Experimental Study on Micro-biological Degradation of 1, 3, 5- TMB in Groundwater

1, 3, 5-TMB (trimethylbenzene) has been considered as priority pollutant by several environmental agencies due to its high toxicity, carcinogenicity and mutagenic activity. Two bacteria with ability of degrading 1, 3, 5- TMB were isolated from crude oil contaminated soil. The optimal pH value and temperature for the growth of these bacteria were 7.0 and 30℃. 1, 3, 5- TMB was used as sole carbon and energy source by both strains. Strain A was identified as Staphylococcus sciuri and Strain C was Microbacterium schleiferi, both of which were facultative anaerobic bacteria. 1, 3, 5-TMB was degraded by strain C with efficiency of 41.2±1.8%. The bacteria offered new source for biodegradation of BTEX and bioremediation of oil-contaminated soil and groundwater.     

Aerobic and anaerobic biodegradation of nonylphenol ethoxylates in estuary sediment of Yangtze River,China

The biodegradation behavior of nonylphenol ethoxylates (NPEOs) in estuary sediment of Yangtze River, China, was investigated. NPEOs were readily degraded in the estuary sediment under both aerobic and anaerobic conditions. The highest biodegradation rate constants for the aerobic biodegradation and anaerobic biodegradation were 0.333 and 0.194 day⁻¹, respectively. Anaerobic biodegradation of NPEOs in estuary sediment was enhanced under sulfate-reducing or nitrate-reducing conditions. The biodegradation constants increased by 23.4 and 56.7% in sulfate-adding treatment and nitrate-adding treatment, respectively. NPEOs were biodegraded through the terminal oxidative pathway in estuary sediment under aerobic conditions while these compounds were biodegraded through the non-oxidative pathway under anaerobic conditions. Estrogenic intermediates were formed during NPEO biodegradation under both aerobic and anaerobic conditions. Both treatments reached their highest estrogenicities on day 21. Short-chain nonylphenol ethoxycarboxylates (NPECs), which were feasibly mobile, were only formed under aerobic conditions.     

反硝化条件下苯生物降解的微环境研究

探讨了厌氧微环境中苯的生物降解.接种物来自北京郊区的稻田土.结果表明, 在富集培养和转移培养微环境中, 苯和甲苯的降解与硝酸盐还原作用同时发生.甲苯比苯更易降解, 甲苯的存在促进了苯的降解.这是一例反硝化条件下苯能被生物降解的研究      

Effect of geochemical conditions on fate of organic compounds in groundwater

In situ microcosms were successfully used to study the degradation of a range of organic compounds in two pristine aquifers, one aerobic (Vejen) and one anaerobic (Villa Farm). Degradation and sorption behavior in the laboratory column microcosms packed with Villa Farm sediment was very similar to that in the in situ microcosms. However, when the columns were packed with quartz and equilibrated with aerated Villa Farm groundwater, behavior mirrored that at Vejen, indicating that oxygen rather than sediment or groundwater composition was the critical parameter. The aromatic and polyaromatic compounds (benzene, toluene,o-xylene, naphthalene) degraded under aerobic conditions only. The organochlorine compounds (trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, 1,4-dichlorobenzene and 1,2-dichlorobenzene) showed little or no sign of degradation either aerobically or anaerobically. Interpretation of the data was complicated by strong sorption to the Villa Farm sediment but tetrachloromethane, nitrobenzene, ando-nitrophenol appeared to degrade under anaerobic conditions only. Phenol degraded rapidly under both sets of conditions.     

Sorption and anaerobic biodegradation of soluble aromatic compounds during groundwater transport. 1. Laboratory column experiments

. This paper deals with sorption and anaerobic biodegradation of the soluble aromatic fraction of jet fuel and how it is influenced by pore-water velocity during transport in a groundwater aquifer. The study was carried out as controlled laboratory column experiments. A binary mixture of toluene and 1,2,4-trimethylbenzene with a concentration ratio of 2:1 was used through the entire investigations. The column experiments were conducted with contaminated sediments and groundwater, taken from wells at a field research site. The columns were operated anaerobically under continuous-flow conditions at 10 °C in a temperature-controlled refrigerator. Two percent sodium azide was added to the injection solution of two of the columns to prevent biodegradation of the studied organic mixture. Chloride was used as a conservative tracer to characterize the hydrodynamic parameters such as dispersivity and porosity of the columns. The results showed that both compounds in the mixture were attenuated because of sorption and biodegradation processes in the columns. 1,2,4-trimethylbenzene was attenuated more significantly than toluene. Biodegradation of toluene was coupled mainly with the microbial reduction of ferric iron, whereas 1,2,4-trimethylbenzene, in contrast, was mostly sorbed. Their sorption and biodegradation were studied with different pore-water velocities, and a mass balance approach was applied to calculate biodegradation rates. The biodegradation rates of toluene were –0.16, –0.21, and –0.26 (unit: mM day^–1) for pore-water velocities of 96, 82.4, and 54.9 (unit: cm day^–1), respectively. This indicates that a decrease in the pore-water velocity significantly enhanced the biodegradation of toluene, consistent with other reports in the literature. For 1,2,4-trimethylbenzene the biodegradation rates were –0.05, –0.13 (unit: mM day^–1) for pore-water velocities of 96 and 82.4 (unit: cm day^–1), respectively. The biodegradation rate of 1,2,4-trimethylbenzene did not increase at the lowest pore water velocity as expected. This might be a result of substrate competition.     

Intrinsic bioremediation of MTBE-contaminated groundwater at a petroleum-hydrocarbon spill site

An oil-refining plant site located in southern Taiwan has been identified as a petroleum-hydrocarbon [mainly methyl tert-butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylenes (BTEX)] spill site. In this study, groundwater samples collected from the site were analyzed to assess the occurrence of intrinsic MTBE biodegradation. Microcosm experiments were conducted to evaluate the feasibility of biodegrading MTBE by indigenous microorganisms under aerobic, cometabolic, iron reducing, and methanogenic conditions. Results from the field investigation and microbial enumeration indicate that the intrinsic biodegradation of MTBE and BTEX is occurring and causing the decrease in MTBE and BTEX concentrations. Microcosm results show that the indigenous microorganisms were able to biodegrade MTBE under aerobic conditions using MTBE as the sole primary substrate. The detected biodegradation byproduct, tri-butyl alcohol (TBA), can also be biodegraded by the indigenous microorganisms. In addition, microcosms with site groundwater as the medium solution show higher MTBE biodegradation rate. This indicates that the site groundwater might contain some trace minerals or organics, which could enhance the MTBE biodegradation. Results show that the addition of BTEX at low levels could also enhance the MTBE removal. No MTBE removal was detected in iron reducing and methanogenic microcosms. This might be due to the effects of low dissolved oxygen (approximately 0.3 mg/L) within the plume. The low iron reducers and methanogens (<1.8×10³ cell/g of soil) observed in the aquifer also indicate that the iron reduction and methanogenesis are not the dominant biodegradation patterns in the contaminant plume. Results from the microcosm study reveal that preliminary laboratory study is required to determine the appropriate substrates and oxidation-reduction conditions to enhance the biodegradation of MTBE. Results suggest that in situ or on-site aerobic bioremediation using indigenous microorganisms would be a feasible technology to clean up this MTBE-contaminated site.     

汽油污染含水层中芳香烃的自然去除与生物降解特征

石油烃污染地下水是一个普遍而严重的环境问题.用砂卵石、中粗砂、细砂、粉砂和粘土等在实验室内按照自然界沉积物层序制作了一个含水层物理模型,具有给水、排水、监测、抽提、淋滤与注入等功能.利用该模型开展石油烃污染地下水的特征研究结果表明,苯、甲苯、乙苯和二甲苯(benzene,toluene,ethylbenzene,xylene;BTEX)各溶解组分能够被自然去除,其中甲苯自然衰减的速率系数为0.057 5～0.150 4 d-1,二甲苯为0.068 3～0.104 6 d,乙苯大约为0.047 8 d,苯为O.017 8～0.040 6 d.甲苯与二甲苯容易被去除,然而苯的去除则需要较长的时间.作为BTEX去除反应的电子受体,溶解氧、硝酸盐在需氧或厌氧条件下具有优先利用的机会,而硫酸盐则缺乏优先利用的机会.BTEX溶解组分浓度的降低,加上电子受体浓度的降低,可以表明含水层存在需氧条件与硝酸盐还原条件下的内在生物降解作用.其意义在于通过增加含水层中电子受体的浓度,将有助于内在生物降解能力的增强,从而能够提高含水层中污染物去除的效果.     

Sorption and anaerobic biodegradation of soluble aromatic compounds during groundwater transport. 2. Computer modeling

. The natural attenuation of a binary mixture of toluene and 1,2,4-trimethylbenzene, which was previously experimentally demonstrated in anaerobic column experiments, was simulated with the newly-developed PHREEQC model to reveal the biogeochemical processes involved. The processes considered in this model include advection, diffusion, sorption, redox reactions (e.g., oxidation of toluene and 1,2,4-trimethylbenzene coupled to the reduction of microbial ferric iron), precipitation of secondary minerals such as siderite and magnetite, and dissolution of hydrous ferric oxides, as well as other thermodynamic equilibrium reactions. The functions of advection and diffusion built into the PHREEQC were conventionally simulated. The sorption was kinetically simulated based on a bicontinuum model, whereas biodegradation was described using a multiple-term Monod model. The processes mentioned above were coupled with a geochemical equilibrium model. The consistency between the experimental and modeling results indicates that the processes defined and the controlling parameters chosen could describe the coupled interactions between transport and biogeochemical reactions for the studied system. The discrepancy between modeling and experimental observations, however, also revealed the limitation of the modeling approach. In general, the model approach, which incorporates simplified mathematical representations of the true physico-chemical dynamics of the sorption and biodegradation processes of toluene and 1,2,4-trimethylbenzene under anaerobic conditions is a very efficient and good predictive tool in management and remediation of contaminant groundwater aquifers.     

Natural gradient experiment on transport of jet fuel derived hydrocarbons in an unconfined sandy aquifer

This paper deals with a field experiment, combining the push–pull and tracer tests, conducted under natural gradient conditions at the international Oslo airport. The studied aquifer, showing very complex hydrogeological settings, has been contaminated by a jet fuel spill. The tracer solutes—bromide, toluene, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene and naphthalene, have been injected into the plume. Their migration and changes in concentration of the electron acceptors and metabolic by-products have been monitored. Fast removal of both the non-reactive tracer as well as the aromatic organics has been observed. The tracer pulse could only be detected 2 m downgradient from the injection points. At this point, toluene and o-xylene have been completely removed, however, trimethylbenzenes and naphthalene have been detected. Their depletion, based on calculations of available electron acceptors, can, to a large extent, be accounted for intrinsic biodegradation, with Fe(III) and sulphate reductions as the major controlling processes.     

Assessment of MTBE biodegradation in contaminated groundwater using C and C analysis: Field and laboratory microcosm studies

Radiolabelled assays and compound-specific stable isotope analysis (CSIA) were used to assess methyl tert-butyl ether (MTBE) biodegradation in an unleaded fuel plume in a UK chalk aquifer, both in the field and in laboratory microcosm experiments. The ¹⁴C-MTBE radiorespirometry studies demonstrated widespread potential for aerobic and anaerobic MTBE biodegradation in the aquifer. However, δ¹³C compositions of MTBE in groundwater samples from the plume showed no significant ¹³C enrichment that would indicate MTBE biodegradation at the field scale. Carbon isotope enrichment during MTBE biodegradation was assessed in the microcosms when dissolved O₂ was not limiting, compared with low in situ concentrations (2 mg/L) in the aquifer, and in the absence of O₂. The microcosm experiments showed ubiquitous potential for aerobic MTBE biodegradation in the aquifer within hundreds of days. Aerobic MTBE biodegradation in the microcosms produced an enrichment of 7‰ in the MTBE δ¹³C composition and an isotope enrichment factor (ε) of −1.53‰ when dissolved O₂ was not limiting. However, for the low dissolved O₂ concentration of up to 2 mg/L that characterizes most of the MTBE plume fringe, aerobic MTBE biodegradation produced an enrichment of 0.5-0.7‰, corresponding to an ε value of −0.22‰ to −0.24‰. No anaerobic MTBE biodegradation occurred under these experimental conditions. These results suggest the existence of a complex MTBE-biodegrading community in the aquifer, which may consist of different aerobic species competing for MTBE and dissolved O₂. Under low O₂ conditions, the lower fractionating species have been shown to govern overall MTBE C-isotope fractionation during biodegradation, confirming the results of previous laboratory experiments mixing pure cultures. This implies that significant aerobic MTBE biodegradation could occur under the low dissolved O₂ concentration that typifies the reactive fringe zone of MTBE plumes, without producing detectable changes in the MTBE δ¹³C composition. This observed insensitivity of C isotope enrichment to MTBE biodegradation could lead to significant underestimation of aerobic MTBE biodegradation at field scale, with an unnecessarily pessimistic performance assessment for natural attenuation. Site-specific C isotope enrichment factors are, therefore, required to reliably quantify MTBE biodegradation, which may limit CSIA as a tool for the in situ assessment of MTBE biodegradation in groundwater using only C isotopes.     

应用质量通量评估地下水中BTEX和乙醇的自然衰减

近年来,应用于修复石油烃污染地下水的监测自然衰减技术得到了广泛深入研究,同时质量通量方法已逐渐成为评 估地下水燃油污染场地自然衰减监测修复效能的重要手段。通过在室内砂槽中添加乙醇汽油组分,监测其自然衰减,利用 质量通量方法,得出了BTEX和乙醇的质量减少率、自然衰减速率常数K;结合非反应示踪剂溴离子,评价了BTEX和乙醇 自然衰减因素中吸附和微生物的联合降解效应。结果表明,自然衰减是地下水中燃油组分修复的重要机制,质量通量方法 是评估自然衰减的有效方法之一。BTEX和乙醇在自然衰减过程中被去除的比例分别为78.88%和98.71%,其中约98%的 BTEX 因吸附和生物降解联合作用被去除,接近100%的乙醇因内在生物降解作用被去除;BTEX 的自然衰减速率为 0.077d-1~0.167d-1,乙醇为0.353d-1,自然条件下乙醇比BTEX更容易衰减。     

SF6在地下水应用中的研究现状

SF6是无味、无毒的惰性气体,难被生物降解,不易被有机质吸附,即使是在强还原环境下也没有明显地降解。目前大气中SF6的浓度约以7%的速度增长,而且已实现了大气和地下水中SF6的测试技术,其具有较为简单的分析和取样流程。SF6作为一种新的示踪剂在地下水的研究中具有潜在的应用价值,它能够较好地描述地下水运动规律、径流机理,测试地下水的滞留时间和运移速率,解释地下水的循环过程和混合作用等,在地下水的研究中发挥着重要的作用。然而我国对SF6的研究还处在起步阶段,实现SF6在地下水研究中的应用,建立SF6的长期大气观测站迫在眉睫,联合运用多种多示踪剂解决地下水中科学问题是发展的趋势之一。     

四氯乙烯在不同地下水环境的生物共代谢降解

四氯乙烯是地下水中常见的污染物,采用生物方法进行处理的优点是可以实现无害化、无二次污染、处理成本低。四氯乙烯只能在厌氧条件下发生还原脱氯,目前对产甲烷环境下四氯乙烯的降解研究较多,而对较弱还原环境,如反硝化、铁锰还原和硫酸盐还原环境下四氯乙烯的脱氯行为研究甚少。本文采用批实验,研究了在不同地下水环境,包括反硝化、铁还原、硫酸盐还原、混合电子受体和天然地下水环境下四氯乙烯的脱氯性能。结果表明,铁还原环境的四氯乙烯脱氯效果最好,天然地下水环境次之,四氯乙烯的去除率分别达到91.34%和84.71%,四氯乙烯很快转化为三氯乙烯,并可以进一步转化为二氯乙烯,四氯乙烯的降解符合准一级反应动力学方程。在反硝化、硫酸盐还原、混合电子受体环境,四氯乙烯的去除以挥发为主,降解只占很小的比例,且最终的降解产物只有三氯乙烯。地下水中三价铁的存在,对于四氯乙烯脱氯起促进作用;而当地下水中硝酸盐和硫酸盐的浓度较高时,四氯乙烯脱氯受到抑制。     

Field investigation of the natural attenuation and intrinsic biodegradation rates at an underground storage tank site

 Contamination of groundwater by petroleum-hydrocarbons is a widespread environmental problem. Natural attenuation is a passive remedial approach to degrade and dissipate contaminants in soil and groundwater. In this study, a mass flux approach was used to calculate the contaminant mass reduction and field-scale decay rate at a gasoline spill site. The mass flux technique is accomplished using the differences in total contaminant mass flux across two cross sections of the contaminant plume. The mass flux calculation shows that up to 88% of the dissolved BTEX (benzene, toluene, ethylbenzene, and xylene isomers) removal was observed by natural attenuation processes. The efficiency of intrinsic biodegradation was evaluated by the in situ tracer method. A first-order decay model was applied for the natural attenuation and intrinsic biodegradation rate calculation. Results reveal that intrinsic biodegradation process was the major cause of the BTEX reduction among the natural attenuation mechanisms, and iron reduction was the dominant biodegradation pattern within the plume. Approximately 87% of the BTEX removal was caused by intrinsic biodegradation processes. The calculated BTEX natural attenuation and intrinsic biodegradation rates were 0.24 and 0.16% l/day, respectively. Results suggest that natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the efficiency of the natural attenuation. Received: 6 December 1999 · Accepted: 11 July 2000     

Degradation of carbon disulphide (CS2) in soils and groundwater from a CS2-contaminated site

This study is the first investigation of biodegradation of carbon disulphide (CS₂) in soil that provides estimates of degradation rates and identifies intermediate degradation products and carbon isotope signatures of degradation. Microcosm studies were undertaken under anaerobic conditions using soil and groundwater recovered from CS₂-contaminated sites. Proposed degradation mechanisms were validated using equilibrium speciation modelling of concentrations and carbon isotope ratios. A first-order degradation rate constant of 1.25 × 10^?2 h^?1 was obtained for biological degradation with soil. Carbonyl sulphide (COS) and hydrogen sulphide (H₂S) were found to be intermediates of degradation, but did not accumulate in vials. A ¹³C/¹²C enrichment factor of ?7.5 ± 0.8 ‰ was obtained for degradation within microcosms with both soil and groundwater whereas a ¹³C/¹²C enrichment factor of ?23.0 ± 2.1 ‰ was obtained for degradation with site groundwater alone. It can be concluded that biological degradation of both CS₂-contaminated soil and groundwater is likely to occur in the field suggesting that natural attenuation may be an appropriate remedial tool at some sites. The presence of biodegradation by-products including COS and H₂S indicates that biodegradation of CS₂ is occurring and stable carbon isotopes are a promising tool to quantify CS₂ degradation.     

Prediction of 1,2,4-trichlorobenzene natural attenuation in groundwater at a landfill in Kaifeng,China

1,2,4-trichlorobenzene (1,2,4-TCB) is one of the most common pollutants in landfill leachate that impacts shallow drinking groundwater quality; accordingly, the transport mechanism and capacity for remediation of this compound are important to the management of local water resource. In this study, a series of indoor experiments and analytical predictions revealed that the transportation of 1,2,4-TCB in groundwater is similar in medium sand and fine sand. Specifically, the peak time increases with distance between monitoring points and the source point, but the peak relative concentrations decrease with distance, indicating that the concentration of 1,2,4-TCB in groundwater is controlled by adsorption and biodegradation. In addition, transportation of water in a fine sand column was lower than that in a medium sand column; therefore, the adsorption and biodegradation of 1,2,4-TCB in groundwater was lower in the medium sand column. These findings demonstrate that 1,2,4-TCB in groundwater could be removed by natural degradation after about 5 years, but that other methods (permeable reactive barriers, air sparging or biosparging) should be applied in the field to shorten the remediation period and enhance water supply safety around landfill.     

Estimation of kinetic Monod parameters for anaerobic degradation of benzene in groundwater

To date, evidence for the degradation of benzene under anaerobic conditions has been established only in few studies under field and laboratory conditions. Recently, we demonstrated the mineralization of benzene under sulfate-reducing conditions in a large-scale column experiment at a field site by balancing electrons (Vogt et al. in Biodegradation, 2007, in press). Here, from a modelling approach, kinetic Monod parameters are estimated for the degradation of benzene in the columns, Monod kinetics proved useful to simulate benzene concentrations at the column outflow. The uncertainty of the obtained parameters is determined in a sensitivity analysis. A total mass of degraded benzene of 23 g or 80% of the total influx over a period of three months was calculated. The estimated maximum utilization rate was calculated to be around 70 times lower than from aerobic benzene degradation experiments.     

Bioremediation of 2,4,6-trinitrotoluene-contaminated groundwater using unique bacterial strains: microcosm and mechanism studies

Groundwater at many military factory, munition storage and maneuver sites is contaminated by explosives chemicals that were released into the subsurface. The 2,4,6-trinitrotoluene (TNT) is among the most common explosive pollutants. In this study, two TNT-degrading strains, isolated from TNT-contaminated soils and wastewater sludge, were applied for TNT biodegradation. Based on the 16S rDNA sequence analyses, these two bacterial strains were identified as Achromobacter sp. and Klebsiella sp. via biochemical and DNA analyses. Microcosm study was conducted to evaluate the feasibility and efficiency of TNT biodegradation under aerobic conditions. Results indicate that TNT degradation by-products were detected in microcosms (inoculated with Achromobacter sp. and Klebsiella sp.) with cane molasses addition. Klebsiella sp. and Achromobacter sp. used TNT as the nitrogen source and caused completely removal of TNT. Two possible TNT biodegradation routes could be derived: (1) part of the TNT was transformed to nitrotoluene then transformed to nitrobenzene followed by the nitro substitute process, and trinitrobenzene, dinitrobenzene, and nitrobenzene were detected; and (2) TNT was transformed via the nitro substitute mechanism, and dinitrotoluene followed by nitrotoluene isomers were detected. The initial TNT degradation involved the reduction or removal of the nitro substitute to an amino derivative or free nitrite. Results show that the second route was the dominant TNT biodegradation pathway. The produced by-products were also degraded without significant accumulation during the degradation process. These findings would be helpful in designing a practical system inoculated with isolated TNT degradation strains for the treatment of TNT-contained groundwater.     

反硝化增强去除乙醇对多孔介质渗透性的影响

随着乙醇混合汽油的不断推广应用,乙醇将成为地下水中与苯、甲苯、乙苯及二甲苯的同分异构体（BTEX）共存的一种新型污染物。通过4 个含水砂柱实验,研究了乙醇存在及其强化去除对含水介质渗透性能的影响。结果表明：在有限溶解氧与反硝化增强修复条件下,乙醇去除率达92% 以上;生物过程对介质渗透能力影响程度随乙醇初始浓度、消耗速率与补充频率而变化：乙醇初始浓度接近1 000 mg/L 和3 000 mg/L 时,乙醇消耗快,补充频率高,渗透系数下降总体上有连续性,最大下降幅度达一个数量级（×10-1 cm/s）;乙醇初始浓度达到5 000 mg/L 时,渗透性下降显著,可下降两个数量级,但乙酸的积累可影响生物活性,并使得渗透性变化出现反复;当不含乙醇时,汽油溶解组分对介质渗透性能的影响相对不明显。     

四氯乙烯的生物吸附和厌氧生物降解研究

四氯乙烯(PCE)的广泛使用和不合理的处置已经使其成为地下水中普遍存在的有毒有害的有机污染物。PCE在厌氧条件下通过还原脱氯发生生物降解,按照非水溶性生物降解模型,有机物先吸附到厌氧活性污泥中,解吸后再进行生物降解。利用间歇试验进行厌养污泥对PCE的吸附降解实验研究。试验结果表明：厌氧污泥对PCE的吸附在0.5 h达到吸附平衡,在1.0 h达到解吸平衡。对实验结果的回归分析表明：PCE的吸附和解吸均符合Freundlich等温吸附方程。厌氧污泥在微生物的作用下将PCE还原脱氯为TCE和DCEs。