TiO2 Photocatalytic Process Research Articles

An innovative combination of anodic oxidation using Cu/SnO2–Sb2O5 rotating cylinder anode with TiO2 photocatalytic process for treating hospital wastewater

Treatment of hospital wastewater was achieved successfully using a novel combined process composed of an anodic oxidation with Cu/SnO2–Sb2O5 rotating cylinder anode and a photocatalysis process with titanium oxide nanoparticles. Cu/SnO2–Sb2O5 anode and TiO2 nanoparticles were characterized by x-ray diffractometer (XRD) and scanning electron microscopy (SEM). The feasibility of the combined process was evaluated using response surface methodology (RSM). Three operating factors were studied namely current density (10–20 mA/cm2), pH (4–8), and TiO2 dosage (0.3–0.7 g/L). Results showed that current density has the major effect on the COD removal with a contribution percent of 40 %. The optimal conditions were current density of 20 mA/cm2, pH of 4, and TiO2 dosage of 0.7 g/L in which COD removal of 91.2 % was achieved with claiming a total electrical energy (EECT) of 39.41 kWh/ m3. An interesting synergistic effect with a synergy of 21.26 % was recognized in the combined process due to the high productivity of hydroxyl radicals resulting from the interaction between the individual processes. Results confirmed that coupling anodic oxidation with photoctalysis is a promising method for treating hospital wastewater.

Influence of UV-A Light Modulation on Phenol Mineralization by TiO2 Photocatalytic Process Coadjuvated with H2O2

Influence of UV-A Light Modulation on Phenol Mineralization by TiO2 Photocatalytic Process Coadjuvated with H2O2

A review of prospects and challenges of photocatalytic decomposition of volatile organic compounds (VOCs) under humid environment

AbstractVolatile organic compounds (VOCs) are harmful for humans and the surrounding ecosystem. Emissions from these pollutants have caused a significant reduction in air quality, which has an effect on people's health. Alkanes, alkenes, alcohols, aromatics, and other VOC pollutants have all been broken down by TiO2 photocatalytic processes. Due to several operating inefficiencies and deactivation issues in humid environments, the practical application of photocatalysis has not been realized on a broader scale. The effectiveness of photo‐oxidation of VOCs is impacted by a variety of environmental conditions. In the photocatalytic oxidation of the VOCs, relative humidity (RH) is critical. Therefore, it is important to review the recent findings on how humidity affects the photocatalytic breakdown of VOCs in air. To satisfy this need, this work provides a critical review of the related literature with focus on the fundamentals of photocatalysis, photocatalytic degradation of air pollutants, and the influence of humidity on the photocatalytic process degradation for selected air pollutants. It also highlights the kinetic models and typical photocatalytic reactor and supports for VOC removal.

Photocatalytic Degradation of Sulfamethoxazole from a Synthetic Pharmaceutical Wastewater Using Titanium Dioxide (TiO2) Powder as a Suspended Heterogeneous Catalyst

Some medications in aquatic media pose a serious environmental risk. Sulfamethoxazole (SMX) is a member of the sulfonamide group. Photocatalysis offers a promising technique to degrade organic pollutants into environmentally friendly substances. This study examined the effect of operating conditions (pH, time, and temperature) of the ultraviolet (UV)/TiO2 photocatalytic process on the degradation of SMX in an aqueous solution. Decreasing the pH value positively affects SMX degradation, and better removal values were obtained at a pH equal to 4. The optimum operating conditions for complete degradation in a solution containing 500 mg/L of SMX, TiO2 0.5 mg/L irradiation time of 420 min, and pH 4. Under these conditions, Chemical Oxygen Demand (COD) removal was 62.6% at a temperature of 25 ℃. The effect of temperature was studied at three temperatures (25, 40, and 60 ℃) with pH 4. The elevation of temperature increased the COD removal rate to 99.62% at 60 ℃. Finally, the results of the reaction kinetics study showed that a first-order kinetics model described organic contamination removal data over time, and the obtained activation energy was 42.195 kJ/mol.

N-doped TiO2 nano particles for photocatalytic degradation of coliform and fecal coliform from hospital wastewater effluent

<p>The photocatalytic process as an advanced oxidation process (AOP) has gained worldwide attention in the water and wastewater industry. The photocatalytic process can be used for water and wastewater disinfection. The aim of this study was to remove coliforms and faecal coliforms from real hospital wastewater using UV and UV/N doped TiO2 photocatalytic process. Secondary wastewater samples were collected from Ali-ebne Abitaleb Hospital, Zahedan. The real wastewater samples containing N-doped TiO2 nanoparticles were exposed to UV light in a reactor. Multi-tube fermentation method (MPN/100ml) was used to count the coliform and faecal coliform bacteria and evaluate the process efficiency. The results showed that the mechanism of inactivation of coliforms and faecal coliforms by N-doped TiO2 nanoparticles and UV light followed the first-order equation, and the simultaneous application of N-doped TiO2 nanoparticles and UV light (N-doped TiO2/UV) increased the efficiency of the photocatalytic process and completely inactivated the coliforms and faecal coliforms in 10 minutes. The results of this study also showed that with increasing contact time, the removal efficiency of coliforms and faecal coliforms increased in the presence of UV light. The highest efficiency of the nanoparticles in bacterial inactivation was achieved at a dose of 120 mg/l in the presence of UV light and was 100%. The nano-photocatalytic process can be used as an efficient method to remove coliforms and faecal coliforms from hospital wastewater, and the N-doped TiO2/UV process is a reliable antibacterial method for water and wastewater disinfection.</p>

Online chemiluminescence determination of the hydroxyl radical using coumarin as a probe.

The hydroxyl radical (˙OH) is one of the strongest oxidizing species, which can react with a variety of organic and inorganic chemicals. Although ˙OH is widely used for degradation of environmental pollutants, detection of ˙OH remains a major challenge due to its high reactivity and short lifetime, especially online detection. In this study, a novel method for online detection of ˙OH by flow oxidization chemiluminescence (F-OCL) using coumarin as a probe was established. The concentrations of ˙OH determined by this new method were consistent with those determined by HPLC analysis. Because the new method has a short response speed, it was successfully used to quantify the dynamic change of ˙OH in the TiO2 photocatalytic process and Fenton reaction in real time. Furthermore, a combination of two chemiluminescence systems was developed to track the dynamics of ˙OH and hydrogen peroxide (H2O2) in homogeneous or heterogeneous Fenton reactions occurring in soil slurry. The proposed method and strategy have good application potential in online ROS monitoring of both natural and engineered systems.

Applications of waste-derived visibly active Fe-TiO2 composite incorporating the hybrid process of photocatalysis and photo-Fenton for the inactivation of E. coli.

The study reports the applications of waste-derived visibly active Fe-TiO2 composite for the inactivation of E. coli present in water. The Fe/TiO2 catalyst holds remarkable properties of in situ hybrid effect via combining the TiO2-photocatalytic and photo-Fenton process in one system causing increased production of OH˚. The quantum yield (QY) and reaction rate constant of this hybrid process at 40Wm-2 (UV-A irradiation) were found to be significantly higher in less treatment time (45min) of E. coli inactivation. 23% synergy of in situ hybrid process over single processes was also observed. The increase in the K+ concentration at regular intervals confirmed the cell wall damage. In fully inactivated samples, no regrowth of cells was observed even after 24 and 48h of dark study. Additionally, even after 100 recycles, the Fe/TiO2 catalyst demonstrated an exceptional durability/recyclability efficacy. The findings of this study highlight the potential of the hybrid process as a viable idea for post-treatment of the wastewater that can be implemented effectively in practice.

Enhanced Photocatalytic Water Decontamination by Micro-Nano Bubbles: Measurements and Mechanisms.

Despite recent advancements in photocatalysis enabled by materials science innovations, the application of photocatalysts in water treatment is still hampered due to low overall efficiency. Herein, we present a TiO2 photocatalytic process with significantly enhanced efficiency by the introduction of micro-nano bubbles (MNBs). Notably, the removal rate of a model organic contaminant (methylene blue, MB) in an air MNB-assisted photocatalytic degradation (PCD) process was 41-141% higher than that obtained in conventional macrobubble (MaB)-assisted PCD under identical conditions. Experimental observations and supporting mechanistic modeling suggest that the enhanced photocatalytic degradation is attributed to the combined effects of increased dissolution of oxygen, improved colloidal stability and dispersion of the TiO2 nanocatalysts, and interfacial photoelectric effects of TiO2/MNB suspensions. The maximum dissolved oxygen (DO) concentration of the MNB suspension (i.e., 11.7 mg/L) was 32% higher than that of an MaB-aerated aqueous solution (i.e., 8.8 mg/L), thus accelerating the hole oxidation of H2O on TiO2. We further confirmed that the MNBs induced unique light-scattering effects, consequently increasing the optical path length in the TiO2/MNB suspension by 7.6%. A force balance model confirmed that a three-phase contact was formed on the surface of the bubble-TiO2 complex, which promoted high complex stability and PCD performance. Overall, this study demonstrates the enhanced photocatalytic water decontamination by MNBs and provides the underlying mechanisms for the process.

Synergistic Generation of Reactive Oxygen Species by Visible Light Activated TiO2 and S. Enterica Interaction

Abstract A lot of human activities have negative impact on water quality and sometimes result in the biological water contamination. Currently used chemical (chlorine, ozone, and etc.) and physical (UV) water disinfection methods have strong environmental disadvantages or suffers from limited efficiency. To overcome these problems, scientists suggest to use photocatalyst activated advanced oxidation processes. One of the most studied photocatalysts which attracts a lot of research interest is titanium dioxide. TiO2 application for the disinfection of water, air or surfaces is increasingly encouraged by researchers. However, to unlock its full potential it is highly desirable to make it suitable for the visible light activation. In the current study the effect of visible light assisted photocatalytic treatment to the outer membrane permeability of Salmonella enterica bacteria and how it changes under different titanium dioxide concentrations was analysed. The results from the treatment of relatively complex Salmonella enterica bacteria organism were compared to the visible light activated TiO2 ability to oxidise considerably simpler objects like methylene blue molecules. The efficiency of TiO2 photocatalytic disinfection process was evaluated using spread plate technique. Membrane permeability of the treated Salmonella enterica bacteria was determined by NPN uptake factor assay. Generation of intracellular reactive oxygen species was evaluated by Dichlorodihydrofluorescein diacetate fluorescence measurements. The key finding of this study was that intense wide spectrum visible light irradiation and TiO2 powder synergistically inactivate S. enterica bacteria and halt its potential to form colonies. High amounts of intracellular reactive oxygen species could be seen as the main suspects for the observed inactivation of S. enterica.

Photolytic and photocatalytic degradation of doxazosin in aqueous solution

Doxazosin (DOX), a selective alpha blocker, is widely used in medical therapy as an effective antihypertensive agent. It is a frequently prescribed drug and for this reason, environmental and ecotoxicological research is of great importance in terms of exposure and risk for both aquatic species and humans. In this study we focused on photolytic and TiO2 photocatalytic degradation processes of doxazosin under different simulated conditions, with the emphasis on identification of degradation products. Photolytic (without TiO2) experiments were performed in the presence and absence of oxygen, while photocatalytic degradation of doxazosin aqueous solution has been carried out under constant oxygen flow. DOX degradation was more efficient in the TiO2/UVA photocatalytic experiment than during photolytic processes (UVA and UVC, UVC-N2).LC-HRMS analyses with electrospray ionization allowed observing the formation of several major degradation products depending on the reaction conditions (presence or absence of oxygen, photocatalysis). The transformation products were identified based on exact mass measurements, isotopic distribution, and fragmentation pattern. Among them, dominated C17H21N5O3 and C17H23N5O4 (cleavage of the dioxane cycle), and C23H25N5O7 (hydroxylation). The detailed degradation pathway has been proposed.Toxicity testing with V. fischeri luminescent bacteria revealed higher toxicity of samples in photolytic rather than photocatalytic experiments which might be attributed to the formation of different products.

Photocatalytic degradation of sulfamethoxazole using TiO2 in simulated seawater: Evidence for direct formation of reactive halogen species and halogenated by-products

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO2 NPs) and reactive species involved in saline waters is not sufficiently established. In this study, TiO2 photocatalytic process under simulated solar irradiation was evaluated in synthetic seawater and compared with deionized water, using sulfamethoxazole (SMX) as model organic compound. For a TiO2 concentration of 100 mg L−1, SMX degradation resulted two times slower in seawater than in deionized water by the determination of their pseudo-first order rate constants of 0.020 min−1 and 0.041 min−1, respectively. Selected scavenging experiments revealed no significant contribution of hydroxyl radicals (OH) on the degradation process in seawater, while these radicals contributed to circa 60% on the SMX depletion in deionized water. Instead, the involvement of reactive halogen species (RHS) as main contributors for the SMX degradation in seawater could be established. A mechanism for the RHS generation was proposed, whose initiation reactions involve halides with the TiO2 photogenerated holes, yielding chlorine and bromine radicals (Cl and Br) that may later generate other RHS. Production of RHS was further confirmed by the identification of SMX transformation products (TPs) and their evolution over time, carried out by liquid chromatography-mass spectrometry (LC-MS). SMX transformation was conducted through halogenation, dimerization and oxidation pathways, involving mainly RHS. Most of the detected transformation products accumulated over time (up to 360 min of irradiation). These findings bring concerns about the viability of photocatalytic water treatments using TiO2 NPs in saline waters, as RHS could be yielded resulting in the generation and accumulation of halogenated organic byproducts.

A new insight into highly contaminated landfill leachate treatment using Kefir grains pre-treatment combined with Ag-doped TiO2 photocatalytic process

This study investigates the performance of the combination of biological pre-treatment with Kefir grains (KGs) and photocatalytic process using Ag-doped TiO2 nanoparticles (NPs) for the simultaneous removal of toxic pollutants from landfill leachate (LFL). After 5 days of 1% (w/v) KGs pre-treatment at 37 °C, TOC, COD, NH4+-N, and PO43- removal rates were 93, 83.33, 70 and 88.25%, respectively. The removal efficiencies were found to be 100, 94, 62.5, 53.16 and 47.52 % for Cd, Ni, Zn, Mn and Cu, respectively. The optimal conditions of Ag-doped TiO2 photocatalytic process were optimized using Box-Behnken design and response surface methodology (BBD-RSM) to enhance the quality of pre-treated LFL. Interestingly, Ag-doped TiO2 photocatalytic process increases the overall removal efficiencies to 98, 96, 85 and 93% of TOC, COD, NH4+-N, and PO43-, respectively. Furthermore, the removal efficiency of toxic heavy metals was gradually improved. In addition, KGs and Ag-doped TiO2 exhibited excellent recyclability showing the potential of combined biological/photocatalytic process to treat hazardous LFL.

3D printed floating photocatalysts for wastewater treatment

Organic contaminants, specifically contaminants of emerging concern (CECs), have a great environmental impact, since the removal of these pollutants is of great difficulty by conventional treatments and the presence of these pollutants in the aquatic medium, even at low concentrations, is extremely hazardous to human health. Advanced oxidation processes and, specifically, TiO2-photocatalytic process is considered an option with positive results for an efficient treatment. However, the photocatalyst must be accessible to the UV radiation, for the activation of the TiO2. For this reason, it is recommendable to use a floating photocatalyst (with lower density than water) if the UV light comes from the solar radiation, because it will be on the water surface. In addition, this characteristic of the catalyst can entail an increase of the process efficiency if the pollutant is mainly located on the surface of water. In this context, the goal of this work is the preparation of floating photocatalysts for the removal of CECs from wastewater. TiO2 is deposited in low-density-polyethylene (LDPE), support with lower density than water and high stability and resistance to degradation. LDPE-TiO2 mixtures were prepared by different methods: mixing TiO2 and LDPE in a hot-cylinder-mixer or using o-xylene or an anionic surfactant as dispersing agent, in order to increase the dispersion of TiO2 before extrusion. Filaments obtained were printed as meshes in a Fused-Deposition-Modelling 3D-printer. The printed photocatalysts improved the activity in comparison with the plate obtained in the cylinder, used as benchmark. Thus, this study opens the doors to the in-situ treatment of CECs, using floating photocatalysts and solar radiation as the sole reagent, a very economical, efficient, easily implantable and environmentally compatible process.

Hybrid UV-C/microfiltration process in membrane photoreactor for wastewater disinfection.

A novel hybrid UV-C/microfiltration process for water disinfection is presented, and its application in continuous mode operation to the removal of different pathogen germs (Escherichia coli, Enterococcus faecalis, and Candida albicans) present in urban wastewater. The membrane photoreactor is based on porous stainless steel membranes coated with a TiO2 layer and illuminated by a UV-C lamp (254nm). A valve actuator in the outlet of the UV-C stream allows operation of the system under conditions of constant transmembrane pressure (TMP) keeping the UV-C contact time in few seconds, significantly lower than the typical irradiation time employed in TiO2 photocatalytic processes. An E. coli removal of up to 4-log in the permeate stream and up to 2-log in the UV-C outlet was achieved with a 0.2μm membrane operating with a TMP of 0.5bar and a UV-C contact time as low as 8s. The microbial balance data from the cells recovered from the membrane confirmed that 96-98% of the removed microorganisms died due to the UV-C action over the membrane surface. Modification of the membrane with a TiO2 layer has been also shown to be a suitable way to improve both the UV-C inactivation and the filtration efficiency. The results reported in this work constitute a proof of concept of the synergy between UV-C and filtration that can be achieved in a hybrid UV-C/microfiltration system, being a good example of process intensification where two products of different quality can be simultaneously obtained.

Removing Humic Acid from Aqueous Solution Using Titanium Dioxide: A Review

Recently, the photocatalytic degradation technique with titanium dioxide (TiO2) has been widely applied for the degradation of humic acid (HA) from aqueous solution due to its ability to achieve complete mineralization of organic contaminants. Because TiO2 is the most commonly used semiconductor photocatalyst, efforts on the modification of TiO2 in order to improve catalyst efficiency were presented in this review manuscript. The key photoreactor operation parameters such as TiO2 loading, pH, temperature, oxygen concentration, concentration and nature of HA, light wavelength, light intensity, the presence of inorganic ions and mechanistic pathway for pollutant removal, and the formation of the intermediates and their effects on the mineralization and disinfection of the photo- process were also assessed. Although we can see an increase in the number of papers that have been published in this area, further progress is needed to improve the understanding of the dynamic interactions between TiO2 photocatalytic oxidation process and HA, as well as to suggest possible future developments in this promising field.

Mineralization of the antineoplastic drug carboplatin by heterogeneous photocatalysis with simultaneous synthesis of platinum-modified TiO2 catalysts

Photocatalytic oxidation of carboplatin, a platinum antineoplastic drug, has been investigated in aqueous heterogeneous solutions containing TiO2 photocatalysts. The current study, besides the photocatalytic degradation of the drug, examines the utilization of the photo-reduction process occurring on the surface of the catalyst, leading simultaneously to the photo-deposition and recovery of platinum. TiO2 photocatalytic process was evaluated for its ability to degrade the molecule of carboplatin and concurrently result in the synthesis of efficient platinum modified TiO2 catalysts. The degradation kinetic was studied under different operational conditions, such as type of photocatalyst, catalyst loading, initial pH and addition of electron acceptors. Three systems were evaluated namely, TiO2 P25 under UV-A and TiO2 Kronos vlp 7000 under UV-A or visible illumination, with respect to their activity for substrate degradation and mineralization and their ability to bind platinum on their surface during photocatalytic oxidation of the drug. The initial degradation rate (r0) decreased in the order TiO2 P25/UV-A > TiO2 Kronos vlp 7000/UV-A > TiO2 Kronos vlp 7000/visible light. For TiO2 P25/UV-A, the addition of 100 mg L−1 H2O2 increases slightly the initial mineralization rate, while degradation rates gradually decrease as photocatalysis takes place in neutral and alkaline pH. Phytotoxicity measurements, showed that heterogeneous photocatalytic oxidation in the presence of TiO2 P25 is capable of reducing the phytotoxicity of carboplatin. For TiO2 P25 and TiO2 Kronos vlp 7000 under UV-A illumination, photo-reduction and deposition of platinum is fully accomplished within 60 min of oxidation, while for TiO2 Kronos vlp 7000 in the presence of visible light, the percentage of platinum deposited on the surface of the catalyst reaches 40%. Platinum photo-deposition is feasible, employing TiO2 P25, even after the catalyst is reused. The synthesized platinum modified TiO2 P25, demonstrated higher photocatalytic efficiency in comparison to the bare one, leading to 100% degradation of the model pollutant malachite green and 40% DOC reduction, after 30 min of photo-oxidation.

Photoelectrocatalytic oxidation of acid green 50 dye in aqueous solution using Ti/TiO2-NT electrode

To further improve the TiO2 photocatalytic process for water treatment, a nanotube Ti/TiO2 electrode (Ti/TiO2-NT) was prepared by anodizing Ti foil in non-aqueous solution inside the voltage range of 35–55 V. The structural and surface morphology of the Ti/TiO2 electrode were examined by X-ray spectroscopy and scanning electronic microscopy, respectively. The nanotube formation rate was influenced by the anodization voltage which affected its morphology. It was observed that the nanotube formation rate increased by increasing the anodizing voltage. The photoelectrocatalytic (PEC) and photocatalytic (PC) oxidation of acid green 50 (AG50) in aqueous solution using the Ti/TiO2-NT electrode were studied and compared. The results demonstrate that PEC oxidation, at all applied potentials between the Ti/TiO2-NT electrode and carbon graphite electrode, highly enhanced the degradation rate of AG50 compared to PC oxidation. Therefore, the application of a potential in the PC process (PEC) favorably influences the performance of the PC process. The PEC oxidation of AG50 under the application of a potential followed apparent first order kinetics. Nanotube photocatalytic reactivity was influenced by annealing temperature and applied potential at fixed pH of the solution. It was found that the best performance of PEC oxidation was achieved by applying an electrical bias of 1.0 V or 1.2 V.

Using Photocatalytic Oxidation and Analytic Techniques To Remediate Lab Wastewater Containing Methanol

This experiment is dedicated to second-year and above undergraduates who are in their experimental session of the analytical chemistry course. Grouped students are required to use a TiO2 photocatalytic oxidation process to treat the methanol-containing wastewater that resulted from their previous HPLC experiments. Students learn to assemble a specified apparatus for a chemical reaction and analytical methods for the determination of environmental pollutants and reaction intermediates. The comprehensive experiment can give students a deep insight into application of several instruments (COD analyzer, UV–vis, GC-FID, and GC–MS) and the principle of photocatalytic oxidation reaction. Meanwhile, upon the completion of the experiment, students not only become aware of the wastes they generate but also understand how chemistry can be utilized for environmental remediation.

Degradation of methylene blue dye in aqueous solution using hydrodynamic cavitation based hybrid advanced oxidation processes

In the present work, degradation of methylene blue (MB) dye in aqueous solution by using hydrodynamic cavitation combined with H2O2 and Bi-doped TiO2 photocatalyst was investigated. Bi-doped TiO2 photocatalyst was prepared by using a sol-gel synthesis method. The synthesized Bi-doped TiO2 material was characterized by X-ray diffraction spectra (XRD), FT-IR and TEM. The effect of various operating parameters such as inlet fluid pressure, solution pH, addition of H2O2 and photocatalyst on the degradation of MB dye were studied. The maximum extent of degradation of methylene blue was obtained at inlet pressure of 5bar and pH 2. The molar ratio of MB: H2O2 i.e. 1:20 was shown 94.64% of MB decolorization over 60min. Combination of hydrodynamic cavitation and H2O2 has shown high synergetic effect than the combination of hydrodynamic cavitation and Bi-doped TiO2 photocatalytic process.

Cytarabine degradation by simulated solar assisted photocatalysis using TiO2

The photochemical degradation of antineoplastic drug cytarabine (CY) by TiO2 photocatalysis under simulated solar light (SSL) radiation, TiO2/S2O82−/SSL and TiO2/H2O2/SSL processes was investigated in the present study. Experimental results indicated that CY was quickly degraded in all the studied treatments and degradation kinetics were dependent by all studied variables (i.e. catalyst dose, initial CY concentration, pH, oxidant concentration). In addition to kinetic studies, the transformation products (TPs) generated during the treatments were investigated using liquid chromatography coupled to high resolution mass spectrometry while mineralization was also followed by ion chromatography and total organic carbon measurements. Based on the identification of TPs and scavenging experiments, the major transformation routes followed were hydroxylation and subsequent oxidation, in all studied treatments. Microtox bioassay was applied before and during the TiO2 photocatalytic process, in order to investigate the potential risk of CY and its TPs to aqueous organisms. The obtained results showed an increase in the acute toxicity in the first stages and a continuously decrease afterwards, leading to very low toxicity levels within 360min of TiO2/SSL treatment. Overall results indicated that photocatalytic degradation of CY can lead to its complete elimination and detoxification of the solution.