ABSTRACT
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.
Subject(s)
Water Purification/methods , Water Supply , Animals , Bacteria , Cryptosporidium , Eukaryota , Filtration , Flocculation , Membranes, Artificial , Organic Chemicals , Permeability , Pest Control , Polypropylenes , Water MovementsABSTRACT
Natural organic matter (NOM) plays a significant role in fouling microfiltration membranes in drinking water treatment processes even though the NOM is retained only to a small extent. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed using 0.22 microm hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) membranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM ( > 30 kDa) was responsible for the major flux decline. Filtration tests on the four fractions of NOM isolated on the basis of hydrophobicity and charge using non-functionalised and anionic resins revealed that the fouling potential for the three waters was hydrophilic neutral > hydrophobic acids > transphilic acids > hydrophilic charged. The low-aromatic hydrophilic neutral compounds were the main determinant of the rate and extent of flux decline. This was linked to the colloidal size fraction ( > 30 kDa) and to the selective concentration of calcium in the fraction leading to organics-Ca2+ bridging. It was also shown that the higher the aromaticity of the NOM the greater the flux decline, and the aromatics mainly resided in the hydrophobic acids fraction. Overall, the fouling mechanism controlling the flux decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane.
Subject(s)
Membranes, Artificial , Organic Chemicals/analysis , Water Purification/methods , Adsorption , Colloids , Filtration , Quality Control , Resins, Plant/chemistry , Water MovementsABSTRACT
Battery operated laryngoscopes have two types of switching, one of which could cause an external spark. Laryngoscopes normally supply 2.8 volts and 0.67 amps, which theoretically gives ample energy for ignition of a cyclopropane/oxygen mixture. Attempts were unsuccessful to ignite a stoichiometric mixture of 17% cyclopropane in oxygen by breaking resistive circuits having up to 5.8 volts and 9.2 amps. It appears extremely unlikely that the common battery-powered laryngoscope can ignite a flammable mixture by sparking when being switched off.
