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In this study, the integration of a 3D printed turbulence promoter into a stirred membrane separation cell during dairy wastewater ultrafiltration was investigated. Its effects, along with the effects of stirring, on the permeate flux and membrane fouling were examined. The experiments were carried out at different transmembrane pressures (0.1, 0.2, and 0.3 MPa) and stirring speeds (RPM: 100–400 min−1), both with and without the application of the turbulence promoter. Various parameters were employed to characterize the membrane performance, such as the permeate flux, the flux decline ratio, and the fouling coefficient. To further investigate the membrane fouling mechanisms, mathematical models were used: the resistance-in-series model, the Makardij model, and the Hermia model. With the resistance-in-series model, we examined whether the membrane fouling was reversible (the deposit could be easily removed by washing operations) or irreversible (irreversible fouling) for each measurement, and with the Makardij model, we investigated whether the rate constant of the fouling or the rate constant of the deposit removal was the most important. In the case of the Hermia model, changes in the cake filtration rate constant were monitored. The results indicate that the combination of the 3D printed turbulence promoter and the stirring speed could effectively reduce membrane fouling during dairy wastewater ultrafiltration. [ABSTRACT FROM AUTHOR]

This comparative study investigates the modification of polyvinylidene fluoride (PVDF) membranes with different nanoparticles (TiO2 or TiO2-based composites containing BiVO4 and/or CNT), using three distinct methods (blending, coating, and grafting) and polyvinylpyrrolidone (PVP). The objective was to enhance the photocatalytic and filtration performance for the separation of oil-in-water emulsions. Regarding the UV activity, the PVDF-TiO2/CNT/PVP-coated membrane presented the best performance. Overall, the addition of 2 wt.% CNT to the TiO2 notably enhanced the photocatalytic activity of the membranes for both UV and visible irradiations. Meanwhile, the presence of 2 wt.% BiVO4 was beneficial only for photocatalysis under visible light irradiation. Regarding the filtration of the oil-in-water emulsions, 2 wt.% CNT or BiVO4 addition resulted in the highest fluxes in the series of the PVDF-TiO2-grafted membranes. The presence of pore former PVP led to relatively high fluxes and photocatalytic activities for all series. Regarding the modification methods, coated membranes showed the highest photocatalytic efficiency and lowest fluxes. Grafted membranes showed relatively high photocatalytic efficiencies and the best filtration performances. [ABSTRACT FROM AUTHOR]

Polyvinylidene fluoride (PVDF) membranes were coated with TiO2 and TiO2-Ag to enhance their efficiency for oil-in-water emulsion separation. The photocatalytic activities of the two modified membranes and their filtration performances were compared in detail. The significantly enhanced photocatalytic activity of the TiO2-Ag composite was proved using a methyl orange (MO) solution (c = 10−5 M) and a crude oil emulsion (c = 50 mg·L−1). The TiO2-Ag-coated membrane reduced the MO concentration by 87%, whereas the TiO2-modified membrane reached only a 46% decomposition. The photocatalytic reduction in the chemical oxygen demand of the emulsion was also ~50% higher using the TiO2-Ag-coated membrane compared to that of the TiO2-coated membrane. The photoluminescence measurements demonstrated a reduced electron/hole recombination, achieved by the Ag nanoparticle addition (TiO2-Ag), which also explained the enhanced photocatalytic activity. A significant improvement in the oil separation performance with the TiO2-Ag-coated membrane was also demonstrated: a substantial increase in the flux and flux recovery ratio (up to 92.4%) was achieved, together with a notable reduction in the flux decay ratio and the irreversible filtration resistance. Furthermore, the purification efficiency was also enhanced (achieving 98.5% and 99.9% COD and turbidity reductions, respectively). Contact angle, zeta potential, scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements were carried out to explain the results. SEM and AFM images revealed that on the TiO2-Ag-coated membrane, a less aggregated, more continuous, homogeneous, and smoother nanolayer was formed due to the ~50% more negative zeta potential of the TiO2-Ag nanocomposite compared to that of the TiO2. In summary, via Ag addition, a sufficiently hydrophilic, beneficially negatively charged, and homogeneous TiO2-Ag-coated PVDF membrane surface was achieved, which resulted in the presented advantageous filtration properties beyond the photocatalytic activity enhancement. [ABSTRACT FROM AUTHOR]

The dairy industry generates wastewater characterised by high levels of biological and chemical oxygen demands representative of their high degree of organic content; mainly carbohydrates, proteins and fats that originate from milk. Several investigations have been conducted into the reuse of dairy wastewater, e.g. membrane processes are a promising method to treat such wastewater. Earlier works have proven that with membrane filtration an appropriate degree of retention can be achieved and the permeate can be reused. However, membrane fouling is a limiting factor in these processes. Advanced oxidation processes (AOPs) are widely used in the fields of water and wastewater treatments and are known for their capability to mineralise a wide range of organic compounds. AOPs also exhibit some other effects on the filtration process, e.g. the microflocculation effect of ozone may play a significant role in increasing the elimination efficiency and causing a decreased level of irreversible fouling. By comparing ozone and Fenton pre-treatment (FPT) processes it can be shown that the fouling propensity of pre-treated pollutants does not depend on the pre-treatment method, while FPT was proven to be more efficient in improving the level of flux.

Membrane separation processes have become increasingly popular in many industries because of their ability to treat wastewater and purify water. However, one of the main problems related to the processes is organic fouling, which can significantly reduce their efficiency and cause membrane damage. This review provides a summary of the various forms of organic fouling that can occur in membrane separation methods and examines the factors that lead to their development. The article evaluates the progress made in different techniques designed to manage and reduce organic fouling, such as physical cleaning methods, chemical cleaning agents, and modifications to the membrane surface, including ultrasonic and membrane vibration methods. The review also highlights recent advances in emerging 3D printing technology to mitigate membrane fouling. Finally, the review provides a brief summary of the conclusions and future directions for research in the field of organic fouling control and mitigation in membrane separation processes. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the performance of composite photocatalytic membranes fabricated by incorporating multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) into polyvinylidene fluoride membrane material for real dairy wastewater treatment. The composite photocatalytic membranes exhibited superior antifouling behavior, lower filtration resistance, better flux, and higher flux recovery ratio than the pristine membrane. Salinity, pH, and lactose concentration are determinant factors that affect filtration resistance and rejection performance during the ultrafiltration of dairy wastewater. Generally, higher irreversible and total resistances and slightly lower chemical oxygen demand (COD) rejections were found at higher salinity (expressed by electric conductivity values of >4 mS/cm) than lower salinity (<4 mS/cm) levels. The presence of lactose in dairy wastewater increased irreversible resistance and severely reduced COD rejection during ultrafiltration due to the ability of lactose to pass through the membranes. It was ascertained that membranes require further treatment after filtrating such wastewater. Lower resistances and slightly better COD rejections were observed at pH 7.5 and pH 9.5 compared to those observed at pH 4. Photocatalytic membranes fouled during the ultrafiltration of real dairy wastewater were regenerated by visible light irradiation. The membrane containing all constituents (i.e., TiO2, carbon nanotubes, and BiVO4) showed the best regeneration performance, exceeding that of the pristine membrane by 30%. [ABSTRACT FROM AUTHOR]

In this work the effects of oxidation pre-treatments (ozonation and Fenton reaction) on membrane filtration of dairy wastewater were investigated, together with the further utilization possibilities of residual wastes. The oxidation pre-treatments enhanced the membrane filtration efficiency, from which the short-term ozone treatment was found to be the most effective method both in terms of increasing the flux and the pollutant removal efficiency. After ozone pre-treatment the phosphate and ammonium content of the wastewater migrated to the permeate, while after Fenton pre-treatment the phosphate content remained in the concentrate, and the ammonium content in the permeate decreased. The concentrate was utilized as biogas resource and it was found that both pretreatments increased the biogas production and its methane content as well. Based on our results it can be concluded that ozone pretreatment combined with membrane separation have improved the efficiency of dairy wastewater treatment and may suit the requirements of circular economy. [ABSTRACT FROM AUTHOR]