Biofilm Characterization and Prevention in Engineered Systems

A major challenge for engineered systems is biofilm formation and growth, or biofouling. Affected systems include water distribution and treatment systems, ship hulls, and medical devices. In water treatment membrane systems, biofilms grow in membrane modules, decreasing membrane efficiency and shortening membrane life. Often, oxidants are used as disinfectants. Although these compounds kill microorganisms, they create carcinogenic disinfection byproducts. Additionally, with increasing water scarcity, the implementation of oxidant-sensitive thin-film composite (TFC) polyamide reverse osmosis (RO) and forward osmosis (FO) membranes for water desalination and waste water reuse is growing. Thus, many conventional solutions are not available for biofouling control.;Given the wide array of biofouling challenges, fundamental study of biofilms and biofilm prevention is needed. In this dissertation, we explore the prevention of biofouling in aquatic systems using two different methods --- contact killing and controlled release --- examining the use of both novel nanomaterials and natural antimicrobial compounds. We show that the toxicity of metallic single-walled carbon nanotubes (SWNTs) is related to their ability to oxidize compounds. Additionally, we demonstrate the effectiveness of composite materials that incorporate copper nanoparticles and plant-derived natural antimicrobial compounds. In order to deliver hydrophobic and hydrophilic antimicrobial compounds to a TFC polyamide membrane surface, a controlled-release platform was developed. This work has expanded the set of tools available for biofilm prevention.;Although much is known about biofouling in both RO and FO, very little is known about biofouling in membrane distillation (MD) --- a process that uses a vapor pressure difference across a water-excluding hydrophobic membrane. In this work, we characterize biofouling in MD with a natural sea water feed. We see that although ∼ 99 % of the bacteria in the feed reservoir die due to temperature related inactivation, a robust biofilm forms on the membrane surface in as little as 4 d. Additionally, in some cases, fouling resulted in a flux decline of 50 % in just 12 h. This study expands our knowledge of biofouling in MD and identifies key organisms present in the MD biofilm.;Novel contributions of this work include: (1) demonstration of enhanced inactivation of E. coli by metallic SWNTs; (2) development of a method for binding biocidal copper nanoparticles to a membrane surface; (3) demonstration of natural antimicrobial compounds in biodegradable thin films; (4) development of a method for encapsulating antimicrobial agents and covalently binding these capsules to polyamide TFC membranes; (5) demonstration of proper biofilm sample preparation for accurate biofilm evaluation and measurement; and (6) identification of key microbial community members in MD.