Stoichiometry of Coagulation Revisited

Shin, Jae-Ki; Spinette, R. F.; O’Melia, Charles R.

doi:10.1021/es071536o

Cited by 84 publications

(46 citation statements)

References 13 publications

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“…DOM is organic matter not associated with the actual cells, although a large fraction or the majority may originate with the algae. DOM has similar functional groups as the cell surface and associates with the flocculant, effectively reducing the quantity of flocculant that can neutralize the surface charges [17,[50][51][52]. DOM is found in our work to vary over the algae cultivation lifecycle, increasing in later stages, but this was not as strong of an effect as the reduction in the flocculant requirements associated with the reduced concentrations of surface functional groups [38].…”

Section: Flocculation With Inorganic Saltsmentioning

confidence: 61%

First-principles flocculation as the key to low energy algal biofuels processing.

Hewson¹,

Wyatt²,

Pierce³

et al. 2012

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This document summarizes a three year Laboratory Directed Research and Development (LDRD) program effort to improve our understanding of algal flocculation with a key to overcoming harvesting as a techno-economic barrier to algal biofuels. Flocculation is limited by the concentrations of deprotonated functional groups on the algal cell surface. Favorable charged groups on the surfaces of precipitates that form in solution and the interaction of both with ions in the water can favor flocculation. Measurements of algae cell-surface functional groups are reported and related to the quantity of flocculant required. Deprotonation of surface groups and complexation of surface groups with ions from the growth media are predicted in the context of PHREEQC. The understanding of surface chemistry is linked to boundaries of effective flocculation. We show that the phase-space of effective flocculation can be expanded by more frequent alga-alga or floc-floc collisions. The collision frequency is dependent on the floc structure, described in the fractal sense. The fractal floc structure is shown to depend on the rate of shear mixing. We present both experimental measurements of the floc structure variation and simulations using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Both show a densification of the flocs with increasing shear. The LAMMPS results show a combined change in the fractal dimension and a change in the coordination number leading to stronger flocs. 4 ACKNOWLEDGMENTSThis program to improve our understanding of algal flocculation and harvesting was initiated through the Laboratory Directed Research and Development (LDRD) program, and the authors of this report are indebted to many people for their continued support. We have benefited in particular from the braider understanding of the bioenergy landscape provided by Ron Pate,

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Section: Flocculation With Inorganic Saltsmentioning

confidence: 61%

First-principles flocculation as the key to low energy algal biofuels processing.

Hewson¹,

Wyatt²,

Pierce³

et al. 2012

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“…It is noteworthy that natural water samples used in the coagulation experiments were prefiltered by 1.2 μm glass fiber filters to remove coarse materials; this resulted in low initial turbidities (<10 NTU) except for batch 4 that also had the highest DOC (Table S1, Supporting Information). According to Shin et al, 18 optimal alum dose for turbidity removal by coagulation is determined by DOC for low turbidity source water due to stoichiometric reactions/interactions between hydrolytic aluminum species and NOM. This explains why the optimal alum dose determined by turbidity removal depended on DOC level as observed in this study.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Mechanisms of Membrane Fouling Control by Integrated Magnetic Ion Exchange and Coagulation

Huang

Cho

Jacangelo

et al. 2012

Environ. Sci. Technol.

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Colloidal natural organic matter (NOM) is an important foulant to low-pressure membranes (LPMs) employed in drinking water treatment. Removal of colloidal NOM by magnetic ion exchange (MIEX), coagulation, and integrated MIEX and coagulation was investigated in this study to determine the relationship between colloidal NOM removal and membrane fouling reduction. The results showed that coagulation did not selectively remove colloidal NOM and the optimal coagulant dose was primarily determined by the concentration of humic substances. Comparatively, MIEX pretreatment preferentially removed humic substances and reduced the coagulant dose needed for colloidal NOM removal as a result of coagulation stoichiometry. A matched-pair analysis showed that integrated MIEX and coagulation pretreatment at much lower coagulant doses was as effective as coagulation in reducing membrane fouling. It is concluded that integrated MIEX and coagulation is potentially a viable pretreatment approach to reduce membrane fouling and in general removal of colloidal NOM in feedwater is an effective approach for membrane fouling control and should be considered in the research, development, and application of novel LPM-based treatment processes.

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“…The predominant Al species of AC and PACl were Al monomer (Al m ) and Al 13 polymer, respectively. Al 13 polymer in PACl used in this study accounted for 87.1% of the total Al concentration, which was analyzed using the method of 27 Al nuclear magnetic resonance [30]. 1000 mg/L Se(IV) and Se(VI) stock solutions were prepared by dissolving Na 2 SeO 3 and Na 2 SeO 4 Á10H 2 O (both from Aldrich) into de-ionized water, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…After coagulant addition, Al or Fe cations hydrolyze quickly and in-situ form abundant precipitates of Al or Fe hydroxide oxides. Contaminant adsorption to Al or Fe hydroxide oxide can play a very important role in the coagulation process [27,28]. Therefore, coagulation may be an effective technology to remove Se through adsorption by Al or Fe hydroxide oxide.…”

Section: Introductionmentioning

confidence: 99%

Removal of Se(IV) and Se(VI) from drinking water by coagulation

Chen

et al. 2015

Separation and Purification Technology

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a b s t r a c t Selenium (Se) is one of contaminants required to be regulated during drinking water treatment, however, little information has been collected to date regarding Se removal by coagulation. In this study, the performance of Se removal by coagulation has been evaluated with respect to the dependence on Se species, coagulant type, water pH and interfering ions. The results showed that a Fe-based coagulant was much more efficient than Al-based coagulants in Se removal. The removal of selenite (Se(IV)) by coagulation was much more pronounced than that of selenate (Se(VI)). With an FC dosage of more than 0.4 mM Fe/L, Se(IV) removal efficiency of more than 98% could be achieved when the initial Se(IV) concentration was 250 lg/L. For Al-based coagulants (AlCl 3 (AC) and polyaluminum chloride (PACl)) Se removal efficiency was positively correlated with the content of Al 13 species during the coagulation process. Adsorption onto hydroxide flocs was the most active coagulation mechanism for Se removal and precipitation also played specific roles at low dosage, especially for Se(IV) removal and with Fe coagulant. High coagulant dosage and weakly acidic pH could enhance the formation of hydroxide flocs having more active adsorption sites and high zeta potential, and thus favored Se removal. These findings are important to understand the efficiency and mechanisms of Se removal by coagulation.

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Stoichiometry of Coagulation Revisited

Cited by 84 publications

References 13 publications

First-principles flocculation as the key to low energy algal biofuels processing.

First-principles flocculation as the key to low energy algal biofuels processing.

Mechanisms of Membrane Fouling Control by Integrated Magnetic Ion Exchange and Coagulation

Removal of Se(IV) and Se(VI) from drinking water by coagulation

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