Abstract
One of the biggest challenges for direct contact membrane distillation (DCMD) in treating wastewater from flue gas desulfurization (FGD) is the rapid deterioration of membrane performance resulting from precipitate fouling. Chemical pretreatment, such as lime-soda ash softening, has been used to mitigate the issue, however, with significant operating costs. In this study, mechanical vibration of 42.5 Hz was applied to lab-scale DCMD systems to determine its effectiveness of fouling control for simulated FGD water. Liquid entry pressure and mass transfer limit of the fabricated hollow fiber membranes were determined and used as the operational constraints in the fouling experiments so that the observed membrane performance was influenced solely by precipitate fouling. Minimal improvement of water flux was observed when applying vibration after significant (~16%) water-flux decline. Initiating vibration at the onset of the experiments prior to the exposure of foulants, however, was promising for the reduction of membrane fouling. The water-flux decline rate was reduced by about 50% when compared to the rate observed without vibration. Increasing the module packing density from 16% to 50% resulted in a similar rate of water-flux decline, indicating that the fouling propensity was not increased with packing density in the presence of vibration.
Highlights
The bulk of the U.S water demand has been satisfied by a combination of surface water and fresh groundwater
This study focused on polyvinylidene fluoride (PVDF)-based Membrane distillation (MD) hollow fiber membranes (HFM) that can be fabricated using nonsolvent induced phase separation (NIPS) through the dry jet-wet spinning process
The objective of this research was to investigate the feasibility of replacing lime-soda ash softening with low-cost mechanical vibration for the control of membrane fouling resulting from the precipitation of Ca2+ in direct contact membrane distillation (DCMD) used for flue gas desulfurization (FGD) wastewater reclamation
Summary
The bulk of the U.S water demand has been satisfied by a combination of surface water and fresh groundwater. Unconventional water resources, such as reclaimed wastewater and brackish groundwater, have become increasingly more important to make up the deficiency [1,2]. Membrane distillation (MD) is a desalination process that relies on vapor pressure gradients across a hydrophobic, microporous membrane to drive the production of distilled water, and can be used for the treatment of these unconventional water sources. This process is suited for locations where low-cost energy (e.g., waste heat or geothermal energy) is readily available. For FGD using wet scrubbers, the water consumption rate was estimated to be about
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