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Graft modified flocculants have recently received increasing attention in the field of water treatment as they have the combinative advantages of synthetic and natural polymeric flocculants. In this work, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) was selected to graft on dextran (DX) with high molecular weight (10.3 × 10 6  g/mol) produced through enzyme-catalyzed process in order to remove dissolved dyes from wastewater. The flocculant (DAB) was fabricated by ultrasound initiated polymerization technique, and the structure characterization of FTIR, 1 H/ 12 C NMR, XRD and XPS spectrum confirmed the successful grafting. Then the Congo red (CR) removal efficiency by DAB was optimized based on the flocculation conditions, including wastewater initial pH, flocculant dosage and initial dye concentration. The effect of suspended solids on the removal of dyes was evaluated in kaolin-CR simulated wastewater. The results indicated that the optimal removal efficiency of CR was 68.1% and 88.2% in single CR and kaolin-CR flocculation system, respectively. The improvement of removal efficiency was attributed to the fact that partial CR molecules were adsorbed onto kaolin particles before flocculation, and were synergistically flocculated accompanied by kaolin particles. Finally, the flocculation mechanism was discussed by a detailed investigation of the zeta potentials, FTIR and XPS spectra of flocs, which can provide important reference for optimizing the flocculation conditions and designing novel high-performance flocculants. [ABSTRACT FROM AUTHOR]

Weak interaction between flocculants and oil is a main bottleneck in the treatment of oil-containing wastewater. To solve this problem, a novel flocculant PAB with cationic micro-block structure and hydrophobic groups of benzene rings was synthesized by ultrasound initiated polymerization technique and applied to remove turbidity and oil from water. To avoid unnecessary addition of reagents in traditional template and micellar copolymerization, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) with self-assembly ability in aqueous solution was employed to synthesize flocculants. The critical association concentration of BMDAC measured by conductivity and surface tension methods was 0.014 mol·L −1 . The results of reactivity ratio, statistical analysis of sequence-length distribution and 1 H NMR provided evidence for the synthesis of copolymer with cationic micro-block. In addition, the apparent viscosity measurement indicated that PAB had an obvious hydrophobic association property. Finally, flocculation tests demonstrated that flocculation performance was greatly improved by adding PAB and the removal rate of oil and turbidity both reached the maximum (87.5% and 92%) at dosage of 40 mg·L −1 and pH of 7.0. Flocculation mechanism investigation demonstrated that the cooperation of charge neutralization, adsorption bridging, and hydrophobic association effect played an important role. The formed flocs by PAB was large, compact, difficult to break, and easy to regrow because of the enhanced interaction between flocculants and oil. In summary, this study can provide important reference in the design of organic flocculants in oily wastewater treatment applications. [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]

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]

• 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]

In this study, papermaking sludge was used as the raw biomass material to produce the lignin-based flocculant (LBF) by grafting quaternary ammonium groups and acrylamide. LBF was used as a coagulant aid with polyaluminum chloride (PAC) to treat reactive and disperse dyes wastewater. Effects of dosing method, pH, hardness and stirring speed on the coagulation behavior and floc properties were studied. Results showed that the superior coagulation efficiency and recovery factor were achieved by PAC + LBF compared with PAC and LBF + PAC. The primary mechanisms of LBF in the treatment of disperse and reactive dye solutions were charge neutralization and bridging effect, respectively. In the dual-coagulation, the impact of pH on the coagulation efficiency was weak during pH range of 5–9. Moderate hardness could enhance the floc properties due to the decrease of electrostatic repulsion and the chelation of Ca(II) and LBF. Besides, flocs coagulated by PAC + LBF had a stronger anti-crush ability. [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]

• Grafting copolymerization occurred at the amino group of MBF was confirmed. • PSA and MBF-g-P(AM-DAC) played different roles in treatment of dyeing wastewater. • MBF-g-P(AM-DAC) improved settlement efficiency for bridging and adsorption. • Flocs possessed surface area of 24.8201 m2/g and adsorption capacity of 140 mg/g. Congo red (CR) is a typical and widely used azo dye in industries. It possesses the serious threat to ecosystem and public for its indiscriminate discharge. Microbial flocculant (MBF) with various functional groups is a potential flocculant applied in dyeing wastewater treatment, and it has the advantages of high treatment efficiency, biodegradability and non-toxicity. In this study, the functional groups, amino group, ammonium group and acyloxy group, were grafted onto MBF to further improve its thermal stability, solubility and performance. Grafting copolymerization occurred at the amino group of MBF was confirmed by XPS. Polyaluminum silicate (PSA) and self-prepared functional microbial flocculant, MBF-g-P(AM-DAC), played different roles in CR wastewater treatment. PSA contributed to charge neutralization, but its yielded flocs were small. On the contrary, MBF-g-P(AM-DAC) possessed weak charge neutralization but big flocs. Its settlement efficiency has significantly improved. The unsaturated active sites on MBF-g-P(AM-DAC) and its flocs contributed to the adsorption of CR in terms of high surface area and adsorption capacity of the flocs. Physical adsorption and chemical adsorption were both discovered in the treatment. [ABSTRACT FROM AUTHOR]