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

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.

Thumb reconstruction without formal pollicization in mirror hand deformity: a series of four cases.

Thumb reconstruction in mirror hands is usually done by pollicization. However, objective pinch strength and power grip data in mirror hands following pollicization are lacking. Alternative thumb reconstruction techniques include doing nothing, rotation osteotomy or syndactylization of the radial digits. In this article, we report a series of four cases of mirror hand deformity where the thumb was not reconstructed by formal pollicization. Two cases had non-classic mirror hand deformity (the forearm contained a radius and an ulna) and the other two had classic ulnar dimelia. In all cases, thumb reconstruction was done by keeping one of the radial fingers in place (without pollicization) as the new thumb; and then (if required) performing a secondary osteotomy procedure to rotate the new thumb into pronation. The four cases were recalled back to the clinic for functional assessment at ages 20 years, 5 years, 4 years and 2 years, respectively. The overall hand function was considered 'fair' in the case with concurrent unique features, and was considered 'excellent' in the other three cases. It was concluded that the technique of thumb reconstruction used in the current series is an acceptable option. However, objective measurements, especially with regards to pinch strength and power grip, need to be compared with the pollicization technique.