Insights into the role of concentration polarization on the membrane fouling and cleaning during the aerobic granular sludge filtration process

The aerobic granular sludge (AGS) effectively mitigates the membrane fouling of a membrane bioreactor. However, the role and effects of the concentration polarization (CP), induced during the AGS filtration process on the membrane fouling and membrane cleaning efficiency, remain unclear. In the present study, the AGS resulted in a higher CP proportion (>50%) and a lower CP resistance (<3 × 10¹² m^-1), compared with the flocculent sludge, owing to the synergistic effect of the hydraulic shear and AGS scouring development, which improved the AGS in suspension and also minimized its deposition on the membrane. High-frequency interactions (contact and collision) between the AGS and membrane enhanced the CP resistance by returning more granular sludge from the cake layer to the CP, which proportionally increased the fouling resistance. Based on the correlation of CP and fouling resistance, the CP resistance was divided into 3 categories: high-intensity (2.76 × 10¹² m^-1), medium-intensity (1.74 × 10¹² m^-1), and low-intensity (0.62 × 10¹² m^-1). At the high-intensity CP, most membrane pores were "sealed" (complete pore blocking [R² > 0.9015]) and the pore blocking condition was the most serious (K-value = 0.0622 s^-1), while the membrane surface became denser and rougher. As a result, the permeability loss after the long-term filtration increased. In the chemical cleaning investigation, the alkaline detergents yielded an enhanced membrane cleaning efficiency to recover permeability. By reducing the CP, the membrane cleaning efficiency was marginally improved. The present study reveals the quantitative role of CP and offers insights into the mechanisms that govern membrane fouling in a membrane bioreactor.

Evaluation of concentration process of bovine, goat and buffalo whey proteins by ultrafiltration

In this research, the protein concentration, the permeate flux, and the predominant fouling mechanisms were investigated during ultrafiltration of different whey samples. The research was carried out at different values of transmembrane pressure and temperature using an experimental design, and a protein concentration of approximately 37 g L-1 was obtained for the bovine whey powder solution, at 60 kPa and 40 °C. The maximum flux observed was 8.9 and 7.9 kg m-2 h-1, respectively, for the bovine whey powder solution and bovine whey, at 50 kPa and 30 °C. Although goat and buffalo whey presented lower permeate flux, probably due to high solutes and calcium contents, protein concentrates of around 40 g L-1 were obtained using the ultrafiltration process. This demonstrates the potential of ultrafiltration to obtain non-bovine protein concentrates. The best fit, verified by Ho and Zydney model, suggests that the fouling for all analyzed whey occurs due to pore blocking and subsequent deposit on the membrane surface.

The influence of aggregation of latex particles on membrane fouling attachments & ultrafiltration performance in ultrafiltration of latex contaminated water and wastewater

The goal of the present study was to investigate the influence of latex particle aggregation on membrane fouling attachments and the ultrafiltration performance of simulated latex effluent using Cetyltrimethyl Ammonium Bromide (CTAB) as a cationic surfactant. Hydrophilic polysulfone and ultrafilic flat heterogeneous membranes, with molecular weight cut off (MWCO) of 60,000 and 100,000, respectively, as well as hydrophobic polyvinylidene difluoride with MWCO of 100,000, were used under a constant flow rate and cross-flow mode in ultrafiltration of latex solution. In addition, a polycarbonate flat membrane with uniform pore size of 0.05μm was likewise used during the experiment. The effects of CTAB on the latex particle size distribution were investigated at various concentrations, different treatment times, and diverse agitation duration times. The effects of CTAB on the zeta potential of membrane surfaces and latex particles were also investigated. The data obtained indicate that the particle size distribution of treated latex effluent experienced significant shifts in the peaks toward a larger size range caused by the aggregation of particles. As a result, the mass of fouling contributing to pore blocking and the irreversible fouling were noticeably reduced. The optimum results occurred in the instance when CTAB was added at the critical micelle concentration of 0.36g/L, for the duration of 10min and with minimal agitation. Notably, a higher stirring rate had an overall negative effect on the membrane fouling minimization.