Aerobic biodegradation of dichloroethylenes in surface and subsurface soils

Laboratory studies were conducted to examine the aerobic biodegradation of dichloroethylenes (cis-1,2-DCE, trans-1,2-DCE and 1,1-DCE) in soil and groundwater. Authentic surface and subsurface materials with no reported DCE exposure history were used. All DCE isomers were observed to biodegrade to varying degrees in the soils examined. Use of radiolabeled [14C] test chemicals allowed correlation of DCE disappearance with mineralization to 14CO2. Study results indicate that naturally occurring microorganisms in soil and groundwater are capable of degrading cis-1,2-, trans-1,2- and 1,1-DCE without laboratory supplementation of exogenous organic nutrients, or previous exposure history. The data further suggest that degradative potential may vary with soil type, DCE isomer structure, and concentration.     

Anaerobic biodegradation of alkylbenzenes and trichloroethylene in aquifer sediment down gradient of a sanitary landfill

The objective of this investigation was to evaluate the anaerobic biodegradability of benzene, toluene, ethylbenzene, ortho-, meta- and para-xylene (BTEX) and trichloroethylene (TCE) in aquifer sediment down gradient of an unlined landfill. The major organic contaminants identified in the shallow unconfined aquifer are cis-dichloroethylene (c-DCE) and toluene. The biodegradative potential of the contaminated aquifer was measured in three sets of microcosms constructed using anaerobic aquifer sediment from three boreholes down gradient of the landfill. The degradability of BTEX and TCE was examined under ambient and amended conditions. TCE was degraded in microcosms with aquifer material from all three boreholes. Toluene biodegradation was inconsistent, exhibiting biodegradation with no lag in one set of microcosms but more limited biodegradation in two additional sets of microcosms. TCE exhibited an inhibitory effect on toluene degradation at one location. The addition of calcium carbonate stimulated TCE biodegradation which was not further stimulated by nutrient addition. TCE was converted to ethylene, a harmless byproduct, in all tests. Benzene, ethylbenzene and xylene isomers were recalcitrant in both ambient and amendment experiments. Biodegradation occurred under methanogenic conditions as methane was produced in all experiments. Bromoethane sulfonic acid (BES), a methanogenic inhibitor, inhibited methane and ethylene production and TCE biodegradation. The results indicate the potential for intrinsic bioremediation of TCE and toluene down gradient of the Wilder's Grove, North Carolina, landfill. The low concentrations of TCE in monitoring wells was consistent with its biodegradation in laboratory microcosms.     

电子受体对深层土壤中石油烃缺氧降解的影响

微生物降解是处理土壤中石油烃 (PHC)污染的有效技术,目前对PHC微生物降解的研究多集中在好氧条件下,对PHC缺氧微生物降解的研究较少,PHC缺氧降解规律尚不清楚。以PHC污染的深层土壤为对象,探究不同质量分数 (500、1 500、5 000 mg·kg⁻¹)的硫酸盐、硝酸盐或混合电子受体对土壤中土著微生物丰度、群落结构以及PHC缺氧降解的影响规律。结果表明,150 d缺氧培养后,添加相同种类电子受体的土壤处理中细菌丰度、潜在PHC降解菌 (变形菌门和厚壁菌门)丰度随电子受体的质量分数增加而增加;添加相同质量分数的不同种类电子受体土壤处理中细菌丰度、潜在PHC降解菌丰度从高到低分别为硝酸盐、混合电子受体、硫酸盐。添加相同种类电子受体的土壤处理中ΣPHC (C₁₀~C₃₀)和C1 (C₁₀~C₁₆)、C2 (C₁₇~C₂₃)、C3 (C₂₄~C₃₀)组分的降解率随着加入电子受体质量分数增加而增加;相同质量分数的不同种类电子受体土壤处理中ΣPHC和C1、C2、C3组分的降解率从高到低分别为硝酸盐、混合电子受体、硫酸盐。土壤中PHC缺氧降解率与细菌丰度、潜在PHC降解菌丰度均存在正相关关系。研究结果可为石油烃污染土壤的修复技术研发提供技术支持。     

Laboratory evidence of MTBE biodegradation in Borden aquifer material

Mainly due to intrinsic biodegradation, monitored natural attenuation can be an effective and inexpensive remediation strategy at petroleum release sites. However, gasoline additives such as methyl tert-butyl ether (MTBE) can jeopardize this strategy because these compounds often degrade, if at all, at a slower rate than the collectively benzene, toluene, ethylbenzene and the xylene (BTEX) compounds. Investigation of whether a compound degrades under certain conditions, and at what rate, is therefore important to the assessment of the intrinsic remediation potential of aquifers. A natural gradient experiment with dissolved MTBE-containing gasoline in the shallow, aerobic sand aquifer at Canadian Forces Base (CFB) Borden (Ontario, Canada) from 1988 to 1996 suggested that biodegradation was the main cause of attenuation for MTBE within the aquifer. This laboratory study demonstrates biologically catalyzed MTBE degradation in Borden aquifer-like environments, and so supports the idea that attenuation due to biodegradation may have occurred in the natural gradient experiment. In an experiment with batch microcosms of aquifer material, three of the microcosms ultimately degraded MTBE to below detection, although this required more than 189 days (or >300 days in one case). Failure to detect the daughter product tert-butyl alcohol (TBA) in the field and the batch experiments could be because TBA was more readily degradable than MTBE under Borden conditions.     

Relationship between the lipid content of fish and their bioconcentration potential of 1,2,4-trichlorobenzene

A significant positive correlation between the lipid content of eight fish species and their bioconcentration factor (BCF) of 1,2,4-trichlorobenzene is demonstrated. The log BCF value on a lipid basis is in good agreement with the log n-octanol/water partition coefficient.     

Microbial aspects of the interaction between soil depth and biodegradation of the herbicide isoproturon

Factors controlling change in biodegradation rate of the pesticide isoproturon with soil depth were investigated in a field with sandy-loam soil. Soil was sampled at five depths between 0-10 and 70-80 cm. Degradation rate declined progressively down the soil profile, with degradation slower, and relative differences in degradation rate between soil depths greater, in intact cores relative to sieved soil. Neither the maximum rate of degradation, or sorption, changed with soil depth, indicating that there was no variation in bioavailability. Differences in degradation rate between soil depths were not associated with the starting population size of catabolic organisms or the number of catabolic organisms proliferating following 100% degradation. Decreasing degradation rates with soil depth were associated with an increase in the length of the lag phase prior to exponential degradation, suggesting the time required for adaptation within communities controlled degradation rates. 16S rRNA PCR denaturing gradient gel electrophoresis showed that degradation in sub-soil between 40-50 and 70-80 cm depths was associated with proliferation of the same strains of Sphingomonas spp.     

Relationship between the loading rate of inorganic mercury to aquatic ecosystems and dissolved gaseous mercury production and evasion

The purpose of our study was to test the hypothesis that dissolved gaseous mercury (DGM) production and evasion is directly proportional to the loading rate of inorganic mercury [Hg(II)] to aquatic ecosystems. We simulated different rates of atmospheric mercury deposition in 10-m diameter mesocosms in a boreal lake by adding multiple additions of Hg(II) enriched with a stable mercury isotope (²⁰²Hg). We measured DGM concentrations in surface waters and estimated evasion rates using the thin-film gas exchange model and mass transfer coefficients derived from sulfur hexafluoride (SF₆) additions. The additions of Hg(II) stimulated DGM production, indicating that newly added Hg(II) was highly reactive. Concentrations of DGM derived from the experimental Hg(II) additions (“spike DGM”) were directly proportional to the rate of Hg(II) loading to the mesocosms. Spike DGM concentrations averaged 0.15, 0.48 and 0.94 ng l⁻¹ in mesocosms loaded at 7.1, 14.2, and 35.5 μg Hg m⁻² yr⁻¹, respectively. The evasion rates of spike DGM from these mesocosms averaged 4.2, 17.2, and 22.3 ng m⁻² h⁻¹, respectively. The percentage of Hg(II) added to the mesocosms that was lost to the atmosphere was substantial (33–59% over 8 weeks) and was unrelated to the rate of Hg(II) loading. We conclude that changes in atmospheric mercury deposition to aquatic ecosystems will not change the relative proportion of mercury recycled to the atmosphere.     

热水洗辅助微生物修复高含油落地油泥

为解决油田落地油泥含油率高但不能直接进行生物无害化处置的问题,探索一种热水洗辅助微生物修复工艺。利用热水洗实验考察了清洗配方和水温对降低含油率的影响;从落地油泥中分离出石油烃降解菌,以用于含油残砂的微生物降解过程,同时探究填料和烃降解微生物对残砂中石油烃降解效果的影响。结果表明,鼠李糖脂清洗剂在总用量为0.5%、水洗时间30 min和50 ℃条件下,可将油泥含油率由107.1 mg·g⁻¹降至为39.3 mg·g⁻¹;水洗后残砂中的土著菌群数量出现了明显下降。分离获得了2株烃降解菌,并优选出具有增加油泥溶氧和保水的沼渣。将烃降解微生物和优选沼渣加入残砂后,石油烃生物降解效率得到显著提升,200 d后含油率降为4.62 mg·g⁻¹。在此过程中,微生物优先降解分子量小的饱和烃和芳香烃组分,对胶质和沥青质等组分降解程度偏低。该研究结果可为油田高含油落地油泥的环保处置提供参考。     

Assessment of the interrelation between photooxidation and biodegradation of selected polyesters after artificial weathering

Three commercially available biodegradable polymers, two different aromatic-aliphatic copolyesters and polylactic acid, intended for the fabrication of agricultural mulching films, in addition to other applications, were subjected to a series of tests with the aim of studying the relationship between their photooxidation and biodegradation. Photooxidation resulted in the rearrangement of polymeric chains, in the case of both copolyesters the events led to polymeric chain crosslinking and the formation of insoluble polymeric gel. The tendency was significantly more pronounced for the copolyester with the higher content of the aromatic constituent. As regards polylactic acid photochemical reactions were not accompanied by crosslinking but instead provoked chain scissions. A biodegradation experiment showed that, despite marked structural changes, the extent of photooxidation was not the decisive factor, which significantly modified the rate of biodegradation in all three materials investigated. The specific surface area of the sample specimens was shown to be more important.     

含氯苯废水的超声降解研究

以氯苯模拟废水为考察对象,研究其浓度、pH、超声时间等因素对氯苯超声降解效率的影响。实验结果表明：超声反应时间小于5min,氯苯降解率很低;5－20min,氯苯降解率成线性增大;超过20min后,氯苯降解率增大缓慢。pH值的增大,氯苯降解率略有减小。水浴温度提高,氯苯降解率增大。反应时间小于15min,初始浓度低的溶液,降解率增加较快,反应时间大于15min,初始浓度高的溶液,降解率增加较快。     

水力负荷对污水地下渗滤系统处理效果的影响

采用人工模拟的方法,研究了0.04、0.06、0.10、0.14和0.18 m3/(m2·d)5个水力负荷下污水地下渗滤系统对生活污水处理效果的影响。实验期间,SS、BOD5、COD、TN、NH4+-N和TP的进水浓度分别处于69.74~79.62、40.75~64.81、211.56~250.72、48.94~87.36、31.25~59.04和2.88~4.05 mg/L之间,出水平均浓度分别为13.63、9.66、31.53、21.08、1.90和0.10 mg/L。结果表明,地下渗滤系统对生活污水具有良好的处理效果,除TN外,其余各项指标均满足《城镇污水处理厂污染物排放标准》(GB/18918-2002)一级处理要求;当水力负荷为0.14和0.18 m3/(m2·d)时,BOD5 与TN去除率降低,出水浓度升高,受水力负荷影响明显;水力负荷对SS与COD影响作用微弱,去除率降幅较小;NH4+-N与TP则基本不受水力负荷变化影响。综合考虑渗滤系统的出水水质与日处理能力,推荐适宜水力负荷为0.10~0.14 m3/(m2·d)。     

Simultaneous sorption of lead and chlorobenzene by organobentonite

Clays or organoclays have been used as a barrier to prevent the transport of hazardous contaminants in landfills. However, clays are known to effectively sorb mostly inorganic contaminants, while organoclays are mainly used for organic contaminants. Since the organoclays are basically clay particles modified with cationic surfactants, there might exist an optimal coverage of cationic surfactant on the clay particles to sorb both inorganic and organic contaminants. In order to determine the optimal mass of cationic surfactants on the bentonites, sodium bentonites were treated with various ratios of hexadecyltrimethylammonium (HDTMA) to bentonites. Chlorobenzene and lead were selected as representative contaminants. When either chlorobenzene or lead exists as a single contaminant, chlorobenzene sorption increased with increasing HDTMA to bentonite ratios, and lead sorption decreased with increasing HDTMA to bentonite ratios. Sorption of chlorobenzene was a function of HDTMA coverage on the bentonites, while lead sorption was much more influenced by the initial lead concentration rather than the mass of HDTMA added to the bentonites.     

An experimental and numerical study of the thermal oxidation of chlorobenzene

A combustion-driven flow reactor was used to examine the formation of chlorinated and non-chlorinated species from the thermal oxidation of chlorobenzene under post-flame conditions. Temperature varied from 725 to 1000 K, while the equivalence ratio was held constant at 0.5. Significant quantities of chlorinated intermediates, vinyl chloride and chlorophenol, were measured. A dominant C-Cl scission destruction pathway seen in pyrolytic studies was not observed. Instead, hydrogen-abstraction reactions prevailed, leading to high concentrations of chlorinated byproducts. The thermal oxidation of benzene was also investigated for comparison. Chemical kinetic modeling of benzene and chlorobenzene was used to explore reaction pathways. Two chlorobenzene models were developed to test the hypothesis that chlorobenzene oxidation follows a CO-expulsion breakdown pathway similar to that of benzene. For the temperatures and equivalence ratio studied, hydrogen abstraction by hydroxyl radicals dominates the initial destruction of both benzene and chlorobenzene. Chlorinated byproducts (i.e., chlorophenol and vinyl chloride) were formed from chlorobenzene oxidation in similar quantities and at similar temperatures to their respective analogue formed during benzene oxidation (i.e., phenol and ethylene).     

Study of the spatial variation of the biodegradation rate of the herbicide bentazone with soil depth using contrasting incubation methods

Vertical and horizontal spatial variability in the biodegradation of the herbicide bentazone was compared in sandy-loam soil from an agricultural field using sieved soil and intact soil cores. An initial experiment compared degradation at five depths between 0 and 80 cm using sieved soil. Degradation was shown to follow the first-order kinetics, and time to 50% degradation (DT(50)), declined progressively with soil depth from 56 d at 0-10 cm to 520 d at 70-80 cm. DT(50) was significantly correlated with organic matter, pH and dehydrogenase activity. In a subsequent experiment, degradation rate was compared after 127 d in sieved soil and intact cores from 0 to 10 and 50 to 60 cm depth from 10 locations across a 160x90 m portion of the field. Method of incubation significantly affected mean dissipation rate, although there were relatively small differences in the amount of pesticide remaining in intact cores and sieved soil, accounting for between 4.6% and 10.6% of that added. Spatial variability in degradation rate was higher in soil from 0 to 10 cm depth relative to that from 50 and 60 cm depth in both sieved soil and intact core assessments. Patterns of spatial variability measured using cores and sieved soil were similar at 50-60 cm, but not at 0-10 cm depth. This could reflect loss of environmental context following processing of sieved soil. In particular, moisture content, which was controlled in sieved soil, was found to be variable in cores, and was significantly correlated with degradation rate in intact topsoil cores from 0 to 10 cm depth.     

Determination of naturally occurring MTBE biodegradation by analysing metabolites and biodegradation by-products

Methyl tert-butyl ether (MTBE) is one of the main additives in gasoline. Its degradation is known to be difficult in natural environments. In this study, significant MTBE degradation is demonstrated at a contaminated site in Leuna (eastern Germany). Since the extent of the plume appeared to be constant over the last 5 years, an extended study was performed to elucidate the degradation processes. Special attention was paid to the production, accumulation and degradation of metabolites and by-products. Groundwater samples from 105 monitoring wells were used to measure 20 different substances. During the degradation process, several intermediates such as tert-butyl alcohol (TBA), tert-butyl formate, formate and lactate were produced. However, the potentially carcinogenic by-product methacrylate was not detected in several hundred samples. At the Leuna site, MTBE degradation occurred under microaerobic conditions. In contrast to hydrocarbons and BTEX, there was no evidence for anaerobic MTBE degradation. Among the degradation products, TBA was found to be a useful intermediate to identify MTBE degradation, at least under microaerobic conditions. TBA accumulation was strongly correlated to MTBE degradation according to the kinetic properties of both degradation processes. Since maximum degradation rates (v(max)) and k(m) values were higher for MTBE (v(max)=2.3 mg/l/d and k(m)=3.2 mg/l) than for TBA (v(max)=1.35 mg/l/d and k(m)=0.05 mg/l), TBA significantly accumulated as an intermediate by-product. The field results were supported by bench scale model aquifer experiments.     

Toxicity and biodegradation of diamines

Phytotoxicity and cytotoxicity of 2,4-diaminotoluene (2,4-D), 4,4'-methylenedianiline (4,4-D), and 1,6-hexanediamine (1,6-D) were investigated by observing the germination of young radish seeds and the viability of HeLa cells, respectively. 2,4-D showed the highest, 4,4-D intermediate, and 1,6-D lowest cytotoxicity. However, the phytotoxicity decreased in the order of 4,4-D > 2,4-D > 1,6-D. Contrary to the results previously reported, in the modified Sturm test the activated sludge degraded 2,4-D and 4,4-D as well as 1,6-D without any pre-acclimation. Ochrobacterium antropi was isolated for degradation of 2,4-D and 4,4-D and Pseudomonas citronellolis for 1,6-D degradation. Thielevia sp. was isolated as 2,4-D degrading fungus and Aspergillus sp. as 4,4-D and 1,6-D degrading fungus. The fungi degraded the diamines faster than the bacteria.     

Biodegradation of polycyclic aromatic hydrocarbons in the natural waters of the Yellow River: effects of high sediment content on biodegradation

The contamination of polycyclic aromatic hydrocarbons (PAHs) has become one of the major problems in the Yellow River of China. As the Yellow River is the most turbid large river in the world, it remains unknown to which extent the high suspended sediment content in the river may affect the fate and effect of PAHs. Here we report the effect of sediment on biodegradation of chrysene, benzo(a)pyrene and benzo(g,h,i)perylene with phenanthrene as a co-metabolism substrate in natural waters from the Yellow River. Biodegradation kinetics of the PAHs in the river water with various levels of sediment contents were studied in the laboratory by fitting with a biodegradation kinetics model for organic compounds not supporting growth. The results indicated that the biodegradation rates of PAHs increased with the sediment content in the water. When the sediment contents were 0, 4 and 10 g/l, the biodegradation rate constants of chrysene with the initial concentration of 3.80 microg/l were 0.053, 0.084 and 0.111 d(-1), respectively. Further studies suggested the enhanced biodegradation rate in the presence of sediment was caused by the following mechanisms: (1) the population of PAH-degrading bacteria in the water system was found to increase with the sediment content; the bacteria population on sediment phase was far greater than that on water phase during the cultivation process; (2) the sorption of PAHs on the sediment phase was well described by the dual adsorption-partition model. Although the sorption capacity of PAH per unit weight of sediment decreased with the increase of the sediment content, the amount of sorbed PAH increased with the sediment content; and, (3) the desorption of PAHs from the solid phase led to a higher concentration near the water-sediment interface. Since the bacteria were also attached to the interface, this resulted in an increased contact chance between the bacteria and PAHs.     

Correlations between experimental and predicted equilibrium distribution coefficient of chlorobenzene and chlorophenol compounds in soil-water systems using partial solubility parameters

Many pesticides are degraded to become chlorinated aromatic compounds in soils. Equilibrium distribution of chlorobenzene and chlorophenol compounds in soil-water systems of Yangmingshan loam, Pingcheng silty clay loam and Annei silty loam was studied with the integral distribution equilibrium equation involving the partial solubility parameters of the chemicals. If the adsorption of chemicals on soils is partitioning in soil organic matter surrounding the soil mineral particles, the absorption constant (Kd) of a chemical in soil-water system could be stated as the distribution coefficient (or partition constant, Koc) of the chemical in the two adjunct immiscible phases--water and soil organic matter. The distribution coefficient (Koc) of chemicals calculated from the integral distribution equilibrium equation agrees well with the experimental adsorption coefficient (Kd, or experimental Koc) of chemicals determined in this study, for all the three different types of soils in water according to multiple-regression analysis. Reference data of Karger or Tijssen are employed to estimate the Koc for both polar and non-polar chemicals. The integral distribution equilibrium equation can exactly describe the distribution behavior of nonionic compound of chlorobenzenes and chlorophenols in soil-water systems.     

Relative rates and partial combustion products from the burning of chlorobenzenes and chlorobenzene mixtures

Relative rates of burning were determined and partial combustion products identified for several chlorobenzenes and benzene-chlorobenzene and chlorobenzene-chlorobenzene mixtures. The results show that both the rate and product distribution depend on the feed stream atomic ratios and are insensitive to the specific chemicals.