Effective adsorbent for arsenic removal: core/shell structural nano zero-valent iron/manganese oxide

Recently, nano zero-valent iron (nZVI) has emerged as an effective adsorbent for the removal of arsenic from aqueous solutions. However, its use in various applications has suffered from reactivity loss resulting in a decreased efficiency. Thus, the aim of this study was to develop an effective arsenic adsorbent as a core/shell structural nZVI/manganese oxide (or nZVI/Mn oxide) to minimize the reactivity loss of the nZVI. As the major result, the arsenic adsorption capacities of the nZVI/Mn oxide for As(V) and As(III) were approximately two and three times higher than that of the nZVI, respectively. In addition, the As(V) removal efficiency of the nZVI/Mn oxide was maintained through 4 cycles of regeneration whereas that of the nZVI was decreased significantly. The enhanced reactivity and reusability of the nZVI/Mn oxide can be successfully explained by the synergistic interaction of the nZVI core and manganese oxide shell, in which the manganese oxides participate in oxidation reactions with corroded Fe²⁺ and subsequently retard the release of aqueous iron providing additional surface sites for arsenic adsorption. In summary, this study reports the successful fabrication of a core/shell nZVI/Mn oxide as an effective adsorbent for the removal of arsenic from aqueous solutions.     

Influence of Na2S on the degradation kinetics of CCl4 in the presence of very pure iron

This paper presents the results of kinetic studies to investigate the effect of FeS film formation on the degradation rate of CCl(4) by 99.99% pure metallic iron. The film was formed by submersing metallic iron grains in an oxygen free HCO(3)(-)/CO(3)(2-) electrolyte solution. When the grains had reached a quasi steady-state value of the corrosion potential, Na(2)S((aq)) was injected. Upon injection, a microm thick poorly crystalline FeS film formed immediately on the iron surface. Over time, the iron became strongly corroded and both the FeS film and the metallic iron grains began to crack leading to exposure of bare metallic iron to the solution. The effect of the surface film on the degradation rate of CCl(4) was investigated following four periods of aging, 1, 10, 30, and 60 days. Relative to the controls, the 1-day sulfide-aged iron showed a substantial decrease in rate of degradation of CCl(4.) However, over time, the rate of degradation increased and surpassed the degradation rate obtained in the controls. It has been proposed that CCl(4) is reduced to HCCl(3) by metallic iron by electron transfer. The FeS film is substantially less conducting than the bulk iron metal or non-stoichiometric magnetite and from the results of this study, greatly decreases the rate of CCl(4) degradation relative to iron that has not been exposed to Na(2)S. However, continued aging of the FeS film results in breakdown and stress-induced cracking of the film, followed by dissolution and cracking of the iron itself. The cracking of the bulk iron is believed to be a consequence of hydrogen embrittlement, which is promoted by sulfide. The increase in CCl(4) degradation rate, as the FeS films age, suggests that the process of hydrogen cracking increases the surface area available for charge transfer.     

Acceleration of the Fe(III)EDTA(-) reduction rate in BioDeNO(x) reactors by dosing electron mediating compounds

BioDeNO(x), a novel technique to remove NO(x) from industrial flue gases, is based on absorption of gaseous nitric oxide into an aqueous Fe(II)EDTA(2-) solution, followed by the biological reduction of Fe(II)EDTA(2-) complexed NO to N(2). Besides NO reduction, high rate biological Fe(III)EDTA(-) reduction is a crucial factor for a succesful application of the BioDeNO(x) technology, as it determines the Fe(II)EDTA(2-) concentration in the scrubber liquor and thus the efficiency of NO removal from the gas phase. This paper investigates the mechanism and kinetics of biological Fe(III)EDTA(-) reduction by unadapted anaerobic methanogenic sludge and BioDeNO(x) reactor mixed liquor. The influence of different electron donors, electron mediating compounds and CaSO(3) on the Fe(III)EDTA(-) reduction rate was determined in batch experiments (21mM Fe(III)EDTA(-), 55 degrees C, pH 7.2+/-0.2). The Fe(III)EDTA(-) reduction rate depended on the type of electron donor, the highest rate (13.9mMh(-1)) was observed with glucose, followed by ethanol, acetate and hydrogen. Fe(III)EDTA(-) reduction occurred at a relatively slow (4.1mMh(-1)) rate with methanol as the electron donor. Small amounts (0.5mM) of sulfide, cysteine or elemental sulfur accelerated the Fe(III)EDTA(-) reduction. The amount of iron reduced significantly exceeded the amount that can be formed by the chemical reaction of sulfide with Fe(III)EDTA(-), suggesting that the Fe(III)EDTA(-) reduction was accelerated via an auto-catalytic process with an unidentified electron mediating compound, presumably polysulfides, formed out of the sulfur additives. Using ethanol as electron donor, the specific Fe(III)EDTA(-) reduction rate was linearly related to the amount of sulfide supplied. CaSO(3) (0.5-100mM) inhibited Fe(III)EDTA(-) reduction, probably because SO(3)(2-) scavenged the electron mediating compound.     

The influence of iron and sulfur mineral fractions on carbon tetrachloride transformation in model anaerobic soils and sediments

The objective of this research was to identify the dissolved species or solid phase mineral fraction(s) best correlated with rates of carbon tetrachloride (CT) reductive transformation in systems modeling sulfate-reducing and iron oxide-rich soils and sediments. We used sulfide (S(-II))-treated goethite as our model system, but also studied Fe(II) and S(-II)-treated goethite, Fe(II)-treated goethite, pure FeS, and Fe(II)-treated FeS in order to isolate and evaluate the influence of different mineral fractions on reaction rates. Initial rates of CT transformation were measured for different pH values and concentrations of added Fe(II), as well as different aging times and conditions. The following dissolved species and iron and sulfur mineral fractions were quantified and compared with CT transformation rates: aqueous Fe(2+) and S(-II), surface associated Fe(II) (including weakly and strongly bound Fe(II)), FeS(s), and Cr(II) reducible solid phase S. Over the pH range of 6-10, CT transformation rates were correlated with surface associated Fe(II), while at pH 8, rates were correlated with weakly bound Fe(II). Aging of S(-II)-treated goethite led to oxidation of surface sulfur and a change in the concentration of weakly bound Fe(II), but did not change the relationship between initial rates and weakly bound Fe(II). The results of this research suggest that surface associated Fe(II) and weakly bound Fe(II) could serve as indicators of the potential for abiotic CT dechlorination in natural soils under sulfate-reducing conditions.     

Zero-valent iron nanoparticles in treatment of acid mine water from in situ uranium leaching

Acid mine water from in situ chemical leaching of uranium (Straz pod Ralskem, Czech Republic) was treated in laboratory scale experiments by zero-valent iron nanoparticles (nZVI). For the first time, nZVI were applied for the treatment of the real acid water system containing the miscellaneous mixture of pollutants, where the various removal mechanisms occur simultaneously. Toxicity of the treated saline acid water is caused by major contaminants represented by aluminum and sulphates in a high concentration, as well as by microcontaminants like As, Be, Cd, Cr, Cu, Ni, U, V, and Zn. Laboratory batch experiments proved a significant decrease in concentrations of all the monitored pollutants due to an increase in pH and a decrease in oxidation-reduction potential related to an application of nZVI. The assumed mechanisms of contaminants removal include precipitation of cations in a lower oxidation state, precipitation caused by a simple pH increase and co-precipitation with the formed iron oxyhydroxides. The possibility to control the reaction kinetics through the nature of the surface stabilizing shell (polymer vs. FeO nanolayer) is discussed as an important practical aspect.     

The impact of zero-valent iron nanoparticles upon soil microbial communities is context dependent

Nanosized zero-valent iron (nZVI) is an effective land remediation tool, but there remains little information regarding its impact upon and interactions with the soil microbial community. nZVI stabilised with sodium carboxymethyl cellulose was applied to soils of three contrasting textures and organic matter contents to determine impacts on soil microbial biomass, phenotypic (phospholipid fatty acid (PLFA)), and functional (multiple substrate-induced respiration (MSIR)) profiles. The nZVI significantly reduced microbial biomass by 29 % but only where soil was amended with 5 % straw. Effects of nZVI on MSIR profiles were only evident in the clay soils and were independent of organic matter content. PLFA profiling indicated that the soil microbial community structure in sandy soils were apparently the most, and clay soils the least, vulnerable to nZVI suggesting a protective effect imparted by clays. Evidence of nZVI bactericidal effects on Gram-negative bacteria and a potential reduction of arbuscular mycorrhizal fungi are presented. Data imply that the impact of nZVI on soil microbial communities is dependent on organic matter content and soil mineral type. Thereby, evaluations of nZVI toxicity on soil microbial communities should consider context. The reduction of AM fungi following nZVI application may have implications for land remediation.     

Abiotic transformation of DDT in aqueous solutions

Significant concentrations of chlorinated pesticides such as 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) and its two main transformation products, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD) and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE) are still present in soil and sediment systems more than 30 years after DDT use was banned in the United States. DDT enters waterways via the runoff from industrial point sources, agricultural lands and atmospheric deposition. We evaluated zero-valent iron (Fe(0)), ferrous sulfide (FeS), as well as combining them with hydrogen peroxide (H(2)O(2)) as viable treatment technologies for degrading DDT in an aqueous solution. Treatment of DDT with Fe(0) and FeS resulted in approximately 88% and 56% transformation of DDT within 150h, respectively. DDE production was insignificant in all systems. The DDT removal was slower with FeS than with Fe(0), but the amounts of DDD and DDE produced did not exceed baseline. Treatment with a 1:1 mixture of Fe(0)-FeS removed about 95% of the added mass of DDT within 4days and generated significant amounts of DDD and minor amounts of DDMU. When small amounts of H(2)O(2) were introduced halfway through the Fe(0) and FeS treatment times, the mass of DDT decreased by 87% and 96%, respectively, within 2days. Our results demonstrate that mixtures of Fe(0)-FeS in combination with H(2)O(2) can be used for rapid and efficient removal of DDT from aqueous solutions.     

Removal of As,Mn, Mo,Se, U,V and Zn from groundwater by zero-valent iron in a passive treatment cell: reaction progress modeling

Three treatment cells were operated at a site near Durango, CO. One treatment cell operated for more than 3 years. The treatment cells were used for passive removal of contamination from groundwater at a uranium mill tailings repository site. Zero-valent iron [Fe(0)] that had been powdered, bound with aluminosilicate and molded into plates was used as a reactive material in one treatment cell. The others used granular Fe(0) and steel wool. The treatment cells significantly reduced concentrations of As, Mn, Mo, Se, U, V and Zn in groundwater that flowed through it. Zero-valent iron [Fe(0)], magnetite (Fe3O4), calcite (CaCO3), goethite (FeOOH) and mixtures of contaminant-bearing phases were identified in the solid fraction of one treatment cell. A reaction progress approach was used to model chemical evolution of water chemistry as it reacted with the Fe(0). Precipitation of calcite, ferrous hydroxide [Fe(OH)2] and ferrous sulfide (FeS) were used to simulate observed changes in major-ion aqueous chemistry. The amount of reaction progress differed for each treatment cell. Changes in contaminant concentrations were consistent with precipitation of reduced oxides (UO2, V2O3), sulfides (As2S3, ZnS), iron minerals (FeSe2, FeMoO4) and carbonate (MnCO3). Formation of a free gas phase and precipitation of minerals contributed to loss of hydraulic conductivity in one treatment cell.     

Investigations on mobility of carbon colloid supported nanoscale zero-valent iron (nZVI) in a column experiment and a laboratory 2D-aquifer test system

Nanoscale zero-valent iron (nZVI) has recently gained great interest in the scientific community as in situ reagent for installation of permeable reactive barriers in aquifer systems, since nZVI is highly reactive with chlorinated compounds and may render them to harmless substances. However, nZVI has a high tendency to agglomerate and sediment; therefore it shows very limited transport ranges. One new approach to overcome the limited transport of nZVI in porous media is using a suited carrier colloid. In this study we tested mobility of a carbon colloid supported nZVI particle “Carbo-Iron Colloids” (CIC) with a mean size of 0.63 μm in a column experiment of 40 cm length and an experiment in a two-dimensional (2D) aquifer test system with dimensions of 110?×?40?×?5 cm. Results show a breakthrough maximum of 82 % of the input concentration in the column experiment and 58 % in the 2D-aquifer test system. Detected residuals in porous media suggest a strong particle deposition in the first centimeters and few depositions in the porous media in the further travel path. Overall, this suggests a high mobility in porous media which might be a significant enhancement compared to bare or polyanionic stabilized nZVI.     

Fractionation and extractability of sulfur, iron and trace elements in sulfidic sediments

This study describes iron and sulfur fractionation, and the related extractability of selected trace elements (As, Cd, Cr, Cu, Ni, Pb and Zn) in estuarine sediments. The sediments were sulfidic, with moderately high concentrations of pore-water sulfide (200-600 micromol l(-1)) and acid-volatile sulfide (AVS; 9.9-129 micromol g(-1)). Pyrite-S concentrations increased with depth, with 63-251 micromol g(-1) at site W1 and 312-669 micromol g(-1) at site W2. The degree of sulfidisation was generally high (>80%), indicating that Fe may be limiting pyrite accumulation. The ratios of AVS to pyrite-S increased with sediment depth, as expected for the pyritisation of solid-phase AVS. Cadmium, Pb and Zn extractability in 1M HCl indicated that these elements are not significantly sequestered during pyritisation, whereas sequestration may be important for As, Cu and possibly Ni. Extractability trends for Cr suggest that diagenesis in sulfidic sediments may enhance Cr reactivity. Overall, replacement of AVS by pyrite during diagenesis may enhance the reactivity of Cd, Cr, Pb and Zn, whereas As, Cu and possibly Ni may be rendered less reactive.     

Regeneration of iron for trichloroethylene reduction by Shewanella alga BrY

Zero valent iron (ZVI), the primary reactive material in several permeable reactive barriers, is often oxidized to ferrous or ferric iron, resulting in decreased reactivity with time. Iron reducing bacteria can reconvert the ferric iron to its ferrous form, prolonging the reduction of chlorinated organic contaminants. In this study, the reduction of Fe(II,III) oxide and Fe(III) oxide by a strain of iron reducing bacteria of the group Shewanella alga BrY(S. alga BrY) was observed in both aqueous and solid phases. S. alga BrY preferentially reduced dissolved ferric iron over the solid ferric iron. In the presence of iron oxide the Fe(II) ions reduced by S. alga BrY efficiently reduced trichloroethylene (TCE). On the other hand, Fe(II) produced by S. alga BrY covered the reactive surfaces of ZVI iron filings and inhibited the reduction of TCE by ZVI. The formation of precipitates on the iron oxide or Fe0 surface was confirmed by scanning electron microscopy. The results suggest that iron-reducing bacteria in the oxidized Fe0 barriers can enhance the removal rate of chlorinated organic compounds and influence on the long-term performance of Fe0 reactive barriers.     

Removal of gaseous elemental mercury by dielectric barrier discharge

The removal of elemental mercury (Hg(0)) with the reactive species produced from dielectric barrier discharge (DBD) was studied. The effects of the operating parameters, such as the applied voltage, residence time, initial concentration and co-existence of other pollutants, were investigated. The removal of Hg(0) was significantly promoted by an increase in the applied voltage of the DBD reactor system. The presence of NO gas decreased the Hg(0) removal efficiency within the range of input powers tested compared to the case of Hg(0)-only due to the competition for ozone between Hg(0) and NO gas in the DBD reactor.     

Deodorization of dimethyl sulfide using a discharge approach at room temperature

The traditional technologies for odor removal of thiol usually create either secondary pollution for scrubbing, adsorption, and absorption processes, or sulfur (S) poisoning for catalytic incineration. This study applied a laboratory-scale radio-frequency plasma reactor to destructive percentage-grade concentrations of odorous dimethyl sulfide (CH3SCH3, or DMS). Odor was diminished effectively via reforming DMS into mainly carbon disulfide (CS2) or sulfur dioxide (SO2). The removal efficiencies of DMS elevated significantly with a lower feeding concentration of DMS or a higher applied rf power. A greater inlet oxygen (O2)/DMS molar ratio slightly improved the removal efficiency. In an O2-free environment, DMS was converted primarily to CS2, methane (CH4), acetylene (C2H2), ethylene (C2H4), and hydrogen (H2), with traces of hydrogen sulfide (H2S), methyl mercaptan (CH3SH), and dimethyl disulfide. In an O2-containing environment, the species detected were SO2, CS2, carbonyl sulfide, carbon dioxide (CO2), CH4, C2H4, C2H2, H2, formaldehyde, and methanol. Differences in yield of products were functions of the amounts of added O2 and the applied power. This study provided useful information for gaining insight into the reaction pathways for the DMS dissociation and the formation of products in the plasmolysis and conversion processes.     

Removal of bisphenol A and some heavy metal ions by polydivinylbenzene magnetic latex particles

In this study, magnetic polydivinylbenzene latex particles MP_DVB with a core-shell structure were tested for the removal of bisphenol A (BPA), copper Cu(II), lead Pb(II), and zinc Zn(II) from aqueous solutions by a batch-adsorption technique. The effect of different parameters, such as initial concentration of pollutant, contact time, adsorbent dose, and initial pH solution on the adsorption of the different adsorbates considered was investigated. The adsorption of BPA, Cu(II), Pb(II), and Zn(II) was found to be fast, and the equilibrium was achieved within 30 min. The pH 5–5.5 was found to be the most suitable pH for metal removal. The presence of electrolytes and their increasing concentration reduced the metal adsorption capacity of the adsorbent. Whereas, the optimal pH for BPA adsorption was found 7, both hydrogen bonds and π–π interaction were thought responsible for the adsorption of BPA on MP_DVB. The adsorption kinetics of BPA, Cu(II), Pb(II), and Zn(II) were found to follow a pseudo-second-order kinetic model. Equilibrium data for BPA, Cu(II), Pb(II), and Zn(II) adsorption were fitted well by the Langmuir isotherm model. Furthermore, the desorption and regeneration studies have proven that MP_DVB can be employed repeatedly without impacting its adsorption capacity.     

Adsorption of hydrogen sulfide on montmorillonites modified with iron

Sodium-rich montmorillonite was modified with iron in order to introduce active centers for hydrogen sulfide adsorption. In the first modification, interlayer sodium cations were exchanged with iron. In another modification, iron oxocations were introduced to the clay surface. The most elaborated modification was based on doping of iron within the interlayer space of aluminum-pillared clay. The modified clay samples were tested as hydrogen sulfide adsorbents. Iron-doped samples showed a significant improvement in the capacity for H2S removal, despite of a noticeable decrease in microporosity compared to the initial pillared clay. The smallest capacity was obtained for the clay modified with iron oxocations. Variations in adsorption capacity are likely due to differences in the chemistry of iron species, degree of their dispersion on the surface, and accessibility of small pores for H2S molecule. The results suggest that on the surface of iron-modified clay hydrogen sulfide reacts with Fe(+3) forming sulfides or it is catalytically oxidized to SO2 on iron (hydro)oxides. Subsequent oxidation may lead to sulfate formation.     

Feasibility study on high-temperature sorption of hydrogen sulfide by natural soils

In this study, seven natural soils were tested for the sorption of hydrogen sulfide from coal gasification gas at high temperature. Results indicate that the LP natural soil has the best performance and the highest sulfur sorption capacity. After extracting free iron oxides, most natural soils have no sorption efficiency. The free iron oxides, therefore, proved to be the major components that react with hydrogen sulfide to form iron sulfides. The sulfur sorption capacity, either determined by EA or breakthrough time, is very close to the theoretical value based on the stoichiometric calculation with the content of free iron oxides. Moreover, the presence of CO is a positive effect while H2 is a negative effect. This can be explained via the water-shift reaction. On the basis of the results of temperature-programmed sulfidation (TPS), the starting temperature for the sorption of hydrogen sulfide is between 623-673 K. From the analyses of temperature-programmed oxidation (TPO) and XPS, the iron polysulfides are the major products and approximately 90% regeneration efficiency can be theoretically achieved while the temperature is controlled higher than 813 K. In the regeneration tests, the results show that the LP natural soil can be regenerated and thus reused after the oxidation process. No significant degeneration occurs on the LP natural soil after five sorption/regeneration cycles. The sulfur sorption capacity of the tenth regenerated soil can be achieved at least 80% compared to the fresh one. The experimental analyzed SO2 concentration from the regeneration process is almost identical to the theoretical calculated equilibrium concentration of the process. Maghemite is the main product after the regeneration process.     

Heterogeneous Fenton oxidation of Direct Black G in dye effluent using functional kaolin-supported nanoscale zero iron

This study investigated kaolin-supported nanoscale zero-valent iron (nZVI/K) as a heterogeneous Fenton-like catalyst for the adsorption and oxidation of an azo dye, Direct Black G (DBG). New findings suggest that kaolin as a support material not only reduced the aggregation of nanoscale zero-valent iron (nZVI) but also improved the adsorption of DBG. It consequently improved Fenton oxidation by increasing the local concentration of DBG in the vicinity of nZVI. This was confirmed by scanning electron microscopy and X-ray diffraction for the surface morphology of nZVI/K before and after the Fenton-like reaction. Furthermore, nZVI/K proved to be a catalyst for the heterogeneous Fenton-like oxidation of the DBG process in the neutral pH range. More than 87.22 % of DBG was degraded, and 54.60 % of total organic carbon was removed in the optimal conditions: 0.6 g/L dosage of nZVI/K, 33 mM H₂O₂, 100 mg/L initial DBG concentration, temperature of 303 K and pH of 7.06. Finally, it was demonstrated that nZVI/K removed DBG from dye wastewater through the processes of adsorption and oxidation.     

Occurrence and abatement of volatile sulfur compounds during biogas production

Volatile sulfur compounds (VSCs) in biogas originating from a biogas production plant and from a municipal sewage water treatment plant were identified. Samples were taken at various stages of the biogas-producing process, including upgrading the gas to vehicle-fuel quality. Solid-phase microextraction was used for preconcentration of the VSCs, which were subsequently analyzed using gas chromatography in combination with mass spectrometry. Other volatile organic compounds present also were identified. The most commonly occurring VSCs in the biogas were hydrogen sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide, and hydrogen sulfide was not always the most abundant sulfur (S) compound. Besides VSCs, oxygenated organic compounds were commonly present (e.g., ketones, alcohols, and esters). The effect of adding iron chloride to the biogas reactor on the occurrence of VSCs also was investigated. It was found that additions of 500-g/m3 substrate gave an optimal removal of VSCs. Also, the use of a prefermentation step could reduce the amount of VSCs formed in the biogas process. Moreover, in the carbon dioxide scrubber used for upgrading the gas, VSCs were removed efficiently, leaving traces (ppbv levels). The scrubber also removed other organic compounds.     

不同粒径零价铁(ZVI)对污水污泥H2S和CH4释放速率的影响

考察了不同粒径零价铁(ZVI),包括200目普通铁粉(200m-ZVI)、800目超细铁粉(800m-ZVI)和纳米铁粉(nZVI,粒径=20 nm),对污水污泥的硫化氢和甲烷释放速率的影响。研究发现:(1)在22 d内,添加0.1%的200m-ZVI使污泥的硫化氢释放速率提高48.0%,而添加0.1%的800-ZVI和nZVI,则使污泥的硫化氢释放速率分别降低33.1%和77.1%;(2)不同粒径ZVI均可以提高污泥沼气中的甲烷浓度,且依次为nZVI>800m-ZVI>200m-ZVI;(3)在23 d内,添加0.1%的200m-ZVI和nZVI使污泥的甲烷累计产生量分别提高了15.5%和40.6%,而添加0.1%800m-ZVI则使甲烷产生量降低了12.5%。nZVI可以有效控制污泥的硫化氢释放,并显著提升污泥在厌氧发酵过程的产甲烷速率。     

Effect of initial sulfide concentration on sulfide and phenol oxidation under denitrifying conditions

The objective of this work was to evaluate the effect of the initial sulfide concentration on the kinetics and metabolism of phenol and sulfide in batch bioassays using nitrate as electron acceptor. Complete oxidation of sulfide (20 mg L(-1) of S(2-)) and phenol (19.6 mg L(-1)) was linked to nitrate reduction when nitrate was supplemented at stoichiometric concentrations. At 32 mg L(-1) of sulfide, oxidation of sulfide and phenol by the organo-lithoautotrophic microbial culture was sequential; first sulfide was rapidly oxidized to elemental sulfur and afterwards to sulfate; phenol oxidation started once sulfate production reached a maximum. When the initial sulfide concentration was increased from 20 to 26 and finally to 32 mg L(-1), sulfide oxidation was inhibited. In contrast phenol consumption by the denitrifying culture was not affected. These results indicated that sulfide affected strongly the sulfide oxidation rate and nitrate reduction.