Evaluation of a photocatalytic reactor membrane pilot system for the removal of pharmaceuticals and endocrine disrupting compounds from water

Recent advances in visible light driven inactivation of bloom forming blue-green algae using novel nano-composites: Mechanism, efficiency and fabrication approaches

Over the years, algae have proved to be a water pollutant due to global warming, climate change, and the unregulated addition of organic compounds in water bodies from diffused resources. Harmful algal blooms (HABs) are severely affecting the health of humans and aquatic ecosystems. Among available anti-blooming technologies, semiconductor photocatalysis has come forth as an effective alternative. In the recent past, literature has been modified extensively with a decisive knowledge regarding algal invasion, desired preparation of nanomaterials with enhanced visible light absorption capacity and mechanisms for algal cell denaturation. The motivation behind this review article was to gather algal inactivation data in a systematic way based on various research studies, including the construction of nanoparticles and purposely to test their anti-algal activities under visible irradiation. Additionally, this article mentions variety of starting materials employed for preparation of various nano-powders with focus on their synthesis routes, analytical techniques as well as proposed mechanisms for lost cellular integrity in context of reduced chlorophyll' a' level, cell rapture, cell leakage and damages to other physiological constituents; credited to oxidative damage initiated by reactive oxidation species (ROS). Various floating and recyclable composited catalysts Ag2CO3-N: GO, Ag/AgCl@ZIF-8, Ag2CrO4-g-C3N4-TiO2/mEP proved to be game-changers owing to their enhanced VL absorption, adsorption, stability, separation and reusability. An outlook for the generalized limitations of published reports, cost estimations for practical implementation, issues and challenges faced by nano-photocatalysts and possible opportunities for future studies are also proposed. This review will be able to provide vast insights for coherent fabrication of catalysts, breakthroughs in experimental methodologies and help in elaboration of damage mechanisms.

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Scale-up of photoreactor with TiO2 thin layer for wastewater treatment

This study is devoted to the scale-up potential of TiO₂/UV photocatalyst for real wastewater treatment including its durability tests. The activity of the prepared TiO₂ layers was first tested in a laboratory reactor on key representative pollutants diclofenac, chloramphenicol and triclosan. A special pilot plant reactor of a two-tube system with 21 stainless steel annulets covered by TiO₂ thin layers and the inner volume of 3.5 L was constructed. Pilot tests were performed with wastewater from the pharmaceutical industry containing danazol and norethisterone with the concentration varying between 4 and 7 mg L^-1 at the flow 18 L h^-1 and municipal wastewater at the output sewage plant for 67,000 inhabitants containing bisphenol A, 4-nonyphenol, estron, ethinylestradiol and triclosan in the concentrations of the individual contaminants varying between 50 and 600 ng L^-1 at the flow 200 L h^-1. After the treatment during the pilot photocatalytic test, the concentration of individual contaminants decreased by 82-100%, while no decrease in the efficiency of the photocatalytic process was recorded during the long-term tests lasting for 3-6 months.

The strategy for organic dye and antibiotic photocatalytic removal for water remediation in an example of Co-SnO2 nanoparticles

A challenging problem to create an efficient photocatalyst suitable for industrial water remediation, aiming to remove cyclic organic compounds attracts increasing attention. The current study aimed to clarify a few "dark spots" in the field, namely to find out if it is possible to make an efficient photocatalyst activated with visible light by using a simple and cheap strategy and what are the key factor impacting its efficiency. In this work, a new procedure to obtain spherical nanoparticles with the same average size but different amounts of oxygen vacancies and defects and dopant concentrations was developed. The approach based on hydrothermal treatment was suggested to obtain rod-shaped nanoparticles. The systematic study of photocatalytic behavior on the example of oxytetracycline and methylene blue degradation under visible light of widely available LED lamp was performed. Based on chemical and computational experiments the main factor affecting the process efficiency was determined.

Occurrence, transformation, bioaccumulation, risk and analysis of pharmaceutical and personal care products from wastewater: a review

Almost all aspects of society from food security to disease control and prevention have benefited from pharmaceutical and personal care products, yet these products are a major source of contamination that ends up in wastewater and ecosystems. This issue has been sharply accentuated during the coronavirus disease pandemic 2019 (COVID-19) due to the higher use of disinfectants and other products. Here we review pharmaceutical and personal care products with focus on their occurrence in the environment, detection, risk, and removal.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10311-022-01498-7.

Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO2 Composite for Photocatalytic Degradation of Phenol

The Fe(III)-doped montmorillonite (Mt)/TiO2 composites were fabricated by adding Fe(III) during or after the aging of TiO2/Ti(OH)4 sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO2 and Fe/Mt/TiO2, respectively. In the xFe-Mt/(1 − x)Fe-TiO2, Fe(III) cations were expected to be located in the structure of TiO2, in the Mt, and in the interface between them, while Fe(III) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO2. The narrower energy bandgap (Eg) lower photo-luminescence intensity were observed for the composites compared with TiO2. Better photocatalytic performance for phenol degradation was observed in the Fe/Mt/TiO2. The 94.6% phenol degradation was due to greater charge generation and migration capacity, which was confirmed by photocurrent measurements and electrochemical impedance spectroscopy (EIS). The results of the energy-resolved distribution of electron traps (ERDT) suggested that the Fe/Mt/TiO2 possessed a larger amorphous rutile phase content in direct contact with crystal anatase than that of the xFe-Mt/(1 − x)Fe-TiO2. This component is the fraction that is mainly responsible for the photocatalytic phenol degradation by the composites. As for the xFe-Mt/(1 − x)Fe-TiO2, the active rutile phase was followed by isolated amorphous phases which had larger (Eg) and which did not act as a photocatalyst. Thus, the physically adsorbed Fe(III) enhanced light adsorption and avoided charge recombination, resulting in improved photocatalytic performance. The mechanism of the photocatalytic reaction with the Fe(III)-doped Mt/TiO2 composite was proposed.

Degradation of Minocycline by the Adsorption-Catalysis Multifunctional PVDF-PVP-TiO2 Membrane: Degradation Kinetics, Photocatalytic Efficiency, and Toxicity of Products

The photocatalytic degradation of minocycline was studied by using polyvinylidene fluoride-polyvinylpyrrolidone-TiO₂ (PVDF-PVP-TiO₂) fiber mats prepared by an electrospinning technology. The influences of the TiO₂ dosage, minocycline concentrations, inorganic anions, pH values, and dissolved organic matter (DOM) concentrations on the degradation kinetics were investigated. A mass of 97% minocycline was degraded in 45 min at 5% TiO₂ dosage. The corresponding decomposition rate constant was 0.069 min^-1. The inorganic anions affected the minocycline decomposition in the order of HCO₃^- > Cl^- > SO₄^2- > NO₃^-, which was confirmed by the results of electron spin resonance (ESR) spectra. The lowest electrical energy per order (E_EO) was 6.5 Wh/L. Over five cycles, there was no change in the photocatalytic performance of the degrading minocycline. Those investigations suggested that effective degradation of minocycline could be reached in the PVDF-PVP-TiO₂ fiber mats with a low energy consumption, good separation and, good recovery. Three photocatalytic decomposition pathways of minocycline were proposed: (i) hydroxyl substitution of the acylamino group; (ii) hydroxyl substitution of the amide group, and (iii) a cleavage of the methyl groups and further oxidation of the amino group by OH. Potential risks caused by TP159 and TP99 should not be ignored, while the TP90 are nontoxic. Tests indicated that the toxicity of the photocatalytic process may be persistent if minocycline and its products were not mineralized completely.

Remediation and mineralization processes for per- and polyfluoroalkyl substances (PFAS) in water: A review

Per- and polyfluoroalkyl substances (PFAS) are synthetic organic molecules used to manufacture various consumer and industrials products. In PFAS, the CF bond is stable, which renders these compounds chemically stable and prevents their breakdown. Several PFAS treatment processes such as adsorption, photolysis and photocatalysis, bioremediation, sonolysis, electrochemical oxidation, etc., have been explored and are being developed. The present review article has critically summarized degradative technologies and provides in-depth knowledge of photodegradation, electrochemical degradation, chemical oxidation, and reduction mineralization mechanism. Also, novel non-degradative technologies, including nano-adsorbents, natural and surface-modified clay minerals/zeolites, calixarene-based polymers, and molecularly imprinted polymers and adsorbents derived from biomaterials are discussed in detail. Of these novel approaches photocatalysis combined with membrane filtration or electrochemical oxidation via a treatment train approach shows promising results in removing PFAS in natural waters. The photocatalytic mineralization mechanism of PFOA is discussed, leading to recommendations for future research on novel remediation strategies for removing PFAS from water.

Engineering and modeling perspectives on photocatalytic reactors for water treatment

The debate on whether photocatalysis can reach full maturity at commercial level as an effective and economical process for treatment and purification of water and wastewater has recently intensified. Despite a bloom of scientific investigations in the last 30 years, particularly with regards to innovative photocatalytic materials, photocatalysis has so far seen a few industrial applications. Regardless of the points of view, it has been realized that research on reactor design and modeling are now equally urgent to match the extensive research carried out on innovative photocatalytic materials. In reality, the development of photocatalytic reactors has advanced steadily in terms of modeling and reactor design over the last two decades, though this topic has captured a smaller specialized audience. In this critical review, we introduce the latest developments on photocatalytic reactors for water treatment from an engineering perspective. The focus is on the modeling and design of photocatalytic reactors for water treatment at pilot- or at greater scale. Photocatalytic reactors utilizing both natural sunlight and UV irradiation sources are comprehensively discussed. The most promising photoreactor designs and models are examined giving key design guidelines. Other engineering considerations, such as operation, cost analysis, patents, and several industrial applications of photocatalytic reactors for water treatment are also presented. The dissemination of key photocatalytic reactor design principles among the scientific community and the water industry is currently one of the greatest obstacles in translating PWT research into widespread real-world application.

Cu2O nanoparticles anchored on carbon for the efficient removal of propofol from operating room wastewater via peroxymonosulfate activation: efficiency, mechanism, and pathway

Anesthetic drug wastage has increasingly become the main resource of operating room sewage, which poses a great risk to the safety of humans and other organisms. Propofol is the most widely used anesthetic drug in the world, and also occupies the largest proportion of the total anesthetic wastage in the operating room. In this work, a 2D Cu₂O anchored carbon catalyst (Cu₂O@NC) was prepared by the assembly-pyrolysis process and successfully applied to peroxymonosulfate (PMS) activation. We took propofol as a typical example and investigated the removal activity through heterostructure-enhanced advanced oxidation processes (AOPs). Through the degradation process, propofol can be removed from 20 ppm to ultralow levels within 5 min using the PMS/Cu₂O@NC system. The degradation pathway of propofol was deduced through quantum chemical calculation and LC/GC-MS results. The final products were verified as CO₂ and H₂O. Moreover, sulfate radicals (SO₄˙⁻) proved to be the dominant reactive oxidation species by radical scavenger experiments and ESR results. In addition, it has great universality for various pharmaceuticals such as tetracycline (TC), amoxicillin (AMX), cephalexin (CPX), and norfloxacin (NFX). Our work provided the possibility to treat operation room sewage in a rapid, high-efficiency, and feasible way.

The 2D Cu₂O@NC catalyst obtained by thermal decomposition of MOF, could effectively enhance the propofol removal from wastewater by activating peroxymonosulfate in the advanced oxidation process.

Comparison of AOPs at pilot scale: Energy costs for micro-pollutants oxidation, disinfection by-products formation and pathogens inactivation

This work evaluated different advanced oxidation processes (AOPs) operated at pilot-scale as tertiary treatment of municipal wastewater in terms of energy efficiency, disinfection by-products formation and pathogens inactivation. Investigated AOPs included UV/H₂O₂, UV/Cl₂, O₃, O₃/UV, H₂O₂/O₃/UV, Cl₂/O₃/UV. AOPs were operated using various ozone doses (1.5-9 mg L^-1), and UV fluences (191-981 mJ cm^-2). Electrical energy costs necessary for the oxidation of contaminants of emerging concern (CEC) (i.e., carbamazepine, fluoxetine, gemfibrozil, primidone, sulfamethoxazole, trimethoprim) were calculated using the electrical energy per order (E_EO) parameter. Ozonation resulted by far the most energy efficient process, whereas UV/H₂O₂ and UV/Cl₂ showed the highest energy costs. Energy costs for AOPs based on the combination of UV and ozone were in the order O₃/UV ≈ Cl₂/O₃/UV > H₂O₂/O₃/UV, and they were significantly lower than energy costs of UV/H₂O₂ and UV/Cl₂ processes. Cl₂/O₃/UV increased bromate formation, O₃/UV and O₃ had same levels of bromate formation, whereas H₂O₂/O₃/UV did not form bromate. In addition, UV photolysis resulted an effective treatment for NDMA mitigation even in combination with ozone and chlorine in AOP technologies. Ozonation (doses of 1.5-6 mg L^-1) was the least effective process to inactivate somatic coliphages, total coliform, escherichia coli, and enterococci. UV irradiation was able to completely inactivate somatic coliphages, total coliform, escherichia coli at low fluence (191 mJ cm^-2), whereas enterococci were UV resistant. AOPs that utilized UV irradiation were the most effective processes for wastewater disinfection resulting in a complete inactivation of selected indicator organisms by low ozone dose (1.5 mg L^-1) and UV fluence (191-465 mJ cm^-2).

Capillary electrophoresis and liquid chromatography for determining steroids in concentrates of purified water from Päijänne Lake

The research was done with partial filling micellar electrokinetic chromatography, microemulsion electrokinetic chromatography, and ultra-high performance liquid chromatography. The study focuses on determination of male and female steroids from cold and hot tap water of households in Helsinki City. The district´s raw water is made run from Päijänne Lake through a water tunnel to the purification plants in Helsinki area. The effluents delivered from the plants to households as tap water were sampled and used for the study. They were concentrated with solid phase extraction to exceed the detection limits of the three methods. With partial filling method the limits were 0.50, 0.48, 0.33, and 0.50 mg/L for androsterone, testosterone, progesterone, and testosterone-glucuronide, respectively. In microemulsion method the limit values were 1.33, 1.11, and 0.40 mg/L for androsterone, testosterone, and progesterone, respectively, and 0.83, 0.45, and 0.50 mg/L for hydrocortisone, 17-α-hydroxyprogesterone, and 17-α-methyltestosterone, respectively. In the tap water samples, progesterone concentrations represented the highest values being 0.22 and 1.18 ng/L in cold and hot water, respectively. They also contained testosterone (in all samples), its glucuronide metabolite (in 25% of the samples), and androstenedione (in 75% of the samples). The ultra-high liquid chromatographic method with mass spectrometric detection was used for identification of the steroids at µg/L level.

LED irradiated photo-Fenton for the removal of estrogenic activity and endocrine disruptors from wastewater treatment plant effluent

The goal of this work was to evaluate the performance of the LED irradiated photo-Fenton process on the removal of (i) estrogenic activity and (ii) seven endocrine disruptors (EDs) (4-octylphenol, 4-nonylphenol, bisphenol A, estrone, 17β-estradiol, 17α-ethinylestradiol, and estriol) from real wastewater treatment plant effluent (WWTPE). EDs are a group of contaminants of emerging concern present in WWTPE and which may be recognized by hormone receptors, thus harming animal and human health. The yeast estrogenic screen test (YES) was used to quantify estrogenic activity promoted by EDs in WWTPE samples before and after photo-Fenton treatment. Tests were performed following a factorial design with different iron (20, 40, and 60 mg L^-1) and hydrogen peroxide (100, 200, and 300 mg L^-1) concentrations in a laboratory scale LED photoreactor (λ = 455 nm, 1.5 L, 1.6 × 10^-6 Einstein s^-1). EDs were analyzed by gas chromatography coupled to a mass spectrometer. Control experiments consisted of Fenton process, iron only, LED irradiation only, and H₂O₂ only. Optimum experimental conditions for LED photo-Fenton resulted in 62% removal of estrogenic activity and 59% mineralization. In addition, treated WWTPE was not toxic to Aliivibrio fischeri and more than 80% of EDs were removed during LED irradiated photo-Fenton. Although Fenton process showed similar efficiency to that obtained by LED photo-Fenton, a higher volume of sludge was generated in the dark. Finally, results obtained in this study confirm the applicability of LED irradiated photo-Fenton process for improving the quality of WWTPE as an alternative to solar photo-Fenton in case solar radiation is not available, thus reducing hazards associated to WWTPE reuse or discharge.

Toward Scaling-Up Photocatalytic Process for Multiphase Environmental Applications

Recently, we have witnessed a booming development of composites and multi-dopant metal oxides to be employed as novel photocatalysts. Yet the practical application of photocatalysis for environmental purposes is still elusive. Concerns about the unknown fate and toxicity of nanoparticles, unsatisfactory performance in real conditions, mass transfer limitations and durability issues have so far discouraged investments in full-scale applications of photocatalysis. Herein, we provide a critical overview of the main challenges that are limiting large-scale application of photocatalysis in air and water/wastewater purification. We then discuss the main approaches reported in the literature to tackle these shortcomings, such as the design of photocatalytic reactors that retain the photocatalyst, the study of degradation of micropollutants in different water matrices, and the development of gas-phase reactors with optimized contact time and irradiation. Furthermore, we provide a critical analysis of research–practice gaps such as treatment of real water and air samples, degradation of pollutants with actual environmental concentrations, photocatalyst deactivation, and cost and environmental life-cycle assessment.

Critical review of photocatalytic disinfection of bacteria: from noble metals- and carbon nanomaterials-TiO2 composites to challenges of water characteristics and strategic solutions

This critical review covers ways to improve TiO₂-based photocatalysts, how water characteristics may affect photocatalytic disinfection, and strategies to tackle the challenges arising from water characteristics. Photocatalysis has shown much promise in the disinfection of water/wastewater, because photocatalysis does not produce toxic by-products, and is driven by green solar energy. There are however several drawbacks that are curbing the prevalence of photocatalytic disinfection applications: one, the efficiency of photocatalysts may limit popular utilization; two, the water characteristics may present some challenges to the process. TiO₂-based photocatalysts may be readily improved if composited with noble metals or carbon nanomaterials. Noble metals give TiO₂-based composites a higher affinity for dissolved oxygen, and induce plasmonic and Schottky effects in the TiO₂; carbon nanomaterials with a tunable structure, on the other hand, give the composites an improved charge carrier separation performance. Other than photocatalyst materials, the characteristics of water/wastewater is another crucial factor in the photocatalysis process. Also examined in this review are the crucial impacts that water characteristics have on photocatalysts and their interaction with bacteria. Accordingly, strategies to address the challenge of water characteristics on photocatalytic disinfection are explored: one, to modify the semiconductor conduction band to generate long-lifetime reactive species; two, to improve the interaction between bacteria and photocatalysts.

Surrogates for on-line monitoring of the attenuation of trace organic contaminants during advanced oxidation processes for water reuse

The large number of trace organic contaminants (TrOCs) in wastewater has resulted in severe concerns to human health. Ozonation and UV/H₂O₂ are widely used to remove TrOCs in wastewater treatment process. Owing to the trace concentrations of TrOCs in wastewater, real-time monitoring of the abatement efficiency of TrOCs through ozonation and UV/H₂O₂ is quite challenging. Instead of a direct measurement of all the TrOCs, the research community has begun to use different surrogates to monitor the attenuation of TrOCs during AOPs. Various surrogates have been developed over the past few decades. In this review, the different types of surrogates are summarized, including ultraviolet spectroscopy and fluorescence spectroscopy. Strong linear correlations have been found for the removal of TrOCs using AOPs, and the abatement of UV absorption spectroscopy at 254 nm or total fluorescence (TF). Moreover, a two-phase linear correlation can better describe the ozone-resistant TrOCs compared with a single linear correlation. Two different kinds of predictive models exist that use surrogates as the input for ozonation: the regression model and kinetic model. The development of the models requires a further understanding of the impacts of water quality, seasonal variations, and storm events on the kinetic parameters. For the in situ monitoring system, the light-emitting diode (LED) is one of the most promising light sources, although the sensitivity and accuracy still need to be improved.

Recent Advances in the Rejection of Endocrine-Disrupting Compounds from Water Using Membrane and Membrane Bioreactor Technologies: A Review

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants.

3D printed photoreactor with immobilized graphitic carbon nitride: A sustainable platform for solar water purification

Solar-energy-enabled photocatalysis is promising for sustainable water purification. However, photoreactor design, especially immobilizing nano-sized photocatalysts, remains a major barrier preventing industrial-scale application of photocatalysis. In this study, we immobilized photocatalytic graphitic carbon nitride on chitosan to produce g-C₃N₄/chitosan hydrogel beads (GCHBs), and evaluated GCHB photoreactivity for degrading phenol and emerging persistent micropollutants in a 3D printed compound parabolic collector (CPC) reactor. The CPC photocatalytic system showed comparable performance with slurry reactors for sulfamethoxazole and carbamazepine degradation under simulated sunlight, and it maintained the performance for contaminant removal in real water samples collected from water/wastewater treatment plants or under outdoor sunlight irradiation. Global drinking water production was estimated for the CPC system, and it holds promise for small-scale sustainable water treatment, including, but not limited to, the production of high-quality potable water for single houses, small communities, rural areas, and areas impacted by natural disasters in both developed and developing countries.

Organic phosphorus removal using an integrated advanced oxidation-ultrafiltration process

Non-reactive phosphorus (nRP) contains condensed phosphates and organic phosphorus (OP) species that are recalcitrant in secondary wastewater treatment and tend to remain in final effluents. To meet ultra-low effluent P discharge limits, persistent nRP must be removed. The objective of this study was to evaluate the use of an advanced oxidation process (AOP) which couples TiO₂/UV photolysis with ultrafiltration to oxidize and remove nRP species. Initial tests utilized OP model compounds, adenosine triphosphate (ATP) and aminoethylphosphonate (AEP), in a binary mixture to evaluate AOP treatment and to elucidate possible mechanisms of phosphorus removal. The results were consistent with a model of preferential ATP binding to the TiO₂ surface compared to AEP. On UV light exposure, AEP was removed from solution due to the photooxidation of ATP freeing up binding sites for AEP adsorption and subsequent oxidation. Orthophosphate released during AOP treatment was retained on the TiO₂ solids. The AOP was applied to three municipal wastewaters and one automotive industry effluent for P removal. In all cases, phosphorus removal was found to occur through filtration, surface complexation and UV oxidation. Total phosphorus removal efficiencies between 90 and 97% were observed for the municipal wastewater effluents and 44% removal was observed in the industrial effluent after treatment using AOP.

Performance of ozone and peroxone on the removal of endocrine disrupting chemicals (EDCs) coupled with cost analysis

Micropollutants such as endocrine disruptors are one of the most important groups of chemicals polluting water resources. Conventional treatment systems may not be effective for the removal of endocrine disrupting chemicals (EDCs), and the fate of these chemicals should be carefully monitored in the effluent of wastewater treatment plants (WWTPs). Additional treatment methods such as advanced oxidation processes can be used for the removal of endocrine disruptors. This study presents the existence of endocrine disruptors in 4 different effluents: (i) municipal WWTP effluent, (ii) textile industry WWTP effluent, (iii) organized industrial zone (OIZ) WWTP effluent and (iv) pharmaceutical industry discharge and also presents their removal efficiencies by ozonation and peroxone oxidation. A broad spectrum of removal efficiencies was observed for the EDCs present in the samples since the oxidation efficiency of wastewaters containing EDCs mainly depends on the wastewater matrix and on the type of the EDCs. Ozonation was found to be a lower-cost option than peroxone oxidation at the investigated conditions.

Efficient degradation of sodium diclofenac via heterogeneous Fenton reaction boosted by Pd/Fe@Fe3O4 nanoparticles derived from bio-recovered palladium

Dehalogenation of emerging pollutants has attracted worldwide attention. In this study, novel bio-Pd/Fe@Fe₃O₄ nanoparticles (NPs) were proposed to boost the heterogeneous Fenton reaction for degradation of sodium diclofenac (DCF). Specifically, Enterococcus faecalis (E. faecalis) was employed to achieve bio-recovered palladium (bio-Pd). Results showed that expected preparation of bio-Pd/Fe@Fe₃O₄ NPs was confirmed by various characterization techniques. The prepared bio-Pd/Fe@Fe₃O₄ NPs were spherical morphology with average size of 9 nm. Under the optimum conditions, the removal efficiency of 10 mg/L DCF in 20 min and 40 min reached as high as 94.69% and 99.65%, respectively. The dechlorination and mineralization efficiencies of DCF were 85.16% and 59.21% in 120 min, respectively. The main degradation pathway of DCF was complete mineralization with the final products CO₂, chloride ions and H₂O. The improvement of dechlorination efficiency was ascribed to the accelerated corrosion of nano zero valent iron (nZVI) by Pd/Fe galvanic effect and the rise of active hydrogen. Meanwhile, more ferrous ions were released into this solution, resulting in the higher heterogeneous Fenton reaction rate driven by bio-Pd/Fe@Fe₃O₄ NPs. Therefore, the findings suggested that bio-Pd/Fe@Fe₃O₄ NPs were effective catalysts for DCF dechlorination and mineralization. The work provided a novel strategy for degradation of halogen-containing environmental pollutants.

Removal of Pharmaceutical Contaminants in Wastewater Using Nanomaterials: A Comprehensive Review

BACKGROUND

The limitless presence of pharmaceutical contaminants in discharged wastewater has emerged as a threat to aquatic species and humans. Their presence in drinking water has although raised substantial concerns, very little is known about the fate and ecological impacts of these pollutants. As a result, these pollutants are inevitably introduced to our food chain at trace concentrations. Unfortunately, the conventional wastewater treatment techniques are unable to treat pharmaceuticals completely with practical limitations. The focus has now been shifted towards nanotechnology for the successful remediation of these persistent pollutants. Thus, the current review specifically focuses on providing readers brief yet sharp insights into applications of various nanomaterials for the removal of pharmaceutical contaminants.

METHODS

An exhaustive collection of bibliographic database was done with articles having high impact and citations in relevant research domains. An in-depth analysis of screened papers was done through standard tools. Studies were categorized according to the use of nanoscale materials as nano-adsorbents (graphene, carbon nanotubes), nanophotocatalysts (metal, metal oxide), nano-filtration, and ozonation for promising alternative technologies for the efficient removal of recalcitrant contaminants.

RESULTS

A total of 365 research articles were selected. The contemporary advancements in the field of nanomaterials for drinking and wastewater treatment have been thoroughly analyzed along with their future perspectives.

CONCLUSION

The recommendations provided in this article will be useful to adopt novel strategies for on-site removal of the emerging contaminants in pharmaceutical effluents and related industries.

Removal of trace organic contaminants by melamine-tuned highly cross-linked polyamide TFC membranes

In recent years, forward osmosis (FO) has represented numerous potential applications in safe water production. In this study, we improved the performance of FO thin film composite (TFC) membranes for the removal of trace organic compounds (TOrCs) by tuning the chemistry of its top active layer. The TFC membranes were synthesized by interfacial polymerization (IP) reaction between amine-containing monomers, e.g., meta-phenylene diamine (MPD) or para-phenylenediamine (PPD), and an acid chloride monomer, e.g., trimesoyl chloride (TMC). Owing to three free amine functionals over main core, melamine was used in the amine monomers solution to increase cross-linking among polyamide chains. Chemical and morphological characterization of the prepared membranes confirmed that melamine was successfully incorporated into the chemical structure of the top PA layer. Two agricultural toxic materials (atrazine and diazinon) were used to investigate the capability of the newly fabricated membranes in the removal of TOrCs. The obtained results showed that melamine-improved FO membranes provided higher atrazine and diazinon rejections in two different FO membrane configurations, including active layer facing feed solution (ALF) and active layer facing draw solution (ALD). The highest rejections of both diazinon (99.4%) and atrazine (97.3%) were achieved when the melamine modified MPD-based membrane served in ALF mode with 2 M NaCl as a draw solution.

Antibiotics mineralization by electrochemical and UV-based hybrid processes: evaluation of the synergistic effect

Antibiotics are not efficiently removed in conventional wastewater treatments. In fact, different advanced oxidation process (AOPs), including ozone, peroxide, UV radiation, among others, are being investigated in the elimination of microcontaminants. Most of AOPs proved to be efficient on the degradation of antibiotics, but the mineralization is on the one hand not evaluated or on the other hand not high. At this work, the UV-based hybrid process, namely Photo-assisted electrochemical oxidation (PEO), was applied, aiming the mineralization of microcontaminants such as the antibiotics Amoxicillin (AMX), Norfloxacin (NOR) and Azithromycin (AZI). The influence of the individual contributions of electrochemical oxidation (EO) and the UV-base processes on the hybrid process (PEO) was analysed. Results showed that AMX and NOR presented higher mineralization rate under direct photolysis than AZI due to the high absorption of UV radiation. For the EO processes, a low mineralization was found for all antibiotics, what was associated to a mass-transport limitation related to the low concentration of contaminants (200 µg/L). Besides that, an increase in mineralization was found, when heterogeneous photocatalysis and EO are compared, due to the influence of UV radiation, which overcomes the mass-transport limitations. Although the UV-based processes control the reaction pathway that leads to mineralization, the best results to mineralize the antibiotics were achieved by PEO hybrid process. This can be explained by the synergistic effect of the processes that constitute them. A higher mineralization was achieved, which is an important and useful finding to avoid the discharge of microcontaminants in the environment.

Efficient treatment of traditional Chinese pharmaceutical wastewater using a pilot-scale spiral symmetry stream anaerobic bioreactor compared with internal circulation reactor

It is a technical barrier to efficiently treat traditional Chinese pharmaceutical (TCP) wastewater, due to its high chemical oxygen demanding (COD) concentration (>5000 mg/L). This study proposed and employed a spiral symmetry stream anaerobic bioreactor (SSSAB) to treat TCP wastewater. Results showed that a pilot-scale SSSAB (150 L) could achieve COD removal efficiency of 94.8% and volumetric removal rate (VRR) of 19.7 ± 0.7 kg COD·(m³·d)^-1 under room temperature, which were much higher than operation performance in internal circulation (IC) anaerobic reactor (COD removal efficiency and VRR were 85% and 11.3 ± 0.8 kg COD·(m³·d)^-1, respectively). The maximum COD volume removal rate could attain 43.4 kg COD·(m³·d)^-1. The characteristics of granular sludge in SSSAB were investigated from both temporal and spatial scales. During the operation period, the anaerobic granular sludge in SSSAB was of higher concentration and superior properties compared to the IC anaerobic reactor. The sludge concentration exhibited a spatially decline trend, decreasing from 61 g L^-1 in the bottom to 34 g·L^-1at the top of the bed, yet the average biomass concentration was still higher than that in IC reactor. According to shock tests with fluctuated real wastewater. the resistance of SSSAB to hydraulic and loading shock was up to 4.3 m h^-1 and 42 (kg COD· h) · (m³)^-1, respectively. The study demonstrated the proposed SSSAB is a promising reactor to treat high-concentration TCP wastewater.

Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in Source Water and Their Treatment in Drinking Water

Per-and polyfluoroalkyl substances (PFAS) occurrence in drinking water and treatment methods for their removal are reviewed. PFAS are fluorinated substances whose unique properties make them effective surface-active agents with uses ranging from stain repellants to fire-fighting foams. In response to concerns about drinking water contamination and health risks from PFAS exposure, the United States Environmental Protection Agency published Health Advisories (HAs) for perfluorooctanoic acid and perfluorooctane sulfonic acid. The occurrence of six PFAS in drinking water has been reported in the Third Unregulated Contaminant Monitoring Rule (UCMR3), and subsequent analysis of the dataset suggested that four percent of water systems reported at least one detectable PFAS compound and 1.3 percent of water systems reported results above the HAs. Many treatment technologies have been evaluated in the literature, with the most promising and readily applied treatment technologies being activated carbon, anion exchange resins, and high-pressure membrane systems. From these data and literature reports, research and data gaps were identified and suggestions for future research are provided.

Solar Photocatalytic Degradation of Sulfamethoxazole by TiO2 Modified with Noble Metals

Application of solar photocatalysis for water treatment is intensively studied. In this work, we investigated TiO2 modified with platinum (Pt/TiO2) and palladium (Pd/TiO2) using sulfamethoxazole (SMX) as the model contaminant. We considered the following parameters: (i) level of TiO2 modification with Pt/Pd, (ii) initial concentration of photocatalysts, (iii) geographic location where processes were conducted, and (iv) natural water matrix. The catalysts characterized by SEM, EDX, DRS, and XRD techniques showed successful deposition of Pd and Pt atoms on TiO2 surface that enabled light absorption in the visible (Vis) range, and therefore caused efficient SMX removal in all tested conditions. A comparison of the rate constants of SMX degradation in various conditions revealed that modification with Pd gave better results than modification with Pt, which was explained by the better optical properties of Pd/TiO2. The removal of SMX was higher with Pd/TiO2 than with Pt/TiO2, independent of the modification level. In the experiments with the same modification level, similar rate constants were achieved when four times the lower concentration of Pd/TiO2 was used as compared with Pt/TiO2. Formation of four SMX transformation products was confirmed, in which both amine groups are involved in photocatalytic oxidation. No toxic effect of post-reaction solutions towards Lepidium sativum was observed.

Highly efficient modified lead oxide electrode using a spin coating/electrodeposition mode on titanium for electrochemical treatment of pharmaceutical pollutant

In this study, Ti/TiO₂/PbO₂ anodes consisting of a PbO₂ coating growth on the TiO₂ interlayer deposited on titanium substrates were prepared combining different deposition technics: electrochemical method using anodization (Anod), electrodeposition (EL), and sol gel spin coating (SG). Different kinds of anodes have been tested for the removal of ampicillin, a pharmaceutical pollutant, from water. The structure and the surface morphology of the prepared multiple coatings were characterized by scanning electron microscopy and Energy-Dispersive X-ray spectroscopy respectively. Electrochemical impedance spectroscopy was also investigated in order to study the electrocatalytic activity of the anodes. The performance of the electrodes was evaluated through high performance liquid chromatography and chemical oxygen demand (COD) measurements. It was noticed that ampicillin could be mineralized by anodic oxidation process using Ti/TiO₂/PbO₂ anodes. The best results were obtained for Ti/TiO₂^SG/PbO₂^EL as anode with a 64% of COD removal after 300 min of treatment and a fast decrease in the amount of ampicillin was reached after almost one hour. Experimental results demonstrate that Ti/TiO₂^SG/PbO₂^EL anode presents the best ability for the degradation of ampicillin through anodic oxidation compared to the Ti/TiO₂^SG/PbO₂^SG and Ti/TiO₂^Anod/PbO₂^EL electrodes.

The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?

Advanced oxidation processes via semiconductor photocatalysis for water treatment have been the subject of extensive research over the past three decades, producing many scientific reports focused on elucidating mechanisms and enhancing kinetics for the treatment of contaminants in water. Many of these reports imply that the ultimate goal of the research is to apply photocatalysis in municipal water treatment operations. However, this ignores immense technology transfer problems, perpetuating a widening gap between academic advocation and industrial application. In this Feature, we undertake a critical examination of the trajectory of photocatalytic water treatment research, assessing the viability of proposed applications and identifying those with the most promising future. Several strategies are proposed for scientists and engineers who aim to support research efforts to bring industrially relevant photocatalytic water treatment processes to fruition. Although the reassessed potential may not live up to initial academic hype, an unfavorable assessment in some areas does not preclude the transfer of photocatalysis for water treatment to other niche applications as the technology retains substantive and unique benefits.

From micro to macro-contaminants: The impact of low-energy titanium dioxide photocatalysis followed by filtration on the mitigation of drinking water organics

This study evaluated strategies targeting macro- and micro-organic contaminant mitigation using low-energy titanium dioxide photocatalysis. Energy inputs of 1, 2, and 5 kWh m^-3 resulted in incomplete oxidation of macro-organic natural organic matter, signified by greater reductions of UV₂₅₄ and specific ultraviolet UV absorbance (SUVA) in comparison to dissolved organic carbon (DOC). The rate of UV₂₅₄ removal was 3 orders of magnitude greater than the rate of DOC degradation. Incomplete oxidation improved operation of downstream filtration processes. Photocatalysis at 2 kWh m^-3 increased the bed life of downstream granular activated carbon (GAC) filtration by 340% relative to direct filtration pretreatment. Likewise, photocatalysis operated ahead of microfiltration decreased fouling, resulting in longer filter run times. Using 2 kWh m^-3 photocatalysis increased filter run time by 36 times in comparison to direct filtration. Furthermore, levels of DOC and UV₂₅₄ in the membrane permeate improved (with no change in removal across the membrane) using low-energy photocatalysis pretreatments. While high-energy UV inputs provided high levels of removal of the estrogenic micro-organics estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethynlestradiol (EE2), low-energy photocatalysis did not enhance removal of estrogens beyond levels achieved by photolysis alone. In the cases of E1 and E3, the addition of TiO₂ as a photocatalyst reduced degradation rates of estrogens compared to UV photolysis. Overall, process electrical energy per order magnitude reductions (EEOs) greatly improved using photocatalysis, versus photolysis, for the macro-organics DOC, UV₂₅₄, and SUVA; however, energy required for removal of estrogens was similar between photolysis and photocatalysis.

Membrane-based separation of potential emerging pollutants

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Occurrence and ecotoxicological assessment of pharmaceuticals: Is there a risk for the Mediterranean aquatic environment?

Due to their pseudo-persistence and their biological activity, pharmaceuticals are emerging contaminants of major concern for the environment. The aim of this review is to provide an updated inventory of the contamination of aquatic environments by 43 drugs representing different classes of pharmaceuticals, such as antibiotics, anti-inflammatory drugs, anti-depressants, sex hormones, lipid regulators and beta-blockers. The data collected is focused on contamination levels reported in marine coastal waters and in waste and river waters flowing into the Mediterranean Sea. The most widely produced/prescribed classes of medicines are compared with the substances most widely searched for in the environment. Ranges of pollution levels according to the type of water body are also presented, to examine the fate in sewage treatment plants and the persistence in the environment of the targeted molecules. Levels of pharmaceuticals ranged from 100 to 10,000 or even 100,000 ng·L^-1 in sewage waters, dropping to 1 to 10,000 ng·L^-1 in rivers and to not detected to 3000 ng·L^-1 in sea water. However, this paper evidences a lack of data for seawater and also for several countries along the southern coast of the Mediterranean Sea. In order to assess the risk for aquatic ecosystems associated with pharmaceuticals, experimental ecotoxicological values obtained using normalized acute and/or chronic bioassays carried out with different trophic levels were collected for each drug. Targeted biological species and associated bioassays are classified on the basis of their sensitivity to each class of compounds. Occurrence and ecotoxicology are then linked by using the Hazard Quotient (HQ) to assess the environmental risk caused by pharmaceuticals in the Mediterranean Basin. Correlations between HQ and frequency of detection of pharmaceuticals highlighted thirteen compounds that are cause for concern in Mediterranean fresh and sea waters, such as 17α-ethinylestradiol, metoprolol, 8 antibiotics and 3 analgesics/anti-inflammatories.

Porous Electrospun Fibers Embedding TiO2 for Adsorption and Photocatalytic Degradation of Water Pollutants

Using a bipolymer system consisting of polyvinylpyrrolidone (PVP) and poly(vinylidene fluoride) (PVDF), P25-TiO₂ was immobilized into thin film mats of porous electrospun fibers. Pores were introduced by dissolving sacrificial PVP to increase surface area and enhance access to TiO₂. The highest photocatalytic activity was achieved using a PVDF:PVP weight ratio of 2:1. Methylene blue (MB) was used to visualize contaminant removal, assess the sorption capacity (5.93 ± 0.23 mg/g) and demonstrate stable removal kinetics ( k_MB > 0.045 min^-1) under UVA irradiation (3.64 × 10^-9 einstein/cm²/s) over 10 cycles. Treatment was also accomplished via sequential MB sorption in the dark and subsequent photocatalytic degradation under UVA irradiation, to illustrate that these processes could be uncoupled to overcome limited light penetration. The photocatalytic mat degraded bisphenol A and 17α-ethynylestradiol in secondary wastewater effluent (17 mg TOC/L), and (relative to TiO₂ slurry) immobilization of TiO₂ in the mat mitigated performance inhibition by co-occurring organics that scavenge oxidation capacity. This significantly lowered the electrical energy-per-order of reaction (EEO) needed to remove such endocrine disruptors in the presence of oxidant scavenging/inhibitory organics. Thus, effective TiO₂ immobilization into polymers with affinity toward specific priority pollutants could both increase the efficiency and reduce energy requirements of photocatalytic water treatment.

Compact light-emitting diode optical fiber immobilized TiO2 reactor for photocatalytic water treatment

A key barrier to implementing photocatalysis is delivering light to photocatalysts that are in contact with aqueous pollutants. Slurry photocatalyst systems suffer from poor light penetration and require post-treatment to separate the catalyst. The alternative is to deposit photocatalysts on fixed films and deliver light onto the surface or the backside of the attached catalysts. In this study, TiO₂-coated quartz optical fibers were coupled to light emitting diodes (OF/LED) to improve in situ light delivery. Design factors and mechanisms studied for OF/LEDs in a flow-through reactor included: (i) the influence of number of LED sources coupled to fibers and (ii) the use of multiple optical fibers bundled to a single LED. The light delivery mechanism from the optical fibers into the TiO₂ coatings is thoroughly discussed. To demonstrate influence of design variables, experiments were conducted in the reactor using the chlorinated pollutant para-chlorobenzoic acid (pCBA). From the degradation kinetics of pCBA, the quantum efficiencies (Φ) of oxidation and electrical energies per order (E_EO) were determined. The use of TiO₂ coated optical fiber bundles reduced the energy requirements to deliver photons and increased available surface area, which improved Φ and enhanced oxidative pollutant removal performance (E_EO).

Treatment of secondary effluent by sequential combination of photocatalytic oxidation with ceramic membrane filtration

The aim of the present work was to experimentally evaluate an alternative advanced wastewater treatment system, which combines the action of photocatalytic oxidation with ceramic membrane filtration. Experiments were carried out using laboratory scale TiO₂/UV photocatalytic reactor and tubular ceramic microfiltration (CMF) system to treat the secondary effluent (SE). A 100-nm pore size CMF membrane was investigated in cross flow mode under constant transmembrane pressure of 20 kPa. The results show that specific flux decline of CMF membrane with and without TiO₂/UV photocatalytic treatment was 30 and 50%, respectively, after 60 min of filtration. Data evaluation revealed that the adsorption of organic compounds onto the TiO₂ particles was dependent on the pH of the suspension and was considerably higher at low pH. The liquid chromatography-organic carbon detector (LC-OCD) technique was used to characterise the dissolved organic matter (DOM) present in the SE and was monitored following photocatalysis and CMF. The results showed that there was no removal of biopolymers and slight removal of humics, building blocks and the other oxidation by-products after TiO₂/UV photocatalytic treatment. This result suggested that the various ions present in the SE act as scavengers, which considerably decrease the efficiency of the photocatalytic oxidation reactions. On the other hand, the CMF was effective for removing 50% of biopolymers with no further removal of other organic components after photocatalytic treatment. Thus, the quantity of biopolymers in SE has an apparent correlation with the filterability of water samples in CMF.

Application of a micro-meso-structured reactor (NETmix) to promote photochemical UVC/H2O2 processes – oxidation of As(iii) to As(v)

A micro-meso-structured reactor (NETmix) was used for the first time to promote UVC/H₂O₂ processes.

Slurry photocatalytic membrane reactor technology for removal of pharmaceutical compounds from wastewater: Towards cytostatic drug elimination

The potential of photocatalytic membrane reactors (PMR) to degrade cytostatic drugs is presented in this work as an emerging technology for wastewater treatment. Cytostatic drugs are pharmaceutical compounds (PhCs) commonly used in cancer treatment. Such compounds and their metabolites, as well as their degraded by-products have genotoxic and mutagenic effects. A major challenge of cytostatic removal stands in the fact that most drugs are delivered to ambulant patients leading to diluted concentration in the municipal waste. Therefore safe strategies should be developed in order to collect and degrade the micro-pollutants using appropriate treatment technologies. Degradation of cytostatic compounds can be achieved with different conventional processes such as chemical oxidation, photolysis or photocatalysis but the treatment performances obtained are lower than the ones observed with slurry PMRs. Therefore the reasons why slurry PMRs may be considered as the next generation technology will be discussed in this work together with the limitations related to the mechanical abrasion of polymeric and ceramic membranes, catalyst suspension and interferences with the water matrix. Furthermore key recommendations are presented in order to develop a renewable energy powered water treatment based on long lifetime materials.