PubMed Health⌕ Search

Biomedical subjects

Peter Jarvis

Publications and source records attributed to Peter Jarvis.

5 recordsLinked to original sources
PubMed2006

The impact of zeta potential on the physical properties of ferric--NOM flocs.

The physical properties of natural organic matter (NOM) flocs, such as size, growth rate, and strength, were investigated using a laser diffraction particle sizing device. Conditions were set such that varying carbon coagulant ratio and zeta potential could both be investigated. Results demonstrated a link between zeta potential and coagulation and flocculation performance, with the production of strong flocs and low residual concentrations when the zeta potential was minimized. The overall strength of the connection points within the floc were determined by a combination of steric interactions, polymer bridging, van der Waals forces, and electrostatic forces. Hence, both dose ratio and zeta potential are important in understanding floc properties. Floc growth was dominated by dose ratio, whereas the response to elevated shear was strongly related to zeta potential. The steady-state floc size was a combination of both factors. This allowed the continued development of a qualitative model in order to engineer optimal floc properties when coagulating NOM.

Ferric Compounds↗
PubMed2006

Floc structural characteristics using conventional coagulation for a high doc, low alkalinity surface water source.

Removal of natural organic matter (NOM) is well established using metal salt coagulants. In addition, flocculant aids are also commonly used to improve solid removal. The objectives of this paper is to describe the impacts of both NOM and polymer on floc structure. The study offers a comparison of floc physical characteristics for coagulant precipitate flocs, organic-coagulant flocs and organic-coagulant-polymer flocs for optimum coagulant and polymer doses. A ferric sulphate-based coagulant was used as the primary coagulant and the polymer selected was a high molecular weight (MW) cationic polydiallyldimethylammonium chloride (polyDADMAC). Floc size, breakage, re-growth and settling characteristics were measured. Precipitate flocs were larger than organic flocs and had better settling characteristics when compared to NOM-coagulant flocs. When polymer was added, floc size and compaction was seen to further reduce. An explanation was offered in terms of the mode of flocculation involved. Floc breakage behaviour showed that polymer reduced the rate of floc degradation but did not greatly improve floc re-growth potential after breakage, which was generally poor for all of the suspensions.

Alkalies↗
PubMed2005

How the natural organic matter to coagulant ratio impacts on floc structural properties.

Periods of elevated natural organic matter (NOM) loadings at water treatment works (WTW) can lead to operational problems as a result of deterioration in floc structural quality. This study used a range of diagnostic tools to evaluate floc structure with increasing organic fraction in the floc. It was observed that when the organic fraction in the floc went significantly over a mass ratio of 1 mg of DOC to 1 mg of Fe (coagulant), the floc size, settling velocity, fractal dimension, and strength were seen to decrease even when the NOM removed during coagulation remained high. A model was proposed to explain these changes that was dependent upon the adsorption of NOM on primary particle surfaces. The operational significance of these results suggests that for the coagulant under investigation the correct coagulant dose must be applied to give good floc structure.

Ferric Compounds↗
PubMed2005

Breakage, regrowth, and fractal nature of natural organic matter flocs.

The growth, breakage, regrowth, and fractal nature of flocs was investigated by use of a laser diffraction particle sizing device. A range of coagulants were investigated for the coagulation of natural organic matter (NOM) and compared to other coagulated systems. The results showed NOM floc structural characteristics varied in steady-state size depending upon which coagulant was used. When compared to other systems, the order of floc size was Fe precipitate > Fe-NOM > latex (in NaCl solution). Floc regrowth after exposure to high shear was limited for all of the flocs under investigation other than for latex in an inert electrolyte. This highlighted differences in the internal bonding structure of flocs, with the results suggesting that physical bonds have a capacity to re-form after breakage. Fractal dimension analysis by small-angle laser light scattering (SALLS) had limited applicability to large flocs that dominated all of the systems under investigation, but the degree of compaction increased as flocs were broken in high shear. This provided a possible mechanistic reason for the irreversible breakage seen.

Alum Compounds↗