Wenyu Wang

Effect of pH with different purified aluminum species on coagulation performance and membrane fouling in coagulation/ultrafiltration process

The influences of solution pH on coagulation/ultrafiltration (C-UF) process were investigated by using three purified Al species of polyaluminium chloride (PACl). A series of online-simulation experiments were developed to assess the coagulation removal efficiencies (turbidity, UV254), floc properties and membrane fouling in this paper. The results showed that change of pH had a significant impact on coagulation efficiencies, floc properties, membrane flux as well as the whole process. Under acidic condition, the hydrolysis action of aluminum salts was restrained which is bad for charge neutralization. While under alkaline region, absorption was the dominant mechanism to combine HA-Kaolin. Meanwhile, HA is apt to soluble by deprotonating under alkaline region which is hard to remove. These common effects made the experiment results complex. HA removal efficiency of Ala and Alb were higher than that of Alc, but the turbidity removal by Alc was slightly higher under the same pH condition. Flocs generated by Ala at pH 6 had advantages such as larger size and the most loosely structure which contributed the most to alleviating membrane fouling. Membrane fouling with Alb and Alc in alkaline range was more serious than that in acidic range.

Purification, characterization and application of dual coagulants containing chitosan and different Al species in coagulation and ultrafiltration process.

The objective of this study was to investigate the effect of different Al species and chitosan (CS) dosages on coagulation performance, floc characteristics (floc sizes, strength and regrowth ability and fractal dimension) and membrane resistance in a coagulation-ultrafiltration hybrid process. Results showed that different Al species combined with humic acid in diverse ways. Ala had better removal efficiency, as determined by UV254 and dissolved organic carbon, which could be further improved by the addition of CS. In addition, the optimal dosage of different Al species was determined to be 4.0mg/L with the CS concentration of 1.0mg/L, by orthogonal coagulation experiments. Combining Ala/Alb/Alc with CS resulted in larger flocs, higher recovery, and higher fractal dimension values corresponding to denser flocs; in particular, the floc size at the steady state stage was four times larger than that obtained with Al species coagulants alone. The results of ultrafiltration experiments indicated that the external fouling percentage was significantly higher than that of internal fouling, at around 85% and 15%, respectively. In addition, the total membrane resistance was significantly decreased due to CS addition.

Flocculation performance of lignin-based flocculant during reactive blue dye removal: comparison with commercial flocculants

A novel lignin-based flocculant (LBF) with superior flocculation performance was prepared from paper mill sludge in this work. The functional groups of LBF and alkaline lignin (AL) were determined by Fourier transform infrared spectroscopy (FTIR). The flocculation performance of LBF integrated with polyaluminum chloride (PAC) was tested in reactive dye wastewater treatment. Floc properties and color removals in multiple flocculation systems were discussed. Results indicated that the dye removal (93%) was greatly facilitated as the LBF was integrated with PAC (PAC + LBF). In addition, floc properties and color removals were significantly improved in the presence of Ca2+ and Mg2+. In contrary, flocculation performance was greatly restricted in the presence of SO42−. LBF was less pH sensitive and shear sensitive than polyacrylamide (PAM) due to the enhanced charge neutralization and bridging action. On the basis of that, LBF could be used as a promising flocculant in dye wastewater treatment.

Characterization of dissolved organic matter and membrane fouling in coagulation-ultrafiltration process treating micro-polluted surface water

Coagulation-ultrafiltration (C-UF) is widely used for surface water treatment. With the removal of pollutants, the characteristics of organic matter change and affect the final treatment efficiency and the development of membrane fouling. In this study, we built a dynamic C-UF set-up to carry out the treatment of micro-polluted surface water, to investigate the characteristics of dissolved organic matter from different units. The influences of poly aluminum chloride and poly dimethyldiallylammonium chloride (PDMDAAC) on removal efficiency and membrane fouling were also investigated. Results showed that the dosage of PDMDAAC evidently increased the UV254 and dissolved organic carbon removal efficiencies, and thereby alleviated membrane fouling in the C-UF process. Most hydrophobic bases (HoB) and hydrophobic neutral fractions could be removed by coagulation. Similarly, UF was good at removing HoB compared to hydrophilic substances (HiS) and hydrophobic acid (HoA) fractions. HiS and HoA fractions with low molecule weight accumulated on the surface of the membrane, causing the increase of transmembrane pressure (TMP). Membrane fouling was mainly caused by a removable cake layer, and mechanical cleaning was an efficient way to decrease the TMP.

Optimization of coagulation pre-treatment for alleviating ultrafiltration membrane fouling: The role of floc properties on Al species

This study investigated membrane fouling in a coagulation/ultrafiltration (C-UF) process by comparing the floc properties and humic acid (HA) removal efficiency of three hydrous Al(III) species (Ala, Alb, and Alc). The results indicated that the coagulation and membrane mechanisms were different for all three Al species because of the differences in floc properties. The HA removal efficiency increased with increasing Al dosage until an equilibrium was reached at the optimal dosage of 6 mg L-1. In addition, membrane fouling gradually decreased as the Al dosages increased. Regardless of coagulant type, the OH and COOH functional groups of HA reacted with the Al species. Both external and internal membrane fouling were strongly dependent on the porosity of the cake layer and on the size distribution of the floc particulates, respectively. The pore area of the cake layer formed by the Ala-coagulated effluent was large because of the strong charge neutralization. Moreover, Ala generated large and loose flocs with a porous cake layer that mitigated external fouling. However, the internal fouling with the Alc coagulant was significant because the concentration of residual aggregates in the membrane pores was high.

Evaluation of molecular weight, chain architectures and charge densities of various lignin-based flocculants for dye wastewater treatment

In this work, four alkaline lignin (AL) based flocculants with distinct molecular weight, chain architectures and charge densities (denoted as AL-g-DMC1, AL-g-DMC2, AL-GTA1 and AL-GTA2) were prepared from paper mill sludge, which were designed via graft copolymerization of dimethyl diallyl ammonium chloride (DMC) or etherification of 2, 3-epoxypropyl trimethyl ammonium chloride (GTA). The characteristics of the aforementioned flocculants were evaluated by a series of analysis technologies, which essentially confirmed the successful introduction of quaternary ammonium groups onto the AL. The flocculation performances of the four synthesized lignin-based polymers as the coagulant aids for PAC were investigated in disperse dye (DY) wastewater treatment, and the effects of dosages, initial pH, coexisting ions, humic acid (HA) or kaolin particles were also studied. The results indicated that branched copolymers with high molecular weight like AL-g-DMC1 and AL-g-DMC2 exerted excellent color removals and satisfactory floc properties in comparison with linear polymers with low molecular weight (AL-GTA1 and AL-GTA2). Furthermore, AL-g-DMC1 and AL-g-DMC2 exhibited remarkable tolerance on pH alteration and coexisting ions owing to their strong bridging action.

Effect of pH on floc properties and membrane fouling in coagulation–ultrafiltration hybrid process with different Al-based coagulants

AbstractImpacts of pH on floc properties and membrane fouling in coagulation–ultrafiltration process with different Al-based coagulants were investigated. Polyaluminum chloride (PAC) was prepared with alkali-titration method and Al speciation distribution was tested with Al-Ferron method. Three kinds of coagulants (AC(AlCl3), PACb, and PACc) consisted primarily of Ala (monomeric species), Alb (medium polymer species), and Alc (colloidal or solid species), respectively, were used as coagulants under pH conditions of 4.0, 6.0, and 8.0. Floc properties were evaluated using a laser diffraction particle sizing device and ultrafiltration experiments were conducted by a dead-end batch unit. The results indicated that pH condition and aluminum species had significant influence on size and fractal dimension value of flocs. For the three Al species, relatively low pH condition was favorable to form larger flocs, while it would diminish the floc growth rate. And the loosest flocs were formed at pH 4.0. Under the sam...