Ruihua Li

Compound bioflocculant and polyaluminum chloride in kaolin-humic acid coagulation: Factors influencing coagulation performance and floc characteristics

The objective of this study was to investigate the influence of coagulant dosage and pH on coagulation performance and floc properties using polyaluminum chloride (PAC) and compound bioflocculant (CBF) dual-coagulant in kaolin-humic acid (HA) treatment. Results showed that as PAC dosage rose, comparatively better coagulation efficiencies and floc characteristics were achieved due to stronger charge neutralization and sweeping effect. Addition of CBF could enhance coagulation performance and floc properties, including size, strength and recoverability, except fractal dimension. Solution pH had a significant effect on coagulation efficiencies and flocs formation. Under acidic condition, flocs showed higher strength and recoverability but lower fractal dimension, where charge neutralization was the foremost mechanism. More compact flocs were generated under alkaline condition due to the sweeping effect of hydrolyzed Al species.

Coagulation behavior and floc structure characteristics of cationic lignin-based polymer-polyferric chloride dual-coagulants under different coagulation conditions

To recycle papermaking sludge, a novel lignin-based flocculant with high cationic degree and molecular weight was introduced. The product, lignin–diallyl dimethyl ammonium chloride–acrylamide (LDA) was combined with polyferric chloride (PFC) to treat simulated humic acid (HA) solution. To identify its flocculation mechanisms, coagulation efficiencies and floc properties under different dosing methods and pH conditions were studied. Results showed that LDA was superior to polyacrylamide, poly diallyldimethylammonium chloride as well as lignin–acrylamide with regards to dissolved organic carbon (DOC) and turbidity removal efficiencies, which demonstrated its significant flocculating efficiency. Compared with single PFC, the addition of LDA enhanced the coagulation performance and floc properties, including floc size, growth rate and the recovery ability within the investigated pH range. The dosing sequence also had an effect on the coagulation mechanism and performance. When PFC was dosed first, negatively charged Fe(III) hydrolysates-colloids were neutralized and bridged by LDA. On the contrary, colloids–LDA complexes with slight negative charge were destabilized by the entrapment and sweeping effect of Fe(III) hydrolysates. As a result, coagulation efficiencies were in the following order: PFC dosed firstly (PFC + LDA) > LDA dosed firstly (LDA + PFC) > PFC. PFC + LDA achieved the maximum floc size and growth rate, whereas flocs with the most open structure was formed by LDA + PFC. Moreover, the effect of solution pH on coagulation behavior was noteworthy due to the variance of hydrolyzed Fe species. PFC was more sensitive to pH with regards to coagulation efficiencies and flocs structure. The variations caused by different pH values decreased after the addition of LDA. Regardless of the coagulant types, the optimal coagulation performance and floc characteristics were achieved under acidic conditions, especially at pH 6. Overall, LDA could introduce strong charge neutralization and adsorption bridging effect within a relatively wider pH range and offer a positive effect on coagulation behavior and flocs properties.

Effects of chlorination operating conditions on trihalomethane formation potential in polyaluminum chloride-polymer coagulated effluent.

In this study, coagulation performance of polyaluminum chloride (PAC) and PAC-lignin acrylamide (PAC+LAM) in reservoir water treatment was contrastively analyzed. Effects of operating conditions including chlorine dose, contact time and pH on the formation potential of trihalomethanes (THMs) during chlorination in coagulated effluent were also investigated. Comparing with PAC, PAC+LAM achieved higher efficiency in the removal of THMs precursors. TTHM yield in unfiltered water samples (UW) was greater than that of filtered water (FW) due to the residual dissolved organic matter (DOM) in the suspended particles or micro flocs. Meanwhile, operating conditions during chlorination had a significant influence on THMs formation potential. With chlorine dose rising, mass ratio of CHCl3 to TTHM increased, whereas that of CHBr2Cl decreased due to higher Cl2/Br(-) molar ratio. TTHM and CHCl3 levels rose with the increase of pH. Under a given chlorination condition, there was a minor effect of contact time on THM speciation.

Effects of papermaking sludge-based polymer on coagulation behavior in the disperse and reactive dyes wastewater treatment

In this study, papermaking sludge was used as the raw biomass material to produce the lignin-based flocculant (LBF) by grafting quaternary ammonium groups and acrylamide. LBF was used as a coagulant aid with polyaluminum chloride (PAC) to treat reactive and disperse dyes wastewater. Effects of dosing method, pH, hardness and stirring speed on the coagulation behavior and floc properties were studied. Results showed that the superior coagulation efficiency and recovery factor were achieved by PAC+LBF compared with PAC and LBF+PAC. The primary mechanisms of LBF in the treatment of disperse and reactive dye solutions were charge neutralization and bridging effect, respectively. In the dual-coagulation, the impact of pH on the coagulation efficiency was weak during pH range of 5-9. Moderate hardness could enhance the floc properties due to the decrease of electrostatic repulsion and the chelation of Ca(II) and LBF. Besides, flocs coagulated by PAC+LBF had a stronger anti-crush ability.

Comparison of epichlorohydrin-dimethylamine with other cationic organic polymers as coagulation aids of polyferric chloride in coagulation-ultrafiltration process.

Epichlorohydrin-dimethylamine (DAM-ECH) copolymer was acquired by polycondensation of hazardous reagents: epichlorohydrin (analytical reagent, A.R.) and dimethylamine (A.R.) with ethanediamine (A.R.) as cross-linker. Its coagulation and membrane performance as coagulation aid of polyferric chloride (PFC) was evaluated by comparing with other two cationic coagulation aids: poly dimethyl diallyl ammonium chloride (PDMDAAC) and polyacrylamide (PAM) in humic acid-kaolin (HA-Kaolin) simulated water treatment. Firstly, optimum dosages of PFC&DAM-ECH, PFC&PDMDAAC and PFC&PAM were identified according to their coagulation performance. Then their impacts (under optimum dosages) on membrane fouling of regenerated cellulose (RC) ultra-membrane disc in coagulation-ultrafiltration (C-UF) process were reviewed. Results revealed that small addition of DAM-ECH was the effective on turbidity and DOC removal polymer. Furthermore, in the following ultra-filtration process, external membrane fouling resistance was demonstrated to be the dominant portion of the total membrane fouling resistance under all circumstances. Meanwhile, the internal membrane fouling resistance was determined by residual of micro-particles(1) that cannot be intercepted by cake layer or ultrafiltration membrane.

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.

Coagulation behavior of kaolin-anionic surfactant simulative wastewater by polyaluminum chloride-polymer dual coagulants

In this study, polyaluminum chloride (PAC) and cationic polymers were used to treat kaolin suspension in the presence of sodium dodecyl benzene sulfonate (SDBS). Effects of PAC dosage, pH, and rotation rate on the coagulation efficiency and floc properties were studied. And the interaction of chemicals and kaolin-SDBS was discussed. Results showed that dual coagulants could decrease the influence of SDBS on the turbidity removal compared with PAC. PAC + polyacrylamide dual coagulant showed superior performance, and the maximal removal ratios of turbidity and dissolved organic carbon were 98.5 and 42.2%, respectively. Optimal coagulation performance was achieved at pH 5–7, where charge neutralization of Al hydrolysates and bridging of polyacrylamide were the primary mechanisms. And flocs with compact structure and small size were formed. Flocs coagulated by PAC were prone to be broken at the pH of raw water after introducing high rotation rate. After dosing polyacrylamide, floc size was enhanced under alkaline condition. Meanwhile, flocs showed stronger recoverability and an open structure because the regeneration mechanism was mainly the bridging effect of polyacrylamide.

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.

Application of enteromorpha polysaccharides as coagulant aid in the simultaneous removal of CuO nanoparticles and Cu2+: Effect of humic acid concentration

Humic acid (HA) influences the aggregation and stability of nanoparticles (NPs), which determine the removal performance of NPs in coagulation. Consequently, in this study, the impact of HA concentration on the simultaneous removal of CuO NPs, Cu2+, and natural organic matter (NOM) was investigated. Enteromorpha polysaccharides (Ep), as the novel recycling coagulant aid, were integrated with polyaluminum chloride (PAC) to treat composite contaminants in this coagulation process. Removal performance, floc properties, zeta potential, scanning electron microscope (SEM) images, and Fourier Transform Infrared Spectra (FT-IR) were measured and analyzed. Results showed that PAC with Ep (PAC-Ep) was more beneficial for improving removal performances than PAC alone. Further, the coagulation performance became better with the increase in HA concentration. When the HA concentration was 10 mg/L (used PAC-Ep), the removal efficiencies of CuO NPs and Cu2+ were both more than 80%; and in particular, the highest removal efficiency of turbidity was 98%. However, excessive HA (more than 10 mg/L) reduced the removal efficiency of Cu by more than 31%. Smaller and denser flocs with better recoverability were formed as the HA concentration increased. Furthermore, because of affluent functional groups, HA was easily adsorbed on the surface of NPs and combined with dissociative Cu2+, thereby forming a composite contaminant. During the coagulation process, the colloidal system was destabilized preferentially by the charge neutralization between composite contaminants and PAC. Furthermore, a chelated reticular structure was formed by the conjunction of carboxyl and hydroxyl groups (from Ep) and Al (III) species (from PAC). Flocs were further enlarged and precipitated by bridging and sweeping of this structure.

Exploration of polyepoxysuccinic acid as a novel draw solution in the forward osmosis process

Polyepoxysuccinic acid (PESA) is a green corrosion scale inhibitor. When PESA is used for wastewater desalination in the forward osmosis (FO) process, the diluted PESA solution could be used for cooling systems. In our investigation, the effects of membrane orientation, temperature and flow rate on FO performance are studied using PESA as a draw solute. The results show that the effect of temperature on water flux is obvious, but the water flux increase is higher from 25 °C to 35 °C than that from 35 °C to 45 °C. Compared to the FO mode, the water flux increases faster in the pressure-retarded osmosis mode (PRO mode) at high flow rate due to the reduction of concentrative internal concentration polarization (CICP). Compared with polyaspartic acid (PASP) and NaCl, the water flux of PESA is the lowest under the same conditions. However, PESA has the lowest specific reverse solute flux (Js/Jw) at both membrane orientations. For example in the FO mode this value is 0.46 g L−1, whereas that of NaCl and PASP is 1.12 and 0.74 g L−1, respectively. This means that PESA has lower loss to the feed side than NaCl and PASP in the FO process, which greatly reduces the replenishment cost of the draw solute. The use of PESA as the draw solute in the FO process to treat dyeing water has the advantages of stable water flux (within 20 min), high dye rejection (nearly 1) and reversible membrane fouling (restored to 97%). The nanofiltration (NF) process indicates the good performance of PESA recovery with a high specific water flux (0.94 LMH per bar) and rejection rate (97.8%). Thus, the overall performance of PESA demonstrates that it is a promising draw solute.