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Biofouling of reverse osmosis (RO) membranes is a major impediment in both wastewater reuse and desalination of sea/brackish waters. A benefit to the industry would be a simple screening approach to evaluate biofouling resistant RO membranes for their propensity to biofoulants. To observe the relationship between initial membrane productivity and control of biofilm formation governed by surface modification to the aromatic polyamide thin-film composite RO membranes, three different RO membranes developed by the FilmTec Corporation including FilmTec's commercial membrane BW30 (RO#1) and two experimental membranes (RO #2 and #3) were used. RO #2 and RO #3 were modified with a proprietary aliphatic group and with an extra proprietary aromatic group, respectively. Membrane swatches were fixed on coupons in rotating disk reactor systems without filtration and exposed to water with indigenous organisms supplemented with 1.5 mg/L organic carbon under continuous flow. After biofouling had developed, the membranes were sacrificed and subjected to several analyses. Staining and epifluorescence microscopy revealed more cells on RO #2 and #3 compared to RO #1. Based on image analysis of 5-μm thick stained biofoulant cryo-sections, the accumulation of hydrated biofoulants on RO #1 and #3 were from 0.87 to 1.26 μm/day, which was lower than that on RO#2 (2.19 μm/day). Biofoulants increased the hydrophobicity of RO #2 to the greatest amount, up to 32°, as determined by contact angle. In addition, a wide range of changes of the chemical elements of the RO surfaces was observed with X-ray photoelectron spectroscopy analysis. RO #2 with the highest initial membrane productivity showed the poorest biofouling resistance. A combination of these novel approaches showed good agreement and suggested that membrane productivity, heterogeneity of anti-biofouling agents on membrane surface, stability of surface chemical elements and the role of virgin RO surface hydrophobicity should be jointly considered during the development of anti-biofouling polyamide thin-film RO surfaces.

This review summarizes the microbial mechanisms responsible for removal of carbon, nitrogen. and sulfur compounds in treatment wetlands (TWs) and identifies, categorizes and compares various techni ...

The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) application rate on microbial community structure and on the diversity of dominant 2,4-D degrading bacteria in an agricultural soil was examined using cultivation-independent molecular techniques coupled with traditional isolation and enumeration methods. Fingerprints of microbial communities established under increasing concentrations of 2,4-D (0-500 mg kg-1) in batch soil microcosms were obtained using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene segments. While a 2,4-D concentration of at least 100 mg kg-1 was required to obtain an apparent change in the community structure as visualized by DGGE, the greatest impact of 2,4-D concentration occurred in the 500 mg kg-1 treatment, resulting in significantly reduced diversity of the dominant populations and enrichment by Burkholderia-like populations. The greatest diversity of 2,4-D degrading isolates was cultivated from the 10 mg kg-1 treatment, indicating that under these conditions, cultivation was more sensitive than DGGE for detecting changes in community structure. Most of these isolates harbored homologs of Ralstonia eutrophus JMP134 and Burkholderia cepacia tfdA catabolic genes. Results from this study revealed that agriculturally relevant application rates of 2,4-D may provide a temporary selective advantage for organisms capable of utilizing 2,4-D as a carbon and energy source.

Ultra-clean sampling methods and approaches typically used in pristine environments were applied to quantify concentrations of Hg species in water and microbial biomass from hot springs of Yellowstone National Park, features that are geologically enriched with Hg. Microbial populations of chemically-diverse hot springs were also characterized using modern methods in molecular biology as the initial step toward ongoing work linking Hg speciation with microbial processes. Molecular methods (amplification of environmental DNA using 16S rDNA primers, cloning, denatured gradient gel electrophoresis (DGGE) screening of clone libraries, and sequencing of representative clones) were used to examine the dominant members of microbial communities in hot springs. Total Hg (THg), monomethylated Hg (MeHg), pH, temperature, and other parameters influential to Hg speciation and microbial ecology are reported for hot springs water and associated microbial mats. Several hot springs indicate the presence of MeHg in microbial mats with concentrations ranging from 1 to 10 ng g 1 (dry weight). Concentrations of THg in mats ranged from 4.9 to 120,000 ng g 1 (dry weight). Combined data from surveys of geothermal water, lakes, and streams show that aqueous THg concentrations range from l to 600 ng L 1 . Species and concentrations of THg in mats and water vary significantly between hot springs, as do the microorganisms found at each site. � 2006 Published by Elsevier Ltd.

Sources of variation in scoring bands in arbitrarily primed PCR (AP PCR) fingerprints of bacterial isolates were identified, and their effect on computer matching of fingerprints was determined. E. coli and five Salmonella serotypes were fingerprinted. PCR reactions and gel electrophoresis analysis of PCR products were replicated, including comparisons in the same gel and in different gels. Bands in the images were assigned by two different people on a presence–absence basis. Variations in scoring the images occurred at all levels, and prevented correct identification of isolates. E. coli was distinguished from Salmonella, but discrimination among different Salmonella serotypes and between two isolates of the same serotype was poor. Our results suggest that computer analysis of AP PCR fingerprints scored on a presence–absence basis may not correctly match isolates. Side-by-side visual comparison of isolates is recommended.