(665d) Evaluating Pretreatment Technologies to Mitigate Fouling/Scaling in Membrane Distillation

Membrane distillation (MD) is a thermally-driven membrane-based technology that has attracted attention for treating high-salinity wastewater, such as produced water streams resulted from unconventional oil and gas explorations. Lower operating temperature compared to other conventional distillation-based technologies, the potential to harvest low-grade heat and integrate with renewable resources, and modularity of membrane units are some of the attractive features that can make MD a cost-effective technology for treating high-salinity water streams in distributed locations. Currently, there are two major challenges preventing MD from commercialization: 1) low energy efficiency and 2) fouling/scaling. Energy efficiency can be improved by intensifying MD and by designing better heat integration technologies. Fouling is a known to be a more challenging issue. Without addressing fouling/scaling issue properly, not only the maintenance cost will increase but also the whole treatment may fail in a short time.

Fouling could be mitigated by designing better membranes (engineering the materials and the surface) or by designing proper pretreatment technologies. The former is extensively studied, while the latter is rarely studied for MD applications. There is a need to better understand the fouling mechanism, foulants, and scaling materials in MD. Additionally, designing cost-effective pretreatment approaches to treat high-salinity water is critical. In this presentation, we discuss our efforts to alleviate the fouling and scaling in MD. To enhance fouling, we decided to choose vacuum MD (VMD); high salinity produced water from Permian Basin was utilized as the wastewater. Different pretreatment methods, including flocculation, electrocoagulation, filtration, acidification, accelerated precipitation, as well as combined treatments were investigated. Long-term VMD tests were carried out and membranes were characterized after filtration tests to characterize foulants. We will provide a preliminary techno-economic analysis of the pretreatment technologies studied in our efforts.