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Environmental Science & Technology
Vol. 48 (22), 2014, Pages: 1315513164

Biofouling and Microbial Communities in Membrane Distillation and Reverse Osmosis

Katherine R. Zodrow , Edo Bar-Zeev , Michael J Giannetto , and Menachem Elimelech



Abstract

Membrane distillation (MD) is an emerging desalination technology that uses low-grade heat to drive water vapor across a microporous hydrophobic membrane. Currently, little is known about the biofilms that grow on MD membranes. Here, we use estuarine water collected from Long Island Sound in a bench-scale direct contact MD system to investigate the initial stages of biofilm formation. For comparison, we studied biofilm formation in a bench-scale reverse osmosis (RO) system using the same feed water. Each of these membrane desalination systems exposes the natural microbial community to vastly different environmental conditions -- high temperatures with no hydraulic pressure in MD and low temperature with hydraulic pressure in RO. Over the course of 4 days, we observed a steady decline in bacteria concentration (nearly 2 orders of magnitude) in the MD feed reservoir. Even with this drop in planktonic bacteria, one case of a 50 % flux decline in MD over 12 h with pre-filtered sea water was observed. Biofilm morphologies on MD and RO membranes were markedly different. MD membrane biofilms were heterogeneous and contained several colonies, while RO membrane biofilms, although thicker, were a homogenous mat. Phylogenetic analysis using next-generation sequencing of 16S ribosomal DNA showed significant shifts in the microbial communities. Bacteria representing the orders Burkholderiales, Rhodobacterales, and Flavobacteriales were most abundant in the MD biofilms. Based on the results, we propose two different regimes for microbial community shifts and biofilm development in RO and MD systems.

 


 
 
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