Xiaomin Tang

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.

Algae removal from raw water by flocculation and the fractal characteristics of flocs

AbstractThe feasibility of flocculation treatment of algae-containing raw water using poly(acrylamide-acryloyloxyethyl trimethyl ammonium chloride-butyl acrylate) (PADB) was investigated. The effects of flocculant dosage and initial pH of raw wastewater on the removal of turbidity and chlorophyll-a (Chl-a) from raw water were examined. The flocculation efficiency of PADB was compared with that of cationic polyacrylamide (CPAM), polymeric ferric sulfate (PFS), and polyaluminum chloride (PAC). PADBs proved to be highly efficient flocculants for the removal of Chl-a; meanwhile, flocculation tests also demonstrated the superiority of PADB over CPAM, PFS, and PAC in the removal of Chl-a. The removal of turbidity and Chl-a by PADB were higher than 94 and 99%, respectively, in the pH range of 6–8 at 3 mg L−1 PABD dosage and at 40% cationic degree. The Chl-a removal efficiency of PADB was 7.6, 17.9, and 52.8% higher than that of CPAM, PFS, and PAC, respectively. Optical microscopy was used to investigate the frac...

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.

Investigation of sludge conditioning performance and mechanism by examining the effect of charge density on cationic polyacrylamide microstructure

AbstractThe relation between the microstructure and sludge conditioning performance and mechanism of cationic polyacrylamide (CPAM) (low charge density (CD) CPAM C1, medium CD CPAM C4, and high CD CPAM C7) was extensively studied and recognized in this study. Igarashi and Pyun models based on reactivity ratio characterized the microstructure of the polymers. Results indicated that the blockness percent and mean sequence length of acrylamide (AM) unit decreased, whereas those of cationic unit increased with CD. Effect of dosage on sludge conditioning performance and mechanism was studied by measuring turbidity, filter cake moisture content (FCMC), specific resistance of filtration (SRF), floc size distribution, and zeta potential. The longest AM unit sequence length and separated cationic unit of C1 were concluded to be responsible for bridging. Moreover, the conditioning disadvantages of AM were as follows: narrow flocculation window, high optimum dosage, and maximum FCMC. On the contrary, the highest cat...

Optimization of flocculation process by response surface methodology for diethyl phthalate removal using anionic polyacrylamide

AbstractDiethyl phthalate (DEP) are classified as endocrine disruptors in water. In the present study, response surface methodology (RSM) was employed for flocculation process optimization in DEP removal from water. Two different copolymers, anionic polyacrylamide (APAM), were used as flocculants in this flocculation process including APAM1 and APAM2. APAM1 was polymerized by ultraviolet (UV) initiation, and APAM2 was polymerized without UV-initiation. The analysis result of variance demonstrated that the model was highly significant and reliable. Optimization by RSM with APAM1, the optimum conditions were dosage of 11.01 mg L−1, pH of 8.93, and stirring time of 6.29 min. And the optimum conditions with APAM2 were dosage of 13.68 mg L−1, initial pH of 8.73, and stirring time of 6.80 min. DEP removal efficiency of 83.97% was achieved by using flocculants APAM1 and 72.47% for APAM2. Scanning electron microscopy images and spectrum from nuclear magnetic resonance spectrometer (1H NMR) suggested that UV-initi...

UV-Initiated Polymerization of Cationic Polyacrylamide: Synthesis, Characterization, and Sludge Dewatering Performance

P(AM-DAC-BA) was synthesized through copolymerization of acrylamide (AM), acryloyloxyethyl trimethyl ammonium chloride (DAC), and butylacrylate (BA) under ultraviolet (UV) initiation using response surface methodology (RSM). The influences of light intensity, illumination time, and photoinitiator concentration on the intrinsic viscosity [η] of P(AM-DAC-BA) were investigated. RSM model based on the influencing data was established for optimizing synthetic conditions. It was found that, at light intensity 1491.67 μw·cm−2, illumination time 117.89 min, and photoinitiator concentration 0.60‰, there was a better material performance achieved. Thus P(AM-DAC-BA) prepared under the above conditions showed excellent dewatering performance that, with 40 mg·L−1 P(AM-DAC-BA) at pH 7, the residual turbidity of supernatant and the dry solid content were up to 38 NTU, 28.5%, respectively.

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.

The investigation of the specific behavior of a cationic block structure and its excellent flocculation performance in high-turbidity water treatment

The fabrication of a cationic polyacrylamide (CPAM) with high efficiency and economy has been highly desired in the field of high-turbidity water treatment. This study introduced an ultrasound (US)-initiated template polymerization (UTP) method to develop a novel cationic templated polyacrylamide (TPAA) with a microblock structure. TPAA was prepared using acrylamide (AM) and sodium (3-acrylamidopropyl)trimethylammonium chloride (ATAC) as the monomers and sodium polyacrylate (NaPAA) as the template. Factors that affected polymerization such as the ultrasound power, ultrasound time, initiator concentration, pH, and mAM : mATAC and nNaPAA : nATAC values were investigated. The properties of the polymers were characterized by Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results indicated the successful formation of a cationic microblock structure in TPAA. In addition, TPAA displayed favorable thermal decomposition properties and a rough and coarse surface morphology, as shown by analyses using TGA and SEM, respectively. Moreover, a zip (type I) template polymerization mechanism was identified via analyses of the association constant (KM), conversion (Cv) and polymerization rate (Rp). The flocculation performance of the templated copolymer TPAA was evaluated by treating high-turbidity water. According to the results for the zeta potentials and FTIR spectra of the generated flocs, it was indicated that the cationic microblocks in the templated copolymer could greatly enhance its charge neutralization, patching and bridging ability, and therefore excellent flocculation performance (residual turbidity: 5.8 NTU, Df: 1.89, floc size d50: 608.404 μm and floc kinetic: 15.86 × 10−4 s−1) for treating high-turbidity water was achieved.