Jun Zhai

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.

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 0.014u202fmol·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 40u202fmg·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.

Characterization and coagulation–flocculation performance of a composite coagulant: poly-ferric-aluminum-silicate-sulfate

AbstractComposite coagulant has received widespread attention and research for its excellent coagulation performance in recent years. In this study, a new composite coagulant poly-ferric-aluminum-silicate-sulfate was synthesized using water glass, FeSO4·7H2O, Al2(SO4)3·18H2O, and NaClO3, their structures and morphologies were characterized and compared by X-ray diffraction, infrared spectra, and scanning electron microscopy. In addition, to obtain the optimum synthetic conditions resulting in the maximum turbidity removal efficiency, single-factor method was used to examine the parameters such as Si/[Al+Fe], Al/Fe, and aging time by municipal wastewater treatment. The coagulation–flocculation process showed that chemical oxygen demand and turbidity removal efficiency could achieve 77 and 99.4%, respectively, when the optimum synthesis conditions were Si/[Al+Fe], Al/Fe, OH/[Al+Fe], aging time, and reaction temperature of 0.4:1, 3:7, 0.3, 24xa0h, and 80°C, respectively. In addition, when the Si/[Al+Fe] of coa...

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.

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 11.01u2009mgu2009L−1, pH of 8.93, and stirring time of 6.29u2009min. And the optimum conditions with APAM2 were dosage of 13.68u2009mgu2009L−1, initial pH of 8.73, and stirring time of 6.80u2009min. 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...

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.