In-situ cathodic electrolysis coupled with hydraulic backwash inhibited biofilm formation on a backwashable carbon nanotube membrane.

Electro-coupled membrane filtration (ECMF) is an innovative and green technology for water and wastewater treatment. However, the dynamics of biofouling development in the ECMF system has yet been determined. This fundamental question was systematically investigated in this study through laboratory dead-end ECMF experiments. It was found that the ECMF process with an applied voltage of 3 V and a backwash interval of 60 min was capable of completely eradicating membrane biofouling in an extended filtration time of 1450 min. In contrast, membrane biofouling was much severer with a longer backwash interval of 720 min or without backwash. The complemental permeate analysis and membrane characterization results revealed that biofouling during ECMF involved two sequential stages. During the first stage, dead bacteria and their degradation debris formed a loose deposit layer on the membrane surface. The continuous accumulation of this layer decreased the electrochemical performance of the membrane cathode. As such, bacteria in the top deposit layer proliferated and secreted extracellular polymeric substances, which led to irreversible fouling in the second stage. Therefore, timely removal of the initial deposit layer by hydraulic backwash was crucial in preventing irreversible membrane biofouling. These findings provided novel insights into the synergistic effects of cathodic electrolysis and hydraulic backwash for biofouling mitigation.

Refractory fluorescent dissolved organic matter in conventional and membrane-based drinking water treatment processes.

Fluorescent dissolved organic matter (fDOM) has been generally considered a refractory DOM component for drinking water treatment. However, this judgement is made without clear understandings on the removal behaviors of individual fDOM fractions. Therefore, the removals of high, medium and low molecular weight (MW), as well as hydrophobic fDOM fractions in a natural surface water were determined in this study for selected bench- and full-scale water treatment processes. The results showed that low MW (<1000 Da) and hydrophobic fractions of protein-like fDOM were more refractory than other fractions and even released during coagulation and ozonation processes. The corresponding removal efficiencies ranged -25.7%-68.6%. Besides, similar-sized, tyrosine- and tryptophan-like fDOM (F-Tyr and F-Trp) fractions exhibited distinct removal behaviors. Coagulation and powdered activated carbon (PAC) adsorption were ineffective in removing both types of fractions. Ozonation and ion exchange (IX) more effectively removed F-Trp, while F-Tyr fractions were more prone to nanofiltration (NF). Moreover, the integration of coagulation and IX pretreatment moderately enhanced F-Trp removal, but not F-Tyr removal by NF. However, the release of protein-like substances during ozonation, coagulation, and activated carbon-sand filtration adversely affected fDOM removal in a full-scale treatment plant. These findings highlighted the persistency of protein-like fDOM fractions in drinking water treatment processes.

Preparation and characterization of flame retardant n-hexadecane/silicon dioxide composites as thermal energy storage materials.

Flame retardant n-hexadecane/silicon dioxide (SiO(2)) composites as thermal energy storage materials were prepared using sol-gel methods. In the composites, n-hexadecane was used as the phase change material for thermal energy storage, and SiO(2) acted as the supporting material that is fire resistant. In order to further improve flame retardant property of the composites, the expanded graphite (EG) was added in the composites. Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) were used to determine chemical structure, crystalloid phase and microstructure of flame retardant n-hexadecane/SiO(2) composites, respectively. The thermal properties and thermal stability were investigated by a differential scanning calorimeter (DSC) and a thermogravimetric analysis apparatus (TGA), respectively. The SEM results showed that the n-hexadecane was well dispersed in the porous network of the SiO(2). The DSC results indicated that the melting and solidifying latent heats of the composites are 147.58 and 145.10 kJ/kg when the mass percentage of the n-hexadecane in the composites is 73.3%. The TGA results showed that the loading of the EG increased the charred residue amount of the composites at 700 degrees C, contributing to the improved thermal stability of the composites. It was observed from SEM photographs that the homogeneous and compact charred residue structure after combustion improved the flammability of the composites.