Events Calendar

Astani Civil and Environmental Engineering Ph.D. Seminar

Speaker: Christopher Morrow and Ryan Gustafson, Astani CEE Ph.D. Candidates

Abstract: Towards Sustainable Wastewater Reuse: Salinity Control in Osmotic Membrane Bioreactors

By: Christopher Morrow


Alongside climate change comes an increase in drought duration and severity. In response, low energy wastewater recycling methods are becoming increasingly attractive. Our group has developed an osmotic membrane bioreactor system (OMBR) with a low energy Membrane Distillation (MD) re-concentration step driven by waste heat for potable wastewater reuse applications. A membrane bioreactor with a submerged forward osmosis (FO) module subsystem has been tested for high-strength domestic wastewater treatment. In the FO process, relatively pure water is transported from the mixed liquor into the draw solution; the mixed liquor suspended solids become concentrated and the draw solution becomes diluted. At the same time, a small amount of salt from the draw solution diffuses across the membrane from the draw solution into the mixed liquor. Consequently, bioreactor salinity increases. This reverse salt diffusion (RSD) can affect biological processes, particularly at higher concentrations. In this presentation, RSD from two membrane configurations will be evaluated; the first is a membrane cassette submerged in the bioreactor and the second is a side-stream process external to the bioreactor. In the submerged configuration, the draw solution is recirculated through a frame skinned with FO membrane and in the external configuration, both the feed and draw solutions have crossflow along the membrane selective and structural layers, respectively. Two advantages of external operation are: 1) crossflow on the feed side scours foulants away from the membrane, and 2) increasing crossflow velocity (CFV) on the draw side reduces dilutive concentration polarization. These result in increased water flux, but may also change RSD, which alters the composition of the foulant layer and/or the bioreactor salinity. Bench-scale FO experiments to determine the specific reverse salt flux (SRSF) with each configuration were carried out. The bench-scale results were used as inputs to initialize a model and predict the steady-state salt concentration of the pilot-scale bioreactor. Further analysis was carried out to examine the affect of changing the solids retention time (SRT), membrane area, and reactor volume to optimize system performance and maintain low salinity OMBRs.


TITLE: Waste-heat-driven membrane distillation (MD) and long-term hydrophobicity of MD membranes

By: Ryan Gustafson

Abstract:
Global concern regarding water scarcity, climate change, and environmental health have resulted in increased interest in new water treatment technologies, particularly technologies for water reuse and desalination applications with low electrical energy requirements. Increased interest in water reuse and environmental health have resulted in more stringent regulatory requirements for producers of industrial and municipal wastewaters. One technology poised to address these concerns is MD. MD is a thermally driven separation process that is used to distill water from an impaired feed water source using a hydrophobic membrane. Maintaining the hydrophobicity of the MD membrane is vital to maintaining the characteristic high rejection of non-volatile contaminants that is key to the application of MD to water treatment. It is though that long-term exposure of MD membranes to flowing water at high temperature and high salinity will result in reduced membrane hydrophobicity over time, but this has not been proven. Another key aspect of MD technology for its application to water treatment is its ability to be driven by low-grade waste-heat. While most MD researchers assume that low-grade waste-heat will be available and easily transferrable to the MD module, few have demonstrated successful operation of waste-heat-driven MD systems. Further, the small amount of research available on these systems lacks detailed analysis of the impacts of waste heat source variability on water production. Finally, an analysis of system-wide heat transfer behavior and the impact of different system configurations on water production in WHD-MD systems is not available in existing studies. In my presentation, I will discuss

Location: John Stauffer Science Lecture Hall (SLH) - 102

Audiences: Everyone Is Invited

Contact: Evangeline Reyes