Photocatalysis Using UV-A and UV-C Light Sources for Advanced Oxidation of Anti-Cancer Drugs Spiked in Laboratory-Grade Water and Synthetic Urine

Advanced photocatalysis as a viable and sustainable wastewater treatment process: A comprehensive review

In our era, water pollution not only poses a serious threat to human, animal, and biotic life but also causes serious damage to infrastructure and the ecosystem. A set of physical, chemical, and biological technologies have been exploited to decontaminate and/or disinfect water pollutants, toxins, microbes, and contaminants, but none of these could be ranked as sustainable and scalable wastewater technology. The photocatalytic process can harmonize the sunlight to degrade certain toxins, chemicals, microbes, and antibiotics, present in water. For example, transition metal oxides (ZnO, SnO2, TiO2, etc.), when integrated into an organic framework of graphene or nitrides, can bring about more than 90% removal of dyes, microbial load, pesticides, and antibiotics. Similarly, a modified network of graphitic carbon nitride can completely decontaminate petrochemicals. The present review will primarily highlight the mechanistic aspects for the removal and/or degradation of highly concerned contaminants, factors affecting photocatalysis, engineering designs of photoreactors, and pros and cons of various wastewater treatment technologies already in practice. The photocatalytic reactor can be a more viable and sustainable wastewater treatment opportunity. We hope the researcher will find a handful of information regarding the advanced oxidation process accomplished via photocatalysis and the benefits associated with the photocatalytic-type degradation of water pollutants and contaminants.

Remarkably fast and reusable photocatalysis by UV annealed Cu2O-SnO2 p-n heterojunction

Powdered micro- or nano-particles photocatalyst has separation and recovery challenges, which may create a second pollution to environment and harmful to animals. To address those issues, SnO2, Cu2O and Cu2O-SnO2 p-n heterojunction thin films are formed on glass substrates using efficient co-sputtering method that is commonly employed for large-area high-definition display panel. Using first-order kinetics, 100 °C ultraviolet (UV) annealed Cu2O-SnO2 p-n heterojunction shows the superb fast degradation rate constant of 0.21 and 0.16 min-1 for methylene blue (MB) and methyl orange (MO) organic dyes, respectively, as photogenerated electron-hole pairs is increased. Record best degradation rate constants of 0.19 and 0.11 min-1 for respective MB and MO are still achieved even after four repeated cycles. The 100 °C UV annealed Cu2O-SnO2 film catalyst displays greater degradation efficiency in both dyes, reaching 100% degradation at room temperature after 30 and 35 min of illumination for MB and MO respectively. The scavenger experiments show that hydroxyl (·OH) and superoxide radicals (·O2-) are the major active species in the degradation of dye. The 100 °C UV annealed Cu2O-SnO2 film catalyst showed stability as well as reusability towards the dye degradation. As a result, the present work delivers an effective way to enhance the photocatalytic performance and also an easy recovery of the catalyst, which can be explored for various emerging pollutants.

Anticancer drugs in wastewater and natural environments: A review on their occurrence, environmental persistence, treatment, and ecological risks

The consumption of anticancer drugs (also known as chemotherapy drugs or antineoplastic drugs) has augmented over the last decades due to increased cancer incidence. Although there is an increasing concern about the presence of pharmaceutical compounds in natural environments and urban/domestic wastewater, anticancer drugs used in chemotherapy and anticancer medication have received less attention. In this review, the occurrence, environmental persistence, and known and potential ecological impacts of anticancer drugs is discussed. This review shows that these compounds are being increasingly detected in effluents of hospitals, influents and effluents of wastewater treatment plants, river surface water and sediments, groundwater, and even drinking water. Anticancer drugs can impact aquatic organisms such as algae, crustaceans, rotifers, and fish and may promote changes in soil and water microbial communities that may alter ecosystem functioning. Our knowledge of technologies for the removal of anticancer drugs is still limited, and these drugs can be dispersed in nature in a diffuse way in an uncontrolled manner. For this reason, an improved understanding of the presence, persistence, and ecological impacts of anticancer drugs in wastewater and natural environments is needed to help design management strategies, protect aquatic microorganisms, and mitigate potential ecological impacts.

Degradation of Agro-Industrial Wastewater Model Compound by UV-A-Fenton Process: Batch vs. Continuous Mode

The degradation of a model agro-industrial wastewater phenolic compound (caffeic acid, CA) by a UV-A-Fenton system was investigated in this work. Experiments were carried out in order to compare batch and continuous mode. Initially, batch experiments showed that UV-A-Fenton at pH 3.0 (pH of CA solution) achieved a higher generation of HO•, leading to high CA degradation (>99.5%). The influence of different operational conditions, such as H2O2 and Fe2+ concentrations, were evaluated. The results fit a pseudo first-order (PFO) kinetic model, and a high kinetic rate of CA removal was observed, with a [CA] = 5.5 × 10−4 mol/L, [H2O2] = 2.2 × 10−3 mol/L and [Fe2+] = 1.1 × 10−4 mol/L (kCA = 0.694 min−1), with an electric energy per order (EEO) of 7.23 kWh m−3 order−1. Under the same operational conditions, experiments in continuous mode were performed under different flow rates. The results showed that CA achieved a steady state with higher space-times (θ = 0.04) in comparison to dissolved organic carbon (DOC) removal (θ = 0−0.020). The results showed that by increasing the flow rate (F) from 1 to 4 mL min−1, the CA and DOC removal rate increased significantly (kCA = 0.468 min−1; kDOC = 0.00896 min−1). It is concluded that continuous modes are advantageous systems that can be adapted to wastewater treatment plants for the treatment of real agro-industrial wastewaters.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Wireless UV-A LEDs-driven AOP in the treatment of agro-industrial wastewaters

A wireless UV-A LEDs lab-scale reactor powered by a resonant inductive coupling (RLC) system was built to maximize the UV photon absorption of agro-industrial wastewaters. The UV-A LEDs (λ = 365 nm) energy was supplied through a magnetic field generated inside of the photoreactor by induction coils placed on the external wall made of polyvinyl chloride. Immersing the light sources in the wastewater increases the photon transfer efficiency and the reaction rate. Maximum magnetic field and optical irradiance were obtained at 26.8 and 27.0 kHz, respectively. As proof-of-concept, elderberry wastewater (EW), olive washing wastewater (OWW) and white and red winery wastewaters (WWW and RWW) were treated combining the wireless UV-A LEDs with the Advanced Oxidation Process (AOP) - Fenton reagent. Fenton experiments were performed using [Fe²⁺] = 10 mg L^-1_, [H₂O₂] = 500 mg L^-1, pH = 3 and a reaction time of 4 h. With EW a DOC removal of 35% (k = 0.0696 h^-1) was achieved, whereas adding the wireless UV-A LEDs (f = 26.8 kHz) 53% was attained (k = 0.1722 h^-1). The Electric Energy per Order (E_EO) for the wireless UV-A LEDs consumption was calculated (E_{EO LEDs} = 48.7 kWh m^-3 order^-1) and for all the remain equipment (air pump, RC box and power amplifier), E_{EO total} = 495 kWh m^-3 order^-1. Experiments with OWW presented a DOC removal of 62% and a E_{EO LEDs} = 40.5 kWh m^-3 order^-1; RWW shown 40% of DOC removal and a E_{EO LEDs} = 68.4 kWh m^-3 order^-1, while with WWW 35% of DOC removal and a E_{EO LEDs} = 79.8 kWh m^-3 order^-1 were obtained. This work shows that wireless UV-A LEDs can be a promising alternative to conventional UV lamps and wired LEDs in the treatment of real wastewaters. However, optimization of the induction system is still needed, as well as the number and wavelength of the LEDs (e.g. UV-C LEDs) to reduce the overall treatment costs.

Effective treatment of hospital wastewater with high-concentration diclofenac and ibuprofen using a promising technology based on degradation reaction catalyzed by Fe0 under microwave irradiation

Real hospital wastewater was effectively treated by a promising technology based on degradation reaction catalyzed by Fe⁰ under microwave irradiation in this work. Fe⁰ powders were synthesized and characterized by different techniques, resulting in a single-phase sample with spherical particles. Optimum experimental conditions were determined by a central composite rotatable design combined with a response surface methodology, resulting in 96.8% of chemical oxygen demand reduction and 100% organic carbon removal, after applying MW power of 780 W and Fe⁰ dosage of 0.36 g L^-1 for 60 min. Amongst the several organic compounds identified in the wastewater sample, diclofenac and ibuprofen were present in higher concentrations; therefore, they were set as target pollutants. Both compounds were completely degraded in 35 min of reaction time. Their plausible degradation pathways were investigated and proposed. Overall, the method developed in this work effectively removed high concentrations of pharmaceuticals in hospital wastewater.

Threat and sustainable technological solution for antineoplastic drugs pollution: Review on a persisting global issue

In the past 20 years, the discharge of pharmaceuticals and their presence in the aquatic environment have been continuously increasing and this has caused serious public health and environmental concerns. Antineoplastic drugs are used in chemotherapy, in large quantities worldwide, for the treatment of continuously increasing cancer cases. Antineoplastic drugs also contaminate water sources and possess mutagenic, cytostatic and eco-toxicological effects on microorganisms present in the aquatic environment as well as on human health. Due to the recalcitrant nature of antineoplastic drugs, the commonly used wastewater treatment processes are not able to eliminate these drugs. Globally, various anticancer drugs are being consumed during chemotherapy in hospitals and households by out-patients. These anti-cancer agents enter the water bodies in their original form or as metabolites via urine and faeces of the out-patients or the patients admitted in hospitals. Due to its high lipid solubility, the antineoplastic drugs accumulate in the fatty tissues of the organisms. These drugs enter through the food chain and cause adverse health effects on humans due to their cytotoxic and genotoxic properties. The United States Environmental Protection Agency (US-EPA) and the Organization for Economic Cooperation and Development (OECD) elucidated new regulations for the management of hazardous pharmaceuticals in the water environment. In this paper, the role of antineoplastic agents as emerging water contaminants, its transfer through the food chain, its eco-toxicological properties and effects, technological solutions and management aspects were reviewed.

Photocatalytic degradation of an agro-industrial wastewater model compound using a UV LEDs system: kinetic study

An ultraviolet light emitting diode (UV-A LED) system was built to test the capability of performing heterogeneous photocatalysis using TiO₂ P25. The LEDs maximum wavelength is 365 nm with an irradiance power of 85 W m^-2. The device was tested in batch and continuous (CSTR) mode in a laboratorial scale reactor. The degradation of an agro-industrial wastewater model compound (p-hydroxybenzoic acid, pHBA) was investigated, assessing the effect of different experimental conditions such as pH, pHBA and TiO₂ concentration keeping constant the UV-A LEDs power and temperature. The photodegradation of different concentrations of pHBA with [TiO₂] = 500 mg L^-1, I_UV = 85 W m^-2 and a T = 21 °C were analysed by pseudo-first order kinetics. The results were applied to the Langmuir-Hinshelwood model yielding k_c = 0.885 mg L^-1 min^-1 and k_LH = 0.217 L mg^-1. In a comparative experiment the UV-A LEDs system showed faster kinetics (k = 0.0134 min^-1) than solar radiation (I_UV = 23 W m^-2; k = 0.0077 min^-1), with [pHBA] = 75 mg L^-1 and [TiO₂] = 500 mg L^-1. The values of the Electric Energy per Order (E_EO) = 115 kWh m^-3 order^-1 and the Specific Applied Energy (E_SAE) = 318 kWh mol^-1 order^-1 were obtained with [TiO₂] = 1000 mg L^-1 and [pHBA] = 50 mg L^-1. Analogous results were obtained ([TiO₂] = 500 mg L^-1) in a CSTR with a slight decrease in the first order kinetic constant due to the "non-ideal" reactor: from 0.0284 to 0.0158 min^-1 and from 0.0143 to 0.00825 min^-1 with [pHBA] = 50 mg L^-1 and 75 mg L^-1, respectively. This work shows that photocatalytic reactors with UV-A LEDs can advantageously replace conventional UV mercury lamps based reactors in the photodegradation of phenolic compounds.

Environmental Remediation of Antineoplastic Drugs: Present Status, Challenges, and Future Directions

The global burden of cancer is on the rise, and as a result, the number of therapeutics administered for chemotherapy is increasing. The occupational exposure, recalcitrant nature and ecotoxicological toxicity of these therapeutics, referred to as antineoplastic (ANP) drugs, have raised concerns about their safe remediation. This review provides an overview of the environmental source of ANPs agents, with emphasis on the currently used remediation approaches. Outpatient excreta, hospital effluents, and waste from pharmaceutical industries are the primary source of ANP waste. The current review describes various biotic and abiotic methods used in the remediation of ANP drugs in the environment. Abiotic methods often generate transformation products (TPs) of unknown toxicity. In this light, obtaining data on the environmental toxicity of ANPs and its TPs is crucial to determine their toxic effect on the ecosystem. We also discuss the biodegradation of ANP drugs using monoculture of fungal and bacterial species, and microbial consortia in sewage treatment plants. The current review effort further explores a safe and sustainable approach for ANP waste treatment to replace existing chemical and oxidation intensive treatment approaches. To conclude, we assess the possibility of integrating biotic and abiotic methods of ANP drug degradation.