Global increases in water demand and decreases in both the quantity and quality of fresh water resources have served as the major driving forces to develop sustainable use of water resources. One viable alternative is to explore non-traditional (impaired quality) water sources such as wastewater and seawater. The current paradigm for wastewater treatment is based on technologies that are energy intensive and fail to recover the potential resources (water and energy) in wastewater. Also, conventional desalination technologies like reverse osmosis (RO) are energy intensive. Therefore, there is a need for the development of sustainable wastewater treatment and desalination technologies for practical applications. Processes based on microbial electrochemical technologies (METs) such as microbial fuel cells (MFCs), microbial electrolysis cells (MECs) and microbial desalination cells (MDCs) hold promise for the treatment of wastewater with recovery of the inherent energy, and MDCs could be used for both desalination of seawater and energy recovery. METs use anaerobic bacteria, referred to as exoelectrogens, that are capable of transferring electrons exogenously to convert soluble organic matter present in the wastewater directly into an electrical current to produce electrical power (MFC and MDC) or biogas (MEC). In my dissertation, I investigated the three types of METs mentioned above to: 1) have a better insight on the effect of 4 oxygen intrusion on the microbial community structure and performance of air-cathode MFCs; 2) improve the desalination efficiency of air-cathode MDCs using ion exchange resins (IXRs); and 3) enrich for extremophilic exoelectrogens from the Red Sea brine pool using MECs. The findings from these studies can shape further research aimed at developing more efficient air-cathode MFCs for practical applications, a more efficient integrated IXRMDC configuration that can be used as a pre-treatment to RO, and exploring extreme environments as a source of extremophilic exoelectrogens for niche-specific applications of METs.