Degradation Of Monochlorobenzene Research Articles

The interface mechanism of ball-milled natural pyrite activating persulfate to degrade monochlorobenzene in soil: Intrinsic synergism of S and Fe species

Ball-milled natural pyrite has been proven to be an efficient and economical catalyst for persulfate (PDS) activation; however, the synergistic interface mechanism between S and Fe species transformation remains a large challenge. Herein, ball-milled pyrite was used in the degradation of monochlorobenzene (MCB) from soil, and the surface characteristics and identification of the S and Fe species in the ball-milled natural pyrite during the Fenton-like reaction were reported. The pyrite/PDS system was found to eliminate 93.8 % of the 95.6 mg/kg MCB in the soil. Ball milling changed the fundamental pathway of reactive species (RS) generation, and the FeIV contribution increased to 33.0 % for MCB degradation. Compared with heterogeneous activation, homogeneous activation induced by dissolved Fe(II) played an important role. Self-oxidation induced by sulfur vacancy sites (SVs) also occurred during MCB degradation (30.8 %). An exploration of the mechanism of the interfacial reaction at the microscopic level revealed that ball milling promoted the formation of SVs and increased the reducibility of S(-II) on pyrite, thus accelerating Fe(III) reduction and Fe(II) dissolution, limiting the generation of an Fe(III) passivation layer at the pyrite–water interface and promoting RS generation for MCB degradation. These findings provide new insights into the interface mechanism for PDS activation in a ball-milled pyrite/PDS system.

Significant roles of surface functional groups and Fe/Co redox reactions on peroxymonosulfate activation by hydrochar-supported cobalt ferrite for simultaneous degradation of monochlorobenzene and p-chloroaniline

CoFe2O4/hydrochar composites (FeCo@HC) were synthesized via a facile one-step hydrothermal method and utilized to activate peroxymonosulfate (PMS) for simultaneous degradation of monochlorobenzene (MCB) and p-chloroaniline (PCA). Additionally, the effects of humic acid, Cl-, HCO3-, H2PO4-, HPO42- and water matrices were investigated and degradation pathways of MCB and PCA were proposed. The removal efficiencies of MCB and PCA were higher in FeCo@HC140–10/PMS system obtained under hydrothermal temperature of 140 °C than FeCo@HC180–10/PMS and FeCo@HC220–10/PMS systems obtained under higher temperatures. Radical species (i.e., SO4•-, •OH) and nonradical pathways (i.e., 1O2, Fe (IV)/Co (IV) and electron transfer through surface FeCo@HC140–10/PMS* complex) co-occurred in the FeCo@HC140–10/PMS system, while radical and nonradical pathways were dominant in degrading MCB and PCA respectively. The surface functional groups (i.e., C-OH and CO) and Fe/Co redox cycles played crucial roles in the PMS activation. MCB degradation was significantly inhibited in the mixed MCB/PCA solution over that in the single MCB solution, whereas PCA degradation was slightly promoted in the mixed MCB/PCA solution. These findings are significant for the provision of a low-cost and environmentally-benign synthesis of bimetal-hydrochar composites and more detailed understanding of the related mechanisms on PMS activation for simultaneous removal of the mixed contaminants in groundwater.

Cysteine enhanced degradation of monochlorobenzene in groundwater by ferrous iron/persulfate process: Impacts of matrix species and toxicity evaluation in ISCO

Monochlorobenzene (MCB), a solvent and synthetic intermediate, has been widely detected in groundwater at industrial contaminated sites. Cysteine (Cys) enhanced Fe2+/persulfate (Fe2+/Cys/PS) process with high degradation efficiency of organic pollutants has the potential for in-situ chemical oxidation of MCB. In this study, we systematically explored the impacts of common anions (CO32−, HCO3−, SO42−, NO3−, NO2−, PO43−, HPO42−, H2PO4−, Cl−, Br−), cations (NH4+, Mg2+, Al3+, Mn2+, Cu2+) and natural organic matter (NOM) on the degradation kinetics of MCB by the novel Fe2+/Cys/PS process and evaluated the ecotoxicity. The results showed that the removal of MCB in absence of matrices was enhanced by Cys due to its reduction and complexation ability. All of the anions inhibited the MCB degradation through the scavenging of SO4•− and HO•, though the inhibition degree of SO42−and NO3− was slight. Cations such as NH4+, Mg2+ and Al3+ hardly interfered with the reaction. Low concentrations of Cu2+ and NOM promoted the MCB oxidation, but the promotion strength weakened and turned into inhibition with the increased concentration of Cu2+ and NOM. The toxicity assessment of the transformation products (TPs) in the presence of Cl− and Br− based on the quantitative structure-activity relationships model showed the potentially higher toxicity of some TPs than their parent MCB. These results indicate that groundwater matrices may interfere with the MCB oxidation process. To accurately evaluate the effects of groundwater matrices on Fe2+/Cys/PS process for MCB oxidation and its potential toxicity, the field tests should be carried out in the future.

Mechanistic insights into adsorptive and oxidative removal of monochlorobenzene in biochar-supported nanoscale zero-valent iron/persulfate system

Nanoscale zero-valent iron (nZVI) supported on rice stalk (RS) derived biochar composite (nZVI/RS) was synthesized as persulfate (PS) activator, achieving efficient adsorptive and catalytically oxidative removal for monochlorobenzene (MCB). Development of porous structures and enhanced aromaticity of RS with increased pyrolysis temperatures promoted MCB adsorption, with removal efficiencies of MCB rising from 11.2% for nZVI/RS300 to 72.3% for nZVI/RS700 after the adsorption for 14 h. The best PS activation performance was achieved for nZVI/RS500, with MCB removal efficiency being further increased to 98.8% after the oxidation for 3 h and reaction stoichiometric efficiency (RSE) reaching a maximum of 4.1% under conditions of 0.2 g·L−1 nZVI/RS500, 50.0 μM MCB, 2.0 mM PS and pH0 6.5. The pre-adsorption of MCB was a rate-promoting step in the oxidative degradation processes within the nZVI/RS-PS systems under low RS pyrolysis temperatures (<500 °C). However, excessive adsorptive capacity of nZVI/RS600 and nZVI/RS700 induced blocking of the active sites and low PS activation efficiencies. In addition to transformation of nZVI and surface functional groups on RS500, electron transfer from sp2 hybridized carbon enhanced by internal electron migration of sp3-sp2 hybridized carbon was also responsible for PS activation, producing SO4•−, ·OH and 1O2 for MCB degradation through both radical and nonradical pathways. Six degradation intermediates were identified with possible degradation pathways of MCB in the nZVI/RS500-PS system being proposed. Additionally, 80.2% and 67.4% of MCB removal rates were achieved in tap water and groundwater contaminated by MCB respectively. These findings have significant implications for the synthesis and application of metal-carbon composite based multifunctional materials with strong adsorption and catalytic potential for activating PS to completely remove organic contaminants in groundwater.

Enhanced degradation of monochlorobenzene in groundwater by ferrous iron/persulfate process with cysteine

Monochlorobenzene (MCB) pollution in the groundwater has attracted extensive attention due to its high toxicity and refractory. Ferrous-activated persulfate process (Fe2+/PS) is feasible to degrade MCB; however, the slow redox cycle of Fe2+/Fe3+ and the narrow valid pH range limit its application. In this study, cysteine (Cys) cooperating with the Fe2+/PS process (Fe2+/Cys/PS) can be employed to enhance the MCB degradation owing to its reduction and complexation ability, in which the effects of Cys, Fe2+, PS concentrations, and the value of pH were evaluated. Existences of sulfate radicals (SO4−) and hydroxyl radicals (HO) were confirmed by radical scavenger tests and Electron paramagnetic resonance (EPR) studies, in which HO was mainly responsible for MCB degradation in Fe2+/Cys/PS process. According to the aforementioned results, a potential mechanism and a plausible pathway of MCB degradation were proposed. The Fe2+/Cys complex can be repeatedly reused in practical applications. Likewise, the excellent performance of Fe2+/Cys/PS process in the degradation of MCB was also observed in the real groundwater. In summary, the novel Fe2+/Cys/PS process might provide a potentially effective technique for remediation of organic-contaminated groundwater.

Degradation of benzene derivatives in the CuMgFe-LDO/persulfate system: The role of the interaction between the catalyst and target pollutants

A novel insight on the role of interactions between target pollutants and the catalyst in the copper-containing layered double oxide (LDO)-catalyzed persulfate (PS) system was elucidated in the present study. 4-Chlorophenol (4-CP), as a representative benzene derivative with a hydroxyl group, was completely removed within 5 min, which was much faster than the reaction of monochlorobenzene (MCB) without a hydroxyl group, with the degradation efficiency of 31.7% in 240 min. Through the use of radical quenching and surface inhibition experiments, it could be concluded that the interaction between 4-CP and CuMgFe-LDO, rather than free radicals, played a key role in the decomposition of 4-CP, while only the free radicals participated in the MCB degradation process. According to electron paramagnetic resonance and X-ray photoelectron spectroscopy data, the formation of a Cu(II)-complex between phenolic hydroxyl groups and surface Cu(II) was primarily responsible for the degradation of phenolic compounds, in which PS accepted one electron from the complex and generated sulfate radicals and chelated radical cations. The chelated radical cations transferred one electron to Cu(II) followed by Cu(I) generation and pollutant degradation successively.

Compound-Specific Isotope Analysis (CSIA) Application for Source Apportionment and Natural Attenuation Assessment of Chlorinated Benzenes

In light of the complex management of chlorobenzene (CB) contaminated sites, at which a hydraulic barrier (HB) for plumes containment is emplaced, compound-specific stable isotope analysis (CSIA) has been applied for source apportionment, for investigating the relation between the upgradient and downgradient of the HB, and to target potential CB biodegradation processes. The isotope signature of all the components potentially involved in the degradation processes has been expressed using the concentration-weighted average δ13C of CBs + benzene (δ13Csum). Upgradient of the HB, the average δ13Csum of −25.6‰ and −29.4‰ were measured for plumes within the eastern and western sectors, respectively. Similar values were observed for the potential sources, with δ13Csum values of −26.5‰ for contaminated soils and −29.8‰ for the processing water pipeline in the eastern and western sectors, respectively, allowing for apportioning of these potential sources to the respective contaminant plumes. For the downgradient of the HB, similar CB concentrations but enriched δ13Csum values between −24.5‰ and −25.9‰ were measured. Moreover, contaminated soils showed a similar δ13Csum signature of −24.5‰, thus suggesting that the plumes likely originate from past activities located in the downgradient of the HB. Within the industrial property, significant δ13C enrichments were measured for 1,2,4-trichlorobenzene (TCB), 1,2-dichlorobenzene (DCB), 1,3-DCB, and 1,4-DCBs, thus suggesting an important role for anaerobic biodegradation. Further degradation of monochlorobenzene (MCB) and benzene was also demonstrated. CSIA was confirmed to be an effective approach for site characterization, revealing the proper functioning of the HB and demonstrating the important role of natural attenuation processes in reducing the contamination upgradient of the HB.

Iron oxides stimulate microbial monochlorobenzene in situ transformation in constructed wetlands and laboratory systems

Natural wetlands are transition zones between anoxic ground and oxic surface water which may enhance the (bio)transformation potential for recalcitrant chloro-organic contaminants due to the unique geochemical conditions and gradients. Monochlorobenzene (MCB) is a frequently detected groundwater contaminant which is toxic and was thought to be persistent under anoxic conditions. Furthermore, to date, no degradation pathways for anoxic MCB removal have been proven in the field. Hence, it is important to investigate MCB biodegradation in the environment, as groundwater is an important drinking water source in many European countries. Therefore, two pilot-scale horizontal subsurface-flow constructed wetlands, planted and unplanted, were used to investigate the processes in situ contributing to the biotransformation of MCB in these gradient systems. The wetlands were fed with anoxic MCB-contaminated groundwater from a nearby aquifer in Bitterfeld, Germany. An overall MCB removal was observed in both wetlands, whereas just 10% of the original MCB inflow concentration was detected in the ponds. In particular in the gravel bed of the planted wetland, MCB removal was highest in summer season with 73±9% compared to the unplanted one with 40±5%. Whereas the MCB concentrations rapidly decreased in the transition zone of unplanted gravel to the pond, a significant MCB removal was already determined in the anoxic gravel bed of the planted system. The investigation of hydro-geochemical parameters revealed that iron and sulphate reduction were relevant redox processes in both wetlands. In parallel, the addition of ferric iron or nitrate stimulated the mineralisation of MCB in laboratory microcosms with anoxic groundwater from the same source, indicating that the potential for anaerobic microbial degradation of MCB is present at the field site.

APPLICATION OF MODIFIED NANONATURALLY MONTMORILLONITE IN MONOCHLOROBENZENE REMEDIATION IN RIVER WATER

As the inland waterway transportation developed rapidly in China, the frequency of hazardous chemical leakage accidents is increasing every year. Such pollution to inland river environment has become a world-wide issue. Montmorillonite (Mont) is typical 2:1 layer type silicate clay and due to their special structure, it has been used in organic pollution removal process. In order to improve their ability in pollution adsorption, the pillared Mont was made in this work. Since the common toxic structure in most chemical pollutants is the halogen atom-benzene ring part, we select a typical compound Monochlorobenzene (MCB) as the aim contaminant. In this research, the original Mont, Na –Mont, TiO2 and TiO2 –Mont were prepared and used in MCB degradation experiment as catalysts. The influence of catalyst amount, promoter ( H2O2 ) amount, MCB concentration and reaction time to MCB removal rate were studied, respectively in detail.

Effect of Oxygen and Hydrogen Peroxide on the Photocatalytic Degradation of Monochlorobenzene in Aqueous Suspension

The influences of oxygen and hydrogen peroxide () on the degradation and mineralization of monochlorobenzene (MCB) during UV/ process were investigated. Experimental results indicated that oxygen was a determining parameter for promoting the photocatalytic degradation. The presence of oxygen reduced the illumination time needed for the complete decay of MCB from 240 to 120 min. The photocatalytic degradation of MCB in UV// photocatalysis followed a simplified two-step consecutive kinetics. The rate constants of degradation () and mineralization () were increased from 0.016 to 0.046 min−1and from 0.001 to 0.006 min−1, respectively, as the initial concentration of dissolved oxygen (DO) was increased from 1.6 to 28.3 mg L−1. Owing to the fact that acted as an electron and hydroxyl radicals () scavenger, the addition of should in a proper dosage range to enhance the degradation and mineralization of MCB. The optimal dosage for MCB degradation was 22.5 mg L−1, whereas the most efficient dosage for MCB mineralization was 45.0 mg L−1. In order to minimize the adverse effects of higher dosage, including the capture of radicals and competitive adsorption, and to improve the photocatalytic degradation of MCB, the sequential replenishment of was suggested. For the stepwise addition of a total dosage of 45.0 mg L−1, a complete destruction of MCB was observed within 120 min of irradiation. Additionally, the mineralization efficiency was about 87.4% after 240 min of illumination time.

Influence of water flux and redox conditions on chlorobenzene concentrations in a contaminated streambed

AbstractSignificant natural attenuation may occur on the passage of groundwater plumes through streambed sediments because of the transition from anaerobic to aerobic conditions and an increased microbial activity. Varying directions and magnitudes of water flow in the streambed may enhance or inhibit the supply of oxygen to the streambed and thus influence the redox zoning. In a field study at a small stream in the industrial area of Bitterfeld‐Wolfen, we observed the variability of hydraulic gradients, streambed temperatures, redox conditions and monochlorobenzene (MCB) concentrations in the streambed over the course of 5 months. During the observation period, the hydrologic conditions changed from losing to gaining. Accordingly, the temperature‐derived water fluxes changed from recharge to discharge. Redox conditions were highly variable between − 170 and 368 mV in the shallow streambed at a depth of 0·1 m below the streambed surface. Deeper in the streambed, at depths of 0·3 m and 0·5 m, the redox conditions were more stable between − 198 and − 81 mV and comparable to those typically found in the aquifer. MCB concentrations in the streambed at 0·3 and 0·5 m depth increased with increasing upward water flux. The MCB concentrations in the shallow streambed at 0·1 m depth appeared to be independent of the hydrologic conditions suggesting that degradation of MCB may have occured. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Heterogeneous photocatalytic degradation of monochlorobenzene in water

This investigation evaluated the photocatalytic degradation of monochlorobenzene (MCB) in an aqueous TiO 2 suspension. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO 2 dosage. However, the solution pH had insignificant effect on the degradation efficiency. The heterogeneous photocatalytic degradation of MCB followed the Langmuir–Hinshelwood kinetics. The adsorption coefficient of MCB ( K) and the observed degradation rate constant ( k) were calculated as 13.4 mM −1 and 0.0054 mM min −1, respectively. In addition, a 0.255 dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e −–h + pair recombination. Both mineralization and dechlorination occurred during the photocatalytic degradation of MCB. Under the operating condition of initial MCB concentration of 0.1 mM, light intensity of 5.68 μEinstein s −1, TiO 2 dosage of 1.0 g L −1, and solution pH of 7, about 93.7% of MCB was mineralized after 240 min of irradiation. Nevertheless, 64.3% of the stoichiometric amount of Cl − ions was released into the bulk solution. The simulation results derived from the X-ray photoelectron spectroscopy (XPS) analysis was suggested that the interaction between Cl − ions and TiO 2 surface tended to lower the released amount of Cl − ions.

Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase

The reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO 2 process, including substrate adsorption, degradation, and mineralization, was studied. The theoretical maximum quantity of MCB that could be adsorbed onto TiO 2 surface in aqueous phase was 0.18 ± 0.04 μmol m −2 of TiO 2. In accordance with the upper limit of the relative surface coverage of MCB molecules to surface hydroxyls of TiO 2 was around 2.2%, the water molecules as the major adjacent species near TiO 2 surface would compete with MCB molecules. Increasing the initial substrate concentration to an appropriate value or enhancing the affinity between the MCB and the TiO 2 surface by adjusting the solution pH would promote the photocatalytic degradation. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition. Generally, 90% of the total organic carbon (TOC) was mineralized after 240 min illumination time in the examined pH range except solution pH 11. The suppressed mineralization of MCB at solution pH 11 was ascribed to the lack of adsorption. A simplified 2-step consecutive kinetic model was used to simulate the mineralization.

Biodegradation of chlorobenzene in a constructed wetland treating contaminated groundwater

Monochlorobenzene (MCB) is an important groundwater contaminant world-wide. In this study, a horizontal subsurface flow constructed wetland with an integrated water compartment was fed with MCB contaminated groundwater originating from the local aquifer. Analysis of spatial concentration dynamics of MCB and oxygen was combined with isotope composition analysis of MCB for assessing in situ biodegradation. Removal of MCB was most effective in the upper layer of the soil filter, reaching up to 77.1%. Trace oxygen concentrations below 0.16 mg L(-1) were observed throughout the wetland transect, suggesting a considerable limitation of aerobic microbial MCB degradation. Enrichment of 13C in the residual MCB fraction at increasing distance from the inflow point indicated microbial MCB degradation in the wetland. The observed isotope shift was higher than expected for aerobic MCB degradation and thus pointed out a significant contribution of an anaerobic degradation pathway to the overall biodegradation.

Assessment of in situ biodegradation of monochlorobenzene in contaminated groundwater treated in a constructed wetland

The degradation of monochlorobenzene (MCB) was assessed in a constructed wetland treating MCB contaminated groundwater using a detailed geochemical characterisation, stable isotope composition analysis and in situ microcosm experiments. A correlation between ferrous iron mobilisation, decreasing MCB concentration and enrichment in carbon isotope composition was visible at increasing distance from the inflow point, indicating biodegradation of MCB in the wetland. Additionally, in situ microcosm systems loaded with 13C-labelled MCB were deployed for the first time in sediments to investigate the biotransformation of MCB. Incorporation of 13C-labelled carbon derived from the MCB into bacterial fatty acids substantiated in situ degradation of MCB. The detection of 13C-labelled benzene indicated reductive dehalogenation of MCB. This integrated approach indicated the natural attenuation of the MCB in a wetland system. Further investigations are required to document and optimise the in situ biodegradation of MCB in constructed and natural wetland systems treating contaminated groundwater.

Isotopic fractionation indicates anaerobic monochlorobenzene biodegradation

The concentration and isotopic composition of monochlorobenzene (MCB) was monitored in the plume of an anaerobic, contaminated aquifer in Bitterfeld, Germany. An enrichment in the carbon isotopic composition of more than 4 delta units was found at the fringes of the plume relative to the center (-26.5 %), suggesting the occurrence of in situ biodegradation of MCB. A similar enrichment was measured in a detailed cross-section of the plume and in depth-specific samples obtained in a multilevel sampling well. The latter samples gave a good correlation of MCB concentrations and respective isotopic composition according to the Rayleigh equation. On the other hand, batch experiments using the aerobic MCB-degrading strains Ralstonia sp. DSM 8910, Acidovorax facilis UFZ B517, Rhodococcus erythropolis UFZ B528, and Pseudomonas veronii UFZ B547 showed that the known aerobic pathway initiated by dioxygenases does not result in a significant isotopic fractionation. Thus, a novel anaerobic pathway resulting in an isotopic fractionation appears to be the predominant process of MCB degradation in this aquifer. The study also clearly demonstrates the usefulness of isotopic fractionation analysis to prove biodegradation directly in the field, even when microcosm studies are not available and a metabolic pathway has not yet been elucidated.

Chlorobenzene biodegradation under consecutive aerobic–anaerobic conditions

The biodegradation of monochlorobenzene, the main contaminant in a quaternary aquifer at Bitterfeld, Central Germany, was studied in microcosm experiments employing either original groundwater or defined mineral media together with the indigenous microbial community from the polluted site. The impact of consecutive aerobic–anaerobic–aerobic incubations on monochlorobenzene biodegradation, microbial diversity, and pH development was examined. The related changes in microbial community composition were analyzed by 16S rRNA gene-based single-strand conformation polymorphism (SSCP) fingerprints and sequencing of dominant bands and by quantitative analysis of bacterial respiratory chain quinones as biomarkers. Under aerobic conditions, the indigenous microbial community of the groundwater degraded monochlorobenzene mainly via the modified ortho-pathway. Respiratory chain quinones and SSCP analysis suggested dominance of the genera Acidovorax and Pseudomonas. A shift to anoxic conditions resulted in monochlorobenzene biotransformation but no dechlorination. The ability to degrade monochlorobenzene aerobically remained preserved throughout a fortnightly anoxic period at sufficiently high buffer capacity. Acidification, caused by monochlorobenzene biodegradation, was alkalinity-controlled. At low initial alkalinity a substantial decrease in pH, monochlorobenzene degradation, and total counts of live cells, accompanied by a change of the microbial community composition, was observed.

Degradation of chlorobenzenes in soil slurry by a specialized organism.

The microbial degradation of monochloro-, 1,2-dichloro-, 1,4-dichloro-, and 1,2,4-trichlorobenzene in soil slurries was examined with single compounds as well as in mixtures. The indigenous soil populations brought about the degradation of monochlorobenzene when incubated at 27 degrees C in slurries with 29% (w/w) suspended solids. In contrast, the other chlorobenzenes persisted during an incubation period of 1 month. Supplementation with buffer, mineral salts and acetate did not significantly influence the degradation. However, inoculation with Pseudomonas aeruginosa strain RHO1, a monochloro- and 1,4-dichlorobenzene-degrading organism, to a titre of 1 x 10(5) cells/g soil, led to rapid and complete degradation of 0.8 mM growth substrate within 30 h. In addition, the strain was able to degrade 1,2-dichloro- and 1,2,4-trichlorobenzene with stoichiometric release of chloride in the presence of acetate, ethanol, monochloro- or 1,4-dichlorobenzene as growth substrates. In mixtures of chlorobenzenes the co-metabolism of 1,2-dichloro- and 1,2,4-trichlorobenzene occurred until the growth substrates monochloro- and 1,4-dichlorobenzene were degraded. The degradation was faster in the slurries of garden soil containing 8% organic carbon than in soil with the lower content of 2.6%.