Iron-manganese oxide loaded sludge biochar as a novel periodate activator for thiacloprid efficient degradation over a wide pH range

Novel enhanced defluorination of perfluorooctanoic acids by biochar-assisted ultrasound coupling ferrate: Performance and mechanism

An ultrasound (US)/biochar (BC)/ferrate (Fe (VI)) system was firstly proposed to enhance perfluorooctanoic acid (PFOA) defluorination. It achieved 93 % defluorination optimally, higher than the sum of 77 % (28 % and 49 % for US/BC and US/Fe (VI) respectively), implying synergistic effect. Besides, the mechanism study confirmed that, this system can not only increase the specific surface area of BC and the generation of reactive oxidant species (ROS), enriching the active sites and forming new oxygen-containing functional groups, but also promote the formation of intermediate iron species. The PFOA degradation in the US/BC/Fe (VI) was probably an adsorption-degradation process, both ROS and electron transfer promoted the defluorination. Additionally, its sustainability was also demonstrated with 14 % reduced defluorination percentage after five cycles of BC. Overall, the synergistic effect of the US/BC/Fe (VI) and its enhancing mechanism for PFOA defluorination were clarified firstly, which contributes to the development of biochar for assisting polyfluoroalkyl substances degradation.

Preparation of Mn-doped sludge biochar and its catalytic activity to persulfate for phenol removal

In recent years, the increasing prevalence of phenolic pollutants emitted into the environment has posed severe hazards to ecosystems and living organisms. Consequently, there is an urgent need for a green and efficient method to address environmental pollution. This study utilized waste sludge as a precursor and employed a hydrothermal-calcination co-pyrolysis method to prepare manganese (Mn)-doped biochar composite material (Mn@SBC-HP). The material was used to activate peroxydisulfate (PDS) for the removal of phenol. The study investigated various factors (such as the type and amount of doping metal, pyrolysis temperature, catalyst dosage, PDS dosage, pH value, initial phenol concentration, inorganic anions, and salinity) affecting phenol removal and the mechanisms within the Mn@SBC-HP/PDS system. Results indicated that under optimal conditions, the Mn@SBC-HP/PDS system achieved 100% removal of 100 mg/L phenol within 180 min, with a TOC removal efficiency of 82.7%. Additionally, the phenol removal efficiency of the Mn@SBC-HP/PDS system remained above 90% over a wide pH range (3-9). Free radical quenching experiments and electron spin resonance (ESR) results suggested that hydroxyl radicals (·OH) and sulfate radicals (SO4-) yed a role in the removal of phenol through radical pathways, with singlet oxygen (1O2) being the dominant non-radical pathway. The phenol removal efficiency remained above 90%, demonstrating the excellent adaptability of the Mn@SBC-HP/PDS system under the interference of coexisting inorganic anions or increased salinity. This study proposes an innovative method for the resource utilization of waste, creating metal-biochar composite catalysts for the remediation of water environments. It provides a new approach for the efficiency of organic pollutants in water environments.

Tetracycline removal using NaIO4 activated by MnSO4: Design and optimization via response surface methodology

The appearance of recalcitrant organic pollutants such as antibiotics in water bodies has gained a lot of attention owing to their adverse effects on organisms and humans. The current study aims to develop a novel approach to eliminate antibiotic tetracycline (TC) from a synthetic aqueous solution based on the advanced oxidation process triggered by MnSO4-catalyzed NaIO4. A single-factor experiment was performed to observe the impact of pH, NaIO4 concentration, and MnSO4 dosage on TC decomposition, and a three-factor, three-level response surface experiment with TC removal rate as the dependent variable was designed based on the range of factors determined from the single-factor experiment. The single-factor experiment revealed that the ranges of pH, NaIO4 concentration, and MnSO4 dosage need to be further optimized. ANOVA (analysis of variance) results showed that the data from the response surface experiment were consistent with the quadratic model with high R2 (0.9909), and the predicted values were very close to the actual values. After optimization by response surface methodology, the optimal condition obtained was pH = 6.7, [NaIO4] = 0.39 mM, and [MnSO4] = 0.12 mM, corresponding to a TC removal of 96.56%. This optimization condition was fully considered to save the dosage of the high-priced chemical NaIO4.

Highly efficient activation of periodate by a manganese-modified biochar to rapidly degrade methylene blue

In this study, the manganese oxide/biochar composites (Mn@BC) were synthesized from Phytolacca acinosa Roxb. The Mn@BC was analyzed via techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). The results show that MnOx is successfully loaded on the surface of BC, and the load of MnOx can increase the number of surface functional groups of BC. X-ray photoelectron spectroscopy (XPS) shows that MnOx loaded on BC mainly exists in three valence forms: Mn(Ⅱ), Mn(Ⅲ), and Mn(Ⅳ). The ability of Mn@BC to activate periodate (PI) was studied by simulating the degradation of methylene blue (MB) dye. The degradation experiment results showed that the MB removal rate by the Mn@BC/PI system reached 97.4% within 30 min. The quenching experiment and electron paramagnetic resonance (EPR) analysis confirmed that Mn@BC can activate PI to produce iodate (IO3•), singlet oxygen (1O2), and hydroxyl radical (•OH), which can degrade MB during the reaction. Response surface methodology (RSM) based on Box-Behnken Design (BBD) was used to determine the interaction between pH, Mn@BC and PI concentration in the Mn@BC/PI system, and the optimum technological parameters were determined. When pH = 5.4, Mn@BC concentration 0.56 mg/L, PI concentration 1.1 mmol/L, MB removal rate can reach 98.05%. The cyclic experiments show that Mn@BC can be reused. After four consecutive runs, the removal rate of MB by the Mn@BC/PI system is still 82%, and the Mn@BC/PI system also shows high performance in treating MB in actual water bodies and degrading other pollutants. This study provides a practical method for degrading dyes in natural sewage.

Fabrication of Iron-Containing Biochar by One-Step Ball Milling for Cr(VI) and Tetracycline Removal from Wastewater

Simple ball milling technology can simultaneously improve the adsorption performance of adsorbents for heavy metals and organic pollutants and has attracted increasing attention. Iron-modified biochar (Fe@MBC) was prepared by one-step ball milling, and the characterization results proved that FeCl3 was successfully loaded on biochar. The removal rates of Cr(VI) and tetracycline hydrochloride (TC) by Fe@MBC were increased by 88.27% and 82.64% compared with BC. The average pore size, oxygen-containing functional groups and graphitization degree of Fe@MBC are higher than those of BC, which is more conducive to promoting adsorption. The adsorption isotherms show that the adsorption of Cr(VI) and TC on the Fe@MBC surface conforms to the Langmuir type of single-layer adsorption and the Freundlich model of multilayer adsorption, respectively. The maximum adsorption capacities of Cr(VI) and TC are 25.46 and 66.91 mg·g-1, respectively. Kinetic experiments show that the adsorption process is more consistent with the pseudo-second-order model of chemical adsorption. The adsorption process of Cr(VI) and TC on the Fe@MBC surface is a spontaneous endothermic process that becomes more obvious as the temperature increases. The increase in solution pH has a significant impact on the removal rate of Fe@MBC. When the pH value increased from 3 to 11, the adsorption rates decreased by 53.74% and 17.16%, respectively. The presence of PO43-, CO32-, K+, and Cu2+ significantly affects the adsorption of TC by Fe@MBC, and PO43- and CO32- also affect the adsorption of Cr(VI). Mechanistic studies show that ion exchange, electrostatic interaction, pore filling, and hydrogen bonding contribute to the removal of Cr(VI) and TC by Fe@MBC. The removal mechanism of Cr(VI) also involves complexation and redox reactions, and the removal mechanism of TC involves π-π bonds and van der Waals forces. The results show that Fe@MBC is a green and efficient adsorbent.

Unveiling the mechanisms of peracetic acid activation by iron-rich sludge biochar for sulfamethoxazole degradation with wide adaptability

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) has been extensively concerned for the degradation of organic pollutants. In this study, metallic iron-modified sludge biochar (Fe-SBC) was employed to activate PAA for the removal of sulfamethoxazole (SMX). The characterization results indicated that FeO and Fe2O3 were successfully loaded on the surface of the sludge biochar (SBC). Fe-SBC/PAA system achieved 92% SMX removal after 30 min. The pseudo-first-order kinetic reaction constant of the Fe-SBC/PAA system was 7.34 × 10-2 min-1, which was 2.4 times higher than the SBC/PAA system. The degradation of SMX was enhanced with increasing the Fe-SBC dosage and PAA concentration. Apart from Cl-, NO3- and SO42- had a negligible influence on the degradation of SMX. Quenching experiments and electron paramagnetic resonance (EPR) techniques identified the existence of reactive species, of which CH3C(O)OO•, 1O2, and O2•- were dominant reactive species in Fe-SBC/PAA system. The effect of different water matrices on the removal of SMX was investigated. The removal of SMX in tap water and lake water were 79% and 69%, respectively. Four possible pathways for the decay of SMX were presented according to the identification of oxidation products. In addition, following the ecological structure-activity relationship model (ECOSAR) procedure and the germination experiments with lettuce seeds to predict the toxicity of the intermediates. The acute and chronic ecotoxicity of SMX solution was dramatically diminished by processing with Fe-SBC/PAA system. In general, this study offered a prospective strategy for the degradation of organic pollutants.

Target-prepared sludge biochar-derived synergistic Mn and N/O induces high-performance periodate activation for reactive iodine radicals generation towards ofloxacin degradation

Converting waste activated sludge into catalysts for the removal of antibiotics in water fulfils the dual purpose of waste-to-resource and hazardous pollution elimination. In this study, sludge-derived biochar (SDB) for efficient periodate (PI) activation was first prepared via one-step pyrolysis of potassium permanganate-polyhexamethylenebiguanide conditioned sludge without additional modification. The SDB (750 °C)-PI system degraded 100% ofloxacin (OFL, 41.5 μM) within 6 min and was almost undisturbed by inorganic ions or humic acids. The experimental results confirmed that the predominant role of reactive iodine species (RIS) and the auxiliary involvement of singlet oxygen (1O2) jointly contributed to the OFL degradation. Theoretical calculations further indicated that the synergy between Mn and N/O induced local charge redistribution and improved electron transfer capability of SDB, leading to the formation of electron-rich Mn sites and enhanced Mn(II)↔Mn(III)↔Mn(IV) redox to promote PI activation. More importantly, the enhanced adsorption and charge transfer of PI on the Mn site of the Mn-N/O-C structures induced the I-O bond stretching and the rapid generation of RIS. This study offered a cost-effective strategy for developing SDB-based catalysts, further advancing the comprehension of sludge management and the intricate mechanisms underlying RIS formation in PI-advanced oxidation processes.

Enhanced removal of phenanthrene and nutrients in wetland sediment with metallic biochar: Performance and mechanisms

Polycyclic aromatic hydrocarbon (PAHs) are persistent organic pollutants and pose high risk in aquatic environment. The utilization of biochar is a strategy for PAHs-contaminated remediation but is challenging due to the adsorption saturation and reoccurrence of PAHs desorbed back into water. In this study, iron (Fe) and manganese (Mn) were provided as electron acceptors for biochar modification to enhance anaerobic biodegradation of phenanthrene (Phe). Results revealed that, the Mn(Ⅳ) and Fe(Ⅲ) modification improved the removal of Phe by 24.2% and 31.4% than that of biochar, respectively. Additionally, nitrate removal was improved by 19.5% with Fe(Ⅲ) amendment. The Mn-and Fe-biochar decreased Phe contents by 8.7% and 17.4% in sediment, 10.3% and 13.8% in biochar than that of biochar. Much higher DOC contents were observed with Mn- and Fe-biochar, which provided bioavailable carbon source for microbes and contributed to microbial degradation of Phe. The greater degree of humification, higher proportions of humic and fulvic acid like components in metallic biochar participated in electron transport and further enhancing the degradation of PAHs. Microbial analysis proved the high abundance of Phe-degrading bacteria (e.g. PAH-RHD_α, Flavobacterium and Vibrio), nitrogen removal microbes (e.g. amoA, nxrA, and nir), Fe and Mn bioreduction or oxidation (e. g. Bacillus, Thermomonas, Deferribacter) with metallic biochar. Based on the results, the Fe and Mn modification, especially Fe-modified biochar provided well performance for PAHs removal in aquatic sediment.

Coupling and environmental implications of in situ formed biogenic Fe-Mn minerals induced by indigenous bacteria and oxygen perturbations for As(III) immobilization in groundwater

Iron (Fe)-manganese (Mn) minerals formed in situ can be used for the natural remediation of the primary poor-quality groundwater with coexistence of arsenite [As(III)], Mn(II), and Fe(II) (PGAMF). However, the underlying mechanisms of immobilization and coupling of As, Mn, and Fe during in-situ formation of Fe-Mn minerals in PGAMF remains unclear. The simultaneous immobilization and coupling of arsenic (As), Mn, and Fe in PGAMF during in-situ formation of biogenic Fe-Mn minerals induced by O₂ perturbations and indigenous bacteria (Comamonas sp. RM6) were investigated at the different molar ratios of Fe(II):Mn(II) (1:1, 2:1, and 3:1). Compared with systems without Fe(II) in the presence of Mn(II), the coexisted Fe(II) significantly enhanced Mn(II) bio-oxidation and mineral precipitation, resulting in As immobilization increased by 5, 7, and 7 times at initial Fe(II) concentration of 0.3, 0.6, and 0.9 mM, respectively. Moreover, the As(III) immobilization efficiencies in Mn(II) and Fe(II) mixed system at initial Fe(II) concentration of 0.3, 0.6, and 0.9 mM were 73%, 91%, and 92%, respectively, that were significantly higher than those of single Fe(II) system (30%, 59%, and 74%) and those of single Mn(II) system (12%), indicating that Fe(II) and Mn(II) oxidation synergically enhanced As(III) immobilization. This was mainly attributed to the formation and As adsorption capacity of biogenic Fe-Mn minerals (BFMM). The formed BFMM significantly facilitated simultaneous immobilization of Fe, Mn, and As in PGAMF by oxidation, adsorption, and precipitation/coprecipitation, a coupling of biological, physical, and chemical processes. Fe component was mainly responsible for As fixation, and Mn component dominated As(III) oxidation. Based on the results from this work, biostimulation and bioaugmentation techniques can be developed for in-situ purification and remediation of PGAMF. This work provides insights into the simultaneous immobilization of pollutants in PGAMF, as well as promising strategies for in-situ purification and remediation of PGAMF.

Promoting selective water decontamination via boosting activation of periodate by nanostructured Ru-supported Co3O4 catalysts

The superior catalytic efficiency of ruthenium (Ru)-based nanocomposites in advanced oxidation processes for water decontamination has attracted accumulating attention worldwide. However, rather limited knowledge is currently available regarding their roles in activating periodate (PI), an emerging oxidant with versatile environmental applications. This study firstly delineated that Ru-supported Co₃O₄ (Ru/Co₃O₄), a typical Ru-based nanomaterial, can efficiently accomplish PI activation to eliminate multiple organic micropollutants and inactivate different pathogenic bacteria. Almost all eight micropollutants can be completely removed within 2 min of Ru/Co₃O₄-PI oxidation except sulfamethoxazole (SMX), which was degraded ∼70 % at 2 min with 100 % mineralization after 10 min. The excellent catalytic performance was independent of PI dosages, initial pH, and coexisting water constituents, demonstrating its prominent capability as a selective oxidation strategy. Diverse lines of evidence indicated the dominant role of single oxygen in the Ru/Co₃O₄-PI system, which triggered the generation of five transformation products of SMX with reduced environmental risks. Concurrently, PI was stoichiometrically converted to the eco-friendly IO₃^-. Additionally, Ru/Co₃O₄-PI system achieved 6-log inactivation of different pathogenic bacteria within 1 min, implying the feasibility of rapid water disinfection. Overall, this work demonstrated the excellent promise of Ru-based composites in PI activation for highly efficient and selective water decontamination.

Ball milling-assisted preparation of sludge biochar as a novel periodate activator for nonradical degradation of sulfamethoxazole: Insight into the mechanism of enhanced electron transfer

The non-radical pathway of periodate (PI) activation for the removal of persistent organic contaminants has received increasing attention due to its higher stability and oxidative advantages. In this study, the degradation of sulfamethoxazole (SMX) by ball mill treated magnetic sludge biochar (BM-MSBC) through activation of PI by electron transfer mechanism was reported. Experimental and characterization results showed that the ball milling treatment resulted in a better pore and defect structure, which also significantly enhanced the electron transfer capacity of the sludge biochar. The BM-MSBC/PI system exhibited notable dependence of activator concentration and initial pH, while the effect of PI concentration was not significant. The coexisting substances (common anions and natural organic matters) hardly affect the degradation of SMX in the BM-MSBC/PI system. The phytotoxicity experiments suggested that the treatment of BM-MSBC/PI system could significantly reduce the biological toxicity of SMX solution. This study provides a novel, economical, and facile modification method for the application of sludge biochar in advanced oxidation processes.

Emerging periodate-based oxidation technologies for water decontamination: A state-of-the-art mechanistic review and future perspectives

With the ever-increasing severity of the ongoing water crisis, it is of great significance to develop efficient, eco-friendly water treatment technologies. As an emerging oxidant in the advanced oxidation processes (AOPs), periodate (PI) has received worldwide attention owing to the advantages of superior stability, susceptible activation capability, and high efficiency for decontamination. This is the first review that conducts a comprehensive analysis of the mechanism, pollutant transformation pathway, toxicity evolution, barriers, and future directions of PI-based AOPs based on the scientific information and experimental data reported in recent years. The pollutant elimination in PI-based AOPs was mainly attributed to the in situ generate reactive oxygen species (e.g., ^•OH, O(³P), ¹O₂, and O₂^•-), reactive iodine species (e.g., IO₃^• and IO₄^•), and high-valent metal-oxo species with exceptionally high reactivity. These reactive species were derived from the PI activated by the external energy, metal activators, alkaline, freezing, hydroxylamine, H₂O_2, etc. It is noteworthy that direct electron transport could also dominate the decontamination in carbon-based catalyst/PI systems. Furthermore, PI was transformed to iodate (IO₃^-) stoichiometrically via an oxygen-atom transfer process in most PI-based AOPs systems. However, the production of I₂, I^-, and HOI was sometimes inevitable. Furthermore, the transformation pathway of typical micropollutants was clarified, and the in silico QSAR-based prediction results indicated that most transformation products retained biodegradation recalcitrance and multi-endpoint toxicity. The barriers faced by the PI-based AOPs were also clarified with potential solutions. Finally, future perspectives and research directions are highlighted based on the current state of PI-based AOPs. This review enhances our in-depth understanding of PI-based AOPs for pollutant elimination and identifies future research needs to focus on the reduction of toxic byproducts.

Converting Hybrid Mechanisms to Electron Transfer Mechanism by Increasing Biochar Pyrolysis Temperature for the Degradation of Sulfamethoxazole in a Sludge Biochar/Periodate System

In this study, sludge biochar was prepared under four pyrolysis temperatures (SBC300, SBC500, SBC700, and SBC900) and then was employed to activate periodate (PI) for the degradation of sulfamethoxazole (SMX). Various characterization methods were employed to investigate the effect of pyrolysis temperature on the physicochemical properties of sludge biochar and the activation capacity of periodate. The SMX adsorption capacity of SBCs and the ability of activating PI to degrade SMX increased with the increasing pyrolysis temperature. The degradation of SMX by the SBCs/PI systems was highly dependent on the initial pH of the solution and the dosage of SBCs. Mechanistic studies indicated that the degradation of SMX by the SBCs/PI system was mainly based on an electron-mediated transfer mechanism. Additionally, the electron transfer capacity of the SBCs affected the defects and the degree of graphitization. The contribution of free radicals to SMX degradation decreases with increasing pyrolysis temperature. Toxicity experiments demonstrated that the toxic elimination of SMX by the SBCs/PI system was enhanced with increasing pyrolysis temperature.

Improved Dewaterability of Waste Activated Sludge by Fe(II)-Activated Potassium Periodate Oxidation

Fe(II)-activated potassium periodate (KIO₄) oxidation was used to improve the dewaterability of waste-activated sludge for the first time. Compared with those of raw sludge, the capillary suction time (CST), specific resistance filtration (SRF), and water content of filter cake (W_C) of sludge treated using the Fe(II)/KIO₄ process under the optimal conditions (i.e., the initial pH = 6.8, KIO₄ dose = 1.4 mmol/g volatile suspended solids, Fe(II)/KIO₄ molar ratio = 1.2) decreased by 64.34%, 84.13%, and 6.69%, respectively. For conditioned sludge flocs, the Zeta potential and particle size were increased, and hydrophilic proteins in extracellular polymeric substances (EPS) were partly degraded, accompanied by the transformation of tightly bound EPS into soluble EPS and the conversion of dense sludge flocs into loose and porous ones. During Fe(II)/KIO₄ oxidation, Fe(IV) and the accompanying ^•OH were determined as the predominant reactive species and the underlying mechanism of sludge EPS degradation was proposed. This work provides a prospective method for conditioning the sludge dewaterability.

A sustainable reuse strategy of converting waste activated sludge into biochar for contaminants removal from water: Modifications, applications and perspectives

Conversion of sewage sludge to biochar for contaminants removal from water achieves the dual purpose of solid waste reuse and pollution elimination, in line with the concept of circular economy and carbon neutrality. However, the current understanding of sludge-derived biochar (SDB) for wastewater treatment is still limited, with a lack of summary regarding the effect of modification on the mechanism of SDB adsorption/catalytic removal aqueous contaminants. To advance knowledge in this aspect, this paper systematically reviews the recent studies on the use of (modified) SDB as adsorbents and in persulfate-based advanced oxidation processes (PS-AOPs) as catalysts for the contaminants removal from water over the past five years. Unmodified SDB not only exhibits stronger cation exchange and surface precipitation for heavy metals due to its nitrogen/mineral-rich properties, but also can provide abundant catalytic active sites for PS. An emphatic summary of how certain adsorption removal mechanisms of SDB or its catalytic performance in PS-AOPs can be enhanced by targeted regulation/modification such as increasing the specific surface area, functional groups, graphitization degree, N-doping or transition metal loading is presented. The interference of inorganic ions/natural organic matter is one of the unavoidable challenges that SDB is used for adsorption/catalytic removal of contaminants in real wastewater. Finally, this paper presents the future perspectives of SDB in the field of wastewater treatment. This review can contribute forefront knowledge and new ideas for advancing sludge treatment toward sustainable green circular economy.

Sulfide-modified zero-valent iron activated periodate for sulfadiazine removal: Performance and dominant routine of reactive species production

In this work, sulfide-modified zero-valent iron (S-Fe⁰) was used to activate periodate (IO₄^-, PI) for sulfadiazine (SDZ) removal. 60 μM SDZ could be completely removed within only 1 min by S-Fe⁰/PI process. Compared with other oxidants including H₂O₂, peroxymonosulfate (PMS), peroxydisulfate (PDS), S-Fe⁰ activated PI exhibited better performance for SDZ removal but with lower Fe leaching. Compared with Fe⁰/PI process, S-Fe⁰/PI process could reduce more than 80% Fe⁰ and PI dosage. Inorganic ions and nature organic matters had negligible effect on SDZ removal in S-Fe⁰/PI system inducing its good SDZ removal efficiency in natural fresh water. 80.2% SDZ still could be removed within 2 min after 7th run. S-Fe⁰/PI process also exhibited 2.5 - 20.1 folds enhancement for various pollutants removal compared with Fe⁰/PI process. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical tests, and density functional theory (DFT) calculation were conducted to confirm the presence of sulfurs could enhance the reactivity of S-Fe⁰ thus increased the efficiency of PI activation for antibiotics removal. Electron paramagnetic resonance spectroscopy (EPR) tests, radical quenching experiments, quantitative detection and DFT calculation were performed to illustrate the role of multiple reactive species in SDZ removal and the dominant pathway of multiple reactive species production. IO₃^·, ^·OH, O₂^-·, ¹O₂, Fe^IV, and SO₄^·- all participated in SDZ removal. ^·OH played the major role in SDZ removal and the dominant routine of ^·OH production was IO₄^- → O₂^-· → H₂O₂ → ^·OH. Meanwhile, S-Fe⁰/PI process could efficiently mineralize SDZ and reduce the toxicity. Comparison with other PI activation approaches and SDZ treatment techniques further demonstrated S-Fe⁰ was an efficient catalyst for PI activation and present study process was a promising approach for antibiotics removal.