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Microplastics (MPs), ubiquitous environmental pollutants, pose substantial threats to aquatic ecosystems and organisms, including the model species Daphnia magna. This study examined the effects of polyethylene (PE) and polystyrene (PS) MPs on D. magna, focusing on their ingestion, epigenetic alterations, and transcriptional responses. Exposure experiments revealed a concentration-dependent accumulation of MPs, with PS particles showing higher ingestion rates due to their higher density and propensity for aggregation. Epigenetic analyses demonstrated that exposure to PE MPs significantly reduced the global DNA methylation (5-mC) of Daphnia magna, suggesting hypomethylation as a potential stress response. Conversely, the DNA hydroxymethylation (5-hmC) of Daphnia magna displayed variability under PS exposure. Transcriptional analysis identified a marked downregulation of Vitellogenin 1 (v1) and upregulation of Ecdysone Receptor B (ecr-b), highlighting the occurrence of stress-related and adaptive molecular responses. These findings enhance our understanding of the molecular and epigenetic effects of MPs on aquatic organisms, offering critical insights for the development of effective environmental management and conservation strategies in the face of escalating MP pollution.

Oil-contaminated wastewater presents a significant environmental challenge, necessitating the development of efficient and adaptable treatment technologies. In this study, a pH-responsive chitosan-coated polyethersulfone (Ch/PES) membrane was developed and systematically evaluated for oil/water separation performance under varying pH conditions. PES was chosen as the base membrane material due to its excellent chemical resistance and mechanical durability, while Ch, a biodegradable and environmentally friendly biopolymer with pH-sensitive properties, was applied as a functional surface coating. The Ch/PES membrane was successfully fabricated and characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy, confirming successful surface modification and structural integrity. Additional analyses—including underwater oil contact angle measurements, porosity assessment, and cross-sectional morphological evaluation—demonstrated the membrane’s dynamic pH-responsive wettability and pore size modulation. Oil emulsion separation experiments, conducted using sodium dodecyl sulfate-stabilized emulsions, revealed that the Ch/PES membrane achieved oil removal efficiencies exceeding 97% under acidic conditions. This enhancement was attributed to increased hydrophilicity and reduced effective pore size resulting from chitosan swelling. In contrast, under alkaline conditions, the membrane exhibited greater oleophilicity and maintained a relatively stable pore structure, leading to a reduced separation efficiency of 83.8%. Compared to the unmodified PES membrane, the Ch/PES membrane demonstrated significantly improved responsiveness and adaptability to changes in pH, underscoring its potential as a versatile platform for treating oil-contaminated wastewater of varying chemistries. These findings suggest that the Ch/PES membrane offers a promising, sustainable, and efficient solution for advanced oil/water separation applications.

Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O 2 /L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78–0.95 kg-N/m 3  day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m 3  day, while that of HG-1.13 was 0.0516 kg-FA/m 3  day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.

Biofouling on a membrane leads to significant performance decrease in filtration processes. In this study, an optical coherence tomography (OCT) was used to perform a time-resolved analysis of dynamic biofouling development on a submerged membrane under continuous operation. A real-time change in the biofouling morphology was calculated through the image analysis of OCT scans. Three videos were generated through the acquisition of serial static images. This is the first study that displays the dynamic biofouling formation process as a video. The acquisition of OCT cross-sectional scans of the biofouling allowed to evaluate the time-lapsed evolution for three different time periods (early stage, double layers and long-term). Firstly, at the early filtration stage, membrane coverage and average biofouling layer thickness were found to be linearly correlated with the permeate flux pattern. Secondly, after 3 d of operation, an anomalous morphology was observed, constituted by a double-layered biofouling structure: denser on the bottom and looser on the top. In a long-term operation, the biofouling structure underwent a dynamic evolution over time, resulting in a multi-layered structure. The biofouling formation information was closely associated with filtration performance (i.e. flux) indicating the suitability of OCT as real-time and in-situ biofouling monitoring technique.

Omniphobic membranes, due to their exceptional properties, have drawn significant attention for overcoming the bottleneck in membrane distillation (MD) technology. This study demonstrates an innovative method for fabricating an omniphobic membrane that is simple and facile compared to other methods such as wet/dry etching and photolithography. The surface morphology of springtails was imitated using electrospraying technique to coat a polyvinylidene fluoride substrate with concave-shaped polystyrene beads that were successfully developed by controlling the electrical traction (voltage) and air resistance (humidity). Then, the lipid coating of springtail surfaces was mimicked by dip-coating the membrane in a low-toxicity short-chain perfluoropolyether lubricant. The concave structure’s tiny air pockets increased membrane hydrophobicity significantly, indicated by the fact that the first round of water bouncing took only 16.3 ms. Finally, in MD treatment of seawater containing 1.0 mM sodium dodecyl sulfate, the optimized omniphobic membrane maintained a stable 99.9% salt rejection rate. Here, authors successfully fabricated a springtail-inspired nano-concave reentrant structured polystyrene (PS) membrane using electrospraying technology followed by lubricant dip-coating, which endowed the membrane with omniphobic properties.

Although microplastics (MPs) are intrinsically toxic and function as vectors for organic micropollutants, their discharge from wastewater treatment plant effluents and human activity remains unknown owing to the limitations of detection and treatment technologies. It is imperative to quantify MPs from human activities involving the consumption of various plastic products. This study warns that contact lenses can generate MPs and nanoplastics (NPs) after being discharged into aquatic environments. Identification via micro-Fourier transform infrared spectroscopy revealed that the fragmented particles (from a few tens to a few hundred micrometres) could not be detected as poly(2-hydroxyl methacrylate), the component of contact lenses, owing to changes in its chemical properties. After the degradation process, the median size of the contact lens particles decreased from 313 to 85 µm. Approximately 300,600 g of contact lens waste is discharged into sewage systems daily in the United States of America (USA), where 45 million people wear contact lenses and throw away one-fifth of them every day. Contact lens waste (1 g) has the potential to release 5653.3–17,773.3 particles of MPs. This implies that the currently reported MP amounts in the environmental matrix exclude significant amounts of MPs and NPs from discharged contact lenses. The identification method should be examined, and a registration of the disposal process should be established.

The wastewater effluents from textile industries contain highly toxic metal complex dyes. For instance, azo dye has received significant attention owing to its toxicity and environmental stability. This study investigated the oxidation and coagulation processes to effectively remove azo dye from wastewater effluents. Potassium ferrate (K2FeO4) was selected as an oxidant because it has a high oxidation potential, is environmentally stable, and does not generate toxic byproducts. Moreover, it has a combination effect of coagulation and oxidation. Its performance was compared with a single oxidation process (using NaOCl) and a single coagulation process (using FeCl3·6H2O). Based on the jar test experiment, the optimized pH was estimated to be 3 and the optimal dosage was 56.4 mg/L for K2FeO4, and it removed nearly 100% of orange II azo dye (OD) and lissamine green B dye (LGB). However, its removal efficiency decreased when the pH increased to 12. In all processes, dye removal was completed in 5 min of the reaction. Overall, OD and LGB were effectively removed by K2FeO4, compared to the NaOCl and FeCl3·6H2O. This indicates that the combination of oxidation and coagulation of K2FeO4 outperformed the single treatment process without toxic byproduct production.

Air conditioning using a liquid desiccant (LD) is an energy-efficient air purification and cooling system. However, high energy is required to concentrate or regenerate the LD. This study aimed to investigate the characteristics of membrane fouling in more detail and determine control strategies for LD concentrating using membrane distillation (MD). Two different LDs—lithium chloride (LiCl) and potassium formate (HCOOK)—were used. Because LDs require high concentrations by nature (i.e., 40 wt% for LiCl and 70 wt% for HCOOK), the concentration was started from half of those concentrations. This resulted in a flux decline with severe membrane fouling during the concentration using MD. Different membrane fouling mechanisms were also observed, depending on the LD type. Three different physical membrane fouling control methods, including water flushing (WF), air backwashing (AB), and membrane spacer (SP), were introduced. Results showed that WF was the most effective. Both AB and SP showed a marginal change to no cleaning; however, an initial flux with SP was about 1.5 times higher than no cleaning. Therefore, WF combined with the SP could maintain a high flux and a low fouling propensity in the treatment of a high-concentration solution using MD.

Membrane scaling is a barrier to membrane distillation (MD). In this study, 3D-printed carbon nanotube (CNT) spacer was used to investigate its capability for mitigating membrane scaling during MD and to elucidate the scaling mechanism experimentally and theoretically. CNT spacer was tested under temperature-dependent calcium sulfate scaling conditions, and optical coherence tomography (OCT) and scanning electron microscopy (SEM) were used to measure scaling quantitatively. CNT spacer exhibited unique membrane scaling mechanism, where only a 37% reduction (29 Lm −2 h −1 ) in the initial flux was achieved, even above a volume concentration factor (VCF) of 4. On the other hand, the membrane with a polylactic acid (PLA) spacer (controls) entirely lost flux before reaching a VCF of 3.5. Interestingly, bubble formation was observed in CNT spacer, which could be attributed to the enhanced flux and vaporization rate on membrane surface in the presence of rough-surfaced CNT spacer. Bubbly flow along the membrane channel with CNT spacer can potentially reduce surface scaling on membrane during MD. Moreover, due to the surface roughness of CNT spacer, the initial nuclei might be detached more easily from CNT spacer surface than from smooth PLA surface and grow further into larger crystals in the bulk, resulting in reduced dissolved solutes in the solution. This phenomenon was indirectly corroborated by comparing the experimentally measured fluxes and theoretically computed values from our mechanistic model of MD-crystallization developed in this study. Therefore, this study revealed that CNT spacer with rough surfaces can potentially have benefit of mitigating membrane scaling during MD.