Membrane samples were recovered from all reverse osmosis (RO) elements of the first and second stage (6
elements each) of a RO unit fed with pre-treated surface water to analyse fouling layer
composition. Chemical and microbiological data were averaged based on the results
obtained from analysis of samples from 5 different membrane leaves from each element,
but electron microscopy was performed on a single membrane sample per element due to
the homogeneity of the fouling layers. Membranes from all elements were covered by a
thick, compact, adherent, slimy, lightly brown colored fouling layer, which contained
microbial cells but no salt deposits, except for the last element of the second stage, where a
patchy but sometimes thick layer of BaSO<sub>4</sub> crystals was detected. Total microbial counts
varied between 10<sup>5</sup> cells/cm<sup>2</sup> to 10<sup>6</sup> cells/cm<sup>2</sup> in the elements from both stages. Viable
counts dropped from between 10<sup>5</sup> to 10<sup>6</sup> colony forming units/cm<sup>2</sup> in the first two elements
of the first stage to 10<sup>2</sup> to 10<sup>4</sup>/cm<sup>2</sup> in subsequent elements. Dry weight of the fouling layers
varied between 0.15 to 0.20 mg/cm<sup>2</sup> in all elements except for elements 1 and 4 in stage 1
(0.15 and 0.25 mg/cm<sup>2</sup>, respectively). The proportion of organic matter as a percentage of
dry weight increased in the first stage from approximately 30% in the first two elements to
values around 55% in the elements 4 to 6 and remained constant in all elements of the
second stage. The protein content in the organic fraction decreased linearly from around
70% in element 1, stage 1 to about 40% in element 6, stage 1 and remained constant at the
latter level in all elements of stage 2. The proportion of total carbohydrate in the organic
fraction of about 3% was the same in all elements of both stages. The content of O, S, P, Si,
Fe and Al was similar in the inorganic fractions of foulant layers from all elements. Ba and
Sr increased linearly from the lead to the rear element in stage 1 and remained constant
throughout stage 2. BaSO<sub>4</sub> crystals were detected in significant amounts only in fouling
layers from the last element of stage 2.
Includes 14 references, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 620 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 13 |
| Published : | 03/01/2005 |
