Huaili Zheng

Synthesis and characterization of a dewatering reagent: cationic polyacrylamide (P(AM–DMC–DAC)) for activated sludge dewatering treatment

ABSTRACT P(AM–DMC–DAC), one kind of ternary copolymerized cationic polyacrylamide, was synthesized using acrylamide (AM), methacryloxyethyltrimethyl ammonium chloride (DMC), and acryloxyethyltrimethyl ammonium chloride (DAC) by photopolymerization technique. The copolymer was characterized by means of Fourier transform infrared spectroscopy, thermal gravimetric analysis, and scanning electron microscopy. The optimum synthesis conditions were as follows: mass percentage of photoinitiator being 0.40%, mass percentage of solubilizer being 0.10%, inducing time being 1 h, pH value being 9.0, and mass ratio of AM/DMC/DAC being 4:3:3. At optimum conditions, the performance parameters of copolymer are as follows: thermal stability was 126.0 J g−1, molecular weight was 1.28 × 107, cationic degree was 30.7%, coagulant dosage being 0.5 g kg−1, and the filter cake moisture content (CMC) and filtrate residual turbidity were 65.7% and 3.73 NTU, respectively. Based on the evaluation of the sludge dewatering process, it ...

Plasma-initiated polymerization of chitosan-based CS-g-P(AM-DMDAAC) flocculant for the enhanced flocculation of low-algal-turbidity water

In this work, a highly efficient and environmentally friendly chitosan-based graft flocculant, namely, acrylamide- and dimethyl diallyl ammonium chloride-grafted chitosan [CS-g-P(AM-DMDAAC)], was prepared successfully through plasma initiation. FTIR results confirmed the successful polymerization of CS-g-P(AM-DMDAAC) and P(AM-DMDAAC). P(AM-DMDAAC) was the copolymer of acrylamide- and dimethyl diallyl ammonium chloride. SEM results revealed that a densely cross-linked network structure formed on the surface. XRD results verified that the ordered crystal structure of chitosan in CS-g-P(AM-DMDAAC) was changed into an amorphous structure after plasma-induced polymerization. The flocculation results of low-algal-turbidity water further showed the optimal flocculation efficiency of turbidity removal rate, COD removal rate, and Chl-a removal rate were 99.02%, 96.11%, and 92.20%, respectively. The flocculation efficiency of CS-g-P(AM-DMDAAC) were significantly higher than those obtained by cationic polyacrylamide (CPAM) and Polymeric aluminum and iron (PAFC). This work provided a valuable basis for the design of eco-friendly naturally modified polymeric flocculants to enhance the flocculation of low-algal-turbidity water.

Effects of Surfactants on the Improvement of Sludge Dewaterability Using Cationic Flocculants

The effects of the cationic surfactant (cationic cetyl trimethyl ammonium bromide, CTAB) on the improvement of the sludge dewaterability using the cationic flocculant (cationic polyacrylamide, CPAM) were analyzed. Residual turbidity of supernatant, dry solid (DS) content, extracellular polymeric substances (EPS), specific resistance to filtration (SRF), zeta potential, floc size, and settling rate were investigated, respectively. The result showed that the CTAB positively affected the sludge conditioning and dewatering. Compared to not using surfactant, the DS and the settling rate increased by 8%–21.2% and 9.2%–15.1%, respectively, at 40 mg·L−1 CPAM, 10×10−3 mg·L−1 CTAB, and pH 3. The residual turbidities of the supernatant and SRF were reduced by 14.6%–31.1% and 6.9%–7.8% compared with turbidities and SRF without surfactant. Furthermore, the release of sludge EPS, the increases in size of the sludge flocs, and the sludge settling rate were found to be the main reasons for the CTAB improvement of sludge dewatering performance.

Chemical coagulation process for the removal of heavy metals from water: a review

AbstractHeavy metal pollution has become one of the most urgent environmental issues, which also poses a potential threat to the human health. This article is suggested to review the advance on the performance of chemical coagulation process in removing heavy metal from water. Chemical coagulation process is considered to be a valid method which is determined by the hydrolyzed species of the inorganic coagulants under different raw water and coagulation conditions. And the main mechanisms of the removal of heavy metals are adsorption, complexation, and coprecipitation. Compared with the aluminum-based coagulants, the iron-based coagulants have better performance due to the use of wide pH range and large surface area of the resulting flocs. During the chemical coagulation process, the valence state of arsenic and antimony could affect the removal efficiency. Thus, the oxidants and reductants are often combined with inorganic coagulants used in this process. It is found that pH is an important factor greatl...

Interactions of specific extracellular organic matter and polyaluminum chloride and their roles in the algae-polluted water treatment

Extracellular organic matter (EOM) is ubiquitous in the algae-polluted water and has a significant impact on the human health and drinking water treatment. We investigate the different characteristics of dissolved extracellular organic matter (dEOM) and bound extracellular organic matter (bEOM) recovered from the various growth period of Microcystis aeruginosa and the interactions of them and polyaluminum chloride (PACl). The roles of the different EOM in the algae-polluted water treatment are also discussed. The functional groups of aromatic, OH, NH, CN and NO in bEOM possessing the stronger interaction with hydroxyl aluminum compared with dEOM is responsible for bEOM and algae removal. Some low molecular weight (MW) organic components and protein-like substances in bEOM are most easily removed. And dEOM weakly reacts with PACl or inhibits coagulation, especially dEOM with the high MW organic components. The main coagulation mechanisms of bEOM are the generation of insoluble Al-bEOM through complexation, the bridge of AlO4Al12(OH)24(H2O)127+ (Al13), the adsorption of Al(OH)3(am) and the entrapment of flocs. The adsorption of Al13 and Al(OH)3(am) mainly contribute to dEOM removal. It is also recommended to treat the algae with dEOM and bEOM at the initial stage.

Ultrasound-initiated synthesis of cationic polyacrylamide for oily wastewater treatment: Enhanced interaction between the flocculant and contaminants

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 1H 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.

Optimized preparation of micro-block CPAM by response surface methodology and evaluation of dewatering performance

Micro-block cationic polyacrylamide (P(AM-MAPTAC)) was synthesized through UV-initiated template copolymerization and characterized by FTIR, 1H NMR, SEM and TG/DSC analyses. Furthermore, the main influence factors of the preparation process were optimized through Box–Behnken experiment design and Respond Surface Method (RSM). The maximum intrinsic viscosity of micro-block CPAM was 13.223 dL g−1 under the optimum synthesis conditions. The dewatering performance of micro-block CPAM was evaluated taking activated sludge collected from a dyeing mill as the processing object. Results showed that the micro-block CPAM exhibited excellent dewatering performance. At a 30 mg L−1 dosage of micro-block CPAM, the residual turbidity, filter cake moisture content, specific resistance to filtration and chemical oxygen demand removal rate reached 4.47 NTU, 72.2%, 5.47 (1012 m kg−1) and 79.2%, respectively. Dewatering tests not only demonstrated the superiority of micro-block P(AM-MAPTAC) synthesized by UV-initiated template copolymerization over that synthesized by traditional methods but also demonstrated that increasing the molecular weight can further enhance the dewatering performance of flocculants.

Rapid and efficient removal of heavy metal and cationic dye by carboxylate-rich magnetic chitosan flocculants: Role of ionic groups

A multifunctional carboxylate-rich magnetic chitosan flocculant (Mag@PIA-g-CS) was prepared through surface graft copolymerization on magnetite particles. The effect of monomer molar ratio, initiator and pre-neutralized degree on polymerization rate was determined. Various analytical methods were applied to characterize Mag@PIA-g-CS, exhibiting the successful grafting of polymers, good magnetic feature and core-shell structure. The kinetic process of Ni(II) and malachite green (MG) flocculation by Mag@PIA-g-CS reached equilibrium within <60min with the optimal uptake rate of 98.3% and 87.4%, and exhibited satisfactory removal effect in wide pH range (4.0-8.0 for Ni(II), 5.0-10.0 for MG). Mag@PIA-g-CS exhibited superior flocculation performance over chitosan magnetic flocculant (Mag@CS). The pH-dependent behavior, rapid responsiveness and sensitivity to ionic strength in batch flocculation tests indicated the distinct effect of ionic groups. Moreover, sweeping action of linear molecular chains facilitated further flocculation. Mag@PIA-g-CS showed high stability in extreme environments, and can be easily regenerated and separated.

Enhancement of textile-dyeing sludge dewaterability using a novel cationic polyacrylamide: role of cationic block structures

In this study, a novel cationic polyacrylamide (CPAM) with a microblock structure was successfully synthesized through ultrasonic-initiated template copolymerization (UTP) using allyltrimethylammonium chloride (TM) and acrylamide (AM) as monomers, and sodium polyacrylate (NaPAA) as a template. Fourier transform infrared spectroscopy (FT-IR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), and thermogravimetric analysis (TGA) were employed to characterize the properties of the polymers. The results showed that the novel cationic microblock structure was formed in the template copolymer of TM and AM (TPTA). Besides, the copolymerization was demonstrated to follow an I zip-up (ZIP) template polymerization mechanism through the analysis of association constant (MK) and polymerization kinetics. The flocculation results of textile-dyeing sludge dewatering revealed that the polymer with the novel microblock structure showed an excellent flocculation performance. When the optimal conditions at pH of 7.0, dosage of 40 mg L−1 and the intrinsic viscosity of 2.3 dL g−1, the minimum SRF of 4.9 × 1012 m kg−1 and FCMC of 72.1% were observed. During the flocculation process, the cationic microblocks in TPTA extremely enhanced the ability of charge neutralization and bridging, and contributed much to the excellent flocculation performance in textile-dyeing sludge dewatering.

Effect of the Cationic Block Structure on the Characteristics of Sludge Flocs Formed by Charge Neutralization and Patching

In this study, a template copolymer (TPAA) of (3-Acrylamidopropyl) trimethylammonium chloride (AATPAC) and acrylamide (AM) was successfully synthesized though ultrasonic-initiated template copolymerization (UTP), using sodium polyacrylate (PAAS) as a template. TPAA was characterized by an evident cationic microblock structure which was observed through the analyses of the reactivity ratio, Fourier transform infrared spectroscopy (FTIR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), and thermogravimetry/differential scanning calorimetry (TG/DSC). The introduction of the template could improve the monomer (AATPAC) reactivity ratio and increase the length and amount of AATPAC segments. This novel cationic microblock structure extremely enhanced the ability of charge neutralization, patching, and bridging, thus improving the activated sludge flocculation performance. The experiments of floc formation, breakage, and regrowth revealed that the cationic microblock structure in the copolymer resulted in large and compact flocs, and these flocs had a rapid regrowth when broken. Finally, the larger and more compact flocs contributed to the formation of more channels and voids, and therefore the specific resistance to filtration (SRF) reached a minimum.