Application of a solar UV/chlorine advanced oxidation process to oil sands process-affected water remediation

Principles, challenges and prospects for electro-oxidation treatment of oilfield produced water

The oil industry is facing substantial environmental challenges, especially in managing waste streams such as Oilfield Produced Water (OPW), which represents a significant component of the industrial ecological footprint. Conventional treatment methods often fail to effectively remove dissolved oils and grease compounds, leading to operational difficulties and incomplete remediation. Electrochemical oxidation (EO) has emerged as a promising alternative due to its operational simplicity and ability to degrade pollutants directly and indirectly, which has already been applied in treating several effluents containing organic compounds. The application of EO treatment for OPW is still in an initial stage, due to the intricate nature of this matrix and scattered information about it. This study provides a technological overview of EO technology for OPW treatment, from laboratory scale to the development of large-scale prototypes, identifying design and process parameters that can potentially permit high efficiency, applicability, and commercial deployment. Research in this domain has demonstrated notable rates of removal of recalcitrant pollutants (>90%), utilizing active and non-active electrodes. Electro-generated active species, primarily from chloride, play a pivotal role in the oxidation of organic compounds. However, the highly saline conditions in OPW hinder the complete mineralization of these organics, which can be improved by using non-active anodes and lower salinity levels. The performance of electrodes greatly influences the efficiency and effectiveness of OPW treatment. Various factors must be considered when selecting the electrode material, such as its conductivity, stability, surface area, corrosion resistance, and cost. Additionally, the specific contaminants present in the OPW, and their electrochemical reactivity must be considered to ensure optimal treatment outcomes. Balancing these considerations can be challenging, but it is crucial for achieving successful OPW treatment. Active electrode materials exhibit a high affinity for chloride molecules, generating more active species than non-active materials, which exhibit more significant degradation potential due to the production of hydroxyl radicals. Regarding scale-up, key challenges include low current efficiency, the formation of by-products, electrode deactivation, and limitations in mass transfer. To address these issues, enhanced mass transfer rates and appropriate residence times can be achieved using flow-through mesh anodes and moderate current densities, which have proven to be the optimal configuration for this process.

A Light Touch: Solar Photocatalysis Detoxifies Oil Sands Process-Affected Waters Prior to Significant Treatment of Naphthenic Acids

Environmental reclamation of Canada's oil sands tailings ponds is among the single largest water treatment challenges globally. The toxicity of oil sands process-affected water (OSPW) has been associated with its dissolved organics, a complex mixture of naphthenic acid fraction components (NAFCs). Here, we evaluated solar treatment with buoyant photocatalysts (BPCs) as a passive advanced oxidation process (P-AOP) for OSPW remediation. Photocatalysis fully degraded naphthenic acids (NAs) and acid extractable organics (AEO) in 3 different OSPW samples. However, classical NAs and AEO, traditionally considered among the principal toxicants in OSPW, were not correlated with OSPW toxicity herein. Instead, nontarget petroleomic analysis revealed that low-polarity organosulfur compounds, composing <10% of the total AEO, apparently accounted for the majority of waters' toxicity to fish, as described by a model of tissue partitioning. These findings have implications for OSPW release, for which a less extensive but more selective treatment may be required than previously expected.

Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination

The rising debate on the dilemma of photocatalytic water treatment technologies has driven researchers to revisit its prospects in water decontamination. Nowadays, heterogeneous photocatalysis coupled oxidant activation techniques are intensively studied due to their dual advantages of high mineralization and high oxidation efficiency in pollutant degradation. This paved a new way for the development of solar-driven oxidation technologies. Previous reviews focused on the advances in one specific coupling technique, such as photocatalytic persulfate activation and photocatalytic ozonation, but lack a consolidated understanding of the synergy between photocatalytic oxidation and oxidant activation. The synergy involves the migration of photogenerated carriers, radical reaction, and the increase in oxidation rate and mineralization. This review systematically summarizes the fundamentals of activation mechanism, advanced characterization techniques and synergistic effects of coupling techniques for water decontamination. Besides, specific cases that lead researchers astray in revealing mechanisms and assessing synergy are critically discussed. Finally, the prospects and challenges are put forward to further deepen the research on heterogeneous photocatalytic activation of oxidants. This work provides a consolidated view of the existing heterogeneous photocatalysis coupled oxidant activation techniques and inspires researchers to develop more promising solar-driven technologies for water decontamination.

Sample preparation, analytical characterization, monitoring, risk assessment and treatment of naphthenic acids in industrial wastewater and surrounding water impacted by unconventional petroleum production

Industrial extraction of unconventional petroleum results in notable volumes of oil sands process water (OSPW), containing elevated concentrations of naphthenic acids (NAs). The presence of NAs represents an intricate amalgamation of dissolved organic constituents, thereby presenting a notable hurdle for the domain of environmental analytical chemistry. There is growing concern about monitoring the potential seepage of OSPW NAs into nearby groundwater and river water. This review summarizes recent studies on sample preparation, characterization, monitoring, risk assessment, and treatment of NAs in industrial wastewater and surrounding water. Sample preparation approaches, such as liquid-liquid extraction, solid phase microextraction, and solid phase extraction, are crucial in isolating chemical standards, performing molecular level analysis, assessing aquatic toxicity, monitoring, and treating OSPW. Instrument techniques for NAs analysis were reviewed to cover different injection modes, ionization sources, and mass analyzers. Recent studies of transfer and transformation of NAs provide insights to differentiate between anthropogenic and natural bitumen-derived sources of NAs. In addition, related risk assessment and treatment studies were also present for elucidation of environmental implication and reclamation strategies. The synthesis of the current state of scientific knowledge presented in this review targets government regulators, academic researchers, and industrial scientists with interests spanning analytical chemistry, toxicology, and wastewater management.

Degradation kinetics and disinfection by-products formation of benzophenone-4 during UV/persulfate process

The degradation kinetics, reaction pathways, and disinfection by-products formation of an organic UV filter, benzophenone-4 (BP4) during UV/persulfate oxidation were investigated. BP4 can hardly be degraded by UV alone, but can be effectively decomposed by UV/persulfate following pseudo-first order kinetics. BP4 degradation rate was enhanced with increasing persulfate dosage and decreasing pH from 8 to 5. However, the degradation rate of BP4 at pH 9 was higher than that at pH 8 because of the presence of phenolic group in BP4 structure. and SO 4 - ⋅ were confirmed as the major contributors to BP4 decomposition in radical scavenging experiments, and the second-order rate constants between HO ⋅ and BP4 as well as those between SO 4 - ⋅ and BP4 were estimated by establishing and solving a kinetic model. The presence of B r - and humic acid inhibited the decomposition of BP4, while N O 3 - promoted it. The mineralisation of BP4 was only 9.1% at the persulfate concentration of 50 μM. Six degradation intermediates were identified for the promulgation of the reaction pathways of BP4 during UV/persulfate oxidation were proposed as a result. In addition, the formation of DBP in the sequential chlorination was evaluated at different persulfate dosages, pH values, and water matrix. The results of this study can provide essential knowledge for the effective control of DBP formation with reducing potential hazard to provide safe drinking water to the public.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH₂Cl- and ClO₂-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Electrodegradation of cyclophosphamide in artificial urine by combined methods

The degradation of the chemotherapeutic drug cyclophosphamide in artificial urine was evaluated by Electrochemical Advanced Oxidation Processes (EAOP). The system consisted of an electrochemical flow reactor with a commercial DSA^® electrode (nominal composition Ti / Ru_0,3Ti_0,7O₂) and Ti-mesh cathode. In order to assess the best parameters, the effect of current density, time and flow rate were analyzed using an initial 2³ factorial design. The chosen response variable was the energy efficiency to produce free chlorine species (HClO/ClO^-). After obtaining the most significant factors, the Central Composite Design (CCD) was performed, where the optimum conditions were determined for the current density range (11.714 mA cm^-2 and 66.57 mA cm^-2), flow rate (31.33 mL min^-1) and time range (19 and 37 min). Under an optimized condition, the efficiency of other combined methods (photo-assisted electrochemical, photochemical, sonoelectrochemical and photo-assisted sonoelectrochemical) was evaluated. The efficiency of degradation processes was determined by removal of Chemical Oxygen Demand (COD), creatinine and urea. Analysis by HPLC demonstrates that the cyclophosphamide was substantially removed during the treatment process of ∼77%. Based on these results, it can be observed that the coupling between electrochemical and photochemical processes is a promising alternative for the treatment of this effluent, as a marked reduction of organic matter is observed (63, 94% of creatinine, 29.62% of urea, 39.1% of TOC) and a low treatment cost ratio.

Enhanced solar inactivation of fungal spores by addition of low-dose chlorine: Efficiency and mechanism

This work demonstrated that the solar inactivation of fungal spores was enhanced by addition of low-dose chlorine. Although the effect of low-dose chlorine alone (2.0 mg/L) on culturability of fungal spores was negligible, the solar/chlorine inactivation on fungal spores performed better than solar alone inactivation, with a lower shoulder length and a higher maximum inactivation rate constant. The enhanced inactivation of Aspergillus niger can be ascribed to the membrane oxidation by chlorine, and the enhanced inactivation of Penicillium polonicum can be ascribed to the membrane oxidation by chlorine and ·OH (·OH plays a major role). The oxidization by chlorine and ·OH led to an increase in membrane permeability of fungal spores, which enhanced the solar inactivation, resulting in an increase in intracellular ROS and more serious morphological damage. Due to the presence of background substances such as dissolved organic matter and metal ions (Fe²⁺, Mn²⁺, etc.), the inactivation efficiency in real water matrices was decreased. The main disinfection by-products (DBPs) produced in the inactivation of fungal spores in chlorine alone and solar/chlorine treatments were dichloroacetic acid, trichloroacetic acid, trichloroacetone and trichloromethane. Generally, DBPs formation in solar/chlorine treatment was lower than those in chlorine alone treatment. Moreover, the regrowth potential of the two genera of fungal spores in R2A medium could be inhibited by adding low-dose chlorine.

Visible-Light Photocatalytic Chlorite Activation Mediated by Oxygen Vacancy Abundant Nd-Doped BiVO4 for Efficient Chlorine Dioxide Generation and Pollutant Degradation

Visible-light photocatalytic chlorite activation has emerged as an efficient oxidation process for micropollutant elimination. However, the in-depth mechanism of chlorite activation is not understood. In this study, using neodymium-doped bismuth vanadate (Nd_xBi_1-xVO_4-δ) as a model catalyst, we describe the oxygen vacancy (OV)-mediated chlorite activation process for efficient ClO₂ generation and cephalexin (CPX) degradation. DFT calculations and in situ DRIFTS suggest that the OV-introduced surface -OH serves as the Brønsted acidic center for chlorite adsorption. The OV-mediated chlorite activation involves multistep reactions that surface hydroxylation and proton transfer from the surface -OH to chlorite, forming metastable chlorous acid (HClO₂) and further disproportionating to ClO₂. As compared with vis-photocatalysis, the vis-photocatalysis coupled with chlorite activation (vis/chlorite) technique exhibits superior performance in antibiotic degradation and achieves efficient microorganism inactivation. This work uncovers the role of OVs on chlorite activation and provides a rational strategy for designing visible-light-driven oxidation techniques in water and wastewater treatment.

Degradation of 2-phenylbenzimidazole 5-sulfonic acid by UV/chlorine advanced oxidation technology: Kinetic model, degradation byproducts and reaction pathways

In this study, the degradation kinetic model and pathways of a UV filter, 2-phenylbenzimidazole-5-sulfonic acid (PBSA) during UV/chlorination were investigated. PBSA hardly degraded under UV irradiation or chlorination alone, but its degradation in UV/chlorination was efficient and followed pseudo-first order kinetics at pH 7. Increasing the chlorine dosage from 12.5 to 200 μM can enhance PBSA degradation, while increasing pH from 5 to 9 caused opposite effect. The second-order rate constants between radicals (∙Cl, ∙ClO, and ∙OH) and PBSA and the contribution of ∙OH during UV/chlorination were determined. ∙Cl and ∙OH were confirmed to be the main contributors to PBSA degradation. The presence of background [Formula: see text] and humic acid can inhibit PBSA degradation, but the presence of Cl^- showed negligible effect. Kinetic model was established, and the prediction correlated well to the experimental results. The mineralization rate in terms of total organic carbon increased with reaction time to 44.9% after 60 min UV/chlorination. The PBSA degradation intermediates in UV/chlorination were identified, and the transformation pathways were proposed accordingly. Furthermore, the formation of chlorinated disinfection by-products (Cl-DBPs) were evaluated in the sequential chlorination for comprehensively evaluation of the efficiency, mechanism, and safety of removing PBSA using UV/chlorination.

Aerobic naphthenic acid-degrading bacteria in petroleum-coke improve oil sands process water remediation in biofilters: DNA-stable isotope probing reveals methylotrophy in Schmutzdecke

There is an increasing interest in treatment of oil sands process water (OSPW) via biofiltration with petroleum coke (PC) as a substratum. In fixed bed biofilters (FBBs) with PC, the dominance of anaerobic digestion of dissolved organics results in poor removal of naphthenic acids (NAs) along with a high degree of methanogenesis. In this study, the operation of FBBs was modified to improve OSPW remediation by supporting the filtering bed with aerobic naphthenic acid-degrading bacteria treating aerated OSPW (FBB_{bioaugmentation}). The results were compared with a biofilter operated under controlled conditions (FBB_control). To this end, a consortium of three aerobic NAs-degrading bacterial strains was immobilized on PC as a top layer (10 cm). These bacteria were pre-screened for growth on 15 different NAs surrogates as a sole carbon source, and for the presence of catabolic genes coding alkane hydroxylase (CYP153) and alkane monooxygenase (alkB) enzymes. The results illustrated that biofiltration in FBB_{bioaugmentation} removed 32% of classical NAs in 15 days; while in the FBB_control, degradation was limited to 19%. The degradation of fluorophore (aromatic) compounds was also improved from 16% to 39% for single ring (O_I), 22% to 29% for double ring (O_II), and 15% to 23% for three rings (O_III) compounds. DNA-Stable Isotope Probing revealed that potential hydrocarbons degraders such as Pseudomonas (inoculated), Pseudoxanthomonas (indigenous) were present up to 9.0% in the ¹³C-labelled DNA fraction. Furthermore, a high abundance of methylotrophs was observed in the Schmutzdecke, with Methylobacillus comprising more than two-third of the total community. This study shows that bioaugmentation rapidly improved OSPW remediation. Aeration mostly contributed to methane consumption in the top layer, thus minimizing its release into the environment.

Role of NOM in the Photolysis of Chlorine and the Formation of Reactive Species in the Solar/Chlorine System

The solar/chlorine system has been proposed as a novel advanced oxidation process (AOP) for efficient pollutant degradation and water disinfection by producing a series of reactive species including hydroxyl radicals (HO^•), chlorine radicals (Cl^•), and so forth. In this study, the role of natural organic matter (NOM) in the photolysis of free available chlorine (FAC) and the formation of HO^• and Cl^• in the solar/chlorine system was investigated employing nitrobenzene and benzoic acid as selective chemical probes. The decay rate of FAC was significantly accelerated in the presence of NOM at pH 5.5 under simulated solar irradiation, likely due to the photoreaction between FAC and the photoexcited NOM. The decay rate of FAC increased upon increasing the electron-donating capacity of NOM, which indicated that phenolic components play a significant role in the photodegradation of FAC. This acceleration mechanism was further verified using 4-nitrophenol as a model phenolic compound. NOM promoted Cl^• formation and quenched HO^• in the solar/chlorine system. The proposed reaction mechanism included the reaction of excited singlet phenolic compounds in NOM with FAC, which yielded Cl^•. This study provides a useful insight into future applications for using the solar/chlorine system as a novel AOP for wastewater treatment or disinfection.

Feasibility of micropollutants removal by solar-activated persulfate: Reactive oxygen species formation and influence on DBPs

As a natural source of visible light and a type of renewable energy, solar energy is extensively used in the field of photochemistry. In this study, solar was employed to activate persulfate (PS) to degrade typical micropollutants. The removal kinetics of aspirin (ASA) and flunixin meglumine (FMME) in the solar/PS system were well fitted by pseudo-first-order models (R² > 0.99). In the system containing 1.0 mM PS activated by solar irradiation at a fluence of 1.14 × 10^-4 E·m^-2·s^-1, 72.6% and 97.5% of ASA and FMME were degraded, and the corresponding kinetic constants were 6.8-9.8 × 10^-2 and 1.6-9.8 × 10^-1 min^-1, respectively. Qualitative and quantitative analyses of the reactive oxygen species (ROS) indicated that sulfate radical (SO₄^·-) played a major role in degradation, with the maximum contributions of 77.7% and 88.8% for the degradation of ASA and FMME, whereas the maximum contributions of hydroxyl radical (·OH) were only 11.6% and 6.5%, respectively. The contributions of singlet oxygen (¹O₂) were less than 15% at pH 5.5, but increased to 25.6% and 45.5% at pH 8.5, respectively. Solar/PS pre-oxidation increased disinfection byproducts (DBPs) (95.8% for trihalomethanes (THMs) and 47.9% for haloacetic acids (HAAs) at pH 7.0) after chlorination in deionized water, and an opposite trend was found in systems coexisting with natural organic matter (NOM). Residual PS after oxidation resulted in a high aquatic toxicity, with an inhibition rate of 18.70% to algae growth. Economic analysis showed that the electrical energy per order values of the system ranged from 23.5 to 86.5 kWh·m^-3·order^-1, indicating that the solar/PS system shows promise for practical applications.

Solar-driven free chlorine advanced oxidation process for simultaneous removal of microcontaminants and microorganisms in natural water at pilot-scale

Contamination of natural water (NW) by emerging contaminants has been widely pointed out as one of the main challenges to ensure high-quality drinking water. Thus, the effectiveness of a solar-driven free chlorine advanced oxidation process simultaneously investigating the elimination of six organic microcontaminants (OMCs) and three bacteria from NW at a pilot-scale was evaluated in this study. Firstly, the solar/free chlorine process was studied at lab-scale using a solar simulator to evaluate the effect of free chlorine concentration (0.5-10 mg L^-1) on OMC degradation and generation of toxic oxyanions (e.g., ClO₃^- ions). Thus, the best free chlorine concentration observed was applied for the simultaneous removal of OMCs and pathogens under natural solar light at pilot scale. At lab-scale, the solar/free chlorine (2.5 mg L^-1) process achieved 80% of total degradation in 5 min (1.4 kJ L^-1 of accumulative UV energy) with an oxidant consumption of 0.3 mg L^-1 and without ClO₃^- generation. Similar results were attained under natural solar irradiation at a pilot-scale. For all bacteria strains, the legally required detection limit (DL = 1 CFU 100 mL^-1) for reclaimed water reuse was attained in a short contact time. Still, more importantly, the solar/free chlorine (2.5 mg L^-1) process effectively avoided the possible bacterial regrowth in the post-treated sample after six days. Finally, the combination of free chlorine with solar irradiation provided a simple and energy-efficient process for OMC and bacteria removal in NW at a pilot-scale.

Solar photo-assisted electrochemical processes applied to actual industrial and urban wastewaters: A practical approach based on recent literature

The application of electrochemical processes for wastewater treatment has increase significantly in the last two decades. However, most of the works are focused on lab-scale systems testing in saline simulated solutions spiked with a reference organic compound, evidencing the scarcity of studies on actual wastewaters through a more realistic practical approach. The aim of the present work is assessing the performance of electrochemical treatments in actual matrices, considering the formation of different oxidants species, apart from hydroxyl radicals, from dissolved ions contained in target effluents as well as both, the regeneration of Fe²⁺ and their combination with a light irradiation source. The degradation of a mix of microcontaminants in water matrices with different complexity by solar photoelectron-Fenton at natural pH and at pilot scale has been carried out at Plataforma Solar de Almería. Higher degradation rates were obtained when focusing on the more complex and saline matrices. In addition, complex industrial wastewaters mineralization was also studied by means of solar assisted electro-oxidation, showing the crucial role of ammonium concentration in the effluent, since it acts as a competitor for active chlorine species and so reducing the mineralization rate.

Bacterial diversity in petroleum coke based biofilters treating oil sands process water

Adopting nature-based solutions for the bioremediation of oil sands process water (OSPW) is of significant interest, which requires a thorough understanding of how bacterial communities behave within treatment systems operated under natural conditions. This study investigates the OSPW remediation potential of delayed petroleum-coke (PC), which is a byproduct of bitumen upgrading process and is readily available at oil refining sites, in fixed-bed biofilters particularly for the degradation of naphthenic acids (NAs) and aromatics. The biofilters were operated continuously and total and active bacterial communities were studied by DNA and RNA-based amplicon sequencing in a metataxonomic fashion to extrapolate the underlying degradation mechanisms. The results of total community structure indicated a high abundance of aerobic bacteria at all depths of the biofilter, e.g., Porphyrobacter, Legionella, Pseudomonas, Planctomyces. However, redox conditions within the biofilters were anoxic (-153 to -182 mV) that selected anaerobic bacteria to actively participate in the remediation of OSPW, i.e., Ruminicoccus, Eubacterium, Faecalibacterium, Dorea. After 15 days of operation, the removal of classical NAs was recorded up to 20% whereas oxidized NAs species were poorly removed, i.e., O₃-NAs: 4.8%, O₄-NAs: 1.2%, O₅-NAs: 1.7%, and O₆-NAs: 0.5%. Accordingly, monoaromatics, diaromatics, and triaromatics were removed up to 16%, 22%, and 15%, respectively. The physiology of the identified genera suggested that the degradation in the PC-based biofilters was most likely proceeded in a scheme similar to beta-oxidation during anaerobic digestion process. The presence of hydrogenotrophic methanogens namely Methanobrevibacter and Methanomassiliicoccus and quantification of mcrA gene (2.4 × 10² to 8.7 × 10² copies/mg of PC) revealed that methane production was likely occurring in a syntrophic mechanism during the OSPW remediation. A slight reduction in toxicity was also observed. This study suggests that PC-based biofilters may offer some advantages in the remediation of OSPW; however, the production of methane could be of future concerns if operated at field-scale.

On the performance of distinct electrochemical and solar-based advanced oxidation processes to mineralize the insecticide imidacloprid

Water contamination by contaminants of emerging concern is one of the main challenges to be solved by our desired sustainable society. In the same time, different technologies for water treatment are becoming enough mature to be implemented. In this work, two different advanced oxidation processes (AOP) were investigated: i) electrochemical processes (electrochemical, photoassisted electrochemical, electro Fered-Fenton, and photo-electro Fered-Fenton - PEF-Fered) using a BDD and DSA® electrodes under UVA and UVC irradiation (9 W) and ii) solar-based AOP using four distinct oxidants (HOCl, H₂O₂, S₂O₈^2-, HSO₅^-) in the presence or absence of Fe²⁺ ions to oxidize and mineralize imidacloprid (IMD: 50 mg L^-1) containing solutions. The PEF-Fered (1.0 mM Fe²⁺ and 50 mg L^-1 h^-1 H₂O₂) under UVA or UVC irradiation and HOCl/UVC (NaCl 17 mM) processes using a BDD and DSA® electrodes (10 mA cm ^-2), respectively, performed equally well to completely oxidize and mineralize (∼90%) IMD at the expense of only ∼0.3 kWh g^-1. Low amounts and highly oxidized byproducts identified through liquid chromatography tandem mass spectrometry were observed for the HOCl/UVC process using a DSA® electrode. Concerning the solar-based AOP, all assessed oxidants (4 mM h^-1) successfully oxidized IMD within 3 h of treatment, whereas only H₂O₂ and HOCl led to significant (∼60%) TOC abatement after 6 h treatment. The use of Fe²⁺ (0.5 or 1.0 mM) had no significant improvement in the oxidation and mineralization of IMD.

Treatment of oil sands process water using petroleum coke: Field pilot

This is the first large-scale field pilot study that examined the feasibility and effectiveness of petroleum coke (PC), produced by a Fluid Coking Process, as an adsorbent for oil sands process water (OSPW) treatment. The pilot program consisted of an inline series of two reactors (pipeline reactor 1, and batch reactor 2) and lasted for approximately 4 months. The quality of treated OSPW as a function of residence time in the PC deposit under natural climatic conditions was assessed by looking at changes in organic compounds (acid extractable fraction (AEF), dissolved organic carbon (DOC), etc.), vanadium, and other trace element concentrations, major ions, conductivity, total suspended solids (TSS), pH and toxicity. The results indicated that the AEF adsorption by PC followed pseudo-second order kinetics and the overall combined removal efficiency of AEF was greater than 80%. Reactor 1 showed higher AEF removal than Reactor 2. DOC decreased about 50% after 4 weeks of retention in the PC deposit. An increase of vanadium concentration after PC contact indicated that vanadium leaching occurred. However, with increased residence time in the PC deposit, vanadium concentration decreased in the cells and tanks by 42% and 98%, respectively. Filtration through the PC deposit reduced the TSS in OSPW to less than laboratory detectable limits. Unlike untreated OSPW, treated OSPW did not show an acute toxic response based on whole effluent toxicity testing using trout, zooplankton, and bacteria. This study demonstrated that PC adsorption is a potentially commercially viable technology for highly efficient treatment of OSPW.

Degradation of cyclohexanecarboxylic acid as a model naphthenic acid by the UV/chlorine process: Kinetics and by-products identification

Degradation kinetics, by-products identification and pathways of a model naphthenic acid, cyclohexanecarboxylic acid (CHA), by the UV/Chlorine process were investigated in this study. Mathematical modeling indicated that the initial CHA decay rate increased rapidly with the chlorine dose when the chlorine dose was lower than 45 mg/L and decreased with further chlorine dose increases. Increasing the chlorine dose from 400 to 800 mg/L resulted in a steady increase in the total removal of CHA after 60 min of UV photolysis. By dividing the 700 mg/L chlorine dose into five separated doses (140 mg/L each) added at 10 min intervals, the total CHA removal increased from 72% to 91%. This implies that the ideal condition of the UV/Chlorine process in degrading CHA is to add chlorine continuously at a constant rate to compensate any chlorine consumption to reduce the radical scavenging effect. It was found that the CHA decay was mainly attributed to the hydroxyl radical (OH) attack and the reactive chlorine species (RCS) contribution was relatively small. Various by-products, including the mono-chlorinated and di-chlorinated by-products, were identified and the reaction pathway for CHA degradation during UV/Chlorine treatment was proposed.

DBP formation and toxicity alteration during UV/chlorine treatment of wastewater and the effects of ammonia and bromide

The UV/chlorine process is efficient for the abatement of micropollutants; yet, the formation of disinfection by-products (DBPs) and the toxicity can be altered during the treatment. This study investigated effluent organic matter characterization, DBP formation and toxicity alteration after the UV/chlorine treatment of wastewater; particularly, typical water matrix components in wastewater, namely, ammonia and bromide, were studied. The raw wastewater contained low levels of ammonia (3 µM) and bromide (0.5 µM). The UV/chlorine treatment efficiently eliminated 90 - 94% of fluorescent components. Compared with chlorination alone, a 20 min UV/chlorine treatment increased the formation of trihalomethanes (THMs), haloacetic acids (HAAs), chloral hydrate (CH), haloacetonitriles (HANs), trichloronitromethane (TCNM) and haloacetamides (HAcAms) by 90 - 508%. In post-chlorination after the UV/chlorine treatment, the formation of CH, HANs, TCNM and HAcAms increased by 77 - 274%, whereas the formation of both THMs and HAAs increased slightly by 11%. Meanwhile, the calculated cytotoxicity and genotoxicity of DBPs increased considerably after the UV/chlorine treatment and in post-chlorination, primarily due to the increased formation of HAAs and nitrogenous DBPs (N-DBPs). However, the acute toxicity of the wastewater to Vibrio fischeri and genotoxicity determined by the umu test decreased by 19% and 76%, respectively, after the 20 min UV/chlorine treatment. An additional 200 µM ammonia decreased the formation of all detected DBPs during the UV/chlorine treatment and 24 h post-chlorination, except that TCNM formation increased by 11% during post-chlorination. The acute toxicity of wastewater spiked with 200 µM ammonia was 32% lower than that of raw wastewater after the UV/chlorine treatment, but the genotoxicity was 58% higher. The addition of 1 mg/L bromide to the UV/chlorine process dramatically increased the formation of brominated DBPs and the overall calculated cytotoxicity and genotoxicity of DBPs. However, the acute toxicity and genotoxicity of the wastewater decreased by 7% and 100%, respectively, when bromide was added to the UV/chlorine treatment. This study illuminated that UV/chlorine treatment can decrease acute and geno- toxicities of wastewater efficiently.

Low-current electro-oxidation enhanced the biodegradation of the recalcitrant naphthenic acids in oil sands process water

Combining electro-oxidation (EO) with biodegradation for real oil sands process water (OSPW) treatment was evaluated in terms of naphthenic acid (NA) biodegradation enhancement. Ion mobility spectrometry (IMS) qualitative analysis showed that EO by graphite was able to degrade the different NA clusters in OSPW including: classical, oxidized and heteroatomic NAs. Applying EO even at current density as low as 0.2 mA/cm² was still able to reduce classical NAs and acid extractable fraction (AEF) by 19% and 7%, respectively. EO pretreatment preferentially broke long carbon chains and highly cyclic carboxylic fractions of NAs in OSPW to improve the biodegradation of NAs. Aerobic biodegradation for 40 days reduced NAs by up to 30.9% when the samples were pre-treated with EO. Applying EO at current densities below 2 mA/cm² maintained current efficiency as high as 48% and resulted in improvement in the biodegradation rate of remaining NAs by up to 2.7 folds. It was further revealed that applying EO before biodegradation could reduce the biodegradation half-life of classical NAs by up to 4.4 folds. 16S amplicon sequencing analysis showed that the samples subjected to biodegradation had increased abundances of Sphingomonadales and Rhodocyclales with increasing applied current density for EO pre-treatments.

Transformation of X-ray contrast media by conventional and advanced oxidation processes during water treatment: Efficiency, oxidation intermediates, and formation of iodinated byproducts

X-ray contrast media (ICM), as the most widely used intravascular pharmaceuticals, have been frequently detected in various environmental compartments. ICM have attracted increasingly scientific interest owing to their role as an iodine contributor, resulting in the high risk of forming toxic iodinated byproducts (I-BPs) during water treatment. In this review, we present the state-of-the-art findings relating to the removal efficiency as well as oxidation intermediates of ICM by conventional and advanced oxidation processes. Moreover, formation of specific small-molecular I-BPs (e.g., iodoacetic acid and iodoform) during these processes is also summarized. Conventional oxidants and disinfectants including chlorine (HOCl) and chloramine (NH₂Cl) have low reactivities towards ICM with HOCl being more reactive. Iodinated/deiodinated intermediates are generated from reactions of HOCl/NH₂Cl with ICM, and they can be further transformed into small-molecular I-BPs. Types of disinfectants and ICM as well as solution conditions (e.g., presence of bromide (Br^-) and natural organic matters (NOM)) display significant impact on formation of I-BPs during chlor(am)ination of ICM. Uncatalyzed advanced oxidation process (AOPs) involving ozone (O₃) and ferrate (Fe(VI)) exhibit slow to mild reactivities towards ICM, usually leading to their incomplete removal under typical water treatment conditions. In contrast, UV photolysis and catalyzed AOPs including hydroxyl radical (HO^•) and/or sulfate radical (SO₄^.-) based AOPs (e.g., UV/hydrogen peroxide, UV/persulfate, UV/peroxymonosulfate (PMS), and CuO/PMS) and reactive chlorine species (RCS) involved AOPs (e.g., UV/HOCl and UV/NH₂Cl) can effectively eliminate ICM under various conditions. Components of water matrix (e.g., chloride (Cl^-), Br^-, bicarbonate (HCO₃^-), and NOM) have great impact on oxidation efficiency of ICM by catalyzed AOPs. Generally, similar intermediates are formed from ICM oxidation by UV photolysis and AOPs, mainly resulting from a series reactions of the side chain and/or C-I groups (e.g. cleavage, dealkylation, oxidation, and rearrange). Further oxidation or disinfection of these intermediates leads to formation of small-molecular I-BPs. Pre-oxidation of ICM-containing waters by AOPs tends to increase formation of I-BPs during post-disinfection process, while this trend also depends on the oxidation processes applied and solution conditions. This review summarizes the latest research findings relating to ICM transformation and (by)products formation during disinfection and AOPs in water treatment, which has great implications for the practical applications of these technologies.

Novel Visible Light-Driven Photocatalytic Chlorine Activation Process for Carbamazepine Degradation in Drinking Water

Photolysis of free chlorine (HOCl/ClO^-) is an advanced oxidation process (AOP) to produce hydroxyl (HO^•) and other radicals for refractory micropollutant degradation. However, HOCl/ClO^- is only conducive to activation and production of radicals by ultraviolet (UV) light. For the first time, we show the use of visible light (>400 nm) to produce HO^• and ClO^•, through use of graphitic carbon nitride (g-C₃N₄) and photogenerated h_vb⁺, e_cb^-, and O₂^•- in the presence of HOCl/ClO^-, which was termed visible light g-C₃N₄-enabled chlorine AOP (VgC-AOP). The VgC-AOP increased the pseudo first-order degradation rate constant of a model micropollutant, carbamazepine, by 16 and 7 times higher than that without g-C₃N₄ and HOCl/ClO^-, respectively, and remained active over multiple use cycles. Effects of water quality [pH, alkalinity, Cu(II), and natural organic matter (NOM)] and the operational conditions (g-C₃N₄ and HOCl/ClO^- concentrations, irradiation wavelength, and dose) were investigated. Of particular significance is its superior performance in the presence of NOM, which absorbs less light at visible light wavelengths and scavenges less surface-bonded reactive species, compared against UV/TiO₂ or UV/chlorine AOPs. The VgC-AOP is practically relevant, feasible, and easily implementable and it expands the potential types of light sources (e.g., LEDs and solar light).

Photodegradation of bitumen-derived organics in oil sands process-affected water

The chemical composition of water-soluble organics in oil sands process-affected water (OSPW) is primarily composed of natural constituents of bitumen that are solubilized and concentrated during aqueous extraction of oil sands. OSPW organics are persistent and acutely toxic, and a leading remediation strategy is long-term ageing in end-pit lakes, despite limited data available on its photochemical fate. Here, direct photolysis of whole OSPW, or of its constituent fractions, was examined at environmentally relevant wavelengths (>290 nm) in bench-top studies. Changes in the chemical profiles of whole OSPW, acid- (AEO), and base-extractable organics (BEO) were characterized by liquid chromatography with ultra-high resolution mass spectrometry in negative (-) and positive (+) ionization modes. Following 18 d of irradiation, photolysis reduced the total ion intensity in all samples in both modes. The most photo-labile species included the O₂^-, O₃^-, O₄^-, O₂S^-, and O₄S^- chemical classes, which were depleted in whole OSPW by 93-100% after only 5 d. In positive mode, detected species were more recalcitrant than those detected in negative mode, with an average reduction across all heteroatomic classes of 75 ± 11.0% after 18 d. Estimated environmental half-lives for heteroatomic classes ranged from 57 d (O₄S^-) to 545 d (O₃N⁺), with a greater recalcitrance for classes detected in positive mode compared to negative mode. Under field conditions in end-pit lakes, natural photolysis may be an important mechanism for effective OSPW remediation, and we suggest that future end-pit lakes be shallow to maximize light penetration and natural photolysis in ageing OSPW.

Generation and application of reactive chlorine species by electrochemical process combined with UV irradiation: Synergistic mechanism for enhanced degradation performance

Saline wastewater originates from many industries, containing a large amount of salt (NaCl) and other toxic and harmful organic matter, which have a great impact on the soil and groundwater. However, the treatment of saline wastewater is a serious problem because organic contents are hard to degrade with the high salinity by the common water treatment technologies. Herein, an electrochemical process coupled with ultraviolet (UV) irradiation was proposed for the saline wastewater treatment. High efficiency of p-nitrophenol (p-NP) and ammonia degradation were contributed from the in situ electrochemical produced active chlorine and photo-induced chlorine radicals. Under the optimal conditions (0.10 A, 0.05 M NaCl, and pH 6.00), approximately 98.91% p-NP was removed after 60 min with the rate constant of 7.521 × 10^-2 min^-1 in the electrochemical process, and 28.99% mineralization rate was obtained, while with the synergistic effect of UV and electrochemistry, approximately 100% of p-NP removal (k = 9.331 × 10^-2 min^-1) was achieved by 30 min treatment and about 83.70% of p-NP can be mineralized to CO₂ after 60 min. The study on the synergistic mechanism of enhanced degradation performance illustrated that Cl with high oxidation capacity played an important role in the p-NP oxidation. Besides, based on the chlorine radical reactions, this method was also effectively applied to remove ammonia nitrogen (92.00% removal of total nitrogen in 100 min) for nitrogen-containing wastewater. Thus, this study offers a promising approach for the treatment of saline industry wastewater.

Comparison of UV/Persulfate and UV/H2O2 for the removal of naphthenic acids and acute toxicity towards Vibrio fischeri from petroleum production process water

The ultraviolet light-activated persulfate process (UV/Persulfate) has received much attention in recent years as a novel advanced oxidation method for the treatment of municipal and industrial wastewater. This work investigated the UV/Persulfate and UV/H₂O₂ processes for the treatment of real oil sands process water (OSPW) at ambient pH condition using a medium pressure mercury lamp (emission between 200 and 530 nm). The degradation performances towards fluorophore organic compounds and naphthenic acids (NAs) in OSPW were evaluated using synchronous fluorescence spectrometry and ultra performance liquid chromatography time-of-flight mass spectrometry, respectively. Compared to the UV/H₂O₂ process, the UV/Persulfate process exhibited higher efficiency to remove both NAs and fluorophore organic compounds. Under 40 min of UV exposure and incident irradiance of 3.50 mW cm^-2, fluorophore organic compounds were greatly degraded by UV/Persulfate (2 mM) and two- and three-ring fused organics were completely removed. 59.4%, 83.8% and 92.2% of O₂-NAs in OSPW were removed with persulfate dosages of 0.5, 2, and 4 mM, respectively. The removal efficiency decreased along with the number of oxygen atoms in NAs (83.8%, 49.3%, and 46.8% for O₂-, O₃-, and O₄-NAs, respectively) with 2 mM of persulfate, because of the formation of oxidized NAs in the same process. The structure-reactivity of O₂-NA compounds fitted pseudo-first order kinetics in UV/Persulfate process with the rate constants ranging from 0.0156 min^-1 to 0.1511 min^-1. NAs with higher carbon numbers and double bond equivalence were more reactive in the UV/Persulfate oxidation process. The acute toxicity of OSPW to Vibrio fischeri was significantly reduced after the UV/Persulfate and UV/H₂O₂ treatments. Overall results demonstrated that the UV/Persulfate oxidation can be an effective alternative for future reclamation of OSPW.

Oxidation of Microcystic-LR via the solar/chlorine process: Radical mechanism, pathways and toxicity assessment

Microcystin-LR (MC-LR) is the most widely distributed and harmful variant toxins released by cyanobacteria, which poses potential threaten to people and aquatic animals when entering natural water. In our research, solar/chlorine process was comprehensively investigated to degrade and detoxify MC-LR. Under the chlorine concentration of 1.0 mg L^-1, MC-LR (1.0 μM) was decreased by 96.7%, 26%, and 9% by solar/chlorine process, chlorination, and solar irradiation respectively. Quenching experiments confirmed that reactive chlorine species (RCS) and hydroxyl radical (HO) were the predominant reactive species in solar/chlorine process at neutral condition, and ozone was generated because of the participation of triplet-state oxygen (O(³P)). The respective contributions of each reactive species were calculated with the order as: RCS, HO, ozone, and solar irradiation. The presence of HCO₃^- and natural organic matter in water inhibited the degradation efficiency of MC-LR. Moreover, the transformation products of MC-LR generated during the solar/chlorine process were identified and a possible pathway was proposed. The hepatotoxicity of MC-LR and its transformation products was compared using protein phosphatase 2A. Our experimental results revealed that the concentration and hepatotoxicity of MC-LR both significantly decreased, and most products were not hepatoxic. Overall, the solar/chlorine process is a promising alternative technology to degrade MC-LR during eutrophication.

Photodegradation of naphthenic acids induced by natural photosensitizer in oil sands process water

Utilization of renewable solar energy driven advanced oxidation processes for oil sands process water (OSPW) remediation has received extensive attention. Naturally existing inorganic photosensitizer in OSPW was investigated in this work to provide information about the application of indirect photolysis treatment of organic contaminants in OSPW. OSPW and OSPW organic fraction were exposed under UV irradiance with fluence of 10 J/cm² to investigate the effect of OSPW inorganic fraction (OSPW-IF) on the non-catalytic photolysis of naphthenic acids (NAs) in OSPW. The results indicated that the inorganic fraction in OSPW enhanced the photodegradation of NAs, with 24.3% of total NA removal in OSPW, while only 12.4% of total NAs were removed in OSPW organic fraction. Moreover, the photodegradation of 1-adamantanecarboxylic acid (ACA) dissolved in OSPW-IF or carbonate buffer was conducted to verify the enhanced photodegradation of NAs by OSPW-IF. The results showed that 30.9% of ACA was removed in the OSPW-IF, while no ACA degradation was observed in carbonate buffer after 60 min of UV exposure, indicating that the OSPW-IF induced the photodegradation of ACA. In addition, nitrate was identified to be the photosensitizer in OSPW-IF responsible for the indirect photolysis of ACA. In the presence of nitrate, both hydroxyl radicals (•OH) and reactive nitrogen species were generated, where •OH was the dominant reactive species that contributed to the degradation of ACA. Ten possible by-products ranging from single to multiple hydroxyl, nitroso, nitro and carbonyl substituted products were proposed to be produced from the nitrate-induced photodegradation process through three different pathways. This study demonstrated that the photolysis of NAs in OSPW due to the presence of natural photosensitizers and nitrate could act as a natural photosensitizer for the remediation of OSPW by the photo-oxidation process.

Full-scale comparison of UV/H2O2 and UV/Cl2 advanced oxidation: The degradation of micropollutant surrogates and the formation of disinfection byproducts

The photolysis of chlorine by UV light leads to the formation of the hydroxyl radicals (OH) as well as reactive chlorine species (RCS) that can be effective as advanced oxidation processes (AOPs) for water treatment. Much of the research to date has been done at laboratory- or bench-scale. This study reports results from a model that demonstrates that the relative effectiveness of the UV/Cl₂ AOP compared to the more traditional UV/H₂O₂ AOP is a function of optical path length. As such, the relative effectiveness of the two treatment options evaluated at small scale may not reflect the relative performance at full-scale, making results previously obtained at small-scale potentially less scalable. This study therefore compares the performance of UV/Cl₂ to UV/H₂O₂ at a full-scale water treatment plant, using sucralose and caffeine as spiked surrogates for contaminants that are reactive solely to OH radicals, and to both OH and RCS, respectively. pH was varied between 6.5 and 8.0. The results demonstrated that when using a medium pressure UV lamp, UV/Cl₂ might lead to approximately twice the production of OH radicals as UV/H₂O₂ at pH 6.5 when using the same molar oxidant concentration, but adding chlorine to the UV reactor at pH 8.0 had a negligible impact on OH radical concentration in comparison to UV alone. The study also confirmed previous small-scale results that RCS can be a major contributor to UV/Cl₂ treatment for compounds such as caffeine that are susceptible to RCS, with UV/Cl₂ effective at both pH 6.5 and 8.0 for such compounds. Disinfection byproducts were monitored, with adsorbable organohalide (AOX) formation increasing by approximately 10 μg-Cl/L due to chlorine photolysis, but only at pH 6.5 and not at pH 8.0. This implies that UV/Cl₂ might increase AOX mostly due to reaction between OH and organic precursors to make them more reactive with chlorine, and not due to RCS. The formation of specific DBPs of current or emerging regulatory interest was minimal under all conditions, except for chlorate. Chlorate yields were in the order of 6-18% of the photolysed chlorine.

Photochemical oxidation of PPCPs using a combination of solar irradiation and free available chlorine

The degradation of pharmaceuticals and personal care products (PPCPs) by using solar photolysis in the presence of free available chlorine (FAC) was investigated in simulated drinking water. The combination of free available chlorine and sunlight irradiation dramatically accelerated the degradation of all the contaminants tested through the generation of hydroxyl radicals, reactive chlorine species (RCS) and ozone. Contaminants containing electron-donating moieties degraded quickly and were preferentially degraded by RCS and/or HO oxidation. Primidone, ibuprofen and atrazine, which contain electron-withdrawing moieties, were mainly degraded by HO. Trace amounts of O₃ contributed greatly to carbamazepine's degradation. Degradation of PPCPs was accelerated in oxygenated solutions. Increasing chlorine concentrations barely enhanced removal of PPCPs bearing electron-withdrawing moieties. Higher pH generally decreased the degradation rate constants along with reduced levels of HO and Cl, but diclofenac, gemfibrozil, caffeine and carbamazepine had peak degradation rate constants at pH 7-8. The cytotoxicity using Chinese hamster ovary (CHO) cell did not show significant enhancement in solar/FAC treated water. Combining chlorination with sunlight may provide a simple and energy-efficient approach for improving the removal of organic contaminants during water treatment.

Electro-oxidation by graphite anode for naphthenic acids degradation, biodegradability enhancement and toxicity reduction

Electro-oxidation (EO) by using graphite anode and at relatively low current densities was successfully applied for the degradation of commercial naphthenic acids (NAs) mixture in water samples. At current densities of 0.5, 2.5, and 5 mA/cm², acid extractable fraction (AEF) was removed by 42.2%, 57.0% and 67.9%, respectively, while classical NAs were degraded by 76.9%, 77.6% and 82.4%, respectively. EO reactivity towards NAs increased with increasing the carbon number (n) and was higher for cyclic NAs compared to the acyclic component. Oxidized NAs containing O₃ and O₄ were also degraded effectively during EO. The biodegradability of organics in the NA mixture was clearly improved by 1.7, 2.5 and 2.7 folds when the samples were pre-treated with EO at current densities of 0.5, 2.5, and 5 mA/cm², respectively. The aromatic fraction in the commercial NA mixture consisted mainly of single-ring aromatics and was degraded effectively by EO. Biodegradation alone was able to reduce the toxicity of the commercial NA mixture towards Vibrio fischeri; however, the combination of EO with biodegradation resulted in a complete removal of the toxicity, showing a synergistic effect of combining these two processes. Coupling EO with aerobic biodegradation can result in an effective and energy-efficient treatment option for NA-bearing waters such as oil sands process water (OSPW) and refinery effluents.

Exposure to Organic Fraction Extracted from Oil Sands Process-Affected Water Has Negligible Impact on Pregnancy and Lactation of Mice

Dissolved organic compounds are major contaminants in oil sands process-affected water (OSPW), of which naphthenic acids (NAs) are one of the main persistent toxicants. In the present study, we explore the toxic effects of the organic fraction extracted from OSPW (OSPW-OF) in mice during pregnancy and lactation. Here, we report that acute oral exposure of female Balb/c mice during gestation, and subchronic exposure throughout gestation and lactation to OSPW-OF (containing naturally occurring levels of NAs found in tailings ponds), had negligible effects on their reproductive performance. Specifically, mating behavior, pregnancy success, embryonic implantation, gestation period, litter size, and offspring viability were not affected by OSPW-OF containing up to 55 mg/L NAs. OSPW-OF exposure also did not affect plasma concentrations of pregnancy-associated hormones or pro- and anti-inflammatory cytokines, and it had minimal effects on liver stress gene expression. This study presents the first comprehensive in vivo analysis of mammalian toxicity associated with OSPW-OF exposure. Overall, our results suggest that the risk of acute and subchronic toxicity to mice exposed to OSPW-OF at environmentally relevant concentrations of NAs in contaminated drinking water is likely negligible.

Icariin attenuates neuroinflammation and exerts dopamine neuroprotection via an Nrf2-dependent manner

Background

Oxidative stress and neuroinflammation are considered the major central events in the process of Parkinson’s disease (PD). Nrf2 is a key regulator of endogenous defense systems. New finds have contacted activation of Nrf2 signaling with anti-inflammatory activities. Therefore, the outstanding inhibition of neuroinflammation or potent Nrf2 signaling activation holds a promising strategy for PD treatment. Icariin (ICA), a natural compound derived from Herba Epimedii, presents a number of pharmacological properties, including anti-oxidation, anti-aging and anti-inflammatory actions. Recent studies have confirmed ICA exerted neuroprotection against neurodegenerative disorders. However, the underlying mechanisms were not fully elucidated.

Methods

In the present study, mouse nigral stereotaxic injection of 6-hydroxydopamine (6-OHDA)-induced PD model was performed to investigate ICA-conferred dopamine (DA) neuroprotection. In addition, adult Nrf2 knockout mice and primary rat midbrain neuron-glia co-culture was applied to elucidate whether ICA-exerted neuroprotection was through an Nrf2-dependent mechanism.

Results

Results indicated that ICA attenuated 6-OHDA-induced DA neurotoxicity and glial cells-mediated neuroinflammatory response. Furtherly, activation of Nrf2 signaling pathway in glial cells participated in ICA-produced neuroprotection, as revealed by the following observations. First, ICA enhanced Nrf2 signaling activation in 6-OHDA-induced mouse PD model. Second, ICA failed to generate DA neuroprotection and suppress glial cells-mediated pro-inflammatory factors production in Nrf2 knockout mice. Third, ICA exhibited neuroprotection in primary neuron-glia co-cultures but not in neuron-enriched cultures (without glial cells presence). Either, ICA-mediated neuroprotection was not discerned after Nrf2 siRNA treatment in neuron-glia co-cultures.

Conclusions

Our findings identify that ICA attenuated glial cells-mediated neuroinflammation and evoked DA neuroprotection via an Nrf2-dependent manner.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1472-x) contains supplementary material, which is available to authorized users.

PPCP degradation and DBP formation in the solar/free chlorine system: Effects of pH and dissolved oxygen

The solar/chlorine process produces multiple reactive species by solar photolysis of chlorine, which can be used as an energy-efficient technology for water treatment. This study investigated the effects of pH and dissolved oxygen (DO) on the degradation of pharmaceuticals and personal care products (PPCPs) and on the formation of disinfection byproducts (DBPs) in the solar/chlorine system. The degradation of 24 structurally diverse PPCPs was enhanced appreciably in the solar/chlorine system compared to solar irradiation and dark chlorination. The reactive species in the solar/chlorine system were identified to be hydroxyl radicals (HO), reactive chlorine species (RCS, i.e., Cl and ClO) and ozone. With increasing pH from 6 to 8, the steady-state concentrations of HO and Cl decreased from 1.23 × 10^-14 M to 4.79 × 10^-15 M and from 9.80 × 10^-16 M to 4.31 × 10^-16 M, respectively, whereas that of ClO increased from 5.30 × 10^-14 M to 2.68 × 10^-13 M and the exposure of ozone increased from 0.44 μM min to 1.01 μM min in 90 min. Accordingly, the removal efficiencies of 6 PPCPs decreased and 11 PPCPs increased. The decreased removal of PPCPs with increasing pH was due to the decrease in HO and Cl, while the increased removal was attributed to the increased ClO and ozone. The presence of DO enhanced the degradation of most PPCPs, indicating the role of ozone on the degradation. The formation of total organic chlorine (TOCl) and known DBPs was enhanced by 60.7% and 159.4%, respectively, in the solar/chlorine system compared to chlorination in a simulated drinking water containing 2.5 mg L^-1 natural organic matter (NOM). As the pH rose from 6 to 8, TOCl formation decreased by 16.2%, while that of known DBPs increased by 58.6% in solar/chlorine. The absence of DO slightly suppressed the formation of TOCl and known DBPs. This study illustrated the significant role of RCS in the solar/chlorine system, which enhanced the degradation of micropollutants but increased the formation of chlorinated DBPs.

Experimental-design-guided approach for the removal of atrazine by sono-electrochemical-UV-chlorine techniques

The aim of the present study was to investigate the electrochemical formation of free chlorine species (HOCl/ClO^-) and their subsequent use for the degradation of the pesticide atrazine. Initially, the process of electrochemical-free chlorine production was investigated using a bench-scale electrochemical flow-cell. The most significant variables (electrolyte concentration ([NaCl]) and inter-electrode gap) of the process were obtained using a 2³ factorial design and the optimum process conditions (1.73 mol L^-1 and 0.56 cm) were determined by a central composite design. Following optimization of free chlorine production, three degradation techniques were investigated, individually and in combination, for atrazine degradation: electrochemical, photochemical and sonochemical. The method using the techniques in combination was denominated sono-photo-assisted electrochemical degradation. Constant current assays were performed and the sono-photo-assisted electrochemical process promoted more efficient removal of atrazine, achieving total organic carbon removal of ∼98% and removal of atrazine to levels below the detection limit (>99%) in under 30 min of treatment. Furthermore, the combination of three techniques displayed lower energy consumption, and phytotoxicity tests (Lactuca sativa) showed that there was no increase in toxicity.

Characterization of disinfection byproduct formation and associated changes to dissolved organic matter during solar photolysis of free available chlorine

Solar irradiation of chlorine-containing waters enhances inactivation of chlorine-resistant pathogens (e.g., Cryptosporidium oocysts), through in situ formation of ozone, hydroxyl radical, and other reactive species during photolysis of free available chlorine (FAC) at UVB-UVA wavelengths of solar light (290-400 nm). However, corresponding effects on regulated disinfection byproduct (DBP) formation and associated dissolved organic matter (DOM) properties remain unclear. In this work, when compared to dark chlorination, sunlight-driven FAC photolysis over a range of conditions was found to yield higher DBP levels, depletion of DOM chromophores and fluorophores, preferential removal of phenolic groups versus carboxylic acid groups, and degradation of larger humic substances to smaller molecular weight compounds. Control experiments showed that increased DBP levels were not due to direct DOM photolysis and subsequent dark reactions with FAC, but to co-exposure of DOM to FAC and reactive species (e.g., O₃, HO^•, Cl^•, Cl₂^•-, ClO^•) generated by FAC photolysis. Because solar chlorine photolysis can enable inactivation of chlorine-resistant pathogens at far lower CT_FAC values than chlorination alone, the increases in DBP formation inherent to this approach can likely be offset to some extent by the ability to operate at significantly decreased CT_FAC. Nonetheless, these findings demonstrate that applications of solar chlorine photolysis will require careful attention to potential impacts on DBP formation.

Degradation of naphthenic acid model compounds in aqueous solution by UV activated persulfate: Influencing factors, kinetics and reaction mechanisms

Naphthenic acids (NAs) are one of the constituents of concerns in oil sands process water (OSPW) because of their persistence and recalcitrance. Herein, we investigated the degradation of five model NA compounds by UV-activated persulfate (UV/persulfate) process under medium-pressure UV lamp irradiation at pH 8.0. UV/persulfate process showed higher degradation efficiency towards cyclohexanoic acid (CHA) compared to UV/H₂O₂ process under the same experimental conditions. CHA (0.39 mM) was completely removed within 30 min when 2 mM persulfate was used as oxidant, while more than 60 min were needed for the UV/H₂O₂ process. The removal of CHA decreased from 100% to 10% when 300 mM tert-butyl alcohol (TBA) was used as the scavenger, indicating that hydroxyl radical (OH) was responsible for the CHA degradation in the UV/persulfate process. Sulfate (SO₄^-) radicals reacted slowly with CHA in the UV/persulfate process with a second-order rate constant of k = 5.3 × 10⁷ M^-1s^-1. Relative kinetics studies using binary mixtures of model NA compounds showed similar structure-reactivity to that under UV/H₂O₂ process. NAs with long carbon chain, cyclic ring, and aromatic ring were more reactive in the UV/persulfate process. The presence of high concentration of chloride ions dramatically inhibited the reaction. The OH radicals in the UV/persulfate process were generated by capturing OH^- in solutions, as evidenced by the decrease of the pH value from 8.0 to 2.8 before and after treatment, respectively, in a pure water matrix. Primary intermediate products (oxy-CHA, hydroxyl-CHA, and dihydroxyl-CHA) of UV/persulfate process were confirmed by UPLC-MS.

Degradation of methadone by the sunlight/FC process: Kinetics, radical species participation and influence of the water matrix

Free chlorine sunlight photolysis (sunlight/FC) markedly enhances the degradation rate of methadone, a synthetic opioid used medically, over that obtained using sunlight alone. The pseudo-first-order rate constants of methadone degradation under acidic conditions ([methadone] = 0.2 μM, [free chlorine] = 4 μM, and pH = 4) for sunlight/FC and sunlight photolysis are 7.0 ± 1.1 × 10^-2 min^-1 and 1.4 ± 0.2 × 10^-2 min^-1, respectively. The improved methadone degradation can be attributed to the production of HO and reactive chlorine species (RCS) during sunlight/FC photolysis. HO and RCS predominantly accounted for degradation during sunlight/FC photolysis under acidic and neutral conditions, while direct photolysis was the major contributor towards methadone degradation in alkaline conditions. The initial pH (pH 4-11) and free chlorine concentration (1-6 μM) significantly influenced the overall degradation efficiency of methadone. The presence of HCO₃^-, Cl^- and dissolved organic matters, which may competitively react with HO and RCS, retard the degradation of methadone in synthetic wastewater. Consequently, a 50% lower methadone degradation rate was observed when deionized (DI) water was replaced with tap water. These results emphasize the need to consider different water matrices when applying sunlight/FC photolysis for water treatment.

Effects of Seasonal Changes on the Toxic Impacts of Oil Sands Process-Affected Water on Daphnia magna

Oil sands process-affected water (OSPW), which can be potentially toxic to aquatic biota, is a major by-product of bitumen mining in northern Alberta. The effects of environmental factors on the toxicity of OSPW are understudied. In the present study, the impacts of seasonal changes in water quality on the toxic effects of OSPW (1 and 10%) on Daphnia magna was examined. Animals were chronically exposed to OSPW under conditions that represented water quality of a cold or warm seasonal condition. At each seasonal scenario survival, growth (length and mass) and reproduction of exposed D. magna were investigated. Survival and length of D. magna were only affected by OSPW in the cold-season treatment. Exposure to OSPW reduced the mass of D. magna in both cold and warm season scenarios. Daphnia magna in the cold-season treatment did not reproduce or produce eggs during the course of the experiment. The results of the present study suggest that seasonal changes in water quality may alter the toxicity of OSPW on D. magna.

Comparative investigation of X-ray contrast medium degradation by UV/chlorine and UV/H2O2

The degradation of iopamidol and diatrizoate sodium (DTZ) by UV/chlorine was carried out according to efficiency, mechanism, and oxidation products, and compared to that by UV/H₂O₂. The pseudo-first order rate (k') of iopamidol and DTZ was accelerated by UV/chlorine compared to that by UV and chlorine alone. k' of iopamidol and DTZ by UV/chlorine increased with increasing chlorine dosage. Both of iopamidol and DTZ could not be effectively removed by UV/H₂O₂ compared to that by UV/chlorine. Secondary radicals (Cl₂^- and ClO) rather than primary radicals (HO and Cl) were demonstrated to be mainly responsible for the enhanced removal of iopamidol and DTZ by UV/chlorine. The oxidation products of iopamidol and DTZ resulting from UV/chlorine and UV/H₂O₂ process were identified, and differences existed in the two systems. IO₃^- (the desired sink of I^-) was the major inorganic product in the UV/chlorine process whereas I^- was the predominant inorganic product in the UV/H₂O₂ process. The formation of chlorine-containing products during the degradation of iopamidol and DTZ by UV/chlorine was also observed. H-abstraction, additions, de-iodination were shared during the degradation of iopamidol by UV/chlorine and UV/H₂O₂. Neutral pH condition was preferred for the removal of iopamidol and DTZ by UV/chlorine. UV/chlorine could also be applied in real waters for the removal of iopamidol and DTZ.

Fate and abundance of classical and heteroatomic naphthenic acid species after advanced oxidation processes: Insights and indicators of transformation and degradation

The toxicological effects from all components in oil sands process-affected water (OSPW) are not known. Alternatively, monitoring the variations and abundance of different classes and compounds after treatments might be a useful approach in OSPW remediation. In this study, the variations in the compositions of classical and heteroatomic naphthenic acids (NAs) after treatment using advanced oxidation processes (AOPs), mainly ozone and peroxone, and two different mass spectrometry methods; ultra-performance liquid chromatography time-of-flight (UPLC-TOFMS) and Fourier transform ion cyclotron resonance (FTICR-MS), were examined. Two markers (O₂S:O₃S:O₄S and O₂:O₄ ratios) were used to reveal changes and similarities of the treated water characteristics with those in natural waters. Both ratios decreased after all treatments, from 2.7:4.8:2.1 and 3.59 in raw OSPW to 0:1.4:0.5 and 0.7, respectively, in peroxone (1:2), becoming close to the reported ratios in natural waters. Toxicity toward Vibrio fischeri showed residual toxic effects after AOPs, suggesting that part of OSPW toxicity may be caused by specific compounds of NAs (i.e., similar reduction (50%) was achieved in both toxicity and abundance in O₂ species with carbon 15-26) and/or generated by-products (e.g., O₃S classes at double bond equivalent (DBE) = 4 and C₉H₁₂O₂ at DBE = 4). Although by-products were generated, the best biodegradability enhancement and chemical oxygen demand reduction were achieved in peroxone (1:2) compared to ozone, suggesting the possibility of using combined OSPW remediation approaches (i.e., peroxone coupled with biological process). The recommended indicators can assist in evaluating the treatments' performance and in examining the best removal levels to accomplish significant toxicity reduction.

Degradation of natural organic matter by UV/chlorine oxidation: Molecular decomposition, formation of oxidation byproducts and cytotoxicity

The degradation of natural organic matters (NOMs) by the combination of UV and chlorine (UV/chlorine) was investigated in this study. UV/chlorine oxidation can effectively degrade NOMs, with the degradation of chromophores (∼80%) and fluorophores (76.4-80.8%) being more efficient than that of DOC (15.1-18.6%). This effect was attributed to the chromophores and fluorophores (double bonds, aromatic groups and phenolic groups) being preferentially degraded by UV/chlorine oxidation, particularly reactive groups with high electron donating capacity. Radical species •OH and •Cl were generated during UV/chlorine oxidation, with the contribution of •OH 1.4 times as high as that of •Cl. The degradation kinetics of different molecular weight (MW) fractions suggests that UV/chlorine oxidation degrades high MW fractions into low MW fractions, with the degradation rates of high MW fractions (>3000 Da) 4.5 times of those of medium MW fractions (1000-3000 Da). In comparison with chlorination alone, UV/chlorine oxidation did not increase the formation (30 min) and formation potential (24 h) of trihalomethanes, but instead promoted the formation and formation potential of haloacetic acids and chloral hydrate. Adsorbable organic halogen (AOX) formed from UV/chlorine oxidation of NOM were 0.8 times higher than those formed from chlorination. Cytotoxicity studies indicated that the cytotoxicity of NOM increased after both chlorination and UV/chlorine oxidation, which may be due to the formation of AOX.

Combined electrochemical, sunlight-induced oxidation and biological process for the treatment of chloride containing textile effluent

This study presents a combined electrochemical, sunlight-induced oxidation and biological process for the treatment of textile effluent. In the first step, RuO₂-TiO₂/Ti and Titanium were used as the electrodes in EO process and color removal was achieved in 40 min at an applied current density of 20 mA cm^-2. The EO process generated about 250 mg L^-1 of active chlorine which hampered the subsequent biological treatment process. Thus, in the second step, sun light-induced photolysis (SLIP) is explored to remove hypochlorite present in the EO treated effluent. In the third step, the SLIP treated effluent was fed to laccase positive bacterial consortium for biological process. To assess the effect of SLIP in the overall process, experiments were carried out with and without SLIP process. In experiments without SLIP, sodium thiosulfate was used to remove active chlorine. HPLC analysis showed that SLIP integrated experiments achieved an overall dye component degradation of 71%, where as only 22% degradation was achieved in the absence of SLIP process. The improvement in degradation with SLIP process is attributed to the presence of ClO radicals which detected by EPR analysis. The oxidation of organic molecules during process was confirmed by FT-IR and GC-MS analysis.

Applicability of light sources and the inner filter effect in UV/acetylacetone and UV/H2O2 processes

Light source is a crucial factor in the application of a photochemical process, which determines the energy efficiency. The performances of acetylacetone (AA) in conversion of aqueous contaminants under irradiation with a low-pressure mercury lamp, a medium-pressure mercury lamp, a xenon lamp, and natural sunlight were investigated and compared with those of H₂O₂ as reference. In all cases, AA was superior to H₂O₂ in the degradation of Acid Orange 7. Using combinations of the different light sources with various cut-off and band-pass filters, the spectra responses of the absorbed photons in the UV/AA and UV/H₂O₂ processes were determined for two colored and two colorless compounds. The photonic efficiency (φ) of the two photochemical processes was found to be target-dependent. A calculation approach for the inner filter effect was developed by taking the obtained φ into account, which provides a more accurate indication of the reaction mechanisms.

Understanding the similarities and differences between ozone and peroxone in the degradation of naphthenic acids: Comparative performance for potential treatment

Ozonation at high doses is a costly treatment for oil sands process-affected water (OSPW) naphthenic acids (NAs) degradation. To decrease costs and limit doses, different peroxone (hydrogen peroxide/ozone; H₂O₂:O₃) processes using mild-ozone doses of 30 and 50 mg/L were investigated. The degradation efficiency of O_x-NAs (classical (O₂-NAs) + oxidized NAs) improved from 58% at 30 mg/L ozone to 59%, 63% and 76% at peroxone (1:1), 50 mg/L ozone, and peroxone (1:2), respectively. Suppressing the hydroxyl radical (•OH) pathway by adding tert-butyl alcohol did significantly reduce the degradation in all treatments, while molecular ozone contribution was around 50% and 34% for O₂-NAs and O_x-NAs, respectively. Structure reactivity toward degradation was observed with degradation increase for both O₂-NAs and O_x-NAs with increase of both carbon (n) and hydrogen deficiency/or |-Z| numbers in all treatments. However, the combined effect of n and Z showed specific insights and differences between ozone and peroxone treatments. The degradation pathway for |-Z|≥10 isomers in ozone treatments through molecular ozone was significant compared to •OH. Though peroxone (1:2) highly reduced the fluorophore organics and toxicity to Vibrio fischeri, the best oxidant utilization in the degradation of O₂-NAs (mg/L) per ozone dose (mg/L) was observed in the peroxone (1:1) (0.91) and 30 mg/L ozone treatments (0.92). At n = 9-11, peroxone (1:1) had similar or enhanced effect on the O₂-NAs degradation compared to 50 mg/L ozone. Enhancing •OH pathway through peroxone versus ozone may be an effective OSPW treatment that will allow its safe release into receiving environments with marginal cost addition.

Assessment of organic pollution of an industrial river by synchronous fluorescence and UV-vis spectroscopy: the Fensch River (NE France)

To rapidly monitor the surface water quality in terms of organic pollution of an industrial river undergoing restoration, optical methods (UV-visible spectrometry and fluorescence) were applied in parallel to classical physical-chemical analyses. UV-visible spectra were analyzed using the maximum of the second derivative at 225 nm (related to nitrates), specific absorbance at 254 nm (SUVA₂₅₄), and the spectral slope between 275 and 295 nm (S _275-295) (related to the aromaticity and molecular weight of dissolved organic carbon). The synchronous fluorescence spectra (wavelength difference = 50 nm) exhibited a high variability in the composition of dissolved organic material between the upstream and downstream sections and also versus time. The principal components analysis of the entire set of synchronous fluorescence spectra helped to define three river sections with different pollution characteristics. Spectral decomposition was applied to the two most upstream sections: five fluorophores, classical in rivers impacted by domestic sewage and related to protein-like (λ _ex = 280 nm) and humic-like fluorescence (M-type with λ _ex ≈ 305-310 nm and C-type with λ _ex ≥ 335 nm), were identified. The irregular shape of the synchronous fluorescence spectra in the most downstream section is likely due to organic pollutants of industrial origin; however, their variability and the complexity of the spectra did not allow the further elucidation of their nature.