Molecular characterization of the bacterial communities in the different compartments of a full-scale reverse-osmosis water purification plant

Abstract

The origin, structure, and composition of biofilms in various compartments of an industrial full-scale reverse-osmosis (RO) membrane water purification plant were analyzed by molecular biological methods. Samples were taken when the RO installation suffered from a substantial pressure drop and decreased production. The bacterial community of the RO membrane biofilm was clearly different from the bacterial community present at other locations in the RO plant, indicating the development of a specialized bacterial community on the RO membranes. The typical freshwater phylotypes in the RO membrane biofilm (i.e., Proteobacteria, Cytophaga-Flexibacter-Bacteroides group, and Firmicutes) were also present in the water sample fed to the plant, suggesting a feed water origin. However, the relative abundances of the different species in the mature biofilm were different from those in the feed water, indicating that the biofilm was actively formed on the RO membrane sheets and was not the result of a concentration of bacteria present in the feed water. The majority of the microorganisms (59% of the total number of clones) in the biofilm were related to the class Proteobacteria, with a dominance of Sphingomonas spp. (27% of all clones). Members of the genus Sphingomonas seem to be responsible for the biofouling of the membranes in the RO installation.

FIG. 1.

Photographs of an autopsy of fouled RO ESPA-2 spiral-wound M elements (Hydranautics ESPA). The feed side of the membrane element (A and B), the feed side of the fouled membrane (C), and the fouled plastic feed channel spacer (D) are shown. The surfaces of the membrane and spacer were completely covered with fouling layers. The fouling layer could be relatively easily scraped from the membrane surfaces (C).

FIG. 2.

Schematic diagram depicting the results of the clone library analyses performed on the samples obtained from the different functional parts of a full-scale RO plant. F was initially pretreated by the sequential application of coagulation, flocculation, sand filtration, UF, and CF processes. The two-stage RO system integrated ESPA-2 spirally wound M elements (Hydronautics ESPA) which were installed in a series inside pressure vessels.

FIG. 3.

DGGE fingerprinting of RO biofilm samples collected from a full-scale water treatment plant. Arrows with numbers indicate the positions of the identified bands.