Comparison of 2-chlorobenzoic acid biodegradation in a membrane bioreactor by B. cepacia and B. cepacia bearing the bacterial hemoglobin gene

Degradation of 2-chlorobenzoic acid (2-CBA), a model recalcitrant chlorinated organic compound, by pure cultures of Burkholderia cepacia strain DNT with (transformed B. cepacia) and without (untransformed B. cepacia) the bacterial hemoglobin (Vitreoscilla hemoglobin, VHb) gene, vgb, was investigated in parallel membrane bioreactors (MBRs). This was done aseptically to prevent contamination during the operation of the MBRs. The objective was to determine whether the degradation of 2-CBA by cometabolism, using acetate as a primary carbon source, under hypoxic conditions might be enhanced for vgb-bearing cells in MBRs. The 2-CBA removal efficiency of transformed B. cepacia (97-99%) was slightly higher than that of untransformed B. cepacia (95-99%) at all stages. The average amount of chloride released from 2-CBA by transformed cells was also higher than for untransformed cells, 92-96% compared to 64-84% of the maximum theoretical amount, the exact value depending on the operating conditions. These results indicate that 2-CBA degradation/transformation is not accompanied by the stoichiometric release of chloride for the untransformed strain. The difference between percentages of 2-CBA removal and chloride release by untransformed cells was attributed to persistence, under hypoxic conditions, of the 2-CBA chlorine atom in 2-CBA metabolites. Growth of transformed cells was also significantly enhanced under hypoxic conditions compared to untransformed cells. For varying media compositions, the transformed cells reached higher cell densities (3.2-5.4 g/L) relative to untransformed cells (2.8-4.7 g/L) at food to microorganism ratios ranging from 0.44-0.59 to 0.38-0.49 g COD/g biomass-d The observed yields thus ranged from 0.16-0.20 and 0.15-0.18 g TSS/g COD for untransformed and transformed cells, respectively. The value of the yield depended on medium composition. The MBR system using vgb-containing B. cepacia maintained a high biomass concentration without oxygen limitations and provided cell-free effluent. Hence, it may be useful for treating high volumes of water contaminated with low levels of recalcitrant organics.     

Influence of solution ionic strength on the collision efficiency distribution and predicted transport distance of a Sphingomonas sp. flowing through porous media

The effects of solution ionic strength on the collision efficiency (alpha) distribution of a Sphingomonas sp. were investigated using multiple sand columns of varying lengths and analyzing the bacteria clean-bed breakthrough concentrations using a distributed colloid filtration theory (D-CFT). Five different probability density functions (PDFs) were investigated and all accurately replicated the lab-scale experimental data, whereas a single alpha value could not. The alpha distribution shifted toward smaller values with decreasing ionic strength and the PDF parameters were strongly correlated to the Debye length, indicating that electrostatic interactions had a direct impact on the alpha distribution. The results indicate that while ionic strength has a large impact on bacterial transport distances for a concentration reduction of a few orders of magnitude, as occurs at the laboratory scale, due to the distributed nature of the collision efficiency, it has a minor effect on predicted transport distances required to achieve concentration reductions on the order of 10(6), which occurs at the field scale. Because of this, bacterial inactivation (e.g., death), rather than physically removing the bacteria from solution via filtration, is likely the key process impacting the transport of viable bacteria at the field scale. Overall, for systems with a distributed alpha, the results indicate that ionic strength has a strong influence on the transport of bacteria at the lab-scale (centimeters to one meter), both ionic strength and bacterial inactivation are important at the meso-scale (tens of meters), and inactivation becomes the dominant mechanism for reducing the transport of viable bacteria at the field scale (hundreds of meters).     

Feather mercury concentrations and physiological condition of great egret and white ibis nestlings in the Florida Everglades

Mercury contamination in the Florida Everglades has reportedly played a role in the recent decline of wading birds, although no studies have identified a mechanism leading to population-level effects. We assessed feather mercury levels in great egret (Ardea alba; n = 91) and white ibis (Eudocimus albus; n = 46) nestlings at breeding colonies in the Florida Everglades during a year (2006) with excellent breeding conditions (characterized by hydrology leading to concentrated prey) and a year with below average breeding conditions (2007). We also assessed the physiological condition of those nestlings based on levels of plasma and fecal corticosterone metabolites, and stress proteins 60 and 70. Mercury levels were higher in both species during the good breeding condition year (great egret = 6.25 μg/g ± 0.81 SE, white ibis = 1.47 μg/g ± 0.41 SE) and lower in the below average breeding year (great egret = 1.60 μg/g ± 0.11 SE, white ibis = 0.20 μg/g ± 0.03 SE). Nestlings were in better physiological condition in 2006, the year with higher feather mercury levels. These results support the hypothesis that nestlings are protected from the harmful effects of mercury through deposition of mercury in growing feathers. We found evidence to suggest shifts in diets of the two species, as a function of prey availability, thus altering their exposure profiles. However, we found no evidence to suggest they respond differently to mercury exposure.     

Spatial distribution of jet fuel in the vadoze zone of a heterogeneous and fractured soil

The goal of the present work is to screen and evaluate all available data before selecting and testing remediation technologies on heterogeneous soils polluted by jet fuel. The migration pathways of non-aqueous phase liquids (NAPLs) in the subsurface relate closely with soil properties. A case study is performed on the vadoze zone of a military airport of north-west Poland contaminated by jet fuel. Soil samples are collected from various depths of two cells, and on-site and off-site chemical analyses of hydrocarbons are conducted by using Pollut Eval® apparatus and GC-MS, respectively. The geological conceptual model of the site along with microscopic and hydraulic properties of the porous matrix and fractures enable us to interpret the non-uniform spatial distribution of jet fuel constituents. The total concentration of the jet fuel and its main hydrocarbon families (n-paraffins, major aromatics) over the two cells is governed by the slow preferential flow of NAPL through the porous matrix, the rapid NAPL convective flow through vertical desiccation and sub-horizontal glaciotectonic fractures, and n-paraffin biodegradation in upper layers where the rates of oxygen transfer is not limited by complexities of the pore structure. The information collected is valuable for the selection, implementation and evaluation of two in situ remediation methods.     

Dynamic and distribution of ammonia-oxidizing bacteria communities during sludge granulation in an anaerobic-aerobic sequencing batch reactor

The structure dynamic of ammonia-oxidizing bacteria (AOB) community and the distribution of AOB and nitrite-oxidizing bacteria (NOB) in granular sludge from an anaerobic-aerobic sequencing batch reactor (SBR) were investigated. A combination of process studies, molecular biotechniques and microscale techniques were employed to identify and characterize these organisms. The AOB community structure in granules was substantially different from that of the initial pattern of the inoculants sludge. Along with granules formation, the AOB diversity declined due to the selection pressure imposed by process conditions. Denaturing gradient gel electrophoresis (DGGE) and sequencing results demonstrated that most of Nitrosomonas in the inoculating sludge were remained because of their ability to rapidly adapt to the settling-washing out action. Furthermore, DGGE analysis revealed that larger granules benefit more AOB species surviving in the reactor. In the SBR were various size granules coexisted, granule diameter affected the distribution range of AOB and NOB. Small and medium granules (d < 0.6 mm) cannot restrict oxygen mass transfer in all spaces of the sludge. Larger granules (d > 0.9 mm) can result in smaller aerobic volume fraction and inhibition of NOB growth. All these observations provide support to future studies on the mechanisms responsible for the AOB in granules systems.     

Effect of temperature and disinfection strategies on ammonia-oxidizing bacteria in a bench-scale drinking water distribution system

The establishment of ammonia-oxidizing bacteria (AOB), a group of autotrophic microorganisms responsible for nitrification in chloraminated distribution systems, was studied in a bench-scale distribution system. The potential significance of temperature and disinfectant residual associated with chloramination in full-scale drinking water distribution systems was assessed. Biofilm development was primarily monitored using AOB abundance and nitrite concentrations. The bench-scale system was initially operated under typical North American summer (22 degrees C) and fall (12 degrees C) temperatures, representing optimal and less optimal growth ranges for these microorganisms. Additional experimentation investigated AOB establishment at a suboptimal winter distribution system temperature of 6 degrees C. The effect of chloramine residual on AOB establishment was studied at higher (0.2-0.6mg/L) and lower (0.05-0.1mg/L) ranges, using a 3:1 (w/w) chlorine:ammonia dosing ratio. Conditions were selected to represent those typically found in a North American distribution system, in areas of low flow and longer retention times, respectively. Finally, the effect of a free chlorine residual on an established nitrifying biofilm was briefly examined. Results clearly indicate that AOB development occurs at all examined temperatures, as well as at selected monochloramine residuals. The maintenance of a disinfectant residual was difficult at times, but was more inhibitory to the nitrifying biofilm than the lower temperature. It can be concluded from the data that nitrification may not be adequately inhibited during the winter months, which may result in more advanced stages of nitrification the following season. Free chlorination can be effective in controlling AOB activity in the short term, but may not prevent reestablishment of a nitrifying biofilm upon return to chloramination.     

Diurnal distribution of airborne bacteria and fungi in the atmosphere of Helwan area, Egypt

Airborne bacterial and fungal composition in an industrial town of Helwan, Egypt, was studied using a slit impactor sampler during the period from March 2006 to February 2007. Airborne bacterial concentrations were usually higher than fungi. Bacteria and fungi had similar diurnal variation patterns. Airborne microorganisms reached their concentration peaks in the evening and gradually decreased during the night time. The hourly concentration peaks of the bacteria and fungi appeared at 20:00 h. A significant difference (P ≤ 0.05) was found between the hourly mean concentrations of airborne fungi in winter compared to other seasons. Fungi concentrations were significantly higher (P ≤ 0.05) on working weekdays than weekends. Aspergillus, Penicillium, Alternaria and Cladosporium were the most predominant airborne fungal genera. Aspergillus showed double peak patterns whereas Penicillium, Alternaria and Cladosporium showed one peak pattern. The diurnal variations of the bacteria and fungi could be divided into four periods: 1) the morning maximum concentration (6:00 h-10:00 h), 2) midday to afternoon pattern (10:00 h-16:00 h), 3) the evening concentration peak (18:00 h-20:00 h) and 4) the gradual decrease of night time concentration (22:00 h-24:00 h). Geographical location, human activity, growth cycle of organisms and meteorological factors were the main criteria controlling the temporal variations of the air microorganisms in the Wadi Hof area.     

Role of biodegradation in the removal of pharmaceutically active compounds with different bulk organic matter characteristics through managed aquifer recharge: batch and column studies

Natural water treatment systems such as bank filtration have been recognized as providing effective barriers in the multi-barrier approach for attenuation of organic micropollutants for safe drinking water supply. In this study, the role of biodegradation in the removal of selected pharmaceutically active compounds (PhACs) during soil passage was investigated. Batch studies were conducted to investigate the removal of 13 selected PhACs from different water sources with respect to different sources of biodegradable organic matter. Neutral PhACs (phenacetine, paracetamol, and caffeine) and acidic PhACs (ibuprofen, fenoprofen, bezafibrate, and naproxen) were removed with efficiencies greater than 88% from different organic matter water matrices during batch studies (hydraulic retention time (HRT): 60 days). Column experiments were then performed to differentiate between biodegradation and sorption with regard to the removal of selected PhACs. In column studies, removal efficiencies of acidic PhACs (e.g., analgesics) decreased under conditions of limited biodegradable carbon. The removal efficiencies of acidic PhACs were found to be less than 21% under abiotic conditions. These observations were attributed to sorption under abiotic conditions established by a biocide (20 mM sodium azide), which suppresses microbial activity/biodegradation. However, under biotic conditions, the removal efficiencies of these acidic PhACs were found to be greater than 59%. This is mainly attributed to biodegradation. Moreover, the average removal efficiencies of hydrophilic (polar) neutral PhACs (paracetamol, pentoxifylline, and caffeine) with low octanol/water partition coefficients (log K_ow less than 1) were low (11%) under abiotic conditions. However, under biotic conditions, removal efficiencies of the neutral PhACs were greater than 98%. In contrast, carbamazepine persisted and was not easily removed under either biotic or abiotic conditions. This study indicates that biodegradation represents an important mechanism for the removal of PhACs during soil passage.     

Analysis of the bacterial community in a laboratory-scale nitrification reactor and a wastewater treatment plant by 454-pyrosequencing

For full understanding of the microbial community in the wastewater treatment bioreactors, one of the feasible and effective ways is to investigate the massive genetic information contained in the activated sludge. In this study, high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in a laboratory-scale nitrification reactor and a full-scale wastewater treatment plant. In total, 27,458 and 26,906 effective sequence reads of the 16S rRNA gene were obtained from the Reactor and the wastewater treatment plant activated sludge samples respectively. The taxonomic complexities in the two samples were compared at phylum and genus levels. According to the pyrosequencing results, even for a laboratory-scale reactor as simple as that in this study, a small size clone library is far from enough to reflect the whole profile of the bacterial community. In addition, it was found that the commonly used informatics tool “RDP classifier” may drastically assign Nitrosomonas sequences into a wrong taxonomic unit resulting in underestimation of ammonia-oxidizing bacteria in the bioreactors. In this paper the reasons for this mistakenly assignment were analyzed and correction methods were proposed.     

Spatial distribution and temporal variation of metals in the vicinity of a municipal solid waste incinerator after a modernization of the flue gas cleaning systems of the facility

In June 1994 and 1997, the concentrations of a number of elements were determined in soil and herbage samples collected in the vicinity of a municipal solid waste incinerator (MSWI) (Tarragona, Catalonia, Spain). In August 1997, an adaptation to the EU legislation on pollutant emissions from the stack was carried out to the incinerator. In June 1999, soil and herbage samples were collected again at the same sampling points and the levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni) and vanadium (V) were measured by ICP-MS or AAS with graphite furnace. The results are compared with those obtained in the 1994 and 1997 surveys. In the period 1997-1999, the only significant changes in soil levels corresponded to Cd and Pb, with decreases of 21.0% and 53.5%, respectively. In vegetation, only Mn levels showed a significant reduction, which contrasts with the notable increases found in the concentrations of As, Hg and Ni. According to the results of this survey, it seems evident that other metal emission sources in the same area of study are masking the environmental improvements carried out in the MSWI.     

Assessment of the microclimatic and human comfort conditions in a complex urban environment: Modelling and measurements

Several complex thermal indices (e.g. Predicted Mean Vote and Physiological Equivalent Temperature) were developed in the last decades to describe and quantify the thermal environment of humans and the energy fluxes between body and environment. Compared to open spaces/landscapes the complex surface structure of urban areas creates an environment with special microclimatic characteristics, which have a dominant effect on the energy balance of the human body. In this study, outdoor thermal comfort conditions are examined through two field-surveys in Szeged, a South-Hungarian city (population 160,000). The intensity of radiation fluxes is dependent on several factors, such as surface structure and housing density. Since our sample area is located in a heavily built-up city centre, radiation fluxes are mainly influenced by narrow streets and several 20–30-year-old (20–30 m tall) trees. Special emphasis is given to the human-biometeorological assessment of the microclimate of complex urban environments through the application of the thermal index PET. The analysis is carried out by the utilization of the RayMan model. Firstly, bioclimatic conditions of sites located close to each other but shaded differently by buildings and plants are compared. The results show that differences in the PET index amongst these places can be as high as 15–20 ^°C${}^{°}\mathrm{C}$ due to the different irradiation. Secondly, the investigation of different modelled environments by RayMan (only buildings, buildings+trees$\mathrm{buildings}+\mathrm{trees}$ and only trees) shows significant alterations in the human comfort sensation between the situations.     

Spatial and temporal distribution of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere of Xiamen, China

An intensive sampling program was conducted from October 2008 to September 2009 at the five different environmental sites in Xiamen, Fujian Province, to study the spatial and temporal characteristics of Polycyclic Aromatic Hydrocarbons (PAHs) in the gaseous and particulate phase, respectively. The PAHs concentrations at different sites were quite distinct during four seasons. The average concentrations of PAHs in winter were about 8.4 times higher than those in spring, and the concentrations of background were 0.56 times lower than those of industrial area. In addition, the higher temperature in summer affected the particle/gas partitioning of PAHs and led to the higher concentrations of gaseous PAHs. Diagnostic ratios of PAHs, which were employed to indicate the primary sources of PAHs in Xiamen, showed that the traffic vehicle exhaust was the largest contributor and the primary source for PAHs in Xiamen, especially in urban area; while the stationary combustion processes, such as petrochemical factories and power plants, were mainly responsible for PAHs sources in the industrial areas. The health risk of PAHs in the particulate phase was higher than those of the gaseous phase at the five sampling sites. The average toxic equivalent (BaP_eq) of the benzo[a]pyrene values for PAHs were 0.14, 0.32, 1.38 and 3.59 ng m^− 3 in spring, summer, autumn and winter, respectively. Furthermore, the results of average BaP_eq in all four seasons indicated that the health risks of particulate PAHs were higher than those of the gaseous PAHs at different sampling sites.     

Spatial distribution of arsenic and heavy metals in willow roots from a contaminated floodplain soil measured by X-ray fluorescence spectroscopy

Under changing redox conditions some plants create plaques at their root surface, which may affect the mobility and uptake of As and heavy metals but it is unknown to what extent this also holds true for willows in contaminated floodplain soils. Therefore, willow roots were sampled from a phytoremediation trial in the contaminated floodplain of the river Elbe (Germany), cryofixed, freeze-dried, and cross sections were mapped for the distribution of As, Ca, Cu, Fe, K, Mn, Ni, S and Zn by synchrotron based X-ray fluorescence spectroscopy. The elements Ca, Cu, Ni, S and Zn were concentrated in the aerenchymatic tissue, and not associated with Fe and Mn. Mixed Fe-Mn plaques covered the surface of the willow roots and As was accumulated in these plaques. The observed association pattern between As and Fe was explained by the different sorption/desorption properties of As(III) and As(V). The Cu and Zn intensities were not associated with the intensity of Fe in the plaque, which seems to be a willow-specific difference compared to other wetland plants. These results suggested that willows are especially suited to stabilize low-phytoextractable elements like Cu and As in their roots and rhizosphere. Thus, short rotation coppicing of willows may be a practical approach to mitigate the adverse effects of floodplain soil contamination.     

Modeling the competitive effect of ammonium oxidizers and heterotrophs on the degradation of MTBE in a packed bed reactor

A mathematical model was used to study effects on the degradation of methyl tert-butyl ether (MTBE) in a packed bed reactor due to the presence of contaminants such as ammonium, and the mix of benzene, toluene, ethylbenzene and xylenes (BTEX). It was shown that competition between the slower growing MTBE degraders and the co-contaminant oxidizers prevented MTBE's degradation when oxygen was limited. In this event, the co-contaminant oxidizers out-competed the MTBE degraders in the reactor's biofilm. However, if the oxygen supply was sufficient, MTBE would be fully degraded after the zone where the co-contaminants were oxidized. The results of the model further indicate that contradicting findings in the literature about the effects of BTEX on the degradation of MTBE are mainly due to differences in the study methodologies. Effects such as short-term toxicity of BTEX and the lack of steady-state conditions may also add to contradictions among reports.     

Effect of nitrite concentration on the distribution and competition of nitrite-oxidizing bacteria in nitratation reactor systems and their kinetic characteristics

Genus Nitrospira and Nitrobacter species are the key nitrite-oxidizing bacteria (NOB) in nitrifying wastewater treatment plants. It has been hypothesized that genus Nitrospira are K-strategists and can exploit low amounts of nitrite more efficiently than Nitrobacter. In contrast, Nitrobacter species are r-strategists that can grow faster than Nitrospira. To elucidate the K/r hypothesis and to analyze the effect of substrate (nitrite) concentration on the competition and distribution of the two NOB, two different reactor types were employed for nitrite oxidation (nitratation) and NOB growth. The continuous biofilm airlift reactor (CBAR) maintained low nitrite concentration due to the complete oxidation of nitrite in continuous operation while the sequencing batch reactor (SBR) was kept in a relatively high nitrite concentration environment due to a cyclic substrate concentration profile. Fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) showed that both Nitrobacter species and genus Nitrospira were present in the CBAR and the SBR. Quantitative FISH analyses of the CBAR showed that Nitrospira occupied 59% of the total bacteria while Nitrobacter occupied only 5%. On the other hand, Nitrobacter, occupying 64%, was the dominant NOB in the SBR, and only 3% of total bacteria belonged to genus Nitrospira. Nitrite oxidation kinetics and quantitative FISH analyses revealed that the specific nitrite oxidation activities of Nitrobacter and Nitrospira are 93.8 and 10.5 mg/g NOB h, respectively, and the specific activity of Nitrobacter is about 9 times higher than that of Nitrospira. In conclusion, the results confirm the K/r hypothesis and the distribution of Nitrobacter and Nitrospira is likely to depend mainly on nitrite concentration. It seems that nitrite load and starvation conditions do not give a direct effect on the distribution of NOB.     

The effect of tidal heights on the distribution and abundance of coliform bacteria in the sediments of two sites in the Mersey Estuary

An investigation of the tidal factors controlling the abundance and distribution of coliform bacteria in the sediments of two intertidal sites in the River Mersey (U.K.) was made during 1976. Samples were collected, at approximately weekly intervals, from September to December. Counts of the total coliform, faecal coliform and E. coli type I, were made in order to relate the numbers of bacteria to the salinity conditions of the tidal waters covering the sites. Correlations were observed between coliform counts, chloride content and tidal heights.     

基于频谱分析的饱和砂土场地直斜群桩承台——土体耦合作用下桩身弯矩分布规律研究

地震荷载作用下,群桩结构受到承台和土体共同作用,不同桩型的桩身弯矩会发生明显变化,尤其在饱和砂土条件下。因此,为研究上述问题,利用浙江大学ZJU400土工离心机进行饱和砂土场地直斜群桩地震动力响应试验,并通过频谱分析的方法,对饱和砂土场地和直斜群桩桩顶承台的频谱成分进行详细分析,之后根据得出的不同频率成分分别对直斜群桩桩身弯矩分布情况进行详细研究。研究结果表明:地震荷载作用下饱和砂土液化前后土体特征频率发生明显变化,液化后土体的特征频率明显变小;随着振动强度的增加,斜桩顶承台特征频率也发生了减小的现象,而直桩桩顶承台特征频率则始终保持在0～2Hz,未发生明显变化;不同振动强度下,不同频率成分对于直斜群桩桩身弯矩包络图的影响发生了较大的变化,在0.05 g工况下0～2 Hz频谱成分对斜群桩桩身弯矩影响要小于2～5 Hz,但其他工况下0～2 Hz频谱成分对于直斜群桩桩身弯矩的影响均最为明显。同时,随着振动强度的增加,土体埋深范围内直群桩桩身弯矩包络图的峰值位置发生了下移。因此,在实际工程中应考虑此问题,适当增加弯矩较大值位置附近的桩身抗弯刚度。     

Determination of the natural stress state in a Brazilian rock mass by back analysing excavation measurements: a case study

The Serra da Mesa Hydroelectric Power Plant, located in the Tocantins river, 210 km north of Brasilia, Brazil, has been completed and power (1200 MW) has been generated since 1998. This project includes one of the largest underground structures in Brazil, totalling 550,000 m³ of underground excavations in rock for the hydraulic circuit which was excavated in very high quality granite. Geotechnical investigations, laboratory tests and geological mapping showed that the rock mass could be considered as a continuous, homogeneous, isotropic and linearly elastic (CHILE) material.

In situ tests, for obtaining the natural stress tensor, namely hydraulic fracturing and small flat jack tests (SFJ), were executed. The hydraulic fracturing tests were performed in two boreholes, at the planned position of the future underground structures. SFJ were executed in a test gallery especially constructed for the purpose. These latter tests confirmed the in situ rock stress data obtained from the hydraulic fracturing tests.

This paper presents a new technique for interpretation of the SFJ results. This is achieved by inputting the SFJ measurements into a 3D program that compiles the influence matrix of the excavated rock mass domain and then, via the least square technique, the determination of the stress tensor. All the equations are fully developed and the methodology is presented in its entirety. The successful application of the methodology is also presented, with comparisons between the results obtained and the in situ stress tensor determined by other methods.