UCLA

The fundamental understanding and control of the interactions that occur between surfaces and chemicals allows us to design materials with enhanced binding and reactive properties for various industrial, environmental, and clinical applications. However, understanding and optimizing these interactions can also be used to limit the attachment and accumulation of undesirable substances and organisms to surfaces which may otherwise hinder their successful operation. This dissertation describes research on the tuning and optimization of surfaces and operating conditions for different purposes ranging from biological treatment of water and wastewater to the prevention of the undesired attachment of microbial biofilms to functional surfaces. Modification of the surface of granular activated carbon (GAC) using the cationic polymer polydialydimethyl ammonium chloride (polyDADMAC) was studied as a strategy to improve the removal of the persistent environmental contaminant class per- and polyfluoroalkyl substances (PFASs). Specifically, complex water matrices were used in these studies to simulate challenging conditions that are environmentally relevant. Amending the surface with polyDADMAC concentrations as low as 0.00025% enhanced GAC’s adsorption capacity for both short- and long-chained PFASs, even in the presence of competing ions. Regeneration with minimum disruption to the adsorbent’s structure was achieved using low-power ultrasound, supporting the consideration of polyDADMAC-modified GAC was an effective, regenerable adsorbent for real environmentally relevant water conditions. The relationships between the influent nutrient ratios in the context of wastewater treatment and the mechanisms responsible for biofilm formation were investigated. Wastewater treatment is an example of a scenario where biofilm formation may be either desirable or undesirable depending on the treatment system being employed. A comprehensive evaluation of the effect of Carbon/Nitrogen ratio in influent wastewater on biofilm characteristics and relevant mechanisms were studied. Pseudomonas aeruginosa was used as a model organism due to its widely understood biofilm formation pathways, as well as its prevalence in the environment, distribution systems, and in clinical settings. The development of a dual-species biofilm of P. aeruginosa and N. winogradskyi was also influenced by C/N, with increase in the relative abundance of the slower-growing N. winogradskyi above C/N=9. These results indicate that altering operational parameters related to C/N may be relevant for mitigating or promoting biofilm formation and function depending on the desired industrial application or treatment configuration. Despite the benefits of chemically- and biologically mediated surface modifications, microbial adhesion to surfaces can also be detrimental in the context of biofouling, which yields industrially relevant surfaces such as water treatment membranes less efficient or causes adverse patient health outcomes in clinical settings. In this context, a culture-independent biofilm quantification protocol was developed to accurately quantify cellular and extracellular components attached to medically relevant surfaces such as urinary catheters. The developed multipronged approach had validated efficacy as it was verified to accurately quantify biofilms of four pathogenic clinical isolates, two types of silicone catheters in vitro and indwelling catheters in patients. Characterization and assessment of synthesized hydrogels made of a modified chitosan/ silver nanoparticle composites showed the potential of these material for antimicrobial and antifouling purposes. Three synthesis methods were compared in terms of their effects on the physical, mechanical, and antimicrobial capabilities of the hydrogels, and evaluation showed the potential for tuning the synthesis to yield materials with different physical and mechanical properties but equally promising antimicrobial and antifouling potential. This gives rise to the possibility of using these composites in a range of industrially relevant scenarios depending on the desired characteristics for use. The quantitative understanding of factors impacting surface modifications and microbial attachment to surfaces will be valuable for improved water treatment systems as well as to limit or help guide biofilm formation on medically- and industrially relevant surfaces.