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Process Integration

In order to exert the comprehensive advantages of CM, some process integration has been attempted.

Li et al. coupled a coal-based CM with an electric field for enhanced oily wastewater treatment. They studied the effects of factors such as electric field strength, oil-water concentration, pH value, pump speed, electrolyte concentration and electrode distance, and found a significant increase in permeate water flux and oil rejection, as well as the antifouling ability of the membranes, after integration [82].

Pan et al. conducted experimental studies aiming at enhancing the microfiltration process through applying gas-liquid two-phase flow by injecting air into a titanium dioxide suspension during its microfiltration with the tubular porous carbon membrane as microfiltration medium. Results show that the gas-liquid two-phase flow can significantly enhance the microfiltration process and cause the maximum steady permeate flux to be 62% higher; the time required for reaching steady flux was accordingly shorter than that of the single-phase flow microfiltration process [83].

Membrane Bioreactor

A membrane bioreactor has been proven effective for wastewater and biomass purification.

Liu et al. developed a CM-aerated biofilm reactor to treat synthetic wastewater. The membrane exhibited a high degree of adhesion and good permeability. Continuous experiments showed that COD and NH4+-N removal efficiency were 90 ± 2 and 92 ± 4% at removal rates of 35.6 ± 3.8 g COD/m2 per day and

9.3 ± 0.6 g NTW-N/m2 per day, respectively. Stoichiometric analysis revealed that 70-90% of the oxygen supplied was consumed by the nitrifier [84].

CMs were also tried for biomass purification by maintaining the activity of penetrants in the fields of protein ultrafiltration [61], biofuel separation through pervaporation [85], water removal from bioethanol [86] and oily wastewater treatment by microfiltration [64].

These promising applications offer a viable alternative to current membranes for separation and purification in advanced fields.

Energy Production

CMs are also applicable for fuel cell and electrocatalytic chemistry. Wang et al. [87] prepared CMs with excellent anticorrosion properties, hydropho- bicity and conductivity, aiming at the modification of the stainless-steel electrode of a proton exchange membrane fuel cell in order to improve its work efficiency. Yang et al. [88] fabricated CMs from common filter paper, which exhibited excellent electrocatalytic activities toward the oxygen reduction reaction, high tolerance of methanol crossover and durability in alkaline solution.

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