Preparation of graphene oxide-doped silica aerogel using supercritical method for efficient removal of emerging pollutants from wastewater.

Emerging pollutants and a large volume of unused dyes from the textile industry have been contaminating water bodies. This work introduces a scalable approach to purifying water by the adsorption of Acid green 25 (AG), Crystal Violet (CV), and Sulfamethoxazole (SMA) from an aqueous solution by graphene oxide (GO) doped modified silica aerogel (GO-SA) with supercritical fluid deposition (SFD) method. Characterization of GO-SA using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) adsorption isotherms revealed the improvement in the adsorbent surface area, and its textural properties. The high removal percentages observed in most of the experimental runs provide evidence of the excellent performance of the adsorbent towards the anionic and cationic dyes along with the antibiotic. The adsorption isotherm and kinetics showed that the Langmuir isotherm and pseudo-second-order kinetic models could explain adsorption. The adsorbent holds a higher adsorption capacity for SMA (67.07 mg g-1) than for CV (41.46 mg g-1) and AG (20.56 mg g-1) due to the higher hydrophobicity that interacts with the hydrophobic adsorbent. The GO-SA successfully removed AG, CV, and SMA with removal percentages of 98.23%, 98.71%, and 94.46%, respectively. The parameters were optimized using Central Composite Design (RSM-CCD). The prepared aerogel showed excellent reusability with a removal efficiency of > 85% even after 5 cycles. This study shows the potential of GO-SA adsorbent in textile and other wastewater purification.

Disinfection of SARS-CoV-2 by UV-LED 267 nm: comparing different variants.

UV irradiation is an efficient tool for the disinfection of viruses in general and coronavirus specifically. This study explores the disinfection kinetics of SARS-CoV-2 variants wild type (similar to the Wuhan strain) and three variants (Alpha, Delta, and Omicron) by 267 nm UV-LED. All variants showed more than 5 logs average reduction in copy number at 5 mJ/cm2 but inconsistency was evident, especially for the Alpha variant. Increasing the dose to 7 mJ/cm2 did not increase average inactivation but did result in a dramatic decrease in the inactivation inconsistency making this dose the recommended minimum. Sequence analysis suggests that the difference between the variants is likely due to small differences in the frequency of specific UV extra-sensitive nucleotide sequence motifs although this hypothesis requires further experimental testing. In summary, the use of UV-LED with their simple electricity need (can be operated from a battery or photovoltaic panel) and geometrical flexibility could offer many advantages in the prevention of SARS-CoV-2 spread, but minimal UV dose should be carefully considered.

Creating anti-viral high-touch surfaces using photocatalytic transparent films.

Antimicrobial and self-cleaning surface coatings are promising tools to combat the growing global threat of infectious diseases and related healthcare-associated infections (HAIs). Although many engineered TiO2-based coating technologies are reporting antibacterial performance, the antiviral performance of these coatings has not been explored. Furthermore, previous studies have underscored the importance of the "transparency" of the coating for surfaces such as the touch screens of medical devices. Hence, in this study, we fabricated a variety of nanoscale TiO2-based transparent thin films (anatase TiO2, anatase/rutile mixed phase TiO2, silver-anatase TiO2 composite, and carbon nanotube-anatase TiO2 composite) via dipping and airbrush spray coating technologies and evaluated their antiviral performance (Bacteriophage MS2 as the model) under dark and illuminated conditions. The thin films showed high surface coverage (ranging from 40 to 85%), low surface roughness (maximum average roughness 70 nm), super-hydrophilicity (water contact angle 6-38.4°), and high transparency (70-80% transmittance under visible light). Antiviral performance of the coatings revealed that silver-anatase TiO2 composite (nAg/nTiO2) coated samples achieved the highest antiviral efficacy (5-6 log reduction) while the other TiO2 coated samples showed fair antiviral results (1.5-3.5 log reduction) after 90 min LED irradiation at 365 nm. Those findings indicate that TiO2-based composite coatings are effective in creating antiviral high-touch surfaces with the potential to control infectious diseases and HAIs.

Nowcasting of fecal coliform presence using an artificial neural network.

At least 2 billion people worldwide use drinking water sources that are contaminated with feces, causing waterborne diseases; poor sanitation, poor hygiene, and unsafe drinking water result in a daily death rate of more than 800 children under 5 years of age from diarrheal diseases. This study shows the feasibility of a novel method to nowcast fecal coliforms' (FC) presence in drinking water sources by applying a multilayer perceptron artificial neuron network (MLP-ANN) model. The model gives a binary answer for FC presence or absence in drinking water sources using a minimum of water quality and geographical parameters, which can be monitored in real-time as predictors with low-cost and in-situ equipment. Using 51,400 samples to train, validate and test the model with temperature, pH, electrical conductivity, turbidity, dissolved oxygen, and total dissolved solids (TDS) as water-quality inputs and the water source type and location (as districts in India) as geographical inputs. The model achieved a total accuracy of 92.8% and a sensitivity of 98.2%, meaning that most FC-contaminated samples were classified correctly. In addition, precision reached 93.1%, meaning that most FC-contamination classifications were actually contaminated. The MLP-ANN performed better than the Linear Regression and K-Nearest Neighbors models, with lower accuracies of 90.2% and 91.0%, respectively. The MLP-ANN model could characterize the water quality geospatially, learn from the parameters whether the water is contaminated by FC, and predict with high accuracy on new testing data. This method can be used as a part of a sensor for FC monitoring and management in water, reducing the time gaps between routine lab testing and thus improving drinking water quality and addressing the SDG 6 targets.

Protocol for UVC uridine actinometry.

Uridine contains the chromophore uracil, a base forming part of RNA. In the range 240-290 nm, the absorption spectra of uridine and DNA are very similar and correspond to the spectral inactivation sensitivity of almost all microorganisms. This makes the uridine (absorption maximum 262 nm) an ideal actinometer for determining the germicidal photon flux in the range of 240 to 290 nm. Uridine actinometry is a simple, environmental-friendly, and easy-to-operate actinometry. Thanks to the uridine absorbance spectrum, it was found to be a perfect fit for the photon flux validation of UVC systems. Conventional UV disinfection systems are generally based on low-pressure (LP) mercury lamps which emit at 254 nm. On the other hand, UV light-emitting diodes (UV-LEDs) are a relatively new source of UV light for water treatment, emitting at various wavelengths. This protocol suggests an accurate, simple, easy to operate and straightforward way to determine the photon flux of UVC systems. Contain between 1 and 3 bullet points highlighting the customization rather than the steps of the procedure.•Because of the uridine absorbance spectrum, it is an ideal actinometer for photon flux validation of UVC systems.•Initial uridine concentration and photoproduct absorbance impact the kinetic order and quantum yield.•The protocol for UVC uridine actinometry is appropriate for UV-LP and UV-LED sources for water disinfection.

Removal of carbamazepine, venlafaxine and iohexol from wastewater effluent using coupled microalgal-bacterial biofilm.

We evaluated the removal capacity of a coupled microalgal-bacterial biofilm (CMBB) to eliminate three recalcitrant pharmaceuticals. The CMBB's efficiency, operating at different biofilm concentrations, with or without light, was compared and analyzed to correlate these parameters to pharmaceutical removal and their effect on the microorganism community. Removal rates changed with changing pharmaceutical and biofilm concentrations: higher biofilm concentrations presented higher removal. Removal of 82-94% venlafaxine and 18-51% carbamazepine was obtained with 5 days of CMBB treatment. No iohexol removal was observed. Light, microorganism composition, and dissolved oxygen concentration are essential parameters governing the removal of pharmaceuticals and ammonia. Chlorophyll concentration increased with time, even in the dark. Three bacterial phyla were dominant: Proteobacteria, Bacteroidetes and Firmicutes. The dominant eukaryotic supergroups were Archaeplastida, Excavata and SAR. A study of the microorganisms' community indicated that not only do the species in the biofilm play an important role; environment, concentration and interactions among them are also important. CMBB has the potential to provide low-cost and sustainable treatment for wastewater and recalcitrant pharmaceutical removal. The microenvironments on the biofilm created by the microalgae and bacteria improved treatment efficiency.

Effective Removal of Acid Dye in Synthetic and Silk Dyeing Effluent: Isotherm and Kinetic Studies.

Here, we propose a low-cost, sustainable, and viable adsorbent (pine tree-derived biochar) to remove acid dyes such as acid violet 17 (AV), which is used in the silk dyeing industry. As a case study, the AV removal process was demonstrated using synthetic effluent and further as a proof of concept using real dye effluent produced from the Sirumugai textile unit in India. The pine tree-derived biochar was selected for removal of aqueous AV dye in batch and fixed-bed column studies. The adsorbent material was characterized for crystallinity (XRD), surface area (BET), surface morphology and elemental compositions (SEM-EDX), thermal stability (TGA), weight loss (DGA), and functional groups (FTIR). Batch sorption studies were performed to evaluate (i) adsorption at various pH values (at pH 2 to 7), (ii) isotherms (at 10, 25, and 35 °C) to assess the temperature effect on the sorption efficiency, and (iii) kinetics to reveal the effect of time, adsorbent dose, and initial concentration on the reaction rate. After systematic evaluation, 2 g/L biochar, 25 mg/L AV, pH 3, 40 °C, and 40 and 360 min in a completely mixed batch study resulted in 50 and 90% dye removal, respectively. The isoelectric point at pH 3.7 ± 0.2 results in maximum dye removal, therefore suggesting that monitoring the ratio of different effluent (acid/wash/dye) can improve the colorant removal efficiency. The Langmuir isotherm best fits with the sorption of AV to biochar, provided a maximal dye uptake of 29 mg/g at 40 °C, showing that adsorption was endothermic. Fixed-bed studies were conducted at room temperature with an initial dye concentration of 25 and 50 mg/L. The glass columns were packed with biochar (bed depth 20 cm, pore volume = 14 mL) at an initial pH of 5.0 and a 10 mL/min flow rate for 120 min. Finally, the regeneration of the adsorbent was achieved using desorption studies conducted under the proposed experimental conditions resulted in 90-93% removal of AV even after five cycles of regeneration.

UV-LED Combined with Small Bioreactor Platform (SBP) for Degradation of 17α-Ethynylestradiol (EE2) at Very Short Hydraulic Retention Time.

Degradation of 17α-ethynylestradiol (EE2) and estrogenicity were examined in a novel oxidative bioreactor (OBR) that combines small bioreactor platform (SBP) capsules and UV-LED (ultraviolet light emission diode) simultaneously, using enriched water and secondary effluent. Preliminary experiments examined three UV-LED wavelengths-267, 279, and 286 nm, with (indirect photolysis) and without (direct photolysis) H2O2. The major degradation wavelength for both direct and indirect photolysis was 279 nm, while the major removal gap for direct vs. indirect degradation was at 267 nm. Reduction of EE2 was observed together with reduction of estrogenicity and mineralization, indicating that the EE2 degradation products are not estrogens. Furthermore, slight mineralization occurred with direct photolysis and more significant mineralization with the indirect process. The physical-biological OBR process showed major improvement over other processes studied here, at a very short hydraulic retention time. The OBR can feasibly replace the advanced oxidation process of UV-LED radiation with catalyst in secondary sedimentation tanks with respect to reduction ratio, and with no residual H2O2. Further research into this OBR system is warranted, not only for EE2 degradation, but also to determine its capabilities for degrading mixtures of pharmaceuticals and pesticides, both of which have a significant impact on the environment and public health.

Practical Chemical Actinometry-A Review.

Actinometers are physical or chemical systems that can be employed to determine photon fluxes. Chemical actinometers are photochemical systems with known quantum yields that can be employed to determine accurate photon fluxes for specific photochemical reactions. This review explores in detail several practical chemical actinometers (ferrioxalate, iodide-iodate, uranyl oxalate, nitrate, uridine, hydrogen peroxide and several actinometers for the vacuum ultraviolet). Each actinometer is described with recommended conditions for its use.

Wavelength-dependent time-dose reciprocity and stress mechanism for UV-LED disinfection of Escherichia coli.

Ultraviolet (UV) disinfection efficiency by low-pressure (LP) mercury lamp depends on the UV fluence (dose): the product of incident irradiance (fluence rate) and exposure time, with correction factors. Time-dose reciprocity may not always apply, as higher UV-LP inactivation of E. coli was obtained at a higher irradiance over shorter exposure time, for the same UV fluence. Disinfection by UV LEDs is limited by low radiant flux compared to mercury LP lamps. Our goal was to determine the UV-LED time-dose reciprocity of E. coli for four different central LED wavelengths (265, 275, 285 and 295 nm) under different fluence rates. Inactivation kinetics determined at UV-LED265 was not affected by the fluence rate or exposure time for a given UV fluence. In contrast, UV-LED275, UV-LED285, and UV-LED295 led to higher inactivation at low fluence rate coupled to high exposure time, for the same UV fluence. The intracellular damage mechanisms for each LED central wavelength were determined by using the bioreporters RecA as an indicator of bacterial DNA damage and SoxS as an indicator of oxidative stress. For 265 nm, higher DNA damage was observed, whereas for 285 and 295 nm, higher oxidative stress (possibly due to reactive oxygen species [ROS] damage) was observed. ROS inactivation of E. coli was predicted to be more effective when keeping the ROS concentration low but allowing longer exposure, for a given UV fluence.

UV-LED disinfection of Coronavirus: Wavelength effect.

UV light-emitting diodes (UV LEDs) are an emerging technology and a UV source for pathogen inactivation, however low UV-LED wavelengths are costly and have low fluence rate. Our results suggest that the sensitivity of human Coronavirus (HCoV-OC43 used as SARS-CoV-2 surrogate) was wavelength dependent with 267 nm ~ 279 nm > 286 nm > 297 nm. Other viruses showed similar results, suggesting UV LED with peak emission at ~286 nm could serve as an effective tool in the fight against human Coronaviruses.

Rapid visible-light degradation of EE2 and its estrogenicity in hospital wastewater by crystalline promoted g-C3N4.

Metal-free, chemically activated crystalline graphitic carbon nitride (g-C3N4) nanorods with enhanced visible-light photoactivity demonstrated rapid photodegradation of 17α-ethinylestradiol (EE2) in water and real hospital wastewater. Pure g-C3N4 and another three crystalline promoted g-C3N4 photocatalysts developed by hydrothermal method were characterized by, High-Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Photoluminescence (PL), Electron spin resonance (ESR), X-ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Spectroscopy (DRS). Hydrothermal-based chemical activation did not alter the crystal structure, functional group or surface morphology, but it enhanced the specific surface area of activated g-C3N4 due to intralayer delamination and depolymerization of g-C3N4. Compared to pure g-C3N4, the activated g-C3N4-3 demonstrated efficient degradation of EE2 (<30 min, 3 mg/l) by visible wavelengths of the solar spectrum. This work provides advanced insight into the construction of heterojunction visible-light photocatalysts and production of O2- via reduction of O2 with photogenerated electrons. Proposed and derived mechanism for photodegradation of EE2 by g-C3N4-3 using gas chromatography-mass spectrometry (GCMS). Yeast Estrogen Screen (YES) was performed to evaluate the estrogenicity of treated water samples. Efficient removal of EE2 estrogenic activity (<45 min, 3 mg/l) was achieved using the visible light-activated g-C3N4. Estrogenicity removal rate corresponded well with EE2-degradation rate.

Trace Organic Compound Removal from Wastewater Reverse-Osmosis Concentrate by Advanced Oxidation Processes with UV/O3/H2O2.

Advanced technologies, such as reverse osmosis (RO), allow the reuse of treated wastewater for direct or indirect potable use. However, even highly efficient RO systems produce ~10-15% highly contaminated concentrate as a byproduct. This wastewater RO concentrate (WWROC) is very rich in metal ions, nutrients, and hard-to-degrade trace organic compounds (TOrCs), such as pharmaceuticals, plasticizers, flame retardants, and detergents, which must be treated before disposal. WWROC could be up to 10 times more concentrated than secondary effluent. We examined the efficiency of several advanced oxidation processes (AOPs) on TOrC removal from a two-stage WWROC matrix in a pilot wastewater-treatment facility. WWROC ozonation or UV irradiation, with H2O2 addition, demonstrated efficient removal of TOrCs, varying between 21% and over 99% degradation, and indicating that radical oxidation (by HO·) is the dominant mechanism. However, AOPs are not sufficient to fully treat the WWROC, and thus, additional procedures are required to decrease metal ion and nutrient concentrations. Further biological treatment post-AOP is also highly important, to eliminate the degradable organic molecules obtained from the AOP.

Multiwell plates for obtaining a rapid microbial dose-response curve in UV-LED systems.

UV light-emitting diodes (UV-LEDs) have emerged as a new technology for water disinfection. Multiwell plates are a common tool in biological research, but they have never been used for UVC/UVB-inactivation experiments of microorganisms. In this study, a novel, rapid and simple UVC/UVB-inactivation assay was developed for a UV-LED system using a multiwell plate setup (96- and 24-well plates). The relative incident irradiance distribution across the exposed area was examined by spectroradiometry and nitrate-nitrite uniformity assay. The two methods showed a good correlation and high distribution factors (>0.89 and >0.94 for 96- and 24-well plates, respectively). In addition, the potential of the new system for determining disinfection efficacy of E. coli and MS2 coliphage by UV-LEDs emitting at central wavelengths of 265 nm and 285 nm was demonstrated. The inactivation rate constants were comparable to those obtained using UV-LED systems with the conventional dish (or beaker) setup, but the multiwell plate method allowed for many more repetitions. The proposed system is an alternative for UV-inactivation dose-response assay, especially when screening assays are desired, since it has the advantage of being fast, comprehensive (with a large number of simultaneous replicates) and easily adapted to various applications as UV-LED based photocatalysis experiments, UV effect on biofilm formation and UV-based AOP degradation experiments.

Ethanol-activated granular aerogel as efficient adsorbent for persistent organic pollutants from real leachate and hospital wastewater.

Hydrophobic aerogels were used to remove three types of persistent organic pollutants: pharmaceutical drugs (i.e. doxorubicin [DOX], paclitaxel [TAX]), phthalates (diethyl phthalate [DEP]), and hydrophilic rhodamine dye (RhB) from synthetic and real wastewaters, using Lumira granular aerogel from Cabot activated with EtOH (ET-GAG). The hydrophobic silica aerogel was characterized by X-ray diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), Brunauer-Emmet-Teller (BET) and attenuated total reflection-Fourier transform infrared spectroscopy. The pollutants were analysed by high-performance liquid chromatography (HPLC)-UV and HPLC-mass spectrometry. The adsorption process was governed by hydrophobic- hydrophobic interactions between the ET-GAG and micropollutants. The adsorption capacity of ET-GAG, examined by batch experiments, for DOX, TAX and DEP were 13.80, 14.28 and 17.54 mg/g respectively. The rate of adsorption to ET-GAG is high in the initial 40 min followed by no change in the rate due to saturation of adsorption sites. ET-GAG was able to completely remove micropollutants from real leachate and hospital wastewater, implying practical applications. Regeneration of the aerogel was studied by solvent extraction. Et-GAG adsorbent demonstrated better removal of toxic chemotherapeutic drugs and phthalates than GAC.

LP-UV-Nano MgO2 Pretreated Catalysis Followed by Small Bioreactor Platform Capsules Treatment for Superior Kinetic Degradation Performance of 17α-Ethynylestradiol.

A successful attempt to degrade synthetic estrogen 17α-ethynylestradiol (EE2) is demonstrated via combining photocatalysis employing magnesium peroxide (MgO2)/low-pressure ultraviolet (LP-UV) treatment followed by biological treatment using small bioreactor platform (SBP) capsules. Reusable MgO2 was synthesized through wet chemical synthesis and extensively characterized by X-ray diffraction (XRD) for phase confirmation, X-ray photoelectron spectroscopy (XPS) for elemental composition, Brunauer-Emmett-Teller (BET) to explain a specific surface area, scanning electron microscopy (SEM) imaging surface morphology, and UV-visible (Vis) spectrophotometry. The degradation mechanism of EE2 by MgO2/LP-UV consisted of LP-UV photolysis of H2O2 in situ (produced by the catalyst under ambient conditions) to generate hydroxyl radicals, and the degradation extent depended on both MgO2 and UV dose. Moreover, the catalyst was successfully reusable for the removal of EE2. Photocatalytic treatment by MgO2 alone required 60 min (~1700 mJ/cm2) to remove 99% of the EE2, whereas biodegradation by SBP capsules alone required 24 h to remove 86% of the EE2, and complete removal was not reached. The sequential treatment of photocatalysis and SBP biodegradation to achieve complete removal required only 25 min of UV (~700 mJ/cm2) and 4 h of biodegradation (instead of >24 h). The combination of UV photocatalysis and biodegradation produced a greater level of EE2 degradation at a lower LP-UV dose and at less biodegradation time than either treatment used separately, proving that synergetic photocatalysis and biodegradation are effective treatments for degrading EE2.

Treatment of Diethyl Phthalate Leached from Plastic Products in Municipal Solid Waste Using an Ozone-Based Advanced Oxidation Process.

Plastic products in municipal solid waste result in the extraction of phthalates in leachate that also contains large amounts of organic matter, such as humic substances, ammonia, metals, chlorinated organics, phenolic compounds, and pesticide residues. Phthalate esters are endocrine disruptors, categorized as a priority pollutant by the US Environmental Protection Agency (USEPA). Biological processes are inefficient at degrading phthalates due to their stability and toxic characteristics. In this study, the peroxone (ozone/hydrogen peroxide) process (O3/H2O2), an O3-based advanced oxidation process (AOP), was demonstrated for the removal of diethyl phthalate (DEP) in synthetic leachate simulating solid-waste leachate from an open dump. The impact of the O3 dose during DEP degradation; the formation of ozonation intermediate by-products; and the effects of H2O2 dose, pH, and ultraviolet absorbance at 254 nm (UVC) were determined during ozonation. Removal of 99.9% of an initial 20 mg/L DEP was obtained via 120 min of ozonation (transferred O3 dose = 4971 mg/L) with 40 mg/L H2O2 in a semi-batch O3 system. Degradation mechanisms of DEP along with its intermediate products were also determined for the AOP treatment. Indirect OH radical exposure was determined by using a radical probe compound (pCBA) in the O3 treatment.

The involvement of superoxide radicals in medium pressure UV derived inactivation.

Today, two types of lamp systems dominate the UV disinfection industry: low-pressure (LP) UV lamps and medium-pressure (MP) polychromatic lamps. Both lamp types have their advantages and disadvantages in microorganism inactivation, with LP lamps being cheaper, having longer life, and working at lower temperature, hence reducing fouling, and MP lamps showing better inactivation per germicidal dose for certain microorganisms. Bacterium-based biosensors were used to compare LP and MP irradiation. These biosensors were Escherichia coli bacteria carrying the lux operon genes under the control of different stress-responding promoters, where activation of the specific promoter is manifested as bioluminescence. MP irradiation, considerably more than LP irradiation, resulted in activation of the superoxide dismutase expression, indicating the formation of superoxide radicals inside the cells. Accordingly, pre-exposure (immunization) of the bacteria to an activator that produces superoxide radicals resulted in lower inactivation and increased resistance to MP irradiation, but not to LP irradiation. This study shows that the difference in germicidal efficiency may result from the production of intracellular superoxide radicals by MP irradiation, at wavelengths other than 254 nm, as emitted by LP lamps.

Nanocellulose production from recycled paper mill sludge using ozonation pretreatment followed by recyclable maleic acid hydrolysis.

Nanocellulose (NC) have garnered much interest worldwide due to its physical and chemical properties. Nanocellulose is produced from biomass materials by bleaching pretreatment, followed by acid hydrolysis. This work demonstrated the production of NC from recycled paper sludge (RPS), a crystalline cellulose rich waste, by ozonation pretreatment, followed by maleic acid hydrolysis. Ozonation resulted in removal of lignin (as evident by TGA analysis), negative zeta potential of RPS and enhanced NC production, from 60 mg/L to over 80 mg/L after 60-120 min of ozone treatment. Maleic acid was successfully recovered, although longer ozonation times reduced the amount of acid available for recovery. These results demonstrate that ozonation can be used as an effective pretreatment for NC production.