Biofilm Formation on Reverse Osmosis Membranes Is Initiated and Dominated by Sphingomonas spp

Abstract

In the water production industry, reverse osmosis (RO) membrane technology is a durable, promising, and much-used separation method. Its application enables the efficient removal of a wide variety of contaminants (i.e., microbial constituents, total dissolved solids, and organic compounds). Feed streams of different qualities (e.g., raw, natural, chemically contaminated or brackish, and seawater) are used to produce high-purity water that is microbiologically safe and biologically stable (15,25). However, the widespread application of this technology is limited because the current generation of RO filtration units experience biofouling problems (14). The design of so-called "spiral wound" membrane elements and the conditions at the membrane, feed-side spacer, and other internal surfaces within these RO filters make them prone to microbial attachment and the subsequent formation of biofilm layers. A variety of microorganisms are involved in the development of these surface-attached complex structures after prolonged operation of the RO system, depending on the type and concentration of contaminants in the feed water and the type of pretreatment (5,6,7,32,38). The biofilm occurrence is a principal problem for proper RO system performance. It can lead to blocking of the feed concentrate channel and to clogging of the membrane. Biofilm formation results in an increased energy requirement of the feed water pumps, a lower flux, and a decrease of permeate quality

The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes

“…In terms of microbial species, the work of Bereschenko et al found that members of the genus Sphingomonas played a very important role in the initial formation and subsequent maturation of biofilms on RO membrane [27,28]. Because they are facultative oligotrophs, they are metabolically well adapted to a low-carbon environment and can proliferate under conditions of limited substrates.…”

“…Bereschenko et al [27] used flow cells connected in parallel to a full-scale RO system to monitor microbial biofilm formation. This approach allowed investigation of microbial biofilms under conditions similar to those in the full-scale RO system.…”

Membrane Fouling and Chemical Cleaning in Three Full-Scale Reverse Osmosis Plants Producing Demineralized Water

“…Biofouling is a major type of fouling at this location, which was confirmed by SEM observations (data not shown) showing microorganisms embedded in a polymeric matrix. Location III, very frequently associated with biofouling problems [20][21][22][23], showed no CFU plate counts and ATP concentrations were very low ( Figure 5). However, 20 days prior to membrane autopsy, an emergency CIP (Table 1 and Figure 3) with oxalic acid had to be performed due to a leak in the UF system (Supplementary Figure S1.3), which possibly explains the very low biomass parameters.…”

“…An inorganic precipitation or scaling layer in contrast would reveal a sandpaper-like structure on the membrane surface. Furthermore, at location III, biofouling was reported in earlier studies and several biofouling key studies were performed at this location [20][21][22][23]. To differentiate between organic fouling and biological fouling, TOC, polysaccharides, proteins, and CFU measurements ( Figure 5) and SEM were performed.…”

“…At locations II and III, the low pH cleaning is performed with a commercial mixed acid detergent, intended to improve foulant solubility. At location III, which has been extensively studied for its biofouling problems [20][21][22][23], sodium bisulfite is used during the high pH cleaning in order to achieve anoxic conditions and improved microbial inactivation. The volumetric flow rate during cleaning at all locations is 9 m 3 h −1 for each membrane vessel in the first stage.…”