Iron Mud Research Articles

Ov-rich γ-MnO2 enhanced electrocatalytic three-electron oxygen reduction to hydroxyl radicals for sterilization in neutral media.

Marine biofouling severely limits the development of the marine economy, and reactive oxygen species (ROS) produced by electrocatalytic antifouling techniques could inactivate marine microorganisms and inhibit the formation of marine biofouling. Compared with an electro-Fenton reaction, a three-electron oxygen reduction reaction (3e- ORR) could generate a hydroxyl radical (˙OH) in situ without the limitation of pH and iron mud pollutants. Herein, Ov-rich γ-MnO2 is designed to enhance the 3e- ORR performance in neutral media and exhibits excellent sterilization performance for typical marine bacteria. DFT calculation reveals that Ov is beneficial to the "end-on" adsorption and activation of O2, and the Mn site could accept the electrons from *OOH and promote its further reduction to form ˙OH; Ov and Mn sites together guarantee the high 3e- ORR efficiency. In addition, liquid chromatography-tandem mass spectrometry (LC-MS/MS) proves the vast formation of ˙OH in the primary reaction stage, which is the key to sterilization. This work explores the reaction mechanism of the 3e- ORR in neutral media and provides the possibility for the application of electrocatalysis technology in the treatment of marine biofouling pollution.

Synthesis of a Magnetic Nanostructured Composite Sorbent Only from Waste Materials.

Water pollution is a big problem for the environment, and thus depollution, especially by adsorption processes, has garnered a lot of interest in research over the last decades. Since sorbents would be used in large quantities, ideally, they should be cheaply prepared in scalable reactions from waste materials or renewable sources and be reusable. Herein, we describe a novel preparation of a range of magnetic sorbents only from waste materials (sawdust and iron mud) and their performance in the adsorption of several dyes (methylene blue, crystal violet, fast green FCF, and congo red). The preparation is performed in a hydrothermal process and is thus easily scalable and requires little sophisticated equipment. The magnetic nanostructured materials were analyzed using FTIR, VSM, SEM/EDX, XRD, and XPS. For crystal violet as a pollutant, more in-depth adsorption studies were performed. It was found that the best-performing magnetic sorbent had a maximum sorption capacity of 97.9 mg/g for crystal violet (methylene blue: 149.8 mg/g, fast green FCF: 52.2 mg/g, congo red: 10.5 mg/g), could be reused several times without drastic changes in sorption behavior, and was easily separable from the solution by simply applying a magnet. It is thus envisioned to be used for depollution in industrial/environmental applications, especially for cationic dyes.

Incorporation of N-doped biochar into zero-valent iron for efficient reductive degradation of neonicotinoids: mechanism and performance

The extensive use of neonicotinoids on food crops for pest management has resulted in substantial environmental contamination. It is imperative to develop an effective remediation material and technique as well as to determine the evolution pathways of products. Here, novel ball-milled nitrogen-doped biochar (NBC)-modified zero-valent iron (ZVI) composites (named MNBC-ZVI) were fabricated and applied to degrading neonicotinoids. Based on the characterization results, NBC incorporation introduced N-doped sites and new allying heterojunctions and achieved surface charge redistribution, rapid electron transfer, and higher hydrophobicity of ZVI particles. As a result, the interaction between ZVI particles and thiamethoxam (a typical neonicotinoid) was improved, and the adsorption–desorption and reductive degradation of thiamethoxam and ·H generation steps were optimized. MNBC-ZVI could rapidly degrade 100% of 10 mg·L−1 thiamethoxam within 360 min, its reduction rate constant was 12.1-fold greater than that of pristine ZVI, and the electron efficiency increased from 29.7% to 57.8%. This improved reactivity and selectivity resulted from increased electron transfer, enhanced hydrophobicity, and reduced accumulation of iron mud. Moreover, the degradation of neonicotinoids occurred mainly via nitrate reduction and dichlorination, and toxicity tests with degradation intermediates revealed that neonicotinoids undergo rapid detoxification. Remarkably, MNBC-ZVI also presented favorable tolerance to various anions, humic acid, wastewater and contaminated soil, as well as high reusability. This work offers an efficient and economic biochar-ZVI remediation technology for the rapid degradation and detoxification of neonicotinoids, significantly contributes to knowledge on the relevant removal mechanism and further advances the synthesis of highly reactive and environmentally friendly materials.Graphical

Enhancing sludge methanogenesis with changed micro-environment of anaerobic microorganisms by Fenton iron mud

Conductive materials have been demonstrated to enhance sludge methanogenesis, but few researches have concentrated on the interaction among conductive materials, microorganisms and their immediate living environment. In this study, Fenton iron mud with a high abundance of Fe(III) was recycled and applied in anaerobic reactors to promote anaerobic digestion (AD) process. The results show that the primary content of extracellular polymeric substances (EPS) such as polysaccharides and proteins increased significantly, possibly promoting microbial aggregation. Furthermore, with the increment of redox mediators including humic substances in EPS and Fe(III) introduced by Fenton iron mud, the direct interspecies electron transfer (DIET) between methanogens and interacting bacteria could be accelerated, which enhanced the rate of methanogenesis in anaerobic digestion (35.21 ± 4.53% increase compared to the control). The further analysis of the anaerobic microbial community confirmed the fact that Fenton iron mud enriched functional microorganisms, such as the abundance of CO2-reducing (e.g. Chloroflexi) and Fe(III)-reducing bacteria (e.g., Tepidimicrobium), thereby expediting the electron transfer reaction in the AD process via microbial DIET and dissimilatory iron reduction (DIR). This work will make it possible for using the recycled hazardous material – Fenton iron mud to improve the performance of anaerobic granular sludge during methanogenesis.

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation.

Fenton iron mud (IM) is a hazardous solid waste produced by Fenton oxidation technology after treating industrial wastewater. Thus, it is necessary and challenging to develop a recycling technology to back-convert dangerous materials into useful products. Herein, we develop a sustainable approach to prepare highly active metal oxides via a solid-state grinding method. IM, as an amorphous material, can disperse and interact well with these supported metal oxides, boosting toluene degradation significantly. Among these IM-based catalysts, the catalyst 8% MnOx/IM-0.2VC exhibits the best performance (T100 = 290 °C), originating from the oxide-support interaction and optimal balance between low-temperature reducibility and oxygen vacancy concentration. In addition, in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) results expound that ring breakage is prone to occur on MnOx, and oxygen vacancies are beneficial to adsorb oxygen and activate oxygen species to boost toluene oxidation following the Mars-van Krevelen mechanism. This work advances a complete industrial hazardous waste recycling route to develop extremely active catalysts.

Deep oxidation of norfloxacin by the electrochemical enhanced heterogeneous catalytic oxidation: The role of electric field and reaction optimization.

In this study, electrochemical (ECG-G: graphite anode and cathode, ECI-G: iron anode and graphite cathode) enhanced heterogeneous activation of peroxymonosulfate (PMS) by CoFe2O4 nanoparticles for the degradation of norfloxacin (NOR) in water was investigated. Although a higher NOR removal efficiency was achieved in ECI-G/CoFe2O4/PMS system, the generation of Fe3+ had resulted in the deposition of iron mud and affect the recovery of CoFe2O4. Under the optimum reaction conditions of CoFe2O4/PMS system, the final removal efficiency of NOR did not show significant difference in ECG-G/CoFe2O4/PMS system (96.0%) and CoFe2O4/PMS system (95.5%), but the value of apparent rate constant significantly increased in ECG-G/CoFe2O4/PMS system (0.21min-1) compared with CoFe2O4/PMS system (0.11min-1). Similar NOR degradation pathways were obtained in these two systems, and the TOC removal efficiency in ECG-G/CoFe2O4/PMS system (28.8%) is almost as low as CoFe2O4/PMS system (26.0%). Therefore, it can be proposed that the applied electric field through active electrodes can accelerate the reaction of heterogeneous catalytic oxidation, but does not participate much in NOR degradation. However, the TOC removal efficiency (30min) could be reached 68.7% as the mass ratio of PMS to CoFe2O4 increased to 5:1 (250mgL-1: 50mgL-1). The ECG-G/CoFe2O4/PMS system is a promising low-cost technique for efficient mineralization of antibiotics in wastewater.

Preparation of Fe3O4@C with water treatment residuals and its potential in the magnetic coagulation process

The resource utilization of water treatment residuals is a hot topic in current research. In this work, a kind of carbon-doped magnetic nanoparticle (Fe 3 O 4 @C) was prepared using backwashing iron mud from the groundwater treatment plant as raw material. The Fe 3 O 4 @C was used for the magnetic coagulation (MC) process to evaluate the superiority of the MC process via comparing it with the traditional coagulation (TC) process. Meanwhile, the Fe 3 O 4 was also used for reference in the MC process to assess the potential and feasibility of the Fe 3 O 4 @C. The synthesized Fe 3 O 4 @C was characterized by SEM, TEM , XRD , VSM , and XPS . Then, coagulation performances and flocs properties were evaluated in both TC and MC processes. In addition, the various roles of magnetic particles in the MC process were discussed. The results showed that the participation of Fe 3 O 4 @C increased the turbidity removal rate from 90.3% to 96.8%, the ultra-violet absorbance at 254 nm (UV 254 ) removal rate from 81.4% to 86.5%, the dissolved organic carbon (DOC) removal rate from 60.4% to 66.9%, and the residual Al content dropped from 2.54 mg/L to 2.07 mg/L. Especially, it is found the Fe 3 O 4 @C had the potential to remove more small molecular weight organic matter during the coagulation process. The flocs were loose and easily broken due to the formation of the Al species-nanoparticle cluster. Fe 3 O 4 @C involved MC process can achieve the same water treatment efficiency as Fe 3 O 4 involved MC process, or even better. Especially, the magnetic seed of Fe 3 O 4 @C based on waste utilization can not only reduce the cost, but also has a good adsorption on small molecular organics. This provides a new reference way for the utilization of iron mud and the development of magnetic seed in the MC process. • Carbon-doped magnetic nanoparticles (Fe 3 O 4 @C) were prepared as magnetic seeds. • Fe 3 O 4 @C could improve the removal of small molecular organics by adsorption. • Recycle utilization of iron sludge was realized.

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Preparation and Characterization of Sludge-Based Magnetic Biochar by Pyrolysis for Methylene Blue Removal

The development of low-cost adsorbent is an urgent need in the field of wastewater treatment. In this study, sludge-based magnetic biochar (SMB) was prepared by pyrolysis of sewage sludge and backwashing iron mud without any chemical agents. The samples were characterized by TGA, XRD, ICP, Organic element analysis, SEM, TEM, VSM and BET. Characterization analysis indicated that the magnetic substance in SMB was Fe3O4, and the saturation magnetization was 25.60 emu·g−1, after the adsorption experiment, SMB could be separated from the solution by a magnet. The batch adsorption experiment of methylene blue (MB) adsorption showed that the adsorption capacities of SMB at 298 K, 308 K and 318 K were 47.44 mg·L−1, 39.35 mg·L−1, and 25.85 mg·L−1, respectively. After one regeneration with hydrochloric acid, the maximum adsorption capacity of the product reached 296.52 mg·g−1. Besides, the adsorption kinetic described well by the pseudo-second order model revealed that the intraparticle diffusion was not just the only rate controlling step in adsorption process. This study gives a reasonable reference for the treatment of sewage sludge and backwashing iron mud. The product could be used as a low-cost adsorbent for MB removal.

In situ produced hydrogen peroxide by biosynthesized Palladium nanoparticles and natural clay mineral for Highly-efficient Carbamazepine degradation

Fenton reaction is an effective method to remove refractory organics such as carbamazepine (CBZ) from water streams. Nevertheless, its application is greatly compromised by extra hydrogen peroxide (H2O2) addition and iron mud accumulation. Herein, Fenton-like process with in situ produced H2O2 by biosynthesized palladium nanoparticles (bioPd-NPs) and natural iron-bearing clay minerals is proposed for CBZ degradation. The bioPd-NPs prepared by Shewanella loihica PV-4 were in the size range of 5–20 nm, which catalyzed the in situ production of H2O2 from formic acid (FA) and oxygen. Then the in situ generated H2O2 underwent Fenton-like reactions with nontronite for CBZ degradation. With bioPd-NPs and nontronite dosage of 1 g/L and FA concentration of 20 mM, the complete CBZ (10 mg/L) degradation was achieved within 60 min. Oxidative radicals such as HO· and H2O2 generated in our constructed system played key roles in CBZ degradation. Intermediates/products identification and theoretical calculation revealed that hydroxylation was the main CBZ degradation pathway. This work provides a promising Fenton-like technology for elimination of CBZ from environment with prevention of additional H2O2 supplementation and excessive iron mud production.

Crucial roles of 3D–MoO2–PBC cocatalytic electrodes in the enhanced degradation of imidacloprid in heterogeneous electro–Fenton system: Degradation mechanisms and toxicity attenuation

Imidacloprid (IMI), as the most-consumed pesticide, has posed a severe threat to the water ecosystem due to its recalcitrance and inefficient elimination in the traditional wastewater treatment. Herein, a heterogeneous electro–Fenton (EF) system coupled with 3D–MoO2–porous biochar (PBC) cocatalytic electrodes, abbreviated as 3D–MPE–EF, is initially applied to promote the elimination of IMI in the agrochemical wastewater from pesticide production. The elimination rate of IMI by 3D–MPE–EF system is 18.15 times higher than that by traditional EF system at pH 7.0. The utilization of 3D–MoO2–PBC electrodes sufficiently compensates for inherent deficiencies of traditional EF system. The circular utilization of Fe is also addressed by 3D–MoO2–PBC cocatalytic electrodes to reduce the consumption of Fe2+ and the deposition of iron mud. Through comparison, MoO2 is considered the most appropriate cocatalyst in terms of the reutilization of Fe and degradation of IMI. Eight mechanisms are identified in the degradation pathways of IMI by UPLC–Q–TOF–MS. The ecotoxicities of IMI are remarkably attenuated in the 3D–MPE–EF system. This study provides insights into the roles of 3D–MoO2–PBC cocatalytic electrodes in the enhanced elimination of IMI in heterogeneous EF system.

Magnetic biochar synthesized with waterworks sludge and sewage sludge and its potential for methylene blue removal

It is more and more urgent to develop low cost magnetic biochar for the removal of pollutants in water. In this study, magnetic biochar composites were prepared by one-step hydrothermal synthesis from sewage sludge and waterworks sludge (backwashing iron mud) and used to remove methylene blue (MB) from water. The synthesized samples were characterized by SEM, EDS, TEM, XRD, FTIR, XPS, VSM and BET. By changing the ratio of sludge and iron mud, three kinds of sludge-based magnetic biochar (SBMB) with good properties were successfully prepared. When the proportion of iron mud was higher, the samples were more magnetic, but when the proportion of sludge was higher, the adsorption capacity of the samples was greater. The magnetic materials in SBMB1, SBMB2 and SBMB3 were Fe3O4, and their saturated magnetization were 22.35 emu g−1, 45.16 emu g−1 and 53.56 emu g−1, respectively. SBMB had a good capacity for methylene blue removal and the process was rapid. In addition, SBMB had good magnetic properties, which can be easily separated from the solution by magnet after the experiment. The maximum adsorption capacities of SBMB1, SBMB2 and SBMB3 were 186.003 mg g−1, 178.786 mg g−1 and 164.316 mg g−1, respectively. In conclusion, this paper reports a simple and environmentally friendly method for the synthesis of magnetic biochar using sludge and iron mud as resources, which can provide a reasonable reference for the treatment of sewage sludge and backwashing iron mud in waterworks.

Stable and efficient sulfamethoxazole and phosphorus removal by an electrolysis-integrated bio-rack constructed wetland system

Pollution of sulfamethoxazole (SMX) in rural domestic sewage are a great challenge for ecological security because of limited treatment. In this study, an electrolysis-integrated bio-rack constructed wetland system (EC-CW-P) without substrates was developed for enhancing SMX removal in rural domestic sewage. The dynamic performance and mechanism of SMX (1 mg L-1) removal, occurrence of antibiotic resistance genes (ARGs) and microbial community composition at 4 ~ 24℃ were assessed. Meanwhile, the simultaneous removal performance of phosphorus in EC-CW-P was also analyzed due to key role of substrate adsorption and iron flocculation. The results revealed that the removal efficiency of SMX could reach 97.13% at 4 ~ 24℃ in the EC-CW-P by the electrocatalysis and adsorption of a ferric iron coagulant and biodegradation. Moreover, efficient removal of 74.12%~99.52% total phosphorus (TP) was obtained through electrocoagulation because of the formation of ferric ions. The occurrence of SMX had no effect on TP removal because of the different removal pathway. Itshouldbeemphasizedthat the removal efficiency of SMX owing to high microbial and plant activity which may be due to the formation of iron film and micro current stimulation and TP owing to adsorption of iron mud remained high (>80%) when the electrode was gradually passivated. Overall, the performance of bio-rack CW system was intensified by electrolysis (iron electrode) with higher bacterial abundance and plant activity in the EC-CW-P. However, the high relative abundance of sul ARGs (from 2.15 × 10-1 to 2.41 × 101 copies 16S rRNA-1) in the influent of the EC-CW-P may pose a severe threat to ecosystem. These results provide a novel perspective for enhancing SMX and phosphorus removal by bio-rack constructed wetland system.

Synthesis of zero-valent iron/biochar by carbothermal reduction from wood waste and iron mud for removing rhodamine B.

This study proposes a new process to synthesize zero-valent iron/biochar (Fe0-BC) by carbothermal reduction using wood waste and iron mud as raw materials under different temperature. The characterization results showed that the Fe0-BC synthesized at 1200 °C (Fe0-BC-1200) possessed favorable adsorption capacity with the specific surface area of 103.18 m2/g and that the zero-valent iron (Fe0) particles were uniformly dispersed on the biochar surface. The removal efficiency of rhodamine B (RB) was determined to evaluate the performance of the prepared Fe0-BC. Fe0-BC-1200 presented the best performance on RB removal, which mainly ascribes to that more Fe0 particles generated at higher temperature. The equilibrium adsorption capacity reached 49.93 mg/g when the initial RB concentration and the Fe0-BC-1200 dosage were 100 mg/L and 2 g/L, respectively, and the pseudo-second-order model was suitable to fit the removal experimental data. LCMC and XRD analyses revealed that the removal mechanism included the physical adsorption of biochar and the redox reaction of Fe0. Moreover, copper existing in the iron mud was also reduced to Cu0, which was beneficial to catalyze the oxidation of iron; the degradation of RB was promoted at the same time.

Resource Recycling of Mn-Rich Sludge: Effective Separation of Impure Fe/Al and Recovery of High-Purity Hausmannite.

Groundwater treatment sludge is a Fe/Mn-rich waste generated in mass production in a groundwater treatment plant for potable water production. The conventional disposal of sludge, such as direct discharge into river/lake, sea, and landfill, is not environmentally sustainable. Herein, a novel method was proposed to effectively separate Fe/Al and recover Mn via a combined hydrochloric acid leaching and hydrothermal route. The sludge contained 14.6% Fe, 6.3% Mn, and 11.5% Al and was first dissolved in 5 M HCl to prepare a leaching solution. Second, the leaching solution was hydrothermally treated, in which 97.1% Fe and 94.8% Al were precipitated as hematite and boehmite and more than 98% Mn was kept. Increasing the reaction temperature to 270 °C was beneficial for Fe/Al removal. With the consumption of abundant H+, the reaction of added glucose and nitrate accelerated as the temperature increased. An optimal pH was utilized for Fe/Al hydrolysis and crystallization, leading to extensive removal of Fe/Al. Third, the residual solution was adjusted to pH 8.3 with NaOH, and approximately, 99.2% Mn was removed as hausmannite with a Mn content of 63.6%. This method exhibited efficient separation of impure Fe/Al from Mn-rich groundwater treatment plant iron mud, and the recycled high-purity hausmannite was a marketable active pharmaceutical ingredient.

Heterogeneous Fenton-like magnetic nanosphere coated with vanadium oxide quantum dots for enhanced organic dyes decolorization

The conventional Fenton reaction has played a vital role in the degradation of pollutants. However, this reaction is prone to forming iron mud, which causes secondary pollution. Additionally, most of the Fenton systems are in homogeneous forms and suffer from intrinsically short lifetimes, hydroxyl radicals that have short diffusion distances (OH) and non-recyclability. Herein, using magnetic composites (Fe3O4@SiO2) as the carrier and vanadium oxide quantum dots (VOxQDs) as the catalyst, we developed a renewable, heterogeneous, magnetic Fenton-like system for dye degradation in polluted wastewater. The VOxQDs of less than 10 nm showed large specific surface areas, enhanced surface-exposed active atoms, and low toxicity, which are favourable for developing an efficient Fenton-like system. In addition, owing to the electrostatic adsorption between the as-prepared catalyst and the dye molecules, the distance for OH sterilization and decolorization can be significantly reduced, overcoming the shortcomings of the short oxidation distance of OH. Accordingly, the degradation of dyes can be achieved in five seconds. Furthermore, the catalysts can be effectively separated and recycled based on their magnetic features, while the secondary pollution from both the catalysts and the incompletely degraded dye molecules into the environment can be avoided. In addition, the Fe3O4@SiO2 is able to maintain a superior morphology, and the composite material (VOxQDs/Fe3O4@SiO2) maintains more than 90% of the degradation effects even after eight repeated tests.

Heterogeneous electro–Fenton using three–dimension NZVI–BC electrodes for degradation of neonicotinoid wastewater

Neonicotinoids (NEOs), as the most widely used pesticides, pose a serious threat to water ecosystems, especially clothianidin (CLO). However, the degradation behavior of CLO, as a new type of persistent organic pollutant, is rarely studied in wastewater treatment. To bridge this gap, heterogeneous electro-Fenton system using three-dimension electrodes made of biochar-supported zero-valent iron nanoparticle hybrid material (NZVI–BC), abbreviated as 3D–ICE–EF system, is invented and initially applied in CLO wastewater degradation, without the addition of Fenton reagent. NZVI–BC in 3D–ICE–EF system can concentrate CLO on electrodes by excellent adsorption and effectively eliminate it to achieve self-cleaning effect. In addition, the deposition of iron mud (Fe(OH)3) and the circular utilization of Fe in Fenton system is effectively improved by the addition of hydroquinone (HQ) in 3D–ICE–EF system. The pH applicable scope of Fenton system is extended to alkaline condition by the applications of NZVI–BC electrodes. The increase in the acidity of electrolyte is considered the primary reason of the high degradation efficiency of CLO in 3D–ICE–EF system at an initial pH of 9.0. The degradation performance of 3D–ICE–EF system tends to be promoted by the increase of current intensity and air flow rate. Seven plausible mechanisms of CLO degradation were identified in 3D–ICE–EF system. The ecotoxicity evaluation of degradation products indicated that CLO degradation in 3D–ICE–EF system exhibits a remarkable tendency to reduce toxicity levels.

Treatment for high-concentration liquid crystal wastewater with a novel Fenton-SBR-microwave pyrolysis integrated process.

A novel Fenton-SBR-microwave pyrolysis integrated process is developed to treat liquid crystal wastewater possessing complex components, high toxicity and strong stability. In this integrated process, Fenton-SBR and microwave pyrolysis are for the removal of chemical oxygen demand (COD) and disposal of iron mud generated in the Fenton process respectively. The effects of H2O2:Fe2+ molar ratio and Fenton dosage on COD removal were optimized. The experimental results revealed that the removal efficiencies for COD and total organic carbon (TOC) were 99.8% and 99.2%, and the values for MLSS and SVI were stable at 4,500 mg L-1 and 65%, respectively. Microscopic examination proved that there were rotifer, Epistylis galea, Opercularia coarctata, vorticella and mormon genus which are indicative microbes for good water quality. Iron mud waste produced in the Fenton reaction was handled with microwave pyrolysis, producing ɑ-Fe2O3 commercial byproduct. The estimated cost including chemical reagents and electricity for this integrated process is about $320 T-1, without consideration of the added value of the ɑ-Fe2O3 byproduct. TOC removals in the Fenton and SBR processes both fit well with pseudo-first-order kinetics and the corresponding half-life times are 0.15 and 7 h, respectively.