Reverse Osmosis (RO) membranes are being used to purify alternative sources of water such as recycled wastewater, brackish water and seawater. This technology is ideal as it can remove almost all substances dissolved in water including salt, microbial contaminants and organic contaminants. However, a major challenge to employing RO membranes is the increase in energy that accompanies fouling of these membranes. Fouling is the accumulation of unwanted material on solid surfaces to the detriment of function. The fouling material can consist of either living organisms (biological or biofouling) or a non-living substance (inorganic or organic). In particular, biological fouling caused by deposition and then growth of microbes in colonies known as biofilms, is a major challenge. Biofilms are difficult to prevent due to sensitivity of RO membranes to chemical disinfectants and once formed are extremely difficult to eradicate by current chemical cleaning methods. In this project the persistence of biofilms will be used to turn the biofouling problem on its head by engineering biofilms that 1) control their own thickness and 2) release molecules (signals) that prevent colonization of this engineered biofilm by other microorganisms. This biofilm will also be engineered to contribute to the removal of the contaminants that can pass through the RO membrane.
The ability to make bacteria dissolve deleterious biofilms by activating a series of genetic pathways (i.e., to secrete enzymes to remove the polymers that cement the bacteria in place and to make the bacteria swim away) has to date not been proposed for RO biofouling control. Therefore, a novel feature of this proposal is the use of metabolic engineering to create the first living membrane comprising RO membranes and a thin beneficial biofilm that will both prevent biofouling as well as remove toxic wastes in water recovery systems. To control the extent of the beneficial biofilm, the PIs will capitalize on the fact that E. coli possesses a novel diguanylate cyclase (c-di-GMP)-binding protein, BdcA. The PIs have engineered BdcA to cause biofilm dispersal. By controlling BdcA production, the extent of biofilm formation by the beneficial biofilm can be limited. The PIs also propose to demonstrate that it is possible to incorporate contaminant degrading enzymes in these beneficial biofilm bacteria to enhance removal of recalcitrant compounds.
By controlling biofilms on RO membranes, chemicals required for disinfection and cleaning will be eliminated and the overall power consumption of this critical water treatment technology will be minimized. This work is also important in terms of gaining insights on how to control biofilm formation for engineering applications, and it may provide insights for controlling biofilm formation to treat chronic diseases. For this work, at least two undergraduates/year will be trained with efforts made to recruit underrepresented groups. Research results will be disseminated to a diverse audience using YouTube as professionally-filmed, instructive videos. Finally, the ongoing water science and education camp for middle schoolers, a part of the popular Science U program at Penn State University, will be expanded from a three day program to a week and a new graduate course on membranes will be developed.
