Bingzhi Liu

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.

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.

Improvement of Sludge Dewaterability by Ultrasound-Initiated Cationic Polyacrylamide with Microblock Structure: The Role of Surface-Active Monomers

Cationic polyacrylamides have been employed widely to improve sludge dewatering performance, but the cationic units are randomly distributed in the molecular chain, which restricts the further enhancement of dewaterability. Common template technology to prepare block copolymers requiring a huge number of templates reduces the polymer purity and molecular weight. Here, we adopted the surface-active monomer benzyl dimethyl 2-(methacryloyloxy)ethyl ammonium chloride (BDMDAC) to synthesize cationic microblocky polyacrylamide initiated by ultrasound. The reactivity ratio of monomers suggested that novel cationic monomer BDMDAC had higher homopolymerization ability, and was thus more prone to forming a microblock structure. The statistical analysis of sequence-length distribution indicated that the number and length of cationic segments increased in the PAB molecules. In addition, the characteristic results of Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and thermogravimetric analysis (TGA) provided evidence for the synthesis of copolymer with cationic microblocks. Finally, the results of dewatering tests demonstrated that sludge dewaterability was greatly improved by adding the synthesized novel flocculants, and the sludge-specific resistance to filtration, filter cake moisture content and residual turbidity all reached a minimum (68.7%, 5.4 × 1012 m·kg−1, and 2.6 NTU, respectively) at 40 mg·L−1. The PAB flocs were large, compact, difficult to break, and easy to regrow. Furthermore, PAB was more effective in the removal of protein from soluble extracellular polymeric substances (SEPSs). In summary, this study provides a novel solution to synthesize cationic microblock polyacrylamide for improving sludge dewatering.

Formation of cationic hydrophobic micro-blocks in P(AM-DMC) by template assembly: characterization and application in sludge dewatering

A template assembly method was introduced to obtain a cationic hydrophobic micro-block structure based amphiphilic electrolyte poly(acrylamide-co-2-methacryloxyethyltrimethyl ammonium chloride) P(AM-DMC) in this work, thereby increasing charge density and enhancing charge neutralization ability at the same charge density. The alteration of copolymerization or homo-polymerization was evaluated by the changes in reactivity ratios, so as to unravel the mechanism of template assembly. The micro-blocks generated by the new distribution of sequences were demonstrated by 1H nuclear magnetic resonance spectroscopy (1H NMR) and differential thermal-thermogravimetric analysis (DSC-TGA). Two negative controls were employed in sludge dewatering experiments to further evaluate the advanced properties of the template-assembled polymer. The results further verified that the positive effect of template assembly on flocculation performance of the polymer was achieved mainly through two ways: improving charge density and generating the micro-block structure. It can be concluded that the introduction of template assembly into polymerization can improve the performance of the polymer.

Waste activated sludge (WAS) dewatering properties of an original hydrophobically modified polyacrylamide containing a cationic microblock structure

Chemical conditioning, as one of the core technologies used for the dewatering pretreatment of sludge, can efficiently improve the dewaterability of WAS and hence reduce the expense of the transportation and disposal of WAS. Cationic polyacrylamide has been widely utilized as a chemical conditioner owing to its high performance and economic advantages. However, high-performance and economical flocculants are still needed. In this study, a novel hydrophobically associating polyacrylamide, which was denoted as TPADL and contained a cationic microblock structure synthesized by a UV-initiated template copolymerization technique, was employed in a dewatering test on WAS. The chemical composition of TPADL was confirmed via hydrogen nuclear magnetic resonance (1H NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Moreover, 1H NMR spectroscopy demonstrated a highly concentrated distribution of cations on the main chain. Furthermore, thermogravimetric analysis (TGA) was utilized to investigate the thermal stability of TPADL, and its apparent viscosity was also measured to evaluate its rheological characteristics. Dewatering tests found that the TPADL flocculant exerted a synergistic function owing to the cationic microblock structure and hydrophobic association and exhibited superior dewatering performance in comparison with normal random cationic polyacrylamide (CPAM). The filter cake moisture content (FCMC) and specific resistance to filtration (SRF) reached 64.98% and 1.3 × 1012 m kg−1, respectively, for TPADL at the optimal dosage of 1.5 mg g−1 dry solids of WAS (calculated value). The floc size distribution revealed that hydrophobic association remarkably increased the floc size owing to enhancements in bridging absorption ability, whereas the cationic microblock structure helped form a denser and more compact floc structure, and the higher charge neutralization ability enabled an increase in floc strength. In addition, the synergistic function significantly improved the regeneration ability of flocs. Scanning electron microscopy (SEM) analysis indicated that the stronger floc structure could act as a skeleton to form pores and a channel-like structure, which made filter cake a favorable draining medium for the release of water and thus contributed to an increase in dewaterability. This study provided an analysis for the development of high-performance and economic flocculants by a combination of the controllable concentrated distribution of cations and hydrophobic association.

Characterization of an inorganic polymer coagulant and coagulation behavior for humic acid/algae-polluted water treatment: polymeric zinc–ferric–silicate–sulfate coagulant

Algae and algae organic matter (AOM) are not the sole pollutants in algae-polluted water. Other pollutants such as colloidal particles and natural organic matter should be simultaneously removed and might influence the treatment of algae and AOM. A new polymeric zinc–ferric–silicate–sulfate (PZFSiS) coagulant was prepared, and the relationship between its structure and performance in the treatment of humic acid (HA)/algae-polluted water was discussed. PZFSiS coagulants prepared under different conditions had different distributions of Fe(III) species. The coagulant possessing the highest Feb content was able to treat turbidity and HA well. As a copolymer of Fe(III), Zn(II) and Si(IV), PZFSiS had a positive charge in water and thus neutralized the negative surface charges of pollutants. The adsorption of hydroxyl polymer formed by Fe/Zn during the hydrolysis process contributed to the removal of organic matter. The dosage of PZFSiS and pH significantly influenced pollutant removal. Colloidal particles in the water competed with the organic matter, markedly decreasing the removal efficiency of organic matter by coagulation.

Removal of dissolved organic matter from algae-polluted surface water by coagulation

AbstractDissolved organic matter (DOM) is ubiquitous in the algae-polluted surface water and it possesses a potential threat to drinking water safety. It is important to investigate the removal efficiency of DOM by coagulation. Polyaluminum chloride a widely used coagulant is applied in the treatment of DOM derived from Minzhu Lake in Chongqing of China. Based on the analysis of dissolved organic carbon, UV254, specific ultraviolet absorbance, and fluorescence excitation-emission matrix spectroscopy, the results indicate that the small proportion of DOM, such as aromatic-like organic substances, is removed with algae and other colloid particles via coagulation, but most of DOM, such as he tryptophan-like and fulvic-like organic substances, is remained in the treated water. Co-flocculation, bridging, adsorption, and entrapment would be the main removal mechanisms of DOM. DOM removal will be slightly improved through optimizing pH of surface water and using a composite coagulant.

A novel carboxyl-rich chitosan-based polymer and its application for clay flocculation and cationic dye removal

Due to the complexity of contaminants, the effectiveness of traditional flocculants toward water purification is insufficient. To break the limitation, a novel polymer flocculant [chitosan grafted poly (acrylamide-itaconic acid), CS-g-P(AM-IA)] was synthesized via ultraviolet-initiated graft copolymerization reaction. Characterization results revealed that the graft copolymers were successfully synthesized and with rougher surface structure. The solubility of CS-g-P(AM-IA) and chitosan grafted polyacrylamide (CS-g-PAM) were greatly improved and they can dissolve in the wide pH range of 2.0-12.0. CaCl2 was used as a source of cation bridge to enhance the flocculation of kaolin particles, and its optimum dosage was 150 mg·L-1. At dosage of 30 mg·L-1 and pH of 5.0, the turbidity removal efficiency of CS-g-P(AM-IA) reached the maximum of 93.8%, whereas those of CS-g-PAM and CS were 96.7% and 76.9%, respectively. The patchwise adsorption of ionic groups embedded in the molecular chain on Ca2+-clay complexes took effect to generate flocs with larger particle size. Besides, the decolorization ability of cationic dyes by CS-g-P(AM-IA) was greatly enhanced due to the role of abundant carboxyl groups. In the crystal violet (CV) adsorption experiment, the maximum CV dye removal efficiency for CS-g-P(AM-IA) reached the maximum of 81.6% at dosage of 0.7 mg·mL-1 and pH of 9.0, while those for CS-g-PAM and CS were 51.7% and 36.5%, respectively.