Microalgae-based advanced wastewater treatment has gained momentum due to the possibility of recovering nutrients for the production of fertilizers, biofuels and fine chemicals from microalgal biomass. The objective of this study is to evaluate the effect of different fouling control strategies on the development of Chlorella vulgaris in a membrane photobioreactor (AMPMBR) treating a secondary wastewater effluent. The experimental results showed a decrease in the fouling rate (bar/hours) of 50% for backwash and relaxation and 60% for nitrogen bubble scouring. Additionally, in-situ non-destructive real time monitoring was employed to visualize and assess the change in morphology of the algae formed on the membrane surface. The use of fouling mitigation led to substantial changes in the biomass morphologies impacting the performance of the AMPMBR. The lowest biomass deposition (5–10 µm) was observed when nitrogen bubble scouring was employed, while the application of relaxation led to the thickest (180 µm), most heterogeneous and porous structure. The use of backwash led to a partial temporary biomass detachment from the membrane surface. This study, provided a better understanding of the impact of fouling mitigation strategies on the biomass formed on the membrane of AMPMBR.

Hypothesis Membrane fouling challenges the viability of oil-field produced water (PW) treatment with ceramic membranes. Surfactants play an important role in irreversible fouling through adsorption phenomena. However, previous studies have shown contradictory results. Hence, a fundamental understanding of surfactants-metal oxides interactions is necessary. Experiments In this work, we assessed the adsorption interactions of anionic SDBS and cationic CTAB with titania, zirconia and alumina surfaces, using the quartz crystal microbalance with dissipation (QCM-D) technique. Findings We found that electrostatic interactions controlled the adsorption of SDBS onto all the surfaces studied, with titania being the most likely to adsorb SDBS. On the contrary, CTAB was adsorbed regardless of the overall metal oxide surface charge. CTAB showed a two-step adsorption at acidic pH (3.0). In the first step, a rigid film was formed with a smaller adsorption capacity compared to the neutral (6.8) and basic (9.4) pH conditions. In the second step, a viscoelastic film was formed. Our results suggest that adsorption was driven by the nature of the surfactant rather than the metal oxide properties. This implies that electrostatic interactions should not be taken as the only predicting factor of adsorption phenomena in the understanding of PW fouling in ceramic membranes as other supramolecular interactions are strongly involved.

In this study at a full-scale desalination installation seven types of commercially available cartridge filter (CF) elements were evaluated in terms of: (i) water production volume (m3), (ii) produced water quality, and (iii) operational cost (€cent/m3). The cost of optimal CF replacement time relative to increased CF pressure drop was determined for three electricity tariffs (0.05, 0.15, and 0.25 €/kWh) to assess further cost reduction. CF 1 was able to achieve the highest water production rate, the lowest produced water SDI, and the lowest cost of operation. The total costs of cartridge filtration varied between 1.22 and 1.70 €cents/m3 produced water, depending on the CF type. Replacing the worst-performing CF type by the best-performing CF type would reduce operational CF costs by about 39.3%, enabling a cost saving of 0.48 €cents/m3 produced water, emphasizing that selection of the right CF enables a large reduction of cartridge filtration costs. Moreover, depending on the electricity tariff an additional 2–16% cost reduction can be achieved by replacing CFs at an optimal time. At high energy cost, it may be more economical to replace cartridge elements more often to reduce the increased cost associated with the required higher pressure.

This study aims to demonstrate the use of metagenomics to assess groundwater quality. Metagenomics revealed a lower alpha diversity for both bacteria and virus in wastewater-exposed groundwater compared to the upstream controls. An increase in the relative abundance of Planctomycetes and Picornaviridae was also observed in wastewater-exposed groundwater. However, comparison of antibiotic resistome cannot clearly differentiate wastewater-exposed groundwater from control. Findings suggest that metagenomics can detect selected microbial signatures indicative of treated wastewater discharge.

Biofilm formation on membranes in activated sludge membrane bioreactors (MBR), commonly identified as biofouling, is a significant problem for MBR operations. A better understanding of microbial species involved in the biofilm formation is needed to develop anti-biofilm measures. A read-based and genome-resolved shotgun metagenomic approach was applied to characterize the composition and functional potential of the sludge and early stage biofilm microbial communities in an MBR process. Read-based analysis revealed that the prevalence of different phyla are relatively similar in both the sludge and biofilm samples, with Proteobacteria as the most dominant, followed by Chloroflexi, Bacteroidetes and Planctomycetes. However, the relative abundance of these phyla slightly varies between the sludge and biofilm. Phyla such as Actinobacteria, bacterial candidate phyla, Chlamydiae, Cyanobacteria/Melainabacteria and Firmicutes are 2 to 4 times more abundant in the biofilm than in the sludge. At the genus level, genera belonging to Proteobacteria (Legionella, Caulobacter, Sphingomonas, Acinetobacter and Rhizobium), Cyanobacteria (Hassallia), and Spirochaetes (Turneriella) are at least twice more abundant in the biofilm. These genera, especially those belonging to Phylum Proteobacteria, are known to play an important role in the formation of biofilms on surfaces. The Alpha diversity is found slightly higher in the biofilm, compared with sludge samples. Functional classification of reads through the SEED subsystem shows that functional classes such as those involved in the metabolism of various molecules are significantly different in the biofilm and sludge. A phylogenomic analysis of the six extracted metagenome assembled genomes (MAGs) shows that three MAGs belong to Proteobacteria, and one MAG belong to each of Chloroflexi, Bacteroidetes and Planctomycetes. The relative abundance of the MAG belonging to Alphaproteobacteria is higher in the biofilm. A functional potential analysis of the MAGs reveals their potential to metabolize carbon and nitrogen sources, as well as the prevalence of antibiotic resistance genes.

The performance of vacuum membrane distillation (VMD) modules can be optimized through careful selection of design parameters. The present study examines how the addition of cylindrical filaments in the feed channel increases momentum mixing and the overall performance of VMD modules under different operating inlet conditions. Three-dimensional transient Computational Fluid Dynamics (CFD) simulations are conducted using Wall-Adapting Local Eddy-Viscosity (WALE) subgrid-scale Large Eddy Simulation (LES) turbulence model. Local concentration, temperature, and flux are coupled at the membrane surface to predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanisms. The predicted and measured vapor flux agrees reasonably well; validating the employed model. The small-scale eddies induced by the presence of spacer filaments promote mixing in the module, thus the temperature and concentration polarization is alleviated and the water vapor flux is immensely improved. The insertions of filaments in the feed channel increase the water permeate rate by more than 50% at higher feed flow rates and inlet temperatures. The pressure drop by the spacer reduces the allowable module length by one order of magnitude, but the module length increases two folds at feed temperature 80℃. Even though the power consumption of the module containing the filaments is increased, the addition of filaments is strongly recommended since the required power for the process could be supplied from readily available low-grade heat source.

Enhancing the properties and structure of the ultrafiltration (UF) membrane via rational manipulation is important to optimize their perm-selectivity performance. To overcome the permeance-selectivity trade-off of nanocomposite membranes, Zirconium dioxide nanofibers (ZrO2 NFs) was synthesized in nano-micro size and then incorporated into the polysulfone (PSf) membrane. The effect of different concentrations of ZrO2 NFs on the membrane properties and performance were investigated. Compared to the pristine PSf membrane, the nanocomposite membranes exhibited a remarkable enhancement in the physiochemical properties, mechanical properties, and the overall performance. The results showed that the nanocomposite membrane (M3, 0.5% ZrO2 NFs) possesses the highest flexibility and tensile strength (43% higher than the pristine PSf). The enhancement of the wettability and enlarge the pore size (2.6 times increase) of this nanocomposite membrane, resulting in a remarkably heightened the pure water permeability (Jw1; 255.8 L m−2 h−1 bar−1). As a result, it achieved the highest permeability during the filtration of BSA solution with no decline in the BSA rejection. Furthermore, compared to the pristine PSf membrane, all nanocomposite membranes exhibited higher mechanical properties. This novel strategy of incorporating the nanofibers, instead of nanoparticles, offers significant opportunities to exploit the various inorganic nanofibers in the fabrication of diverse nanocomposite membrane types.

The efficacy of a baffled osmotic membrane bioreactor-microfiltration (OMBR-MF) hybrid system equipped with thin film forward osmosis membrane for wastewater treatment was evaluated at laboratory scale. The novel OMBR-MF hybrid system involved baffles, that separate oxic and anoxic zones in the aerobic reactor for simultaneous nitrification and denitrification (SND), and a bioreactor comprised of thin film composite-forward osmosis (TFC-FO) and polyether sulfone-microfiltration (PES-MF) membranes. The evaluation was conducted under four different oxic-anoxic cycle patterns. Changes in flux, salinity build-up, and microbial activity (e.g., extracellular polymeric substances (EPS) were assessed. Over the course of a 34 d test, the OMBR-MF hybrid system achieved high removal of total organic carbon (TOC) (86–92%), total nitrogen (TN) (63–76%), and PO4–P (57–63%). The oxic-anoxic cycle time of 0.5–1.5 h was identified to be the best operating condition. Incorporation of MF membrane effectively alleviated salinity build-up in the reactor, allowing stable system operation.

Air Gap Membrane distillation (AGMD) is a thermally driven separation process capable of treating challenging water types, but its low productivity is a major drawback. Membrane fouling is a common problem in many membrane treatment systems, which exacerbates AGMD’s low overall productivity. In this study, we investigated the direct application of low-power ultrasound (8–23 W), as an in-line cleaning and performance boosting technique for AGMD. Two different highly saline feedwaters, namely natural groundwater (3970 μS/cm) and RO reject stream water (12760 μS/cm) were treated using Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes. Theoretical calculations and experimental investigations are presented, showing that the applied ultrasonic power range only produced acoustic streaming effects that enhanced cleaning and mass transfer. Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that ultrasound was capable of effectively removing silica and calcium scaling. Ultrasound application on a fouled membrane resulted in a 100% increase in the permeate flux. Cleaning effects accounted for around 30–50% of this increase and the remainder was attributed to mass transfer improvements. Contaminant rejection percentages were consistently high for all treatments (>99%), indicating that ultrasound did not deteriorate the membrane structure. Scanning Electron Microscopy (SEM) analysis of the membrane surface was used to confirm this observation. The images of the membrane surface demonstrated that ultrasound successfully cleaned the previously fouled membrane, with no signs of structural damage. The results of this study highlight the efficient and effective application of direct low power ultrasound for improving AGMD performance.

Air conditioning has enhanced the work efficiency and improved life style by maintaining comfortable environment. The growing demand of air conditioning has negative impact on energy and environment. In 2015, air conditioning consumed 6% of total global electricity produced and it is expected to increase to 20% by 2050. The leveling-off conventional chiller’s efficiency at 0.85 ± 0.03 kW/Rton due to pairing of dehumidification and cooling processes in one machine is not only the major reason of high energy consumption but also the key limitation in efficiency improvement. The de-coupling of dehumidification and cooling processes can be one of the solution to achieve the quantum jump in the performance, 0.6 ± 0.03 kW/Rton, by improving individual processes. We proposed an improved indirect evaporative cooler system for sensible cooling that can be combined with dehumidification processes to achieve sustainable cooling goals. The experimentation on 800 mm long and 280 mm wide generic cell showed that it can produce temperature differential up to 10 °C with small area of heat transfer. It was showed that the proposed vertical heat exchanger configuration with multi point injection of working air is the best configuration of the indirect evaporative cooler, achieving coefficient of performance level of 78 for cooling alone. We expect that overall coefficient of performance level of 7–8 is achievable by incorporating efficient dehumidification processes. We also presented detailed design parameters that can be used as a reference for commercial system design.