(415e) Biofouling Resistant Polypropylene Feed Spacers for Reverse Osmosis
Biofouling is the accumulation of microorganisms onto the membrane surface and on the feed spacer. Research and development of biofouling prevention has commonly focused on the pretreatment of the feed water, the improvement of cleaning solutions and procedures, and modifications to the membranes themselves. This research focuses on developing low-biofouling polypropylene (PP) feed spacers. This is particularly significant because membrane replacement due to fouling is the single largest operating cost in water separation (Escobar et al. 2005).
PP was functionalized via the addition of a spacer arm with metal chelating ligands. These ligands were charged with copper ions to allow for slow release of ions into the feed water in the membrane systems. Copper ions have been previously used to disinfect water against microbial life. In this work, functionalization of PP was achieved using a spacer arm (glycidyl methacrylate (GMA)), which was polymerized to the PP using benzoyl peroxide as a radical initiator. Iminodiacetic acid (IDA) was then added to the end of the GMA spacer arm to allow for the chelatation of the copper ions. This functionalization was chosen as the focus because these chelating ligands are quite stable and easily synthesized, operate over a diverse range of conditions, have easily controlled binding affinities, and are well suited for model studies.
Characterization of the PP modification was performed using Fourier transform infrared spectroscopic (FTIR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effects on the biological content of water in the presence of the modified spacer were tested using a synthetic water matrix of E.coli and LB broth. Both modified and unmodified spacers were contacted with the feed water for extended periods of time to allow for growth and then placed in stomacher bags where the biofilm was removed. The cells making up the biofilm were then enumerated to show the affect of the modifications, and it was determined that the modified PP displayed consistently one order of magnitude less microbial growth than the unmodified PP.
The effectiveness of the modifications was assessed through crossflow filtration experiments. Both modified and unmodified feed spacers were used with identical membranes in a full recycle mode. The feed water was dechlroniated tap water that had been supplemented with sodium acetate. Flux was measured over different time intervals, after which, the membranes were removed so that the biofilm could be quantified. The membranes that used the modified PP displayed a higher flux during operation and, again, one order of magnitude lower microbial growth as compared to the membrane that used the unmodified PP. Possible leaching of the copper from the spacer during the filtration was monitored by testing permeate and retentate by using inductively coupled plasma (ICP) spectroscopy.