Low-pressure Ultrafiltration Research Articles

Effect of pre-coagulation on mitigating irreversible fouling during ultrafiltration of a surface water

Membrane fouling can be divided into two types: reversible fouling and irreversible fouling. The former can be easily canceled by physical cleaning (e.g., backwashing) while the latter needs chemical cleaning to be mitigated. For more efficient use of membranes, the control of irreversible membrane fouling is of importance. In this study, the effectiveness of pre-coagulation/sedimentation on irreversible membrane fouling was investigated, based on the pilot-scale operation of the membrane unit installed at an existing water purification plant. The membrane employed was a low-pressure ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cut-off of 750,000 daltons. Although pre-coagulation/ sedimentation significantly mitigated membrane fouling mainly through the reduction of reversible membrane fouling, the degree of irreversible fouling was not reduced by the pre-treatment. This was because the irreversible fouling observed during this study was mainly attributed to polysaccharides/protein like fractions of organic substances that cannot be efficiently removed by coagulation/sedimentation. Aluminium used as coagulant was thought to cause irreversible fouling to some extent but did not in the pilot operation, which could probable be explained by the fact that coagulation was conducted at relatively high pH (7.0) in this study.

A low pressure ultrafiltration membrane system for potable water supply to developing communities in South Africa

Three pilot studies were performed in different areas of South Africa, demonstrating that particulate and colloidal turbidity can be reduced to acceptable levels. By operating at a static manifold pressure of between 100 and 140 kPa and a constant flux of 30–40 l/m 2.h, up to 85% removal of NOM and >90% reduction in colour was observed. No microbiological indicator organisms were detected in any of the permeate samples analyzed. During the operation of the membranes for more than 3 years, a loss of only 5% of membrane area was experienced, and a membrane life of >5 years can therefore be expected. The use of polysulphone ultrafiltration capillary membranes at a low operating pressure is able to remove natural organic matter, reduce organic colour (humic and fulvic substances) and partially disinfect the water. Ultrafiltration provides a simple and effective means for the production of potable water for small communities.

Low-pressure ultrafiltration of sucrose and raffinose solutions with anisotropic membranes

Low-pressure ultrafiltration of sucrose and raffinose solutions with anisotropic membranes

Sustained action of injected chelating agents.

Low-pressure ultrafiltration techniques were used to study the unusual effects of ethylenediaminetetraacetic (EDTA) and diethylenetriaminepentaacetic (DTPA) acids on the elimination of radioactive metals from animals. The Ca salt of DTPA was injected into rats 3 days after an injection of Pu/sup 239/, and the ultrafilterability of Pu from the bone, liver, and plasma was measured after killing the rats at intervals of 1, 2, 3, and 7 days after injection. The results show that the diffusibility of Pu remains > 10x greater than that of control animals for at least 7 days. DTPA was compared with EDTA by addition to blood samples taken from rats 15 min after Pu injection; at chelate concentrations of 10/sup -6/ to 10/sup -5/ M, DTPA was found to be more effective in increasing the % ultrafiltered Pu. The ultrafiltration of Sr in blood was also studied and found to be identical with that of controls up to 2 x 10/sup -2/ M EDTA, a concentration unattainable in the blood of living animals. Experiments similar to those with Pu were made with Th/sup 234/ and gave similar results, DTPA again being superior to EDTA. (D.L.C.)