Advanced oxidation process-mediated removal of pharmaceuticals from water: A review

Development of fluorescence surrogates to predict the ferrate(VI) oxidation of pharmaceuticals in wastewater effluents

The removal of pharmaceuticals from wastewater effluents is an emerging concern for environmental scientists and engineers. Ferrate(VI) (Fe^VIO₄^2-, Fe^VI) is a promising oxidant and the removal of pharmaceuticals from wastewater effluents has been investigated in this study. Firstly, Fe^VI oxidation of selected pharmaceuticals was examined by determining the apparent second-order rate constants (k_app) in buffer solutions as a function of pH (5.0-9.5). At pH 8.0, k_app of cimetidine, famotidine, nalidixic acid, ronidazole, dimetridazole, tinidazole, and caffeine are (1.6 ± 0.2)×10³, (7.8 ± 0.3)×10², 2.6 ± 0.4, 1.7 ± 0.1, 0.9 ± 0.3, 0.2 ± 0.1, and < 0.1 M^-1 s^-1, respectively. However, k_app could not be directly employed to predict the removal of pharmaceuticals in the effluents due to the inhibited or enhanced effects of effluent organic matters (EfOM). Therefore, an alternative approach of spectroscopic surrogates was investigated since fluorophore was co-degraded with pharmaceuticals in the wastewater effluents. Particularly, the humic-like fluorescent peak correlated well with the pharmaceutical attenuation. The relationship of the reduction of fluorescence and the removal of pharmaceuticals could be described through a universal equation: [Formula: see text] . The practical utility of the fluorescence surrogate was validated by applying to field samples. Monitoring the changes of the fluorescence surrogate provides a promising, rapid, and inexpensive method for estimating the degradation of pharmaceuticals during Fe^VI treatment of wastewater effluents.

Influence of processing conditions on the synergism between UV irradiation and chlorine toward the degradation of refractory organic pollutants in UV/chlorine advanced oxidation system

The synergy of applying UV/chlorine advanced oxidation process (AOP) for the degradation of organic pollutants was usually reported. However, very limited information is available on the influence of processing conditions on the resulted synergism. In this work, C.I. reactive green 12 (RG12), a refractory textile dye, has been selected as a pollutant model to examine the synergism dependence of operational conditions in UV/chlorine AOP. Initial tests conducted with 500 μM of chlorine and 20 mg L^-1 of RG12 have resulted in a high synergy index (SI) of 3. Operating conditions sensitively affect the value of SI. This latter increased with increasing initial chlorine and RG12 concentrations up to certain optimums at 500 μM of chlorine and 20 mg L^-1 of RG12 and decreased afterward. The best SI value, i.e. 3, was obtained at pH 5, followed by pH 7 (SI = 2.2) and then pH 9-10.5 (SI ~ 2). On the other hand, the synergistic index decreased importantly from 3 at 25 °C to only 1.2 at 55 °C. Finally, by using different radical scavengers, it was found that among various suspected oxidants, only ^●OH and Cl₂^●- play a key role in the synergistic effect between UV and chlorine toward RG12 degradation.

Combination of solar photo-Fenton and adsorption process for removal of the anticancer drug Flutamide and its transformation products from hospital wastewater

The anti-cancer drug Flutamide (FLUT) is widely used and is of great environmental concern. The solar photo-Fenton (SPF) process can be an effective treatment for the removal of this type of micropollutant. The use of a single addition of 5 mg L^-1 of Fe²⁺ and 50 mg L^-1 of H₂O₂ achieved 20% primary degradation and only 3.05% mineralization. By using three additions of 5 mg L^-1 Fe²⁺, with an initial H₂O₂ concentration of 150 mg L^-1, 58% primary degradation was achieved, together with 12.07% mineralization. Consequently, thirteen transformation products (TPs) were formed. The SPF process was further combined with adsorption onto avocado seed activated carbon (ASAC) as an environmentally friendly approach for the removal of remained FLUT and the TPs. Doehlert design was used to assess the behavior of 13 TPs by optimizing the contact time and the adsorbent mass load. The optimal conditions for removal of FLUT and the TPs were 14 mg of ASAC and a contact time of 40 min. Remained FLUT and the TPs were totally removed using the adsorption process. The mechanisms of adsorption of FLUT and the TPs were strongly influenced by their polarity and π-π interactions of the TPs onto ASAC.

Z-scheme binary 1D ZnWO4 nanorods decorated 2D NiFe2O4 nanoplates as photocatalysts for high efficiency photocatalytic degradation of toxic organic pollutants from wastewater

In this study, dimensionally coupled Z-scheme binary nanocomposites from two-dimensional (2D) NiFe₂O₄ nanoplates and one-dimensional (1D) ZnWO₄ nanorods are prepared for efficient degradation of an antibiotic tetracycline (TC) and organic dye rhodamine B (RhB) under solar illumination. NiFe₂O₄/ZnWO₄ nanocomposites were synthesized by a simple and ecological in-situ hydrothermal method without the use of surfactants. Structural and morphological studies revealed the formation of heterostructure and 1D ZnWO₄ nanorods were uniformly distributed over the surface of NiFe₂O₄ nanoplates. Light-harvesting capability was improved and optimized by loading with different amounts of ZnWO₄. Photoluminescence analysis demonstrated inhibited nature of the recombination of photo-excited charge carriers in the nanocomposites. Photocatalytic experiments revealed that the nanocomposite exhibited improved Z-scheme electron-transfer for the degradation of TC under solar illumination. In particular, NFZW-20 nanocomposite demonstrated superior photocatalytic degradation of TC of approximately 98% within 105 min. Furthermore, their photocatalytic performance was investigated by RhB dye under the solar irradiation to achieve 98% of degradation of RhB in 70 min. Improved photocatalytic activities are attributed to the Z-scheme electron-transfer mechanism, which could enhance the superior ability of light absorption and reduced recombination rate of the photogenerated charge carriers.

Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water.

Ozonation using hollow fiber contactor technology and its perspectives for micropollutants removal in water: A review

Membrane contactor is a device generally used for the removal or the absorption of a gas into another fluid. The membrane acts as a barrier between the two phases and mass transfer occurs by diffusion and not by dispersion. This article is a review of the application of membrane contactor technology for ozonation applied to water treatment. The challenge of removing micropollutants is also discussed. In the first part, the ozonation process is mentioned, in particular chemical reactions induced by ozone and its advantages and disadvantages. In the second part, generalities on membrane contactor technology using hollow fibers are presented. Then, the benefit of using a membrane contactor for the elimination of micropollutants is shown through a critical analysis of the influence of several parameters on the ozonation efficiency. The impact of the membrane material is also highlighted. Finally, several modeling approaches are presented as a tool for a better understanding of the phenomena occurring in the contactor and a possible optimization of this process.

Efficient removal of antibiotic oxytetracycline from water using optimized montmorillonite-supported zero-valent iron nanocomposites

In this study, montmorillonite-supported nanoscaled zero-valent iron (Mt-nZVI) composites were fabricated using a facile liquid-phase reduction method to avoid serious agglomeration of nZVI particles in suspensions due to magnetic effect. The morphology, crystal structure, functional groups, and magnetic properties of as-prepared composites were explored using scanning and transmission electron microscope, X-ray diffractometer, Fourier transform infrared spectroscope, X-ray photoelectron spectroscope, zeta potential analyzer, and superconducting quantum interference device. The fabricated composites were then applied to remove antibiotic oxytetracycline from water. The optimal weight ratio of the Mt particles (mean size, 25 μm) to the nZVI particles (size, 60-100 nm) was first determined to be 2:1 (simply denoted as 2Mt-nZVI). Experimental results showed that 99% of 100 mg/L oxytetracycline at pH 5.0 was removed using 0.6 g/L of the 2Mt-nZVI composite and the mineralization reached 70% after 20 min of reaction. Finally, the transformation products and intermediates were detected and identified by a high-resolution liquid chromatography mass spectrometry (LC-MS) and the pathways were proposed during the degradation of oxytetracycline over the 2Mt-nZVI composite.

Efficient Malathion Removal in Constructed Wetlands Coupled to UV/H2O2 Pretreatment

Intensive agriculture has led to the increasing application of pesticides, such as malathion, thus generating large volumes of untreated cropland wastewater (CropWW). In this work, a hybrid system constructed wetlands (CW) coupled in continuous with an optimized UV/H2O2 pretreatment was evaluated for the efficient removal of malathion contained in CropWW. In the first stage, 90 min UV irradiation time (UV IR) and 65 mM hydrogen peroxide (H2O2) were identified as optimal operation parameters through a central composite design. The second stage consisted of CW planted with Phragmites australis collected from the agricultural discharge area and operated as a piston flow reactor. Furthermore, CW hydraulic residence times (HRT) of 1, 2 and 3 days, including hydraulic coupling, were evaluated. The removal efficiencies obtained in the first stage (UV/H2O2) were 94 ± 2.5% of malathion and 45 ± 2.5% of total organic carbon (TOC). In stage two (CW) 65 ± 9.6% TOC removal was achieved during the first 17 days, from which around 24% was associated to the biosorption of malathion byproducts. Subsequently, and until the operation ends, CW removed about 80% of TOC for 2 and 3 days HRT, with no significant differences (p > 0.2), which is higher than those reported in several studies involving only advanced oxidation processes (AOP) with UV IR times above 240 min and even for systems using catalysts. The results obtained indicate that the system UV/H2O2-CW is a technically suitable option for the treatment of CropWW with a high content of malathion mainly found in developing countries. Moreover, the hybrid system proposed also represent significant reduction in the size of the treatment plant.

A comprehensive review on contaminants removal from pharmaceutical wastewater by electrocoagulation process

The pharmaceuticals are emergent contaminants, which can create potential threats for human health and the environment. All the pharmaceutical contaminants are becoming enormous in the environment as conventional wastewater treatment cannot be effectively implemented due to toxic and intractable action of pharmaceuticals. For this reason, the existence of pharmaceutical contaminants has brought great awareness, causing significant concern on their transformation, occurrence, risk, and fate in the environments. Electrocoagulation (EC) treatment process is effectively applied for the removal of contaminants, radionuclides, pesticides, and also harmful microorganisms. During the EC process, an electric current is employed directly, and both electrodes are dissoluted partially in the reactor under the special conditions. This electrode dissolution produces the increased concentration of cation, which is finally precipitated as hydroxides and oxides. Different anode materials usage like aluminum, stainless steel, iron, etc. are found more effective in EC operation for efficient removal of pharmaceutical contaminants. Due to the simple procedure and less costly material, EC method is extensively recognized for pharmaceutical wastewater treatment over further conventional treatment methods. The EC process has more usefulness to destabilize the pharmaceutical contaminants with the neutralization of charge and after that coagulating those contaminants to produce flocs. Thus, the review places particular emphasis on the application of EC process to remove pharmaceutical contaminants. First, the operational parameters influencing EC efficiency with the electroanalysis techniques are described. Second, in this review emerging challenges, current developments and techno-economic concerns of EC are highlighted. Finally, future recommendations and prospective on EC are envisioned.

Synthesis and Characterization of Metal Modified Catalysts for Decomposition of Ibuprofen from Aqueous Solutions

The presence of pharmaceuticals in surface water, drinking water, and wastewater has attracted significant concern because of the non-biodegradability, resistance, and toxicity of pharmaceutical compounds. The catalytic ozonation of an anti-inflammatory pharmaceutical, ibuprofen was investigated in this work. The reaction mixture was analyzed and measured by high-performance liquid chromatography (HPLC). Liquid chromatography-mass spectrometry (LC-MS) was used for the quantification of by-products during the catalytic ozonation process. Ibuprofen was degraded by ozonation under optimized conditions within 1 h. However, some intermediate oxidation products were detected during the ibuprofen ozonation process that were more resistant than the parent compound. To optimize the process, nine heterogeneous catalysts were synthesized using different preparation methods and used with ozone to degrade the ibuprofen dissolved in aqueous solution. The aim of using several catalysts was to reveal the effect of various catalyst preparation methods on the degradation of ibuprofen as well as the formation and elimination of by-products. Furthermore, the goal was to reveal the influence of various support structures and different metals such as Pd-, Fe-, Ni-, metal particle size, and metal dispersion in ozone degradation. Most of the catalysts improved the elimination kinetics of the by-products. Among these catalysts, Cu-H-Beta-150-DP synthesized by the deposition–precipitation process showed the highest decomposition rate. The regenerated Cu-H-Beta-150-DP catalyst preserved the catalytic activity to that of the fresh catalyst. The catalyst characterization methods applied in this work included nitrogen adsorption–desorption, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The large pore volume and small metal particle size contributed to the improved catalytic activity.

UiO-66(Ti)-Fe3O4-WO3 photocatalyst for efficient ammonia degradation from wastewater into continuous flow-loop thin film slurry flat-plate photoreactor

This work presents the characterization of novel synthesized UiO-66(Ti)-Fe₃O₄-WO₃ magnetic photocatalyst and investigates their photocatalytic activity for the photodegradation of ammonia in a designed continuous flow-loop thin-film slurry flat-plate photoreactor (TFSR). Excellent ammonia degradation efficiency was achieved in the presence of the synthesized catalyst at ambient conditions using no more reactive oxidant species. Several independent variables involving catalyst mass, flowrate, pH, irradiation time and initial ammonia concentration as well as corresponding experiments were analyzed and design using the central composite design (CCD). The influence and significance of each parameter and their binary interactions were then evaluated by applying the analysis of variance. The ammonia degradation efficiency of 91.80 % with the desirability of 0.903 were obtained at optimum values of operational parameters including 550 mL/min,10, 0.125 g/L, 60 min and 30 mg/L for solution flowrate, pH, catalyst mass, irradiation time and initial ammonia concentration, respectively. Furthermore, the liquid phase products of ammonia degradation such as nitrate and nitrite ions were completely removed, and purified water was produced using the combination of reverse osmosis process and mixed resins beds. The photocatalyst mechanism study revealed that [Formula: see text] was the predominant reactive oxygen species in the ammonia photodegradation.

Synergistic interaction of diclofenac and its metabolites with selected antibiotics and amygdalin in wastewaters

Diclofenac (DCF), a non-steroidal anti-inflammatory drug (NSAID) belongs to one of the most frequently detected pharmaceutical residues in the environment. Little is known on the interactions of DCF as well as its major biodegradation metabolites 4'-OHDCF and 5-OHDCF with chemical compounds found in wastewater, including antibiotics such as ampicillin and kanamycin. In the present work we examined the potential interactions between DCF, its metabolites 4'-OHDCF and 5-OHDCF and ampicyllin and kanamycin. We also measured the effect of the mixture of DCF with natural compound - amygdalin. We evaluated the following parameters: E. coli K-12 cells viability, growth inhibition of E. coli K-12 culture, genotoxicity, oxidative stress parameters: sodA promoter induction and ROS generation. The reactivity of E. coli SM recA:luxCDABE biosensor strain in wastewaters matrices contaminated with DCF and kanamycin was also monitored. Obtained results indicated that used antibiotics (ampicyllin, kanamycin) enhanced the toxic effect of DCF used individually and in the mixtures with its metabolites 4'-OHDCF and 5-OHDCF toward E. coli. Similar effect was also obtained in genotoxicity assay. The oxidative stress assays revealed that the highest level of ROS generation and sodA promoter induction were obtained also for the mixtures of DCF, its metabolites with antibiotics. It was also showed that amygdalin influenced the activity of DCF and its biodegradation metabolites. The strongest luminescence response of E. coli SM biosensor strain with recA:luxCDABE genetic construct in filtered treated wastewaters, comparable to control sample was noticed. Obtained results showed that DCF and its biodegradation metabolites 4'-OHDCF and 5-OHDCF can interact with tested antibiotics and compounds of natural origin, i.e. amygdalin to form mixtures showing stronger antimicrobial activity against E. coli than parent chemicals. Moreover the assays in wastewater matrices revealed that E. coli SM recA:luxCDABE biosensor strains is a good tool for bacteria monitoring in wastewater environments.

Design a new photocatalyst of sea sediment/titanate to remove cephalexin antibiotic from aqueous media in the presence of sonication/ultraviolet/hydrogen peroxide: Pathway and mechanism for degradation

The aim of the current study was directed to develop a new sea sediment/titanate photocatalyst to remove cephalexin from aqueous media in the presence of ultraviolet (UV) light, hydrogen peroxide (H₂O₂), and ultrasonic waves. The influence of furnace temperature (300, 350, 400, and 500 °C), furnace residence time (1, 2, 3, and 4 h), and ratio of sea sediment: titanium (0-6 v: w) on the physicochemical properties and the cephalexin removal by the sea sediment/titanate photocatalyst was explored. The technique of FTIR, SEM/EDX, XRD, BET, BJH, and Mapping was used to determine the physicochemical properties of the generated photocatalyst. The maximum cephalexin removal (94.71%) was obtained at the furnace temperature of 500 °C, the furnace residence time of 2 h, and the sea sediment: titanium ratio of 1:6 (=12 mL TiO₂/2 g sea sediment). According to the acquired results, the surface area of the optimized catalyst, namely Cat-500-2-12, was computed to be 52.29 m²/g. The crystallite size of titanium oxide on the optimum photocatalyst was calculated ~17.68 nm. The FTIR test confirmed the presence of C=C, O-H, C=O, C-S, and C-H functional groups in the photocatalyst. The transformation pathway for the degradation of cephalexin by the developed system was drawn. The present investigation showed that the developed technique (sea sediment/titanate-UV-H₂O₂-ultrasonic) could be used as a promising alternative for attenuating cephalexin from aqueous solutions.

Improved degradation of etodolac in the presence of core-shell ZnFe2O4/SiO2/TiO2 magnetic photocatalyst

In the present study, susceptibility to photocatalytic degradation of etodolac, 1,8-diethyl-1,3,4,9 - tetrahydro pyran - [3,4-b] indole-1-acetic acid, which is a non-steroidal anti-inflammatory drug frequently detected in an aqueous environment, was for the first time investigated. The obtained p-type TiO₂-based photocatalyst coupled with zinc ferrite nanoparticles in a core-shell structure improves the separation and recovery of nanosized TiO₂ photocatalyst. The characterization of ZnFe₂O₄/SiO₂/TiO₂, including XRD, XPS, TEM, BET, DR/UV-Vis, impedance spectroscopy and photocatalytic analysis, showed that magnetic photocatalyst containing anatase phase revealed markedly improved etodolac decomposition and mineralization measured as TOC removal compared to photolysis reaction. The effect of irradiation and pH range on photocatalytic decomposition of etodolac was studied. The most efficient degradation of etodolac was observed under simulated solar light for a core-shell ZnFe₂O₄/SiO₂/TiO₂ magnetic photocatalyst at pH above 4 (pKa = 4.7) and below 7. The irradiation of etodolac solution in a broader light range revealed a synergetic effect on its photodegradation performance. After only 20 min of degradation, about 100% of etodolac was degraded. Based on the photocatalytic analysis in the presence of scavengers and HPLC analysis, the transformation intermediates and possible photodegradation pathways of etodolac were studied. It was found that ∙O₂^- attack on C2-C3 bond inside pyrrole ring results mostly in the hydroxylation of the molecule, which next undergoes -CH₂COOH detachment to give 1,9-diethyl-3,4-dihydro-pyrano[3,4-b]indol-4a-ol. The obtained compound should further undergo subsequent hydropyran and pyrrole ring breaking to give a family of benzene derivatives.

Use of low frequency ultrasound for water treatment: Data on azithromycin removal

Azithromycin (AZT) is a broad-spectrum antibiotic present in different aqueous matrices due to its incomplete removal using conventional water treatments. Ultrasound (US) is an advanced oxidation technology that has demonstrated its capacity to degrade different types of organic molecules due to the generation of cavitation bubbles or cavities that promote the generation of radicals.

In this paper, data regarding the use of low-frequency US (40 kHz) in the removal of AZT are presented. Tests were carried out at lab scale for 60 min considering a reaction volume of 300 mL (pollutant initial concentration 1.0 mg L⁻¹). The effect of operational parameters such as pH, ultrasound power, the presence of external agents like ferrous ions, hydrogen peroxide, and UV radiation were evaluated. In general, obtained data show that under the experimental reaction conditions, it is feasible to reach extents of AZT removal ∼50.0%, and that the presence of other species in the medium could inhibit the reaction, mainly due to scavenging effects. This information is relevant to future applications of US, at pilot or real scale, in the treatment of water with presence of AZT or similar organic pollutants.

Floating TiO2 photocatalyst for efficient inactivation of E. coli and decomposition of methylene blue solution

The anatase phase TiO₂ films with nanocrystalline structure were successfully deposited on a water-floating non-expanded polystyrene (PS) beads via magnetron sputtering. The combination of UVB light and PS beads with TiO₂ film was used for decomposition of methylene blue as well as inactivation tests for intact and EDTA-treated Escherichia coli bacteria. Crystal structure, elemental composition, elemental mapping, surface morphology and chemical bonds of TiO₂ film were investigated. E. coli inactivation experiments showed that such floating photocatalyst could destroy >90% bacteria in 45 min under UVB irradiation. Results demonstrated that combination of TiO₂ and UVB light leads to disruption of the outer membrane which causes effective inactivation of E. coli bacteria.

Water Depollution and Photo-Detoxification by Means of TiO2: Fluoroquinolone Antibiotics as a Case Study

Photocatalysis by semiconductors is considered one of the most promising advanced oxidation processes (AOPs) and TiO2 is the most well-studied material for the removal of contaminants from the aquatic system. Over the last 20 years, pharmaceuticals have been the most investigated pollutants. They re-enter the environment almost unmodified or slightly metabolized, especially in the aquatic environment, since the traditional urban wastewater treatment plants (WWTPs) are not able to abate them. Due to their continuous input, persistence in the environment, and unpleasant effects even at low concentrations, drugs are considered contaminants of emerging concern (ECs). Among these, we chose fluoroquinolone (FQ) antibiotics as an environmental probe for assessing the role of TiO2 photocatalysis in the degradation of recalcitrant pollutants under environmental conditions and detoxification of surface waters and wastewaters. Due to their widespread diffusion, their presence in the list of the most persistent pollutants, and because they have been deeply investigated and their multiform photochemistry is well-known, they are able to supply rich information, both chemical and toxicological, on all key steps of the oxidative degradation process. The present review article explores, in a non-exhaustive way, the relationship among pollution, toxicity and remediation through titanium dioxide photocatalysis, with particular attention to the toxicological aspect. By using FQs as the probe, in depth indications about the different phases of the process were obtained, and the results reported in this paper may be useful in the improvement of large-scale applications of this technology, and—through generally valid methods—they could be deployed to other pharmaceuticals and emerging recalcitrant contaminants.

Photocatalytic degradation of oily waste and phenol from a local South Africa oil refinery wastewater using response methodology

The photocatalytic degradation of a local South Africa oil refinery wastewater was conducted under UV radiation using an aqueous catalyst of titanium dioxide (TiO2), Degussa P25 (80% anatase, 20% rutile) in suspension. The experiment was carried out in a batch aerated photocatalytic reactor based on a central composite design (CCD) and analyzed using response surface methodology (RSM). The effects of three operational variables viz. TiO2 dosage (2-8 g/L), runtime (30-90 minutes), and airflow rate (0.768-1.48 L/min) were examined for the removal of phenol and soap oil and grease (SOG). The data derived from the CCD, and the successive analysis of variance (ANOVA) showed the TiO2 dosage to be the most influential factor, while the other factors were also significant (P < 0.0001). Also, the ANOVA test revealed the second-order of TiO2 dosage and runtime as the main interaction factors on the removal efficiency. To maximize the pollutant removal, the optimum conditions were found at runtime of 90 minutes, TiO2 dosage of 8 g/L, and an aeration flow rate of 1.225 L/min. Under the conditions stated, the percentage removal of phenol (300 ± 7) and SOG (4000 ± 23) were 76% and 88% respectively. At 95% confidence level, the predicted models developed results were in reasonable agreement with that of the experimental data, which confirms the adaptability of the models. The first-order kinetic constants were estimated as 0.136 min-1 and 0.083 min-1 for SOG and phenol respectively.

Heterogeneous Fenton-like degradation of EDTA in an aqueous solution with enhanced COD removal under neutral pH

By providing the key carbon and nitrogen elements needed for eutrophication, the potential toxicity of ethylenediaminetetraacetic acid (EDTA) prompts the exploration of effective treatment methods to minimize the amount of EDTA released into the environment. In this study, Fe₃O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts to study the mineralization of EDTA in Fenton-like reactions under neutral pH. Fe₃O₄ MNPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET). The effects of pH, ferric ion leaching, and H₂O₂ concentration on chemical oxygen demand (COD) removal of EDTA were investigated. The morphological characterization of the nanoparticles suggests a quasi-spherical structure with small particle size and a surface area of 49.9 m²/g. The results show that Fe₃O₄ MNPs had good catalytic activity for the mineralization of EDTA under pH 5.0-9.0. The optimum conditions for the COD removal of 45% at pH 7.0 were: 40 mM H₂O₂, 10 mM Fe₃O₄, and 1 g/L EDTANa₂·2H₂O at 303 K. Fe₃O₄ MNPs maintained high catalytic activity after five cycles of continuous degradation of EDTA. According to reactive oxidizing species measurements obtained by electron spin resonance (ESR), it was confirmed that HO· free radicals, presented in the H₂O₂/Fe₃O₄ MNPs heterogeneous Fenton-like reaction, were the primary active group in the removal of EDTA. These features can be considered beneficial to the application of Fe₃O₄ MNPs towards industrial wastewater treatment.

Investigation of paracetamol degradation using LED and UV-C photo-reactors

This work investigates the efficiency of LED and UV-C photo-reactors for paracetamol degradation using advanced oxidative processes. Among the evaluated processes, photo-Fenton was the most efficient for both radiations. Degradations greater than 81% (λ 197 nm) and 91% (λ 243 nm) were obtained in the kinetic study. These degradations were also observed by means of the reduction in the peaks in both spectral scanning and high-performance liquid chromatography analysis. The good fit of the Chan and Chu kinetic model shows that the degradation reaction has pseudo-first order behavior. Toxicity tests did not indicate the inhibition of growth of Lactuca sativa seeds and Escherichia coli bacterium. However, the growth of strains of the Salmonella enteritidis bacterium was inhibited in all the samples, demonstrating that only this bacterium was sensitive to solutions. The proposed empirical models obtained from the 2⁴ factorial designs were able to predict paracetamol degradation. These models could, at the same levels assessed, be used to predict the percentage of degradation in studies using other organic compounds. The LED and UV-C photo-reactors were, when employing the photo-Fenton process, able to degrade paracetamol, thus highlighting the efficiency of LED radiation when its power (three times smaller) is compared to that of UV-C radiation.

Molecular Interpretation of Pharmaceuticals’ Adsorption on Carbon Nanomaterials: Theory Meets Experiments

The ability of carbon-based nanomaterials (CNM) to interact with a variety of pharmaceutical drugs can be exploited in many applications. In particular, they have been studied both as carriers for in vivo drug delivery and as sorbents for the treatment of water polluted by pharmaceuticals. In recent years, the large number of experimental studies was also assisted by computational work as a tool to provide understanding at molecular level of structural and thermodynamic aspects of adsorption processes. Quantum mechanical methods, especially based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were mainly applied to study adsorption/release of various drugs. This review aims to compare results obtained by theory and experiments, focusing on the adsorption of three classes of compounds: (i) simple organic model molecules; (ii) antimicrobials; (iii) cytostatics. Generally, a good agreement between experimental data (e.g. energies of adsorption, spectroscopic properties, adsorption isotherms, type of interactions, emerged from this review) and theoretical results can be reached, provided that a selection of the correct level of theory is performed. Computational studies are shown to be a valuable tool for investigating such systems and ultimately provide useful insights to guide CNMs materials development and design.

Coupling Persulfate-Based AOPs: A Novel Approach for Piroxicam Degradation in Aqueous Matrices

The activated persulfate degradation of piroxicam, a non-steroidal anti-inflammatory drug (NSAID) belonging to oxicams, was investigated. Persulfate was activated with thermal energy or (UV-A and simulated solar) irradiation. Using 250 mg/L sodium persulfate at 40 °C degraded almost completely 0.5 mg/L of piroxicam in 30 min. Increasing piroxicam concentration from 0.5 to 4.5 mg/L decreased its removal. The observed kinetic constant was increased almost ten times from 0.077 to 0.755 min−1, when the temperature was increased from 40 to 60 °C, respectively. Process efficiency was enhanced at pH 5–7. At ambient conditions and 30 min of irradiation, 94.1% and 89.8% of 0.5 mg/L piroxicam was removed using UV-A LED or simulated solar radiation, respectively. Interestingly, the use of simulated sunlight was advantageous over UV-A light for both secondary effluent, and 20 mg/L of humic acid solution. Unlike other advanced oxidation processes, the presence of bicarbonate or chloride in the range 50–250 mg/L enhanced the degradation rate, while the presence of humic acid delayed the removal of piroxicam. The use of 0.5 and 10 g/L of methanol or tert-butanol as radical scavengers inhibited the reaction. The coupling of thermal and light activation methods in different aqueous matrices showed a high level of synergy. The synergy factor was calculated as 68.4% and 58.4% for thermal activation (40 °C) coupled with either solar light in 20 mg/L of humic acid or UV-A LED light in secondary effluent, respectively.

Evaluation of hospital laundry effluents treated by advanced oxidation processes and their cytotoxic effects on Allium cepa L

Hospital laundries are responsible for a significant part of the amount of wastewater that is generated in hospitals. Hospital laundry wastewater represents a complex mixture of chemicals that arouse concerns about possible environmental risks. The objective of the present study was to evaluate the cytotoxicity of different laundry effluents from the Regional University Hospital of Maringá, Paraná, Brazil, on Allium cepa L. meristematic root cells. The effluents were characterised as rinsing, wetting, prewashing, washing, softening, wastewater (the effluent generated at the end of the washing process), the wastewater that was treated by physicochemical (PC) processes and the wastewater that was treated by advanced oxidation processes (PC + UV, PC + H₂O₂ and PC + UV/H₂O₂). The mitotic indexes were calculated by scoring 5000 cells per group and the statistical analyses were performed by one-way ANOVA, followed by Tukey's post-test (α = 0.05). Results showed that the rinsing, wetting, prewashing and wastewater laundry effluents were cytotoxic at 24 h of exposure, significantly reducing the mitotic index. Despite the slight cytotoxicity of the PC + UV/H₂O₂ treatment, physicochemical and advanced oxidation processes efficiently reduced the critical parameters of wastewater, such as the biochemical and chemical oxygen demands, to tolerable levels of effluent discharge. It is essential to perform constant monitoring of these effluents in order to reduce the possible occurrence of environmental impacts.

Zebrafish toxicity assessment of the photocatalysis-biodegradation of diclofenac using composites of TiO2 and activated carbon from Argania spinosa tree nutshells and Pseudomonas aeruginosa

The occurrence and persistence of pharmaceutical products (PPs) in the environment have recently been well-documented and are a major concern for public health. Their incidence in aquatic ecosystems is the result of their direct release without any prior treatment or insufficient wastewater treatment. Therefore, an efficient and safe posttreatment process for removing PPs must be developed. In this study, we focused on the ability of photocatalysis or combined photocatalysis and biodegradation to effectively and safely remove diclofenac (DCF) and its by-products from water. The heterogeneous photocatalysis system was based on bio-sourced activated carbon obtained from Argania spinosa tree nutshells and Degussa P25 titanium dioxide (ACP-TiO₂), and biodegradation involved Pseudomonas aeruginosa. Toxicity tests were conducted with zebrafish embryos to evaluate the applicability of the treatment processes. The results showed that photocatalytic treatment with 0.1 mg/L of ACP-TiO₂ 9% for 7.5 h is sufficient to eliminate DCF (50 mg L^-1) and its by-products from water. Low levels of malformation (< 20%) were detected in zebrafish embryos treated with photocatalyzed DCF solutions at 1, 5, and 7 mg L^-1 after 4 days of exposure. After 3 h of incubation, P. aeruginosa was found to reduce the toxicity of DCF (10 mg L^-1) photocatalyzed for 2 and 4 h. Additional studies should be conducted to elucidate the biodegradation mechanism.

Sonophotocatalytic treatment of AB113 dye and real textile wastewater using ZnO/persulfate: Modeling by response surface methodology and artificial neural network

The present study investigates the synergistic performance of the sonophotolytic-activated ZnO/persulfate (US/UV/ZnO/PS) process in the decolorization of acid blue 113 (AB113) dye from aqueous solution and its feasibility for the treatment of real textile wastewater. Decolorization of AB113 solution was modeled by central composite design-response surface methodology (CCD-RSM) and artificial neural network (ANN) approaches and optimized by CCD-RSM and genetic algorithm (GA) approaches. Statistical metrics indicated that both CCD-RSM and ANN approaches seemed satisfactory. However, the results of statistical fit measures indicated a relative superiority of CCD-RSM as compared to the ANN approach. The results of optimization of the process parameters by CCD-RSM and GA approaches appeared to be similar as follows: pH = 6.1, reaction time = 25 min, US power density = 300 W/L, ZnO = 0.88 g/L and PS = 2.43 mmol/L. The synergistic effect of the hybrid US/UV/ZnO/PS process in comparison with its individual processes (US, UV, ZnO, and PS) was found to be 54.3%. Quenching experiments discovered that and HO are the main oxidizing radicals in a mildly acidic condition of the reaction solution. The removal efficiency of AB113 in the presence of some anions decreased in the order of bicarbonate > sulfate > phosphate > nitrate > chloride. Further, the reusability feasibility of ZnO showed that the ZnO material retained its photocatalytic property after five successive cycles of reusability test, while Zn²⁺ ion concentration in the reaction solution was measured to be 2.81 mg/L. The findings also indicated that the integrated process application suppresses extremely chemical and electrical costs. The study of the feasibility of the US/UV/ZnO/PS process in the treatment of real textile wastewater was done by determining COD, TOC and BOD₅/COD ratio. Results demonstrated that the 96.6 and 97.1% reduction of COD and TOC was achieved after 5 and 7 h reaction time, respectively. The obtained BOD₅/COD ratio changed from about 0.15 (for non-treated wastewater) to about 0.61 with increasing reaction time from zero to 90 min. In conclusion, the hybrid US/UV/ZnO/PS system can be proposed as a novel and promising approach to be utilized as a pretreatment technique before a biological treatment process to facilitate the biological treatment of recalcitrant textile wastewater.

Performance comparison of different types of constructed wetlands for the removal of pharmaceuticals and their transformation products: a review

This paper presents a comprehensive and critical comparison of four types of constructed wetlands (CWs): free water surface CW (FWSCW), vertical flow CW (VFCW), horizontal flow CW (HFCW), and hybrid CW (HCW) for the removal of 29 pharmaceuticals (PhCs) and 19 transformation products (TPs) using a global data compiled for 247 CWs reported in 63 peer-reviewed journal papers. Biodegradation (aerobic being more efficient than anaerobic) is the major removal mechanism for 16 out of 29 PhCs besides the influence of other processes (e.g., adsorption/sorption, plant uptake, and photodegradation). The HCW performed better followed by VFCW, HFCW, and FWSCW. The comparatively better removal in HCW might be due to the coexistence of aerobic and anaerobic conditions and longer hydraulic retention time considering more than one compartment enhances the removal of PhCs (e.g., diclofenac, acetaminophen, sulfamethoxazole, sulfapyridine, trimethoprim, and atenolol), which are removed under both conditions and adsorption/sorption processes. The augmentation in dissolved oxygen by the application of artificial aeration improved the removal of PhCs, which are degraded under aerobic conditions. Furthermore, the better performance of aerated CWs could be due to the establishment of various microenvironments with different physicochemical conditions (aerobic and anaerobic), which facilitated the contribution of both aerobic and anaerobic metabolic pathways in the removal of PhCs. The removal of some of the PhCs takes place by the formation of their TPs and the nature of these TPs (persistent or non-biodegradable/biodegradable) plays a major role in their removal process.

Cold plasma enhances the efficacy of aerosolized hydrogen peroxide in reducing populations of Salmonella Typhimurium and Listeria innocua on grape tomatoes, apples, cantaloupe and romaine lettuce

In the present study, we investigated whether cold plasma activation affected the efficacy of aerosolized hydrogen peroxide against S. Typhimurium and L. innocua. Stem scars and smooth surfaces of grape tomatoes, surfaces of Granny Smith apples and Romaine lettuce (both midrib and upper leaves) and cantaloupe rinds were inoculated with two-strain cocktails of S. Typhimurium and 3-strain cocktails of L. innocua. The inoculated samples were treated with 7.8% aerosolized H2O2 with and without cold plasma for various times. For all fresh produce items and surfaces, cold plasma significantly (P < 0.05) improved the efficacy of aerosolized H2O2 against Salmonella and L. innocua. Without cold plasma activation, H2O2 aerosols only reduced populations of Salmonella by 1.54-3.17 log CFU/piece while H2O2 with cold plasma achieved 2.35-5.50 log CFU/piece reductions of Salmonella. L. innocua was more sensitive to the cold plasma-activated H2O2 than Salmonella. Cold plasma activated H2O2 aerosols reduced Listeria populations by more than 5 log CFU/piece on all types and surfaces of fresh produce except for the tomato stem scar area. Without cold plasma, the reductions by H2O2 were only 1.35-3.77 log CFU/piece. Overall, our results demonstrated that cold plasma activation significantly enhanced the efficacy of H2O2 mist against bacteria on fresh produce.

The study of biological activity of transformation products of diclofenac and its interaction with chlorogenic acid

In the present work we compared the biological activity of DCF, 4'-OHDCF and 5-OHDCF as molecules of most biodegradation pathways of DCF and selected transformation products (2-hydroxyphenylacetic acid; 2,5-dihydroxyphenylacetic acid and 2,6-dichloroaniline) which are produced during AOPs, such as ozonation and UV/H₂O₂. We also examined the interaction of DCF with chlorogenic acid (CGA). CGA is commonly used in human diet and entering the environment along with waste mainly from the processing and brewing of coffee and it can be toxic for microorganisms included in activated sludge. In the present experiment the evaluation of following parameters was performed: E. coli K-12 cells viability, growth inhibition of E. coli K-12 culture, LC₅₀ and mortality of Chironomus aprilinus, genotoxicity, sodA promoter induction and ROS generation. In addition the reactivity of E. coli SM recA:luxCDABE biosensor strain in wastewater matrices was measured. The results showed the influence of DCF, 4'-OHDCF and 5-OHDCF on E. coli K-12 cells viability and bacteria growth, comparable to AOPs by-products. The highest toxicity was observed for selected, tested AOPs by-products, in comparison to the DCF, 4'-OHDCF and 5-OHDCF. Genotoxicity assay indicated that 2,6-dichloroaniline (AOPs by-product) had the highest toxic effect. The oxidative stress assays revealed that the highest level of ROS generation and sodA promoter induction were obtained for DCF, 4'-OHDCF and 5-OHDCF, compared to other tested compounds. We have also found that there is an interaction between chlorogenic acid and DCF, which resulted in increased toxicity of the mixture of the both compounds to E. coli K-12, comparable to parent chemicals. The strongest response of E. coli SM biosensor strain with recA:luxCDABE genetic construct in filtered treated wastewaters, comparable to control sample was noticed. It indicates, that E. coli SM recA:luxCDABE biosensor strains is a good tool for bacteria monitoring in wastewater environment. Due to toxicity and biological activity of tested DCF transformation products, there is a need to use additional wastewater treatment systems for wastewater contaminated with pharmaceutical residues.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Remediation of persistent organic pollutants in aqueous systems by electrochemical activation of persulfates: A review

Sulfate-radical-based advanced oxidation processes (SR-AOPs) have been widely applied in environmental remediation during the past decade, especially in the degradation of refractory organic contaminants. The electrochemical method, which is considered as one of the most efficient ways to generate sulfate radical, has been extensively investigated for the activation of persulfate recently. This work presented a thorough assessment towards the performance of electrochemically activated persulfate for the removal of persistent organic pollutants (POPs) in aqueous systems. The mechanism and superiority of electrochemically activated persulfates were revealed accordingly. Some major factors (e.g., electrode material, pH, current density, and persulfate concentration) influencing the electrochemical activation of persulfates to remove POPs were also discussed. Considering the increasing quantity of publications on this subject, it is significant to broader guidelines such as the efficiency for practical application, quantization of organic by-products, and cost-effectiveness of the electrochemical method to optimize active persulfate in the water treatment processes.

Biological performance and fouling mitigation in the biochar-amended anaerobic membrane bioreactor (AnMBR) treating pharmaceutical wastewater

Anaerobic membrane bioreactor (AnMBR) is an advanced technology in treating pharmaceutical wastewater, but the membrane fouling limits its development. In this study, the biochar with adsorption capacity of biopolymers was added in AnMBR to investigate its potential in treating pharmaceutical wastewater and alleviating membrane fouling. In the biochar-amended AnMBR, adsorbable organic halogen (AOX) was removed effectively, and more COD was biotransformed into CH₄. Membrane fouling mitigation was achieved in the third stage with a 56% decrease of average transmembrane pressure difference (TMP) rising rate. The predominant culprit, proteins of extracellular polymeric substance (EPS-proteins) in sludge mixture and cake layer, was reduced significantly. Particularly, the proportion of micromolecular (0.1-0.15 kDa) EPS-proteins in cake layer was 1.5-folds that of the control group. The important bio-foulant genus Arcobacter aggregating on the membrane had less and almost half the relative abundance (16.5%) than that of the control group (30.7%).

Greenhouse gas emissions from advanced oxidation processes in the degradation of bisphenol A: a comparative study of the H2O2/UV, TiO2 /UV, and ozonation processes

To estimate greenhouse gas (GHG) emissions and degradation rate constants (k_obs) from H₂O₂/UV-C, TiO₂/UV-C, and ozonation processes in the degradation of bisphenol A (BPA), the laboratory scale experiments were conducted. In the H₂O₂/UV-C process, the fastest degradation rate constant (k_obs = 0.353 min^-1) was observed at 4 mM of H₂O₂, while the minimum GHG emission was achieved at 3 mM of H₂O₂. In the TiO₂/UV-C process, the fastest rate constant (k_obs = 0.126 min^-1) was achieved at 2000 mg/L of TiO₂, while the minimum GHG emission was observed at 400 mg/L of TiO₂. In the ozonation process, GHG emissions were minimal at 5 mg/L of O₃, but the degradation rate constant kept on increasing as the O₃ concentration increased. There were three major types of GHG emissions in the advanced oxidation processes (AOPs). In the ozonation process, most of the GHG emissions were generated by electricity consumption. TiO₂/UV-C process accounted for a significant portion of the GHGs generated by the use of chemicals. Finally, the H₂O₂/UV-C process produced similar GHG emissions from both chemical inputs and electricity consumption. The carbon footprint calculation revealed that for the treatment of 1 m³ of water contaminated with 0.04 mM BPA, the H₂O₂/UV-C process had the smallest carbon footprint (0.565 kg CO₂ eq/m³), followed by the TiO₂/UV-C process (3.445 kg CO₂ eq/m³) and the ozonation process (3.897 kg CO₂ eq/m³). Our results imply that the increase in removal rate constant might not be the optimal parameter for reducing GHG emissions during the application of these processes. Graphical abstract .

Iron foam combined ozonation for enhanced treatment of pharmaceutical wastewater

In this study, iron foam combined ozonation was employed as an advanced oxidation process to treat the organic contaminants in real pharmaceutical wastewater. It was found that this procedure worked well in a wide range of pH, the existence of iron foam in ozonation system markedly elevated the mineralization level of organic contaminants. Within the reaction time of 120 min, iron foam combined ozonation achieved 53% of DOC removal percentage, which was 21% higher than that of ozone alone. Meanwhile, the biodegradability of the pharmaceutical wastewater was improved, a large part of the organic pollutants containing benzene rings and amino groups were effectively degraded, and a certain amount of phosphate and nitrogen also get removed. In iron foam combined ozonation, zero valent iron played the role as an activator. It was oxidized into iron oxides and oxyhydroxides, the electrons transferring among different valences of iron stimulated the decomposition of ozone and the generation of hydroxyl radicals, which accounted for most of the organic contaminants degradation.

Controllable Synthesis of Mn3O4 Nanowires and Application in the Treatment of Phenol at Room Temperature

Nanosized Mn₃O₄ nanowires are prepared with KMnO₄ and ethanol in mild conditions by facile hydrothermal method. Hydrothermal reaction temperature is optimized to get uniform nanowires. The prepared Mn₃O₄ nanowires exhibit high activity in the treatment of phenol at acid condition and room temperature. The 20 mg Mn₃O₄ nanowires can efficiently dispose of 50 mL phenol solution (0.2 g·L⁻¹) at pH 2 and 25 °C. The nanowires before and after phenol treatment are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and the reaction mechanism is discussed.

Pharmaceuticals residues and xenobiotics contaminants: Occurrence, analytical techniques and sustainable alternatives for wastewater treatment

Emerging contaminants are increasingly present in the environment, and their appearance on both the environment and health of living beings are still poorly understood by society. Conventional sewage treatment facilities that are under validity and were designed years ago are not developed to remove pharmaceutical compounds, their main focus is organic and bacteriological removal. Pharmaceutical residues are associated directly with quantitative production aspects as well as inadequate waste management policies. Persistent classes of emerging compounds such as xenobiotics present molecules whose physicochemical properties such as small molecular size, ionizability, water solubility, lipophilicity, polarity and volatility make degradability, identification and quantification of these complex compounds difficult. Based on research results showing that there is a possibility of risk to human and environmental health the presence of these compounds in the environment this article aimed to review the main pharmaceutical and xenobiotic residues present in the environment, as well as to present the most common methodologies used. The most commonly used analytical methods for identifying these compounds were HPLC and Gas Chromatography coupled with mass spectrometry with potential for characterize complex substances in the environment with low concentrations. An alternative and low-cost technology for emerging compound treatment demonstrated in the literature with a satisfactory performance for several types of sewage such as domestic sewage, wastewater and agroindustrial, was the Wetlands Constructed. The study was able to identify the main compounds that are being found in the environment and identify the most used analytical methods to identify and quantify these compounds, bringing some alternatives combining technologies for the treatment of compounds. Environmental contamination is eminent, since the production of emerging compounds aims to increase along with technological development. This demonstrates the need to explore and aggregate sewage treatment technologies to reduce or prevent the deposition of these compounds into the environment.

Microbial transformation of widely used pharmaceutical and personal care product compounds

Pharmaceutical and personal care products (PPCPs) are commonly used chemicals that are increasingly detected in urban-impacted environments, particularly those receiving treated wastewater. PPCPs may have toxicological effects on the macrofauna that are exposed through contaminated water; thus, there is interest in microbially mediated transformations that may degrade PPCPs. This review discusses specific examples of PPCP transformations that may occur in anoxic environments, including O-methylation and O-demethylation.