) graft modified flocculants CS-g-P(AM-IA-AATPAC), namely CS-g-PAAI, is prepared by microwave initiation and polymerization, and is applied in the removal of Ni2+. The effects of microwave power, microwave irradiation time, initiator concentration and pH on the CS graft polymerization efficiency and flocculant molecular weight were investigated and optimized, so as to further understand the rules of microwave initiation and CS-g-PAAI graft and polymerization. Various characterization methods indicated the successful grafting and synthesis of CS-g-PAAI. Meanwhile, the structural characteristic results manifested that CS-g-PAAI possessed a good thermal stability, a coarse and porous apparent morphology, and its chemistry and crystal structure was evidently changed and affected after graft polymerization. Compared with CS, PAA and CS-g-PAA, the removal efficiency of Ni2+ by CS-g-PAAI is more exceedingly favorable and desirable. The flocculation effect of Ni2+ by CS-g-PAAI is as high as 86.3% at the optimal condition of pH = 9, flocculant dosage = 4 mg/L, the stirring speed = 400 rpm, and flocculation time = 30 min. Meanwhile, the generated Ni2+ floc size (d 50) and fractal dimension (D f) can reach a high value (d 50 = 339.3 µm, D f = 1.98), which accelerates the sedimentation and separation of the formed Ni2+ flocs. CS-g-PAAI shows excellent flocculation and coordination ability by its powerful coordination groups to strengthen the adsorption and chelating of Ni2+ ions and generate colloidal particles for subsequent flocculation. Then, efficient flocculation was carried out and proceeded through the bridging effect, the concomitant sweeping and netting action. [Display omitted] • CS-g-PAAI with both flocculation and coordination chelating effect was successfully synthesized. • There is a significant synergistic effect between flocculation and coordination chelating. • The introduction of IA can significantly improve the flocculation and removal effect of Ni2+. • 4. The Ni2+ floc particle size and fractal dimension conditioned by CS-g-PAAI are large and desirable. [ABSTRACT FROM AUTHOR]

Modified natural polymer flocculants has been the focus of research in environmental engineering field. Natural large molecular compound, chitosan (CTS) with many functional amino and hydroxyl groups can be easily modified to enhance its original functions. This work presents an environmentally friendly chitosan-based cationic polyacrylamide flocculants (CTS-g-PAMA) with enhanced function of sterilization and flocculation. CTS-g-PAMA was synthesized through Ultraviolet (UV)-initiated copolymerization. Structure characterization of FTIR, 1 H NMR, XRD and UV spectrum confirmed the successful grafting of AM and MAPTAC. Scanning electron microscopy (SEM) analysis results showed that CTS-g-PAMA exhibited a porous structure with a prodigious surface area. CTS-g-PAMA was then applied to treat a series of simulated waste water containing kaolin or Escherichia coli . Flocculation tests indicated that CTS-g-PAMA not only showed excellent flocculation effect but also showed high sterilization capability. A series of ONP concentration measurement tests through UV spectra analysis and 3D EEM analysis of suspension before and after flocculation were conducted to study sterilization mechanism, and results revealed the sterilization effect of CTS-g-PAMA was essentially bactericidal, not just antibacterial. [ABSTRACT FROM AUTHOR]

• Amphiphilic CPAM was fabricated through ultrasonic initiated template polymerization. • Comparative characterizations confirmed the microblock structure and amphiphilicity. • Template copolymerization met bimolecular termination of free radical polymerization. • The effect of NaPAA followed template polymerization I (ZIP) mechanism. • Cationic microblocks produced stronger flocs to form more permeable filter cakes. Flocculation is an important pretreatment technique for sludge dewatering, the performance of employed flocculants is the key factor determine the flocculation efficiency. Herein, an amphiphilic cationic polyacrylamide (CPAM) with microblock structure was synthesized through template copolymerization initiated by ultrasonic. The chemical components and cationic microblock structure of copolymers were confirmed through comparative characterization by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (1H NMR) spectrum. The copolymerization mechanism was investigated through kinetics study and association coefficient (K M) determination. The results indicated that the reaction followed free radical copolymerization and terminated mainly through bimolecular termination. The pre-adsorption between acryloyloxyethyltrimethylammonium chloride (DAC) and sodium polyacrylate (NaPAA) before reaction confirmed the template polymerization met the type I (ZIP) mechanism. Cationic microblocks and hydrophobic association together contributed to the optimal dewaterability (FCMC=67.2 %, SRF=3.84×1012 m·kg−1) using TP(AM-DAC-LA). Hydrophobic association enhanced bridging and sweeping effect to promote the floc size growth. Cationic microblocks produced compacter flocs with stronger mechanical strength through enhanced charge neutralization and patching effects, which acted as skeletons to make filter cakes less compressible and more permeable in mechanical dewatering. This work developed a highly effective flocculant for sludge dewatering, the synthesis and working mechanism of which were also given. [ABSTRACT FROM AUTHOR]

• The β-cyclodextrin grafted flocculants were synthesized by ultrasound-assisted method. • The synthesized conditions of CADs were optimized. • CADs showed excellent flocculation performance in treating HA-kaolin wastewater. • The interaction effect between β-CD and HA could improve flocculation performance. In this work, the novel β-cyclodextrin based polymeric flocculants (CADs) were synthesized and applied on the treatment of humic acid (HA)-kaolin wastewater. Acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (DAC) were grafted onto β-cyclodextrin (β-CD) by ultrasound assisted initiation using ceric ammonium nitrate as initiator. The synthesized conditions were optimized by evaluating the intrinsic viscosity and grafting efficiency of CADs. Furthermore, the characterization methods including Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) were used to evaluate and analyze the molecular structure and surface morphology of graft copolymers. In flocculation experiments, the effects of dosage, flocculant types, solution pH and flocs properties on flocculation performance were investigate in detail. CADs exhibited more satisfactory turbidity and HA removal performance than the synthetic cationic flocculants (PAD) and the non-ionic graft polymers (CAM). At the optimum dosage 4 mg/L, the maximum turbidity and HA removal rate of CAD 1# was 97.5% and 68.3%, respectively. Furthermore, CAD 1# exhibited a good flocculation performance and wide flocculation window in the pH range of 2.0–8.0. Lastly, the flocculation mechanism of CAD was detailed discussed by the investigation of zeta potential, surface tension, flocs FTIR and XPS spectra. Results indicated the unique hydrophobic internal structure of β-CD played an important role in improving the removal rate HA of CAD. [ABSTRACT FROM AUTHOR]

A development of coagulation-flocculation is to improve flocculation performance of organic polymer flocculants. It is hopefully achieved via optimizing molecular structure of flocculants. Herein, molecular structure of cationic organic polymer flocculants, P(AM-DAC), was regulated through adjusting the length of cationic block on the molecular chain of P(AM-DAC). The effect of block length of P(AM-DAC) on its characteristics, flocculation performances and flocculation mechanisms in water treatment was rarely considered. The moderate template contributed to P(AM-DAC) (10_4:1) possessing the longest cationic block structure, largest molecular weight and best thermal stability compared with other P(AM-DAC). Molecular dynamics (MD) simulation and the flocculation experiments predicted and confirmed that P(AM-DAC) (10_4:1) performed the best in the treatment of colloidal particles and dyes in terms of removal efficiencies and floc characteristics since the centralized cationic block structure enhanced the interaction among P(AM-DAC) (10_4:1) and pollutants and further improved charge neutralization and bridging of P(AM-DAC) (10_4:1). [Display omitted] • P(AM-DAC) with different block lengths were adjusted via various template sizes. • P(AM-DAC) (10_4:1) owned the longest block length as moderate molecular weight of template. • The strong interaction between P(AM-DAC) (10_4:1) and pollutants was confirmed by MD. • P(AM-DAC) (10_4:1) with concentrated cationic blocks had the best flocculation performance. [ABSTRACT FROM AUTHOR]

Bacteria, especially antibiotic-resistant bacteria, in water threaten public health in countries. Simultaneous flocculation, sterilization and identification of bacteria are great challenge in water treatment. Herein we presented a three-in-one compound through combining a novel Bacitracin-based flocculant (B-g-PAMDAC) and surface enhanced Raman scattering (SERS) labels, the modified Au@AgNPs using graphene oxide (GO) and 4-mercaptophenylboronic acid (4-MPBA). B-g-PAMDAC with bactericidal groups and microblock structure was synthesized via copolymerization and self-assembly. Its functional groups and microblock structure contributed to the excellent performance in flocculation of bacteria. 4-MPBA as bacterial capture bound to the bacterial cell membrane and contributed to recognition of bacteria in flocculation. Bacteria aggregating around Au@AgNPs resulted in abundant "hot spots" and strong Raman signals. SERS labels obviously improved the sensitivity, accuracy and stability of bacteria identification even at low bacterial concentration of 1 × 103 CFU mL−1. They presented distinct fingerprints of bacteria, Escherichia coli , Pseudomonas aeruginosa , Bacillus cereus and Enterococcus faecalis , in Raman mappings. Bacitracin improved sterilization efficiency of B-g-PAMDAC in four bacteria treatment in terms of sterilization rate and time. β-galactosidase and respiratory activity of bacteria revealed sterilization mechanism of B-g-PAMDAC that changed permeability of cell membrane before it reduced the respiration activity of bacteria and ruptured cell wall. ga1 • A novel bacitracin-based flocculant with microblock structure was developed via self-assembly. • GO-Au@AgNPs modified with 4-MPBA acted as a SERS labels with high stability and sensitivity. • The SERS labels revealed characteristic fingerprints of bacteria in SERS spectra. • SERS labels combined with flocculant in water treatment for the first time. • Simultaneous flocculation, identification and sterilization of bacteria were emphasized. [ABSTRACT FROM AUTHOR]

The chitosan (CTS) characterized with many functional amino and hydroxyl groups has been the research focus on flocculants preparation and synthesis because of the facile grafting and modification to enhance and enlarge its original functions. In this study, a new type of graft modified flocculant CTS-g-PAA and its combination with kaolin have been developed for the treatment of acid blue 83 (AB 83). The CTS-g-PAA prepared by ultrasonic initiation of acrylamide (AM), 3-Acrylamide propyltrimethylammonium chloride (AATPAC) and CTS. The factors affecting CTS-g-PAA molecular weight and CTS graft ratio were examined to have a better understanding and comprehending of the ultrasonic initiated polymerization. The structure and morphological characteristics of CTS-g-PAA were investigated and analyzed by infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), differential thermal/thermogravimetric (TG/DSC), scanning electron microscopy (SEM) and X-Ray Diffraction (XRD), respectively. The results indicated that the CTS cyclic structure was broken by ultrasonic initiation and the grafting occurred at amino group with C 2 site of CTS. Meanwhile, the CTS-g-PAA coupled with kaolin exhibited superior flocculation performance better than the single removal effect, and the optimum removal rate for AB 83 could achieve 91.9%. The flocculation mechanism was discussed and summarized based on the conduction of zeta potential, FTIR of floc particles and the adsorption ability of the formed kaolin flocs. During the AB 83 flocculation, the CTS-g-PAA adsorption and flocculation contributed much to the AB 83 removal. The added kaolin particles played a crucial role in the enhancement of AB 83 adsorption and flocculation. The kaolin particles and the formed kaolin floc showed an adsorption effect for AB 83, and the kaolin particles also worked as the bridging between the CTS-g-PAA filled with AB 83 to strengthen the flocculation performance. As a result, the flocculation performance for AB 83 removal was greatly improved. Unlabelled Image • The chitosan (CTS) grafted flocculant CTS-g-PAA was prepared by ultrasonic initiated polymerization of AM, AATPAC and CTS.The skeleton structure of CTS was destroyed by ultrasonic initiated polymerization. • The graft copolymerization mainly occurred at amino group connecting with C 2 site of CTS. • The CTS-g-PAA coupled with kaolin exhibited superior flocculation performance. • The CTS-g-PAA adsorption and flocculation contributed much to the AB 83 removal. [ABSTRACT FROM AUTHOR]

• Organic flocculant was used to treat metalworking wastewater for the first time. • Hydrophobic modified flocculant was polymerized through UVC initiation polymerization. • UVC initiation showed great advantage in polymerization to traditional UV initiation. • Hydrophobic block in flocculant facilitated the adsorption of nonpolar oil/colloids. In this work, a hydrophobically modified cationic polyacrylamide (CPAC) flocculant was polymerized by short-wave ultraviolet (UVC) initiation with acrylamide, acryloyloxyethyl trimethylammonium chloride, and coconut diethanolamide (CDEA) as monomers to enhance the destabilization and separation efficiency of emulsified oil and particles/colloids from metalworking fluids wastewater (MWFs). The parameters for flocculant polymerization were optimized, and the features of UVC-initiated polymerization were studied. Moreover, the structural and morphological characteristics of the polymers were explored, and the flocculation performance of CPAC in MWFs treatment was evaluated. The characterization results suggested that flocculants with a multilayer, loose-sheet morphology and intrinsic viscosity of 11.32 dL g−1 could be successfully polymerized by UVC-initiated polymerization. Compared with traditional UV, UVC irradiation initiation promoted the copolymerization of flocculants with a high monomer conversion rate and intrinsic viscosity. We observed the low dosage requirement and acid resistance of the flocculant synthesized by UVC-initiated polymerization, which produced the lowest residual turbidity, highest chemical oxygen demand, and most efficient oil removal during MWFs treatment among the samples studied. Besides charge neutralization and bridging effects, the adsorption effect between hydrophobic CDEA blocks and nonpolar oil/colloids facilitated the formation of microflocs and improved the flocculation efficiency of the flocculant. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Chitosan-based flocculants with chelation and flocculation capacity are designed and prepared. • Relationship between flocculants structural and chelation-flocculation is investigated. • There is a certain linear relationship between heavy metal concentration and flocculants dosage. • Copper ions in mixed heavy metals solutions is preferentially chelated and flocculated. • The work provided valuable guidance in the design of eco-friendly polymeric flocculants. Abstract Dual-function chitosan-based flocculants with chelation and flocculation capacity, carboxylated chitosan-graft-polyacrylamide (PCA), carboxylated chitosan-graft-polyacrylamide-co-sodium xanthate (PCAXC), and carboxylated chitosan-graft-poly(acrylamide-2-acrylamido-2-methylpropane sulfonic acid) (PCAAF), are designed and prepared by UV initiation method. The physicochemical characteristics of PCA, PCAXC, and PCAAF were characterized by fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and X-ray diffraction pattern to confirm the successful syntheses. Then PCA, PCAXC, and PCAAF are applied to chelate and flocculate Cu, Cr, and Ni from water. Effects of pH, flocculants dosage, reaction time, and stirring speed were investigated systematically to detect the relationship between flocculants structural and chelation-flocculation capacity. The maximum removal rate of Cu and Cr obtained by PCAXC at are 85.1% and 76.1%, respectively, while The maximum removal rate of Ni obtained by PCAAF at is more than 75.7%%. In addition, the relationship between the initial concentration of simulated heavy metal wastewater and the flocculants dosage and the competitive chelation-flocculation properties in the mixed heavy metal solution are also detected in detail. The mechanism can be assigned to the effective interaction between function groups of the flocculants and heavy metal irons by chelation, charge neutralization, and adsorption bridging mechanism. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A functionalized chitosan-based flocculant (CC-g-PCD) is synthesized by UV initiation. • The concentration of algae decreased as the flocculants dosage increased. • The removal efficiency of CC-g-PCD was higher than that of commercially available coagulant. • CC-g-PCD has high efficiency in the removal of algae and turbidity from raw water. Abstract In this work, carboxylated chitosan modified flocculant (CC-g-PCD) was prepared by graft copolymerization technique to enhance the charge-attracting and adhesion of bridges and net-sweeping capacity of flocculants. The dimethyldiallylammonium chloride (DMDAAC), carboxylated chitosan (CMCS), and 3-chloro-2-chloropropyltrimethylammonium chloride (CTA) were utilized for synthesis of CC-g-PCD via photopolymerization techniques. The synthesized CC-g-PCD was characterized by 1H NMR, SEM, XRD, and FTIR, and the characteristic groups on the main chain and surface morphological structure of CC-g-PCD were investigated. The obtained results indicated that CTA and DMDAAC were successfully grafted into the CPCTS. In ordered to evaluate the flocculation performance of CC-g-PCD at various dosages, stirring intensity (G value), and pH value by detecting Chl a, COD, and turbidity, the actual lake water that contains algae was used for flocculation assessment tests. The experimental results of the water sample with flocculation showed that the maximum flocculation efficiency of turbidity (91.1%), Chl a (97.2%), and COD (97.0%) can be achieved by CC-g-PCD at pH 7, G value 200 s−1, and 4.0 mg/L. The comparison results demonstrated that CC-g-PCD had better flocculation efficiency than commercial flocculants. Finally, based on the analysis of algae removal in combination with Zeta potential measurements, the flocculation mechanisms in actual lake water at various dosages and pH values were adsorption bridging and electrical neutralization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A functionalized chitosan-based flocculant (MHCS-g-P(AM-DAC)) is synthesized by UV initiation. • The concentration of algae decreased as the flocculants dosage increased. • The removal efficiency of MHCS-g-P(AM-DAC) was higher than that of commercially available coagulant. • MHCS-g-P(AM-DAC) has high efficiency in the removal of algae and turbidity from raw water. Abstract The graft copolymer flocculant of chitosan namely, maleoyl chitosan-graft-poly(acrylamide–acryloxyethyl trimethyl ammonium chloride) [MHCS-g-P(AM-DAC)], was prepared by UV initiation to improve the solubility and flocculation efficiency of chitosan. Flocculating properties for algae removal were studied systematically. The effects of parameters such as monomer concentration, MHCS content, illumination time, photoinitiator concentration, cationic degree, pH and grafting efficiency over synthesis process of MHCS-g-P(AM-DAC) were studied. The characterization of obtained MHCS-g-P(AM-DAC) were carried out through different analytic techniques. The influences of dosage, pH, and G value on the flocculating properties were also investigated to support that MHCS-g-P(AM-DAC) was more effective than organic flocculant (CPAM) and inorganic coagulant (PFS and PAC) on algae removal. The flocculation mechanisms of MHCS-g-P(AM-DAC) were determinate by obtained zeta values. [ABSTRACT FROM AUTHOR]

In this study, maleyl chitosan- graft -polyacrylamide (MHCS-g-PAM), a novel chitosan-based flocculant, was prepared through UV irradiation, and maleyl chitosan (MHCS) was designed and prepared with maleic anhydride and acrylamide (AM) through maleyl acylation reaction. The effects of monomer concentration, MHCS-to-AM ratio, illumination time, initiator concentration, pH on viscosity, and grafting efficiency were investigated to optimize the synthesis of these substances. MHCS-g-PAM was characterized through Fourier transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, scanning electron microscopy, and thermal gravimetric analysis. Flocculation mechanisms in alga-containing wastewater at various pH levels and dosages were examined in detail on the basis of zeta potential measurements. Zeta potential experiments indicated that the adsorption-bridging and charge neutralization mechanisms played an important role in algal removal. Flocculation tests on algal removal demonstrated that the flocculation performance of MHCS-g-PAM was more effective than that of cationic polyacrylamide, polyferric sulfate, and polymeric aluminium. The optimal Chl- a and COD removal rate obtained by MHCS-g-PAM was 98.6% and 94.9% at pH 7 and 4 mg·L − 1 , respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • P(DAC-NIPAM) significantly improved the removal of levofloxacin and tetracycline. • P(DAC-NIPAM) had strong interaction with antibiotics for its multiple functional groups. • The hydrophobic groups on P(DAC-NIPAM) tightly bridged micelles of antibiotics and SDS. • Compact flocs were formed for shrinkage of P(DAC-NIPAM) molecule at the LCST. • Flocculation simulation further confirmed application feasibility of thermosensitive flocculants. Antibiotics were detected in worldwide natural water especially in COVID-19 period. The common flocculants rarely removed the dissolved antibiotics from natural water and wastewater. The flocculation improvement of organic polymer flocculants might solve the issue of antibiotic pollution or promote the removal efficiencies of antibiotics in water/wastewater treatment plants. Herein, a thermosensitive flocculant, P(DAC-NIPAM), was prepared via one-step method. It was investigated that the relationship between the various functional groups of P(DAC-NIPAM) and its flocculation performances in the treatment of simulated water containing levofloxacin, tetracycline, colloidal particles and natural organic matters. The removal mechanisms were discussed. The results indicated that the rich cationic, hydrophilic and hydrophobic groups of P(DAC-NIPAM) enhanced the interaction between flocculants and pollutants. The bridging of P(DAC-NIPAM) among micelles, charge neutralization, hydrogen bond between P(DAC-NIPAM) and two antibiotics, the shrinkage of P(DAC-NIPAM) molecule and enhancement of hydrophobicity when water temperature was above low critical solution temperature (LCST), co-flocculation and co-settlement of multiple pollutants all contributed to the efficient removal of levofloxacin and tetracycline from water. Flocculation simulation further confirmed that thermosensitive flocculant combined with heating plates was a potential candidate for antibiotic treatment in actual water treatment plants. [ABSTRACT FROM AUTHOR]

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the "bridge" between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L−1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment. [Display omitted] • A flocculant with branch architectures (PAM-g-M(CS-MA)) was synthesized. • PAM-g-M(CS-MA) showed low-dosage and efficient in heavy metals removal. • The maximum removal rates of Cu (93.90%) and Cd (92.47%) can be achieved by PAM-g-M(CS-MA). • Relationship between the branch architectures and flocculation performance was built. • Flocculation mechanism is composed by synergistic chelation, adsorption and bridging-furl effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amphoteric starch-based flocculants were synthesized by low-pressure UV initiation. • Amphoteric starch-based flocculants show high flocculation performance. • Amphoteric starch-based flocculants exhibit low salts sensitivity. • Flocculation mechanism includes charge neutralization, patching and bridging. Surface charges of the suspended colloidal particles in real water can be either negative or positive. Flocculation is one of the most widely used technologies in water treatment. A series of amphoteric starch-based flocculants (denoted as ASBFs) with the same chemically modified functional groups but different charge degrees and intrinsic viscosities were successfully via low-pressure ultraviolet initiation and used for the removal of different charged contaminants from water. The characterization results confirmed the successful grafting acrylamide (AM) and 2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) onto carboxymethyl starch. Different influencing factors, including flocculant dosage, contaminants concentration, pH of solution, stirring speed, sedimentation time and various salts, were investigated systematically. ASBFs with eco-friendliness exhibited high flocculation property, low optimal dosage and low salts sensitivity, for not only kaolin, but also hematite suspensions. The zeta potential (ZP) measurement suggested that the removal mechanism mainly includes charge neutralization, patching and bridging. [ABSTRACT FROM AUTHOR]

[Display omitted] • The copolymerization reaction was separately initiated by photocatalyst and photoinitiator. • The initiation and synthesis mechanisms of CS-g-DAC (T) and CS-g-DAC (V) were different. • CS-g-DAC (V) prepared by V A-044 owned the little higher initiation efficiency than CS-g-DAC (T). • The ratio of C-N to C = N in the molecular structure of CS-g-DAC (T) was lower. • CS-g-DAC (T) possessed the little more outstanding performances in water treatment. Flocculants as the traditional water treatment agents were widely applied in water treatment, sludge thickening and dewatering, oil exploitation and papermaking. The synthesis of organic polymer flocculants via high-efficient initiation system has aroused special attention in the development of flocculant. Herein, a chitosan-based flocculant (CS-g-DAC (T)) was synthesized through ultraviolet (UV) initiation of titanium dioxide (TiO 2) It was compared with other chitosan-based flocculant (CS-g-DAC (V)) synthesized by a traditional photoinitiator, V A-044 , in terms of initiation efficiency, initiation mechanism, flocculant characteristics, molecular structures and flocculant performances in water treatment. Holes (h+), superoxide radicals (O 2 •-) and hydroxyl radicals (OH) were generated in the initiation processes of TiO 2 and V A-044. TiO 2 generated more O 2 •- and less OH compared with V A-044. CS-g-DAC (T) owned the higher ratio of C = N to C-N in molecular structure, the little higher removal efficiency in water treatment and larger floc size than CS-g-DAC (V). The effect of charge neutralization of CS-g-DAC (T) and CS-g-DAC (V) were close. TiO 2 possessed the potential to substitute the traditional photoinitiator in synthesis of organic polymer flocculants and improved the molecular structure and flocculation efficiency of flocculants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chitosan based magnetic composite flocculants are successfully prepared. • The optimal removal rate of Cu(Ⅱ) by MC-g-PAA is over 93.0 %. • MC-g-PAA can effectively increase the floc particle size and fractal dimension of flocs. • The magnetic flocculant has the characteristics of recyclability and recycling. In this study, three magnetic flocculants, namely, MC, MC-g-PAM, and MC-g-PAA, were prepared. The structure characteristics, flocculation performance, and floc characteristics of the three magnetic flocculants were systematically studied and compared. SEM, FT-IR, XPS, XRD, TG–DSC, and VSM characterization results show that MC, MC-g-PAM, and MC-g-PAA are successfully prepared and exhibit good magnetic induction. The removal rates of copper ions by MC, MC-g-PAM, and MC-g-PAA under the optimal coagulation conditions are 93.39 %, 88.64 %, and 61.41 %, respectively. Kinetic fitting shows that the flocculation reaction process of MC and MC-g-PAM conforms to pseudo first-order kinetics, while the flocculation reaction process of MC-g-PAA conforms to pseudo second-order kinetics. The flocs produced by MC-g-PAA have larger particle size and fractal dimension than those by MC and MC-g-PAM. At 80 mg/L dosage and pH 6, the floc size and floc fractal dimension obtained by MC-g-PAA reach the maximum values of 48.28 um and 1.468, respectively. Zeta potential studies show that the flocculation functions of the three flocculants are mainly adsorption bridging, adsorption electric neutralization, and chelating precipitation. Recycling experiments show that MC-g-PAA has good recyclability, and the recovery rate after the fifth use is 77.24 % with the Cu(II) removal rate of 67.53 %. [ABSTRACT FROM AUTHOR]

The fine molecular structure of a flocculant fundamentally determines the internal flocculation mechanism and the final application property. In this work, three series of chitosan-based polymers (CTS-g-PAMD) with divergent charge densities and graft chain distribution were synthesized by graft copolymerization using acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC). Meanwhile, flocculant with linear chain structure (CTS-CTA) was prepared by etherification using 3-chloro-2-hydroxypropyltrimethylammonium chloride (CTA). The characterization results confirmed that various monomers had been successfully introduced into chitosan. The reaction basically happened on —NH 2 at C 2 of chitosan, and the ring structure of chitosan was destroyed by free radical reaction. The obtained flocculants were used to flocculate bentonite and humic acid solution. Besides dose, the effects of chain structure, charge density and chain distribution on flocculation performance were systematically studied. Based on the fractal theory and flocculation kinetics, the effects of structural factors on floc characteristics were also investigated. The results showed that, flocculant with abundant graft chains exerts better flocculation performance and floc characteristic due to enhanced adsorption electrical neutralization and adsorption bridging effect. The effects of charge density and chain distribution on the flocculation performance were disparate in the range of insufficient and excessive doses. Furthermore, on the basis of the quadratic polynomial model, quantitative structure-effect relationships were established, which has guiding significance for the development and utilization of flocculants. Image 1 • Four chitosan-based flocculants with distinct molecular structures were prepared. • The cyclic structure of chitosan was destroyed by graft copolymerization. • Flocculants with "comb" branches exhibited better flocculation performance. • Chain distribution contributed differently under overdose and underdose. • The quantitative structure-activity relationships were established through model. [ABSTRACT FROM AUTHOR]

• Novel functionalized chitosan flocculants are successfully synthesized. • Flocculation conditions for reaching high removal efficiencies are optimized. • Characterization results provided empirical evidence for existence of chelating groups. • "3E" triangular model was used to evaluate its flocculation-chelation properties. • Flocculation-chelation capacity profile indicated multiple potential applications. In order to effectively remove the dissolved heavy metals and the heavy metals on the colloidal particles during the flocculation process, a novel dual-functional chitosan flocculant CMCTS-g-P(AM-CA) is prepared by ultraviolet light-initiated graft polymerization using CMCTS, AM, and ammonium dithiocarbamate. The main influencing factors of monomer concentration, monomer ratio, pH value, photoinitiator concentration, and illumination time are investigated on the basis of intrinsic viscosity, grafting rate, and grafting efficiency of CMCTS-g-P(AM-CA). Characterization results provided empirical evidence for existence of chelating groups. In addition, CMCTS-g-P(AM-CA) was applied to treat the simulated heavy metals and electroplating wastewater. The effect of CMCTS-g-P(AM-CA) dosage, pH value, and reaction G value on flocculation efficiency was also explored. After the two-stage flocculation, the residual concentration of Ni(II), COD, and turbidity of actual electroplating wastewater decreased to 0.96 mg/L, 93.00 mg/L, and 1.71 NTU after flocculation tests at optimal condition, respectively. Finally, the "3E" triangular evaluation model is established and applied to evaluate the flocculation performance of CMCTS-g-P(AM-CA) on the actual heavy metal wastewater further, thereby proving its excellent chelation flocculation performance. [ABSTRACT FROM AUTHOR]

Chitosan-based flocculants are efficient and biodegradable, possessing the potential application in water treatment. A chitosan-based flocculant, CTS-g-PAM, was prepared via grafting copolymerization. Two main structures of CTS-g-PAM were detected by X-ray photoelectron spectroscopy (XPS), and they related to the different performances of CTS-g-PAM in the treatment of model azo dyeing wastewater in terms of removal efficiency, floc size and zeta potential. CTS-g-PAM with the optimal ratio of C N to –NH– owned the best performance. C N reinforced the interaction between CTS-g-PAM and azo dyes and charge neutralization while the flocs formed in the case were large and compacted. However, excessive C N accelerated itself hydrolysis and leaded to the decomposition of CTS-g-PAM, deteriorating the performance of the flocculant. Image 1 • Two different structures of CTS-g-PAM were discovered via XPS. • The ratio of two structures was different in various synthesis conditions. • The moderate C N in CTS-g-PAM contributed to its better performance in the treatment. • C N reinforced the interaction between CTS-g-PAM and azo dyes. • Excessive C N accelerated itself hydrolysis and decomposition of CTS-g-PAM. [ABSTRACT FROM AUTHOR]

• Dual-functional flocculant with pH resistant is synthesized and used to remove heavy metals. • Flocculation conditions for reaching high removal efficiencies are optimized. • Optimal operation modulus was identified using 8 Key performance indicators by 3E triangle model. • Multi-objective programming optimization model was also established to evaluate Operation strategies. • Flocculation for heavy metal removal is superior in terms of engineering performance. Carboxymethyl chitosan (CMCTS) with active hydroxyl and amino groups is easily modified for chelating and capturing heavy metal, thus showing great potential for application in heavy metal-contaminated wastewater treatment. In this work, a dual-functional MACA copolymer [CMCTS-graft-P(AM-TGA)] with pH resistant was successfully designed and prepared by grafting acrylamide and thioglycolic acid onto CMCTS through UV-initiated graft polymerization. The spectroscopy characterization of functional groups and apparent morphology confirm the successful preparation of MACA. Flocculation conditions for reaching high removal efficiencies and investigating chelation capacity are optimized. A multiobjective evaluation model and a triangular environmental impact, economic benefit, and energy consumption (3E) evaluation model were established and employed to assess the 3E performance of MACA in heavy metal-contaminated wastewater flocculation. Optimal operation modulus is identified using 8 Key performance indicators by 3E triangle model. This work enriches knowledge about flocculation and provides guidance for flocculation parameter control. [ABSTRACT FROM AUTHOR]