| 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 |
