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

Filtration Performance of Biofilm Membrane Bioreactor: Fouling Control by Threshold Flux Operation

Membrane fouling is the major factor that restricts the furtherly widespread use of membrane bioreactor (MBR). As a new generation of MBR, biofilm membrane bioreactor (BF-MBR) demonstrates high treatment efficiency and low sludge growth rate, however the filtration performance improvement and membrane fouling control are still the challenges for its further development. This work investigated the filtration performance using resistance in series model and membrane fouling control via threshold flux for BF-MBR. At first, the flux behavior and filtration resistance under various operating conditions, including agitation speed, membrane and TMP, were explored by resistance in series model. Because of the desirable anti-fouling capacity, UP100 and UP030 had the high threshold flux (100 and 90 L m-2 h-1) and low irreversible fouling resistance (1 and 1.3×10-10 m). Higher shear stress produced by higher agitation speed could reduce membrane fouling, while greatly promote the threshold flux (138 L m-2 h-1) and membrane cleaning efficiency (96%). Moreover, increasing shear stress or selecting membrane with large pore size could decrease the fouling rate and raise the threshold flux . As for TMP, high TMP reduced the removal rate for organic and nutrient, and enhanced the irreversible fouling. Besides, the aerobic-BF-MBR (101 L m-2 h-1 and 1.3×10-10 m) with lower foulant concentration had a better filtration performance than anoxic-BF-MBR(90 L m-2 h-1 and 1.5×10-10 m). Additionally, the long-term tests with 10 cycles were conducted to evaluate the industrial application value of BF-MBR (45-58 L m-2 h-1). This work provides the technical support for sustainable filtration performance of BF-MBR.

An Overview of Photocatalytic Membrane Degradation Development

Environmental pollution has become a worldwide issue. Rapid industrial and agricultural practices have increased organic contaminants in water supplies. Hence, many strategies have been developed to address this concern. In order to supply clean water for various applications, high-performance treatment technology is required to effectively remove organic and inorganic contaminants. Utilizing photocatalytic membrane reactors (PMRs) has shown promise as a viable alternative process in the water and wastewater industry due to its efficiency, low cost, simplicity, and low environmental impact. PMRs are commonly categorized into two main categories: those with the photocatalyst suspended in solution and those with the photocatalyst immobilized in/on a membrane. Herein, the working and fouling mechanisms in PMRs membranes are investigated; the interplay of fouling and photocatalytic activity and the development of fouling prevention strategies are elucidated; and the significance of photocatalysis in membrane fouling mechanisms such as pore plugging and cake layering is thoroughly explored.

Existing Filtration Treatment on Drinking Water Process and Concerns Issues

Water is one of the main sources of life's survival. It is mandatory to have good-quality water, especially for drinking. Many types of available filtration treatment can produce high-quality drinking water. As a result, it is intriguing to determine which treatment is the best. This paper provides a review of available filtration technology specifically for drinking water treatment, including both conventional and advanced treatments, while focusing on membrane filtration treatment. This review covers the concerns that usually exist in membrane filtration treatment, namely membrane fouling. Here, the parameters that influence fouling are identified. This paper also discusses the different ways to handle fouling, either based on prevention, prediction, or control automation. According to the findings, the most common treatment for fouling was prevention. However, this treatment required the use of chemical agents, which will eventually affect human health. The prediction process was usually used to circumvent the process of fouling development. Based on our reviews up to now, there are a limited number of researchers who study membrane fouling control based on automation. Frequently, the treatment method and control strategy are determined individually.

Development of iron-based biochar for enhancing nitrate adsorption: Effects of specific surface area, electrostatic force, and functional groups

The problem of nitrate contamination in water has attracted widespread attention. Original biochar has a poor adsorption capacity for nitrate adsorption. Iron impregnation and acid protonation (base deprotonation) are common modification methods for biochar. In order to develop iron-mediated biochar containing multi-functional groups for enhancing nitrate adsorption, Fe-BC@H and Fe-BC@OH were prepared using a two-stage development process, including an iron-based carbon pyrolysis followed by acid protonation (or base deprotonation). The pseudo-second-order kinetic and Langmuir models can well describe the adsorption process which is a physicochemical complex monolayer adsorption. The data proved that Fe-BC@H (9.35 mg/g NO₃^--N) had a stronger adsorption capacity than Fe-BC@OH (2.95 mg/g NO₃^--N). Surface morphologies, functional groups, and mineral compositions of Fe-BC@H and Fe-BC@OH were analyzed through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Characterization results showed that acid protonation can further improve the specific surface area (SSA), pore volume, and Zeta potential of Fe-based biochar, providing more adsorption sites for nitrate and enhancing the electrostatic force between nitrate and biochar. However, these effects were suppressed through base deprotonation. In addition, acid protonation can significantly increase the type and number of functional groups of biochar to enhance the chemisorption of nitrate. Such results suggested that the acid protonation can further improve the adsorption capacity of Fe-based biochar for nitrate, while base deprotonation had an inhibitory effect on that of Fe-based biochar. Overall, this study reveals that specific surface area, electrostatic force, and functional groups are crucial effects of the nitrate adsorption on acid/base modified biochar.

Electrochemical oxidation of landfill leachate using boron-doped diamond anodes: pollution degradation rate, energy efficiency and toxicity assessment

Electrochemical oxidation (EO), due to high efficiency and small carbon footprint, is regarded as an attractive option for on-site treatment of highly contaminated wastewater. This work shows the effectiveness of EO using three boron-doped diamond electrodes (BDDs) in sustainable management of landfill leachate (LL). The effect of the applied current density (25-100 mA cm^-2) and boron doping concentration (B/C ratio: 500 ppm, 10,000 ppm and 15,000 ppm) on the performance of EO was investigated. It was found that, of the electrodes used, the one most effective at COD, BOD₂₀ and ammonia removal (97.1%, 98.8% and 62%, respectively) was the electrode with the lowest boron doping. Then, to better elucidate the ecological role of LLs, before and after EO, cultivation of faecal bacteria and microscopic analysis of total (prokaryotic) cell number, together with ecotoxicity assay (Daphnia magna, Thamnocephalus platyurus and Artemia salina) were combined for the two better-performing electrodes. The EO process was very effective at bacterial cell inactivation using each of the two anodes, even within 2 h of contact time. In a complex matrix of LLs, this is probably a combined effect of electrogenerated oxidants (hydroxyl radicals, active chlorine and sulphate radicals), which may penetrate into the bacterial cells and/or react with cellular components. The toxicity of EO-treated LLs proved to be lower than that of raw ones. Since toxicity drops with increased boron doping, it is believed that appropriate electrolysis parameters can diminish the toxicity effect without compromising the nutrient-removal and disinfection capability, although salinity of LLs and related multistep-oxidation pathways needs to be further elucidated.