Shenglei Sun

Effects of compound bioflocculant on coagulation performance and floc properties for dye removal.

A series of jar tests was conducted to investigate the coagulation performance of using compound bioflocculant (CBF) as a coagulant aid with aluminum sulfate (AS) and polyaluminum chloride (PAC) in synthetic dyeing wastewater treatment. Floc size, growth, breakage, re-growth and sedimentation natural were investigated by PDA2000. The results showed that the corresponding dual-coagulants of AS and PAC enhanced the color removal efficiency, especially at low aluminum dosage. Results also indicated that the floc generated by aluminum salts and CBF had larger size and higher growth rate. In addition, for both AS and PAC the floc recoverability was improved by addition of CBF. The adsorption and bridging effect of CBF performed a positive role in dye wastewater treatment.

Adsorption of nitrate from aqueous solution by magnetic amine-crosslinked biopolymer based corn stalk and its chemical regeneration property.

A novel adsorbent of magnetic amine-crosslinked biopolymer based corn stalk (MAB-CS) was synthesized and used for nitrate removal from aqueous solution. The characters and adsorption mechanisms of this bio-adsorbent were determined by using VSM, TGA, XRD, SEM, TEM, FT-IR and XPS, respectively. The results revealed that the saturated magnetization of MAB-CS reached 6.25 emu/g. Meanwhile, the studies of various factors indicated that this novel magnetic bio-adsorbent performed well over a considerable wide pH range of 6.0 ∼ 9.0, and the presence of PO4(3-) and SO4(2-) would markedly decrease the nitrate removal efficiency. Furthermore, the nitrate adsorption by MAB-CS perfectly fitted the Langmuir isotherm model (R(2)=0.997-0.999) and pseudo second order kinetic model (R(2)=0.953-0.995). The calculated nitrate adsorption capacity of MAB-CS was 102.04 mg/g at 318 K by Langmuir model, and thermodynamic study showed that nitrate adsorption is an spontaneous endothermic process. The regeneration experiments indicated its merit of regeneration and stability with the recovery efficient of 118 ∼ 147%. By integrating the experimental results, it was found that the removal of nitrate was mainly via electrostatic attraction and ion exchange. And this novel bio-adsorbent prepared in this work could achieve effective removal of nitrate and rapid separation from effluents simultaneously.

Characterization of size, strength and structure of aluminum-polymer dual-coagulant flocs under different pH and hydraulic conditions.

The objectives of this study are to investigate the impact of papermaking sludge product (LA) on coagulation performance and floc properties under different solution pH and hydraulic conditions. LA was synthetized by grafting acrylamide onto the lignin that contained in papermaking sludge. Characterization of LA, such as FTIR, SEM, zeta potential and molecular weight, showed that target product was obtained successfully. LA was used in combination with aluminum sulfate or polyaluminum chloride, namely Al-LA (Al was dosed firstly) and LA-Al (LA was dosed firstly), in humic acid water treatment. Floc properties and coagulation behaviors of aluminum salts and the dual-coagulants were comparatively evaluated. Results showed that DOC removal was improved by LA at pH 4 ~ 9 and the removal variations caused by different pH were decreased. Flocs formed at pH 5 and pH 8 gave quite large floc size. Floc recoverability declined as initial pH increased. Floc size, growth rate and recoverability were in the order of Al-LA>LA-Al>Al. Furthermore, flocs formed at pH 7 showed the weakest resistance to increasing shear force. Fractal dimension was rather high at pH 7 and 8 and it was in the following order: Al>LA-Al>Al-LA.

Effects of dissolved organic matter size fractions on trihalomethanes formation in MBR effluents during chlorine disinfection

In this study, effects of dissolved organic matter (DOM) size fractions on trihalomethanes (THMs) formation in MBR effluents during chlorination were investigated by fractionating DOM into >100, 30-100, 10-30, 5-10 and <5 kDa fractions using ultrafiltration (UF) membranes based on molecular weight (MW). Fractions of MW>30 kDa constituted 87% of DOM and were the main THMs precursors, which exhibited higher specific ultraviolet absorbance (SUVA) and THMs formation potential (THMFP) and should be reduced to control THMs formation. For these fractions, THMs formation was mostly attributed to slow chlorine decay, and THMs yield coefficients were low because halogenated intermediates derived from the macromolecular DOM were difficult to decompose to produce THMs. Moreover, there was a strong linear correlation between dissolved organic carbon (DOC) concentration and THMFP (R(2)=0.981), as well as between the SUVA and specific THMFP (R(2)=0.993) in all fractions.

Advanced lignin-acrylamide water treatment agent by pulp and paper industrial sludge: Synthesis, properties and application

A novel flocculant LA (lignin-acrylamide polymer), which was used as aid for aluminum sulfate and polyaluminum chloride in this study, was prepared by grafting acrylamide onto lignin that deriving from pulp and papermaking sludge. Physicochemical properties of LA were measured by X-ray photoelectron spectroscopy and scanning electron microscopy. The experimental outcome indicated acrylamide was grafted onto the lignin backbone successfully. The effects of LA addition were evaluated on coagulation performance and floc characteristics as a function of aluminum (Al) dosage, such as floc size, growth rate, strength and recoverability. Effects of different dosing sequences, Al dosed first and LA dosed first, were also investigated. LA used as coagulant aid markedly enhanced the removal efficiency of turbidity and dissolved organic carbon, especially at low Al dosages. The dissolved organic carbon removal efficiencies of aluminum sulfate and polyaluminum chloride at the Al dosage range selected in this study were improved more than 30% and 5% by LA, respectively. LA dramatically enlarged floc size and it was in the order: Al dosed first > LA dosed first > Al. Floc strength and recoverability were also improved by LA. LA played a significant role in charge neutralization, adsorption and bridging in floc formation.

Coagulation behavior and floc properties of compound bioflocculant–polyaluminum chloride dual-coagulants and polymeric aluminum in low temperature surface water treatment

This study was intended to compare coagulation behavior and floc properties of two dual-coagulants polyaluminum chloride-compound bioflocculant (PAC-CBF) (PAC dose first) and compound bioflocculant-polyaluminum chloride (CBF-PAC) (CBF dose first) with those of PAC alone in low temperature drinking water treatment. Results showed that dual-coagulants could improve DOC removal efficiency from 30% up to 34%. Moreover, CBF contributed to the increase of floc size and growth rate, especially those of PAC-CBF were almost twice bigger than those of PAC. However, dual-coagulants formed looser and weaker flocs with lower breakage factors in which fractal dimension of PAC-CBF flocs was low which indicates a looser floc structure. The floc recovery ability was in the following order: PAC-CBF>PAC alone>CBF-PAC. The flocculation mechanism of PAC was charge neutralization and enmeshment, meanwhile the negatively charged CBF added absorption and bridging effect.

Floc characterization and membrane fouling of polyferric–polymer dual/composite coagulants in coagulation/ultrafiltration hybrid process

Papermaking sludge and spent pickling liquor were recycled to synthesize a macromolecular lignin-acrylamide polymer (LA) and polyferric chloride (PFC), respectively. The dual-coagulant PFC-LA (PFC and LA were dosed orderly), composite coagulant PFCLA (PFC and LA premixed before dosed) and PFC were used in coagulation/ultrafiltration hybrid process in surface water treatment. The objectives of this paper are to comparatively investigate final water quality after coagulation and coagulation/ultrafiltration process and floc properties, including floc size, strength, recoverability and floc structure, with or without LA addition. Additionally, the relationship between membrane fouling and floc characteristics was discussed. The results showed that best final water quality was obtained by PFC-LA, sequentially followed by PFCLA and PFC. Floc size, growth rate, strength and recoverability as well as fractal dimension were also in the order of PFC-LA>PFCLA>PFC. The maximum permeate fluxes before and after backwash operation were obtained by PFC-LA, which gave the largest and most compact flocs. Coagulation suspension after breakage resulted in much more serious membrane fouling for PFC, whereas permeate flux slightly decreased when LA was used in combination with PFC.

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.

Influence of Enteromorpha polysaccharides on variation of coagulation behavior, flocs properties and membrane fouling in coagulation-ultrafiltration process.

Enteromorpha polysaccharides (Ep) were used as a new coagulant aid together with polyaluminum chloride (PACl) in coagulation-ultrafiltration process to purify Yellow River water. The evolution of flocs size, growth rate, strength, recoverability and fractal structure due to Ep addition were systematically studied in this paper. On this basis, membrane fouling caused by the coagulation effluents of PACl and Ep were also investigated. Results indicated that Ep addition lead to 20% increase in coagulation performance, and meanwhile generate flocs with bigger sizes, faster growth rates and higher recovery abilities. Additionally, the flocs formed by PACl presented more compact structure with a larger D(f) value, while much looser flocs were obtained when Ep was added. Results of ultrafiltration experiments implied that with Ep addition, membrane fouling could be significantly reduced due to large size and loosely structures of flocs in coagulation effluents. Considering both the coagulation efficiency and ultrafiltration membrane performance, 0.2 mg/L Ep was determined as the optimal dosage in coagulation-ultrafiltration process in this study.

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.