Synergistic Effects of Microwave Radiation and Nanocarbon Immobilized Membranes in the Generation of Bacteria-Free Water via Membrane Distillation

Abstract

In this study, we introduce microwave-induced membrane distillation (MIMD) where microwave radiation is applied not only to heat water but also to enhance the biocidal effects of nanocarbon immobilized membranes. The three types of membranes used in this study were carbon nanotube immobilized membranes (CNIM), one functionalized with carboxylated nanotubes (CNIM-COOH), and graphene oxide immobilized membrane (GOIM). The membrane performances were evaluated based on the production of water vapor flux and the percentage cell growth inhibition due to the combined effect of microwaves and nanocarbon membranes. These combinations were most effective at a temperature of 80 and 60 °C for the removal of thermophilic and mesophilic cells, respectively. Under microwave heating, the CNIM exhibited the maximum biocidal effect (99.6% for thermophilic and 95.5% for mesophilic cells) followed by CNIM-COOH (92.3% for thermophilic and 65.8% for mesophilic cells) and GOIM (90.1% for thermophilic and 59.4% for mesophilic cells). They were all higher than a plain poly(tetrafluoroethylene) (PTFE) (82.3% for thermophilic and 41.6% for mesophilic cells) membrane without nanocarbons. In MIMD, the biocidal performance as well as the flux were improved due to thermal and nonthermal factors of microwave irradiation. The latter caused higher cell destruction due to the interaction of the microwave with the cellular matter, an improved water vapor flux (30−40%) due to localized superheating, and enhanced hydrogen bonding breakdown of water molecules. Furthermore, MIMD required much lesser (20−25%) energy than conventional MD to carry out the experiments under the same conditions.

Selective Recovery of Ethyl Acetate by Air-Sparged Membrane Distillation Using Carbon Nanotube-Immobilized Membranes and Process Optimization via a Response Surface Approach

“…Membrane distillation (MD) is an effective separation method for removing organic solvents from aqueous media. , In MD, a porous hydrophobic membrane selectively transport vapor molecules through the pores while repelling the liquid phase. − MD offers several advantages in solvent recovery over classical distillation, including lower operating temperatures (well below the boiling point) and lower capital investment. − Furthermore, the heat required in MD can be obtained from alternative energy sources such as solar energy or microwave to make it more energy-efficient. MD can be easily integrated with other membrane processes including ultrafiltration, pervaporation (PV), and RO. − …”

Enhanced Recovery of Aviation Biofuel Precursor Isoprenol Using Nanocarbon-Immobilized Membrane-Based Membrane Distillation

“…However, 5 carbon alcohols have not been studied using membrane distillation. MD uses a partial vapor pressure gradient between the feed and permeate sides as the driving force to transport vapor molecules across the membrane, with a hydrophobic liquid/membrane interface utilized to prevent membrane wetting and pore blocking. − The key benefits of MD include its operation at atmospheric pressure and relatively low temperature (30–75 °C), high nonvolatile species rejection, and relatively low rates of membrane fouling. , …”

“…18−20 The key benefits of MD include its operation at atmospheric pressure and relatively low temperature (30−75 °C), high nonvolatile species rejection, and relatively low rates of membrane fouling. 21,22 The membrane is one of the most critical components in MD, since it has a direct impact on separation efficiency. 23,24 In organic recovery via MD, the membrane−solvent interaction plays an important role in permeation rate through membrane pores.…”

Recent Advancements in the Recovery and Reuse of Organic Solvents Using Novel Nanomaterial-Based Membranes for Renewable Energy Applications

“…Table 1 lists the advantages and disadvantages of various solvent recovery processes. Membranes have mostly been used in gas separation and water purification [ 6 , 7 , 8 , 9 , 10 , 11 ]. However, up until now, using conventional membranes to separate various organic solvents from fermentation broth remains a challenge, mainly due to the chemical instability of conventional polymeric membranes in organic solvents as well as the high solubility of these organic solvents in water [ 12 , 13 ].…”