Bacterial community structure and variation in a full-scale seawater desalination plant for drinking water production

Abstract

Microbial processes inevitably play a role in membrane-based desalination plants, mainly recognized as membrane biofouling. We assessed the bacterial community structure and diversity during different treatment steps in a full-scale seawater desalination plant producing 40,000 m(3)/d of drinking water. Water samples were taken over the full treatment train consisting of chlorination, spruce media and cartridge filters, de-chlorination, first and second pass reverse osmosis (RO) membranes and final chlorine dosage for drinking water distribution. The water samples were analyzed for water quality parameters (total bacterial cell number, total organic carbon, conductivity, pH, etc.) and microbial community composition by 16S rRNA gene pyrosequencing. The planktonic microbial community was dominated by Proteobacteria (48.6%) followed by Bacteroidetes (15%), Firmicutes (9.3%) and Cyanobacteria (4.9%). During the pretreatment step, the spruce media filter did not impact the bacterial community composition dominated by Proteobacteria. In contrast, the RO and final chlorination treatment steps reduced the Proteobacterial relative abundance in the produced water where Firmicutes constituted the most dominant bacterial group. Shannon and Chao1 diversity indices showed that bacterial species richness and diversity decreased during the seawater desalination process. The two-stage RO filtration strongly reduced the water conductivity (>99%), TOC concentration (98.5%) and total bacterial cell number (>99%), albeit some bacterial DNA was found in the water after RO filtration. About 0.25% of the total bacterial operational taxonomic units (OTUs) were present in all stages of the desalination plant: the seawater, the RO permeates and the chlorinated drinking water, suggesting that these bacterial strains can survive in different environments such as high/low salt concentration and with/without residual disinfectant. These bacterial strains were not caused by contamination during water sample filtration or from DNA extraction protocols. Control measurements for sample contamination are important for clean water studies.

Characterisation and comparison of bacterial communities on reverse osmosis membranes of a full-scale desalination plant by bacterial 16S rRNA gene metabarcoding

“…Pseudomonas has been recently identified as one of the major RO-membrane biofoulants in a large-scale desalination plant. 22 Some Pseudomonas produce sticky exopolysaccharides like alginate, which favour their attachment to membrane surfaces. 23 Pseudomonadales also migrate in aggregates of bacterial cells clumped together in an EPS matrix, which enables them to persist as secondary colonisers in a mature biofilm.…”

A review of reverse osmosis membrane fouling and control strategies

“…There are two key components of biofilms, namely the bacteria and the extracellar polymeric substances (EPS) which were excreted by bacteria during the metabolism process . In marine environment, the bacterial community is highly diverse and distinct, with proteobacteria, bacteroidetes, firmicutes and cyanobacteria being the typical ones (Belila et al, 2016;Khan et al, 2013). Depending on different water environment and bacteria community, EPS could have different substances, but are mainly made up of polysaccharides, proteins, glycoproteins, lipoproteins or lipids and nucleic acids (Drews, 2010;Matin et al, 2011;She et al, 2016).…”

“…The EPS could make the biofilm structure stronger, making it more difficult to clean the biofilm (Ben-Dov et al, 2016;Leterme et al, 2016). Also, EPS could function as a barrier to protect bacteria from bactericide (Belila et al, 2016). The final stage is the bacteria detachment, and during this period the bacteria leaves the mature biofilm due to lack of nutrients as well as the increase of population density.…”

Biofouling of FeNP-Coated SWRO Membranes with Bacteria Isolated after Pre-Treatment in the Sea of Cortez

“…Interestingly, most biofouling studies of NP coatings have been carried out with strains that are not native from seawater, such as Escherichia coli and Pseudomonas aeruginosa [20,21]. Those studies are not very useful for the desalination industry, since those strains are not ones that commonly cause RO membrane biofouling.…”