Upon impact: the fate of adhering Pseudomonas fluorescens cells during nanofiltration

Impacts of biofouling on the removal of pharmaceutically active compounds by a nanofiltration membrane

The impacts of biofouling on the retention of pharmaceutically active compounds (PhACs) by a commercially available nanofiltration membrane (NF 270) were systematically studied. Biofouling was achieved through inoculating live and dead Pseudomonas aeruginosa into artificial wastewater. In comparison to a clean membrane, an increase in PhAC rejection during biofouling with live cells was observed. However, the rejection behaviors presented more complex changes during biofouling with dead cells: PhAC rejection was below the clean membrane in the early biofouling stage; however, in the later stage, PhAC rejection was above the clean membrane. In addition, PhAC rejection behaviors present the similar tendency as salt rejection under both biofouling conditions. In addition, solute rejections were much lower for biofouling with dead cells than those for biofouling with live cells. Combined with biofilm characterization under both biofouling conditions, we could conclude that biofilm enhanced osmotic pressure (BEOP) due to higher cell counts and biofilm thickness led to a decrease in PhAC retention, especially for the dead cells. In addition, more dominant steric exclusion in the later stage of biofouling due to higher extracellular polymeric substances (EPS) concentration on the membrane surface resulted in an increase in PhAC retention.

Flow cytometry applications in water treatment, distribution, and reuse: A review

Ensuring safe and effective water treatment, distribution, and reuse requires robust methods for characterizing and monitoring waterborne microbes. Methods widely used today can be limited by low sensitivity, high labor and time requirements, susceptibility to interference from inhibitory compounds, and difficulties in distinguishing between viable and non-viable cells. Flow cytometry (FCM) has recently gained attention as an alternative approach that can overcome many of these challenges. This article critically and systematically reviews for the first time recent literature on applications of FCM in water treatment, distribution, and reuse. In the review, we identify and examine nearly 300 studies published from 2000 to 2018 that illustrate the benefits and challenges of using FCM for assessing source-water quality and impacts of treatment-plant discharge on receiving waters, wastewater treatment, drinking water treatment, and drinking water distribution. We then discuss options for combining FCM with other indicators of water quality and address several topics that cut across nearly all applications reviewed. Finally, we identify priority areas in which more work is needed to realize the full potential of this approach. These include optimizing protocols for FCM-based analysis of waterborne viruses, optimizing protocols for specifically detecting target pathogens, automating sample handling and preparation to enable real-time FCM, developing computational tools to assist data analysis, and improving standards for instrumentation, methods, and reporting requirements. We conclude that while more work is needed to realize the full potential of FCM in water treatment, distribution, and reuse, substantial progress has been made over the past two decades. There is now a sufficiently large body of research documenting successful applications of FCM that the approach could reasonably and realistically see widespread adoption as a routine method for water quality assessment.

Dynamics of silver elution from functionalised antimicrobial nanofiltration membranes

In an effort to mitigate biofouling on thin film composite membranes such as nanofiltration and reverse osmosis, a myriad of different surface modification strategies has been published. The use of silver nanoparticles (Ag-NPs) has emerged as being particularly promising. Nevertheless, the stability of these surface modifications is still poorly understood, particularly under permeate flux conditions. Leaching or elution of Ag-NPs from the membrane surface can not only affect the antimicrobial characteristics of the membrane, but could also potentially present an environmental liability when applied in industrial-scale systems. This study sought to investigate the dynamics of silver elution and the bactericidal effect of an Ag-NP functionalised NF270 membrane. Inductively coupled plasma-atomic emission spectroscopy was used to show that the bulk of leached silver occurred at the start of experimental runs, and was found to be independent of salt or permeate conditions used. Cumulative amounts of leached silver did, however, stabilise following the initial release, and were shown to have maintained the biocidal characteristics of the modified membrane, as observed by a higher fraction of structurally damaged Pseudomonas fluorescens cells. These results highlight the need to comprehensively assess the time-dependent nature of bactericidal membranes.