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Membrane samples were recovered from all reverse osmosis (RO) elements of the first and second stage (6elements each) of a RO unit fed with pre-treated surface water to analyse fouling layercomposition. Chemical and microbiological data were averaged based on the resultsobtained 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 tothe homogeneity of the fouling layers. Membranes from all elements were covered by athick, compact, adherent, slimy, lightly brown colored fouling layer, which containedmicrobial cells but no salt deposits, except for the last element of the second stage, where apatchy but sometimes thick layer of BaSOsub4/sub crystals was detected. Total microbial countsvaried between 10sup5/sup cells/cmsup2/sup to 10sup6/sup cells/cmsup2/sup in the elements from both stages. Viablecounts dropped from between 10sup5/sup to 10sup6/sup colony forming units/cmsup2/sup in the first two elementsof the first stage to 10sup2/sup to 10sup4/sup/cmsup2/sup in subsequent elements. Dry weight of the fouling layersvaried between 0.15 to 0.20 mg/cmsup2/sup in all elements except for elements 1 and 4 in stage 1(0.15 and 0.25 mg/cmsup2/sup, respectively). The proportion of organic matter as a percentage ofdry weight increased in the first stage from approximately 30% in the first two elements tovalues around 55% in the elements 4 to 6 and remained constant in all elements of thesecond stage. The protein content in the organic fraction decreased linearly from around70% in element 1, stage 1 to about 40% in element 6, stage 1 and remained constant at thelatter level in all elements of stage 2. The proportion of total carbohydrate in the organicfraction 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 andSr increased linearly from the lead to the rear element in stage 1 and remained constantthroughout stage 2. BaSOsub4/sub crystals were detected in significant amounts only in foulinglayers from the last element of stage 2. Includes 14 references, table, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 13File Size: 1 file , 620 KB