Transformation of acetaminophen in solution containing both peroxymonosulfate and chlorine: Performance, mechanism, and disinfection by-product formation

Analytical methods for selectively determining hydrogen peroxide, peroxymonosulfate and peroxydisulfate in their binary mixtures

Hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and peroxydisulfate (PDS) are key bulk oxidants in many advanced oxidation processes (AOPs) for treating chemically contaminated water. In some systems these peroxides may coexist in solution either through intentional co-addition or their inadvertent formation (especially H2O2) due to reaction chemistry. While many analytical methods to determine these peroxides individually have been established, mutual interference among the peroxides in such methods has seldom been evaluated, and new methods or variants of established methods to selectively determine peroxides in binary mixtures are lacking. We re-examined five established colorimetric methods-the Permanganate, Titanium Oxalate (Ti-oxalate), Iodide, N.N‑diethyl-p-phenylenediamine (DPD), and 2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) methods-for mutual interference among peroxides and devised variants of these methods for selectively quantifying one peroxide in the presence of another. Hydrogen peroxide can be selectively determined by the Permanganate method at short reaction time; by the Ti-oxalate method; by the DPD method with added peroxidase (POD); or by the ABTS method with added POD. PMS can be selectively determined by the Iodide method; by the DPD or ABTS methods with added iodide ion as catalyst; or by the DPD method with added catalase (CAT) (with co-existing H2O2 but not PDS). The DPD method can be used to determine PDS without interference by H2O2 and-provided the sample is pretreated with l-histidine-without interference by PMS. The recommended methods were successfully applied to binary peroxide mixtures in complex waters, including a tap water and a synthetic water. Overall, the new selective methods will assist mechanistic investigation of AOPs based on these peroxides and support efforts to apply them commercially.

Selective electrophilic attack towards organic micropollutants with superior Fenton-like activity by biochar-supported cobalt single-atom catalyst

The global shortage of freshwater and inadequate supply of clean water have necessitated the implementation of robust technologies for wastewater purification, and Fenton-like chemistry is a highly-promising approach. However, realizing the rapid Fenton-like chemistry for high-efficiency degradation of organic micropollutants (OMs) remains challenging. Herein, one novel system was constructed by a Co single-atom catalyst activating peroxymonosulfate (PMS), and the optimal system (SA-Co-NBC-0.2/PMS) achieved unprecedented catalytic performance towards a model OM [Iohexol (IOH)], i.e., almost 100% decay ratio in only 10 min (the observed rate constant: 0.444 min-1) with high electrophilic species 1O2 (singlet oxygen) generation. Theoretical calculations unveiled that Co-N4 sites preferred to adsorb the terminal-O of PMS (more negative adsorption energy than other O sites: -32.67 kcal/mol), promoting the oxidation of PMS to generate 1O2. Iodine (I)23 (0.1097), I24 (0.1154) and I25 (0.0898) on IOH with higher f- electrophilic values were thus identified as the main attack sites. Furthermore, 16S ribosomal RNA high-throughput sequencing and quantitative structure-activity relationship analysis illustrated the environmentally-benign property of the SA-Co-NBC-0.2 and the tapering ecological risk during IOH degradation process. Significantly, this work comprehensively checked the competence of the SA-Co-NBC-0.2/PMS system for organics abatement in practical wastewater.

The synergistic effect of oxidant-peroxide coupling systems for water and wastewater treatments

With the growing complexity and severity of water pollution, it has become increasingly challenging to effectively remove contaminants or inactivate microorganisms just by traditional chemical oxidants such as O3, chlorine, Fe(VI) and Mn(VII). Up till now, numerous studies have indicated that these oxidants in combination with peroxides (i.e., hydrogen peroxide (H2O2), peroxymonosulfate (PMS), peracetic acid (PAA) and periodate (PI)) exhibited excellent synergistic oxidation. This paper provided a comprehensive review on the combination of aforementioned oxidant-peroxide applied in water and wastewater treatments. From one aspect, the paper thoroughly elucidated the synergy mechanism of each oxidant-peroxide combination in turn. Among these combinations, H2O2 or PMS generally performed as the activator of four traditional oxidants above to accelerate reactive species generation and therein various reaction mechanisms, including electron transfer, O atom abstraction and oxo ligand substitution, were involved. In addition, although neither PAA nor PI was able to directly activate Fe(VI) and Mn(VII), they could act as the stabilizer of intermediate reactive iron/manganese species to improve the latter utilization efficiency. From another aspect, this paper summarized the influence of water quality parameters, such as pH, inorganic ions and natural organic matter (NOM), on the oxidation performance of most combined systems. Finally, this paper highlighted knowledge gaps and identified areas that require further research.

Effective and low-toxicity: A membrane cleaning method using peroxymonosulfate catalytic chlorination

In chemical membrane cleaning, the challenge is to efficiently remove irreversible fouling while minimizing the impact on membrane materials. Particularly, traditional hypochlorite cleaning will further lead to the generation of toxic halogenated by-products. To address these issues, a combined system composed of peroxymonosulfate and chloride (PMS/Cl-) was applied to clean irreversible-humic-acid-fouled polyethersulfone (PES) membranes. After fouled membranes were soaked for 1 h in a PMS/Cl- solution (10 mM/15 mM) at 25 °C under neutral conditions, 94% flux recovery and 96% resistance removal were realized. Surface properties of virgin and cleaned membranes were very similar, confirming the effectiveness of the PMS/Cl- solution in removing irreversible foulants. The stability of membrane separation performance during multiple fouling and cleaning cycles further confirmed the minimal impact on membrane materials. Rapid diminution of the peaks centered in the region of fulvic-like and humic-like components, monitored under 3D-fluorescence for the cleaning solution, was attributed to PMS-catalyzed chlorination, thereby revealing the primary foulant detachment mechanism. Crucially, the approach exhibited lower toxicity than hypochlorite, as evidenced by reduced halogenated by-products and lower acute toxicity to Photobacterium phosphoreum T3. Overall, this novel cleaning system is promising for the efficient and environmentally friendly removal of irreversible organic foulants in practical water-treatment.

Hyperoxidation active species produced by seawater electro membrane reactor assisted electrolytic cell system for simultaneous decyanation and carbon removal

Herein, a novel triple-layered heterojunction catalytic cathode membrane (PVDF/rGO/TFe/MnO2, TMOHccm) was reported and applied in seawater electro membrane reactor assisted electrolytic cell system (SEMR-EC), achieving increased properties for cyanide wastewater treatment. Hydrophilic TMOHccm exhibits higher electrochemical activity (qT* 1.11 C cm-2, qo* 0.03 C cm-2), indicating excellent electron transfer efficiency. Further analysis shows a one-electron redox cycle of exposed transition metal oxides (TMOs) on rGO support mediated oxygen reduction reaction (ORR) process, and calculated results of density functional theory (DFT) demonstrates positive Bader charge (72 |e|) of synthesized catalyst. The developed SEMR-EC was implemented in intermittent-stream operation for treating cyanide wastewater, the system achieved optimized decyanation and carbon removal performance (CN- 100%, TOC 88.49%). Hyperoxidation active species produced SEMR-EC including hydroxyl, sulfate, and reactive chlorine species (RCS) was confirmed. The proposed mechanistic explanation indicated multiple removal pathways relevant to cyanide, organic matter, and iron were elucidated, and the engineering applications prospects were highlighted by cost (5.61 $) and benefit (Ce 399.26 mW m-2 $-1, EFe 248.11 g kWh-1) analysis of the system.

Copper oxides activate peroxymonosulfate for degradation of methylene blue via radical and nonradical pathways: surface structure and mechanism

A one-step hydrothermal method for preparation of copper oxides with different valences using ascorbic acid as a reducing reagent was developed for environmental remediation. The results suggested that the notable degradation performance of CuO₀ may be attributable to the abundant active sites, such as Cu or Cu-O, and was not significantly related to the Cu valence state. In contrast to direct degradation of pollutants by traditional superoxide radicals (O₂^•-), O₂^•- played an important role in the reduction of high-valence Cu ions (Cu(III)). In addition, a series of radical quenching, electron paramagnetic resonance (EPR), and electrochemical experiments validated the existence of direct electron transfer between methylene blue (MB) and PMS mediated by CuO₀ and surface-bound radicals. The results suggested that the CuO₀/PMS system may be less susceptible to diverse ions and natural organic matter other than dihydrogen phosphate anions. The mechanism of MB degradation under alkaline conditions was different from that under acidic conditions in that it was not reliant on radicals or charge transfer but direct oxidation by PMS. This study provides new insights into the heterogeneous processes involved in PMS activation by the copper oxides. Furthermore, this paper devotes to providing theoretical basis on pollutant removal via PMS activated by copper oxides and developing low-cost and high-efficiency catalysts.

Formation of Larger Molecular Weight Disinfection Byproducts from Acetaminophen in Chlorine Disinfection

Acetaminophen is widely used to treat mild to moderate pain and to reduce fever. Under the worldwide COVID-19 pandemic, this over-the-counter pain reliever and fever reducer has been drastically consumed, which makes it even more abundant than ever in municipal wastewater and drinking water sources. Chlorine is the most widely used oxidant in drinking water disinfection, and chlorination generally causes the degradation of organic compounds, including acetaminophen. In this study, a new reaction pathway in the chlorination of acetaminophen, i.e., oxidative coupling reactions via acetaminophen radicals, was investigated both experimentally and computationally. Using an ultraperformance liquid chromatograph coupled to an electrospray ionization-triple quadrupole mass spectrometer, we detected over 20 polymeric products in chlorinated acetaminophen samples, some of which have structures similar to the legacy pollutants "polychlorinated biphenyls". Both C-C and C-O bonding products were found, and the corresponding bonding processes and kinetics were revealed by quantum chemical calculations. Based on the product confirmation and intrinsic reaction coordinate computations, a pathway for the formation of the polymeric products in the chlorination of acetaminophen was proposed. This study suggests that chlorination may cause not only degradation but also upgradation of a phenolic compound or contaminant.

Phase transformation-driven persulfate activation by coupled Fe/N-biochar for bisphenol a degradation: Pyrolysis temperature-dependent catalytic mechanisms and effect of water matrix components

Fe-N co-doped biochar is recently an emerging carbocatalyst for persulfate activation in situ chemical oxidation (ISCO). However, the involved catalytic mechanisms remain controversial and distinct effects of coexisting water components are still not very clear. Herein, we reported a novel N-doped biochar-coupled crystallized Fe phases composite (Fe@N-BC₈₀₀) as efficient and low-cost peroxydisulfate (PDS) activators to degrade bisphenol A (BPA), and the underlying influencing mechanism of coexisting inorganic anions (IA) and humic constituent. Due to the formation of graphitized nanosheets with high defects (AI index>0.5, I_D/I_G = 1.02), Fe@N-BC₈₀₀ exhibited 2.039, 5.536, 8.646, and 23.154-fold higher PDS catalytic activity than that of Fe@N-BC₆₀₀, Fe@N-BC₄₀₀, N-BC, BC. Unlike radical pathway driven by carbonyl group and pyrrolic N of low/mid-temperature Fe@N-BCs. The defective graphitized nanosheets and Fe-Nx acted separately as electron transfer and radical pathway active sites of Fe@N-BC₈₀₀, where π-π sorption assisted with pyrrolic N and pore-filling facilitated BPA degradation. The strong inhibitory effects of PO₄^3- and NO₂^- were ascribed to competitive adsorption of phosphate (61.11 mg g^-1) and nitrate (23.99 mg g^-1) on Fe@N-BC₈₀₀ via electrostatic attraction and hydrogen bonding. In contrast, HA competed for the pyrrolic-N site and hindered electron delivery. Moreover, BPA oxidation pathways initiated by secondary free radicals were proposed. The study facilitates a thorough understanding of the intrinsic properties of designed biochar and contributes new insights into the fate of degradation byproducts formed from ISCO treatment of micropollutants.

Revealing the fundamental role of MoO2 in promoting efficient and stable activation of persulfate by iron carbon based catalysts: Efficient Fe2+/Fe3+ cycling to generate reactive species

Electron-rich iron sites are the main sites for iron-based catalysts to activate persulfate (PS) to generate reactive species, while blocked Fe²⁺/Fe³⁺ cycling usually reduces the catalytic performance of iron-based materials and hinders the generation of reactive species in the reaction. To solve the bottleneck, we synthesized an iron-carbon nanocomposite catalyst loaded with MoO₂ (Fe/Mo-CNs). The promotion of MoO₂ on the Fe²⁺/Fe³⁺ cycle in the system allowed Fe/Mo-CNs to exhibit excellent catalytic performance and environmental adaptability. The degradation rate of bisphenol S (BPS) by the Fe/Mo-CNs/PS system was significantly increased to 0.080 min^-1 compared with the iron-carbon based catalyst/persulfate system, and the degradation efficiency of BPS was maintained at around 85% after four cycles. Density functional theory (DFT) calculations showed that the introduction of MoO₂ reduced the reaction energy barrier of persulfate activated by catalysts to produce reactive species, especially promoted the production of more high valent iron (Fe(IV)). Fe(IV) and reactive oxygen species (SO₄·^-, ·OH, ·O₂^- and ¹O₂) worked together on the efficient degradation of BPS. In addition, the test of an automatic circulating degradation plant had proved that Fe/Mo-CNs had a good practical application prospect. BPS was mainly degraded by ring cleavage and O=S=O bond cleavage, and the toxicity of BPS and its intermediates were also evaluated. This work clarifies the mechanism of improving the catalytic performance of heterogeneous iron-based catalysts by MoO₂ in sulfate radical-based advanced oxidation processes (SR-AOPs), providing a new idea for solving the blockage of Fe²⁺/Fe³⁺ cycle in SR-AOPs.

Direct degradation of methylene blue by unactivated peroxymonosulfate: reaction parameters, kinetics, and mechanism

Advanced oxidation processes (AOPs) are efficient methods for water purification. However, there are few studies on using peroxymonosulfate (PMS) to remove pollutants directly. In this study, about 76% of methylene blue (MB) was removed by PMS directly within 180 min through a non-radical pathway, verified by scavenging tests, electron paramagnetic resonance and kinetic calculations. Additionally, the effects of PMS dosage, MB concentration, temperature, initial pH and competitive anions were determined. High PMS dosage, temperature and pH promoted MB degradation (from 76 to 98%) while MB concentration showed no effect on MB removal. Besides, MB degradation followed pseudo-first-order kinetic with rate constants of 0.0082 to 0.3912 min-1. The second-order rate constant for PMS reaction with MB was 0.08 M-1 s-1 at pH 3-6, but increased dramatically to 4.68 M-1 s-1 at pH 10.50. Chlorine could be catalysed by PMS at high concentration Cl- and degradation efficiency reached 98% within 90 min. High concentration of bicarbonate accelerated MB removal due to the high pH value while humic acid showed a marginal effect on MB degradation. Furthermore, TOC removal rate of MB in the presence of chloride reached 45%, whereas PMS alone caused almost no mineralisation. This study provides new insights into pollutant removal and an additional strategy for water purification.

Bioremediation pretreatment of waste-activated sludge using microalgae Spirulina platensis derived biochar coupled with sodium sulfite: Performance and microbial community dynamics

4-Nonylphenol is a typical endocrine-disrupting compound found in waste-activated sludge. This study evaluates the feasibility of blue-green algae (Spirulina platensis)-based biochar as a carbon-neutral material to improve sodium sulfite (S(IV))-mediated sludge purification. Blue-green algae-based biochar is an effective activator (at 500 °C and 3 × 10^-6 M) of sodium sulfite and removed 75 % of 4-nonylphenol at pH 6 using at 1.7 g/L of dosage. Possible synergistic relationships among the coexisting oxidizing species (SO₃^•-, SO₄^•-, HO•, and ¹O₂), obvious defect structure, and abundant carbonyl oxygen groups on the surface of the biochar together dived advanced oxidation process. The bacterial consortia promoted the decomposition of biologically available substrates in the biosolid mixture, which led to the enrichment of Denitratisoma, and boosted 4-nonylphenol biodegradation. This study outlines a potential carbon-neutral, cost-effective, and sustainable sludge treatment strategy using renewable blue-green algae-based biochar, aiding 4-nonylphenol biodegradation in waste-activated sludge.

Electron delocalization triggers nonradical Fenton-like catalysis over spinel oxides

Nonradical Fenton-like catalysis offers opportunities to overcome the low efficiency and secondary pollution limitations of existing advanced oxidation decontamination technologies, but realizing this on transition metal spinel oxide catalysts remains challenging due to insufficient understanding of their catalytic mechanisms. Here, we explore the origins of catalytic selectivity of Fe-Mn spinel oxide and identify electron delocalization of the surface metal active site as the key driver of its nonradical catalysis. Through fine-tuning the crystal geometry to trigger Fe-Mn superexchange interaction at the spinel octahedra, ZnFeMnO₄ with high-degree electron delocalization of the Mn-O unit was created to enable near 100% nonradical activation of peroxymonosulfate (PMS) at unprecedented utilization efficiency. The resulting surface-bound PMS* complex can efficiently oxidize electron-rich pollutants with extraordinary degradation activity, selectivity, and good environmental robustness to favor water decontamination applications. Our work provides a molecule-level understanding of the catalytic selectivity and bimetallic interactions of Fe-Mn spinel oxides, which may guide the design of low-cost spinel oxides for more selective and efficient decontamination applications.

An alternative approach to the kinetic modeling of pharmaceuticals degradation in high saline water by electrogenerated active chlorine species

A semiempirical approach considering the rate of reactive chlorine species-RCS- production (Φ_E) as a function of current and Cl^- concentration for the modeling of acetaminophen (ACE) degradation is presented. A filter-press reactor having a Ti/RuO₂-ZrO₂ (Sb₂O₃ doped) anode, NaCl (0.04-0.1 mol L^-1) as supporting electrolyte, and operated in continuous mode, was considered. A current of 100 mA and a flow of 11 mL min^-1 favored the electrogeneration of RCS and ACE degradation. Hydraulic retention time and Φ_E were the most relevant parameters for the RCS production. These two parameters, plus the pollutant concentration, were very determinant for the ACE degradation. The model successfully reproduced the ACE removal in distilled water at different concentrations (10, 20, 40, and 60 mg L^-1). The electrochemical system achieved removals between 80 and 100% of ACE in distilled water. The ACE treatment in actual seawater (a chloride-rich matrix, 0.539 mol L^-1 of Cl^-) was assessed, and the degradation was simulated using the developed model. The competing role toward electrogenerated RCS by intrinsic organic matter (3.2 mg L^-1) in the seawater was a critical point, and the simulated values fitted well with the experimental data. Finally, the action of the electrochemical system on ciprofloxacin (CIP) in real seawater and its antimicrobial activity was tested. CIP removal (100% at 120 s) was faster than that observed for ACE (100% of degradation after 180 s) due to CIP has amine groups that are more reactive toward RCS than phenol moiety on ACE. Moreover, the system removed 100% of the antimicrobial activity associated with CIP, indicating a positive environmental effect of the treatment.

Removal of ammonia and phenol from saline chemical wastewater by ionizing radiation: Performance, mechanism and toxicity

Saline chemical wastewater containing ammonia and toxic organic pollutants has been a challenge for conventional wastewater treatment technology. Advanced treatment is thus required. In this study, the removal of ammonia and phenol in saline chemical wastewater by radiation was investigated in detail. The results showed that chloridion in saline chemical wastewater could be transferred to •Cl and •ClO by radiation, which promoted ammonia oxidation, but inhibited phenol degradation. Solution pH affected the types of reactive species, which further affected the removal of ammonia and phenol. When ammonia and phenol co-existed in saline chemical wastewater, the removal efficiency of ammonia was depressed compared to that in the absence of phenol. Similarly, the phenol removal efficiency was also depressed in the presence of ammonia when the solution pH was lower than 7.0. Interestingly, the phenol removal efficiency was improved with increase of either chloridion concentration (2-8 g/L) or dose (2-5 kGy), which was attributed to the formation of intermediate nitrogen-centered radicals that can react with phenol. In addition, the intermediate products of phenol degradation under different conditions were identified. The acute toxicity of saline chemical wastewater after radiation treatment was evaluated. The results of this study could provide an insight into the removal of ammonia and phenol from saline chemical wastewater by radiation technology.

A review on the degradation of acetaminophen by advanced oxidation process: pathway, by-products, biotoxicity, and density functional theory calculation

Water scarcity and the accumulation of recalcitrance compounds into the environment are the main reasons behind the attraction of researchers to use advanced oxidation processes (AOPs). Many AOP systems have been used to treat acetaminophen (ACT) from an aqueous medium, which leads to generating different kinetics, mechanisms, and by-products. In this work, state-of-the-art studies on ACT by-products and their biotoxicity, as well as proposed degradation pathways, have been collected, organized, and summarized. In addition, the Fukui function was used for predicting the most reactive sites in the ACT molecule. The most frequently detected by-products in this review were hydroquinone, 1,4-benzoquinone, 4-aminophenol, acetamide, oxalic acid, formic acid, acetic acid, 1,2,4-trihydroxy benzene, and maleic acid. Both the experimental and prediction tests revealed that N-(3,4-dihydroxy phenyl) acetamide was mutagenic. Meanwhile, N-(2,4-dihydroxy phenyl) acetamide and malonic acid were only found to be mutagenic in the prediction test. The findings of the LC50 (96 h) test revealed that benzaldehyde is the most toxic ACT by-products and hydroquinone, N-(3,4-dihydroxyphenyl)formamide, 4-methylbenzene-1,2-diol, benzoquinone, 4-aminophenol, benzoic acid, 1,2,4-trihydroxybenzene, 4-nitrophenol, and 4-aminobenzene-1,2-diol considered harmful. The release of them into the environment without treatment may threaten the ecosystem. The degradation pathway based on the computational method was matched with the majority of ACT proposed pathways and with the most frequent ACT by-products. This study may contribute to enhance the degradation of ACT by AOP systems.

Selective degradation of acetaminophen from hydrolyzed urine by peroxymonosulfate alone: performances and mechanisms

Owing to the high concentration of pharmaceuticals in urine, the degradation of these organic pollutants before their environmental release is highly desired. Peroxymonosulfate (PMS) is a desirable oxidant that can be applied to environmental remediation; however, the performance and mechanism of PMS for the degradation of pharmaceuticals in the urine matrix have not been investigated. Herein, PMS was first discovered to efficiently degrade typical pharmaceuticals in hydrolyzed urine (HU) by selecting acetaminophen (ACE) as a target compound. Quenching experiments revealed that singlet oxygen (1O2) and hydroxyl radicals (HO˙) were observed in the HU/PMS system, but the principal reactive species (RS) responsible for ACE removal was 1O2. The major constituents of HU, including SO4 2- and organics (creatine, creatinine and hippuric acid), hardly affected the elimination of ACE, whereas Cl-, H2PO4 - and NH4 + would accelerate ACE degradation. Besides, HCO3 - slightly inhibited this process. The ACE degradation efficiency was enhanced using photo-irradiation, including sunlight and visible light, although increasing the reaction temperature could, interestingly, hardly accelerate the degradation rate of ACE. Three-dimensional excitation-emission matrices (3D-EEMs) have indicated that other intermediates that have a higher fluorescence intensity might be generated in the HU/PMS system. Finally, nine intermediate products were determined and the degradation pathways of ACE were proposed. Overall, the results of this study illustrated that PMS is an efficient oxidant for the degradation of ACE in HU.

Enhanced degradation of tetrabromobisphenol A by Fe3+/sulfite process under simulated sunlight irradiation

Degradation of tetrabromobisphenol A (TBBPA), an emerging micropollutant, by photo/Fe³⁺/sulfite process was investigated under different operational conditions and water matrices. 91% of TBBPA was efficiently degraded within 30 min in the Fe³⁺/sulfite system under sunlight irradiation when the initial pH was 6.0, which is much higher than that of TBBPA without irradiation (52%). The acceleration of radical generation and direct photolysis by photo irradiation were responsible for the enhanced TBBPA degradation. Although this process showed better performance on TBBPA degradation in weak acid conditions, the high removal efficiency was also achieved at near-neutral pH. HO, SO₄^- and direct photolysis contributed to TBBPA degradation. Direct photolysis and SO₄^- presented the dominant contribution. The degradation rate increased with elevating the Fe³⁺ dose (10-40 μM), but slightly decreased when the Fe³⁺ dose was further raised to 100 μM. Similarly, the degradation efficiency initially increased with increasing the sulfite dose (100-400 μM), but decreased when the sulfite concentration reached 1000 μM. Dissolved oxygen played a crucial role in TBBPA degradation, the presence of water matrices such as humic acid (0.8-4.0 mg/L), bicarbonate (0.5-10 mM) and chloride (0.5-10 mM) retarded TBBPA degradation. This study proposed a new efficient strategy to enhance TBBPA degradation in the Fe³⁺/sulfite process.