The development of improved strategies to monitor and control biofouling of membranes in the water industry
Low, Jiun Hui
Date of Issue2016-08-31
Interdisciplinary Graduate School
The use of membranes in water treatment processes has greatly increased our global supply of portable water and helped alleviate water scarcity. However, the problem of membrane fouling, especially biofouling, continues to plague the water industry and hinders our quest in making clean water readily available to more people at lower costs. In this study, various strategies were developed and investigated in an attempt to further understand the causes of reverse osmosis biofouling, prevent or delay the onset of biofouling, and to monitor the rate of biofouling online. The effects of three main biofilm exopolysaccharides produced by Pseudomonas aeruginosa, Psl, Pel, and alginate, on RO membrane performance were investigated. Among the three, it was found that the presence of the Psl polysaccharide in P. aeruginosa biofilms contributed the most to biofilm resistance, with up to 69% faster fouling rates and 70% increase polysaccharide production, and the absence of Pel and alginate polysaccharide did not have a significant impact on P. aeruginosa biofouling, contributing to only a 3% difference in fouling rates. Nitric oxide (NO) has recently been shown to function as a signal for the dispersal of biofilms formed by a wide range of microorganisms. At the concentrations at which NO acts as a signal, it is non-toxic to bacteria and thus represents a molecule with significant potential to disperse mixed species biofilms responsible for RO biofouling based on an environmentally responsible and non-toxic approach. The efficacy NO as treatment to control fouling of RO membranes was investigated, and it was found that NO significantly reduced biofouling rates for both single and mixed species biofouling by 52% and 92% respectively, without significantly altering the community diversity of the mixed species biofilm. A complementary approach to the control of biofouling is to develop strategies to determine when fouling is occurring, but to do so at an early stage, before it is a problem so that remedial action can be implemented to control fouling. To address this, a canary cell was developed to model biofouling in an industrial spiral wound module under similar hydrodynamic conditions. Non-invasive techniques including ultrasonic time domain reflectometry and electrochemical impedance spectroscopy were also investigated as tools to provide real-time biofouling information that precedes the actual rise in transmembrane pressure such as in situ biofilm thickness measurements and changes in electrical conductivity at the membrane boundary layer, allowing for the early detection of biofouling. The findings in this study have demonstrated that alternative, non-toxic strategies can be effective in controlling biofilm and have also shown that different polysaccharides have specific roles in mediating biofouling. In addition, the development and optimization of a canary modeling technique allows for future development of sensors to monitor biofouling in RO operations.
DRNTU::Engineering::Civil engineering::Water resources