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Results for “Flocculation”

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PubMed2005

Influence of chitosan characteristics on the coagulation and the flocculation of bentonite suspensions.

Ten chitosan preparations with different molecular weights (MW) and degrees of deacetylation (DD) were tested for coagulation of 5 g L(-1) bentonite suspensions at pH 5 and 7 in demineralized water (DW) and in tap water (TW). Coagulation was better in TW than in DW for every condition and lower doses of chitosan were required at pH 5 than at pH 7. More than 95% of residual turbidity (after sedimentation in the absence of chitosan) was removed using less than 0.10 mg L(-1) chitosan in either TW or DW at pH 5 or in TW at pH 7. Higher doses were required for removal of turbidity in DW at pH 7, but in all cases the effective concentrations of chitosan were much lower than required for complete neutralization of the negative charge on the bentonite particles. Removal of turbidity was best for the higher MW chitosans in either the B series (89.5% DD) or the C series (95% DD) of chitosans. Overall, the results were consistent with destabilization of bentonite by the combined mechanisms of electrostatic patch and bridging. The improved performance of chitosan in TW could have been due to improved attachment to bentonite due to the presence of sulfate and other counter-ions in TW.

Acetylation↗

PubMed2005

Alkylamine odors from degradation of flocculant polymers in sludges.

The cationic organic polymers used to enhance thickening and dewatering processes are potential sources of strong odors. These polymers vary in chemical structure, and some may be more susceptible to biotic or abiotic degradation than others. The product organic amines will be volatilized most noticeably at high pH, as in lime addition. These possibilities were examined using several structural types of polymers combined with anaerobically digested sludge. Two commonly used polymers gave significant production of trimethylamine (TMA), which was released upon lime addition. Their structures were correlated with reactions that yield TMA. An initial ester hydrolysis step appears to be biologically mediated, but subsequent steps can occur due to alkaline conditions. An alternative cationic polymer structure did not generate TMA but required a much higher dose to effect sufficient conditioning of the sludge. The acrylamide-based polymers were shown to be the predominant source of TMA in limed sludges.

Biodegradation, Environmental↗

PubMed2005

Rheological characteristics of the cationic polyelectrolyte flocculated wastewater sludge.

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The stress-sweep experiments and the small-amplitude-oscillatory-shearing (SAOS) tests were conducted. The stress-sweep measurements demonstrate that addition of polymer coagulants to sludge samples could significantly influence the corresponding complex shear modulus G*. Furthermore, the SAOS tests indicate that the sludge samples treated with polymer coagulants will form more rigid structures. The original sludge samples mostly show typical viscoelastic liquid-like behavior. However, the solid-like behaviors were always observed in the samples treated with polymers.

Elasticity↗

PubMed2003

Flocculation in mixtures of cationic polyelectrolytes and anionic surfactants.

The phase behavior of mixtures of a cationic polyelectrolyte ('Jaguar') and an anionic surfactant (either sodium dodecyl sulfate or sodium lauryl ether sulfate) has been studied. For a given polyelectrolyte (and added NaCl) concentration, with increasing surfactant concentration, three phase regions were identified. The first region is a single homogeneous phase. Within this region, at some surfactant concentration, above the critical aggregation concentration, stable open-network 'particles' form, typically approximately 100 nm in size, which are net positively charged. However, as the surfactant concentration is increased further, these particles aggregate and form a two-phase system, i.e. a separated gel phase, containing a high percentage of water, co-existing with an aqueous surfactant phase. At some higher surfactant concentration still, the particles become sufficiently negatively charged that they re-stabilize. Beyond this surfactant concentration, therefore, the system reverts to being a single, homogeneous phase. Within the two-phase (aggregated particle) region an iso-electric point for the particles has been observed at a certain surfactant concentration, by electrophoresis. Furthermore, in this aggregated, gel-phase region, there appear to be typically approximately 2-4 surfactant molecules associated with each cationic site of the polymer chains. It is postulated that association of the anionic surfactant molecules occurs within the polyelectrolyte chains, binding them together, to form the particles referred to. These associated surfactant structures have been referred to here as 'internal' micelles. A crude estimate has been made, based on turbidity/time measurements, that there may be up to approximately 1000 polymer chains in each primary particle, bound together by the internal surfactant micelles. Small-angle light scattering studies of the aggregating particles indicate a fractal dimension for the aggregates, which would correspond to a diffusion-limited aggregation process.

Anions↗

PubMed1950

Liver function during pregnancy and the puerperium, as measured by the cephalin-cholesterol flocculation, the thymol turbidity, and the bromsulfalein tests.

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Cholesterol↗

PubMed2002

Comment on "experimental analysis of centrifugal dewatering process of polyelectrolyte flocculated waste activated sludge".

In summary, after supernatant liquid was exhausted in the author's experiments, menisci formed, and shrinkage, not pore evacuation and drying, was the mechanism causing removal of water thereafter. Results of centrifugal filtration experiments cannot be applied to solid bowl centrifugation because solid compression conditions are quite different in the two types of machines.

Centrifugation↗

PubMed1960