N. Booker

THE FOULING OF MICROFILTRATION MEMBRANES BY NOM AFTER COAGULATION TREATMENT

Microfiltration membranes used in drinking-water treatment are fouled by both colloidal material and natural organic matter (NOM) present in the raw water. The relative importance of these contributions to fouling may depend on whether or not the water is pretreated before microfiltration, and on the type and extent of any pretreatment. In this study, the causes of fouling were determined for microfiltration of a surface water through a polypropylene hollow-fibre membrane. Fouling was caused by colloidal material when the raw water was filtered untreated, and by NOM when the raw water was coagulated before filtration. The components of NOM which cause fouling of microfiltration membranes are not yet well-established, and were also investigated in this study. NOM from the raw water was fractionated into four specific classes of compounds on the basis of hydrophobicity and charge. The rates of fouling by each NOM fraction were measured separately. The major contribution to fouling was attributed to the NOM fraction comprising small, neutral, hydrophilic compounds. The NOM fractions comprising humic and fulvic acids made only a minor contribution to fouling.

A permeability-controlled microfiltration membrane for reduced fouling in drinking water treatment.

A novel surface-modified polypropylene microfiltration membrane is investigated for its potential use in drinking water treatment. The flux decline rate of the modified membrane is substantially lower than the original polypropylene membrane for filtration of a soft, high-natural organic matter (NOM) surface water because a progressive adjustment in membrane permeability counteracts the flux decline due to fouling. In general, the prospects for reduced flux decline by membrane modification depend upon the characteristics of raw water such as hardness, particulate and NOM properties and concentration, and pretreatment strategies.

The Role of Organic Polyelectrolytes in High Rate Alternatives to Primary Separation

Treatment of sewage with a CDS (continuously deflective separator) unit has produced a treated effluent quality of 5 NTU and 20 mg/l TSS at hydraulic loading rates of 57 m3m-2h-1. This performance required the production of strong floes formed using high doses (10 mg/l) of a low charge density (CD), high molecular weight (MW), cationic polyelectrolyte. Laboratory experiments suggested that this dose could be reduced to 2.5 mg/l if a medium CD, very high MW, cationic polyelectrolyte was used. The laboratory tests also indicated that the concentration of residual polyelectrolyte in the treated effluent would be reduced by a factor of ten if very high MW polyelectrolytes were used.

Rapid Sewage Clarification with Magnetite Particles

As discharge standards for wastewaters have become increasingly stringent, the need for a diverse range of treatment technologies has become more urgent. Physico-chemical processes based on coagulation chemistry have been applied to wastewater treatment, and have been found especially effective for suspended solids removal. This paper describes a novel way to engineer a process based on coagulation/flocculation chemistry. The process is based on the use of very fine magnetite particles, which not only remove the necessity for an extended period of flocculation but also provide very rapid solid-liquid separation by utilisation of their magnetic properties.