“In Search of the (Membrane) Holy Grail: A 20-Year Journey”

Mark Benjamin
Civil and Environmental Engineering, University of Washington

ABSTRACT: Natural organic matter (NOM) is universally recognized as a major foulant of membranes used for drinking water treatment. The fouling has been attributed to adsorption of NOM in membrane pores and/or to formation of a gel layer that covers the membrane surface. Colloids, humics, and polysaccharides have each been implicated as major contributors to this fouling material. Most efforts to reduce the impact of this fouling have focused on pretreatment with conventional coagulants or powdered activated carbon.
We have developed a new micron-sized, granular adsorbent by mild heating of aluminum hydroxide and demonstrated that it can adsorb NOM rapidly and more efficiently than conventional additives. In addition, a cake layer of the new adsorbent imposes very little hydraulic resistance. As a result, when these adsorbents are used as the media for precoat filtration, a substantial portion of the NOM can be removed from the feed with only a few seconds of contact time, thereby reducing DBP formation potential and also dramatically reducing the fouling of downstream membranes. Our recent research has focused identifying the chemical characteristics of the fouling fraction of the NOM, on ways to efficiently backwash the adsorbents off of the support material after their capacity to collect the contaminants has been exhausted, and on regeneration of adsorbent.
At virtually every step in the research, we have encountered unexpected and challenging issues, many of which we have overcome, but others of which we continue to struggle with. The presentation will provide an overview of the successes, the frustrations, and the excitement we still feel about the potential of this new process.