Development of a Novel Polymer-Modified Graphene Oxide Nanocomposites for Controlling Calcium Sulfate Scaling and Biofouling on Reverse Osmosis Membrane: Mechanistic Study

Abstract

Reverse Osmosis (RO) is a promising environment friendly desalination technology for clean water production. However, the performance of RO is getting affected by the mineral scaling and biofouling. During this research, various unknown interactions occurring in RO systems between minerals, microorganisms, antiscalants and antimicrobial nanomaterials were investigated. The first goal of this dissertation was to understand and investigate the calcium sulfate scaling on reverse osmosis membranes in terms of effect of different concentrations of calcium ions and effect of temperature of feedwaterfeed water. It was noted that the mineral scaling tends to increase with the increase in temperature and concentration of ions. Moreover, the results showed that the functional groups of membranes such as hydroxyl and carboxyl, tend to interact with gypsum during scaling. To investigate the interaction of seawater microorganisms with antiscalants and with calcium sulfate, various bacterial strains were isolated and identified from Gulf seawater. The identification results showed that the isolated bacteria include Halomonas aquamarina, Pseudomonas fragi, Pseudomonas stutzeri and others. It was noted that the bacterial strains have the capability to utilize antiscalants as a carbon and energy source, thereby, degrading them and making them ineffective against scaling. Moreover, the isolated bacterial strains were also found to be capable of mediating/inducing calcium sulfate precipitation on RO membranes. The results of these interactions showed that microorganisms may enhance mineral scaling via (i) biodegradation of antiscalants and (ii) biomineralization of calcium sulfate. Therefore, it is important to modify RO membranes to tackle both mineral scaling and biofouling, simultaneously. In this research, the polyamide RO membranes were modified with antimicrobial nanomaterial (graphene oxide) and polymer antiscalants to improve the surface characteristics of RO membranes and to give rise to antifouling characteristics in membranes. The results showed that the newly modified membranes have the capability to control calcium sulfate scaling. In addition, the antibiofouling tests performed through determining bacteriostasis rates also showed that the modified membranes inhibited the growth of bacteria. Overall, the results of this research provided in-depth information about various interactions occurring in RO systems and demonstrated the potential of membrane modification technique to control various types of membrane fouling, simultaneously