Kinetic and microbial community analysis of methyl ethyl ketone biodegradation in aquifer sediments

Methyl ethyl ketone (MEK) is a common groundwater contaminant often present with more toxic compounds of primary interest. Because of this, few studies have been performed to determine the effect of microbial community structure on MEK biodegradation rates in aquifer sediments. Here, microcosms were prepared with aquifer sediments containing MEK following a massive spill event and compared to laboratory-spiked sediments, with MEK biodegradation rates quantified under mixed aerobic/anaerobic conditions. Biodegradation was achieved in MEK-contaminated site sediment microcosms at about half of the solubility (356 mg/L) with largely Firmicutes population under iron-reducing conditions. MEK was biodegraded at a higher rate [4.0 ± 0.74 mg/(L days)] in previously exposed site samples compared to previously uncontaminated sediments [0.51 ± 0.14 mg/(L days)]. Amplicon sequencing and denaturing gradient gel electrophoresis of 16S rRNA genes were combined to understand the relationship between contamination levels, biodegradation, and community structure across the plume. More heavily contaminated sediments collected from an MEK-contaminated field site had the most similar communities than less contaminated sediments from the same site despite differences in sediment texture. The more diverse microbial community observed in the laboratory-spiked sediments reduced MEK concentration 47 % over 92 days. Results of this study suggest lower rates of MEK biodegradation in iron-reducing aquifer sediments than previously reported for methanogenic conditions and biodegradation rates comparable to previously reported nitrate- and sulfate-reducing conditions.     

Treatment of raw and ozonated oil sands process-affected water under decoupled denitrifying anoxic and nitrifying aerobic conditions: a comparative study

Batch experiments were performed to evaluate biodegradation of raw and ozonated oil sands process-affected water (OSPW) under denitrifying anoxic and nitrifying aerobic conditions for 33 days. The results showed both the anoxic and aerobic conditions are effective in degrading OSPW classical and oxidized naphthenic acids (NAs) with the aerobic conditions demonstrating higher removal efficiency. The reactors under nitrifying aerobic condition reduced the total classical NAs of raw OSPW by 69.1 %, with better efficiency for species of higher hydrophobicity. Compared with conventional aerobic reactor, nitrifying aerobic condition substantially shortened the NA degradation half-life to 16 days. The mild-dose ozonation remarkably accelerated the subsequent aerobic biodegradation of classical NAs within the first 14 days, especially for those with long carbon chains. Moreover, the ozone pretreatment enhanced the biological removal of OSPW classical NAs by leaving a considerably lower final residual concentration of 10.4 mg/L under anoxic conditions, and 5.7 mg/L under aerobic conditions. The combination of ozonation and nitrifying aerobic biodegradation removed total classical NAs by 76.5 % and total oxy-NAs (O3–O6) by 23.6 %. 454 Pyrosequencing revealed that microbial species capable of degrading recalcitrant hydrocarbons were dominant in all reactors. The most abundant genus in the raw and ozonated anoxic reactors was Thauera (~56 % in the raw OSPW anoxic reactor, and ~65 % in the ozonated OSPW anoxic reactor); whereas Rhodanobacter (~40 %) and Pseudomonas (~40 %) dominated the raw and ozonated aerobic reactors, respectively. Therefore, the combination of mild-dose ozone pretreatment and subsequent biological process could be a competent choice for OSPW treatment.     

Bioremediation of Polyaromatic Hydrocarbon-Contaminated Sediments in Aerated Bioslurry Reactors

Treatment of dredged sediments contaminated by polyaromatic hydrocarbons (PAHs) is a significant problem in the New York/New Jersey (NY/NJ) Harbor. 0.5 m³-scale slurry-phase bioreactors were used to determine whether bioaugmentation with a PAH-degradative bacterial consortium, or with the salt marsh grass S. alterniflora, could enhance the biodegradation of PAHs added to dredged estuarine sediments from the NY/NJ Harbor. The results were compared to biodegradation effected by the indigenous sediment microbial community. Sediments were diluted 1:1 in tap water and spiked to a final concentration of 20 mg/kg dry weight sediment of phenanthrene, anthracene, acenaphthene, fluorene, fluoranthene, and pyrene. The sediment slurry was then continuously sparged with air over 3 months. In all bioreactors a rapid reduction of greater than 95% of the initial phenanthrene, acenaphthene, and fluorene occurred within 14 days. Pyrene and fluoranthene reductions of 70 to 90% were achieved by day 77 of treatment. Anthracene was more recalcitrant and reductions ranged from 30 to 85%. Separate experiments showed that the sediment microbial communities mineralized ¹⁴C-pyrene and ¹⁴C-phenanthrene. PAH degradation, and the number of phenanthrene-degrading bacteria, were not enhanced by microbial or plant bioaugmentation. These data demonstrate that bioaugmentation is not required to effect efficient remediation of PAH-contaminated dredged sediments in slurry-phase bioreactors.     

Development of a sediment bioassay to determine bioavailability of PAHs to fish

Recent work has shown that MFO induction and loss of control of steroid hormone production occurs in fish after exposure to pulp mill effluents, PCBs, PAHs, and some pesticides. We had recently developed laboratory assays to evaluate the effluents on these responses, but were lacking a protocol for a sediment assay. This paper describes the development of a sediment test capable of demonstrating MFO induction in fish. MFO responses were evident in rainbow trout within 4 days of exposure to contaminated sediments. Further testing showed that fish were responding to chemicals from the sediments, but not from bottom water, and a survey of sediment from thirteen contaminated areas showed that MFO induction more closely paralleled PAH levels in the sediments than the observed PCB concentrations. The sites showing MFO induction were also the sites where sediment toxicity was demonstrated with laboratory bioassays using Daphnia magna and Hyalella azteca. The protocol has been further refined to describe the quantity of sediment required and duration of testing. This test will enable us to study the biochemical effects of exposure to contaminated sediments. The protocol could also be used to prioritize areas of contamination and to evaluate dredging impacts and remediation success.     

Biodegradation of Pyrene in Marine Beach Sediments

The potential of chitosan (0.1% dry weight equivalent) as a bioremediation additive for removal of the recalcitrant polycyclic aromatic hydrocarbon (PAH) pyrene in marine beach sediments was investigated using an open irrigation system over a 63-day period. Osmocote, a slow release fertilizer, was used as the key nutrient supplement at a concentration of 1% in sediment (dry weight equivalent). Osmocote significantly (p < .05) enhanced nutrient levels, and the metabolic activity of the indigenous microbial biomass. Both additives were comparable in stimulating pyrene biodegradation rates; with chitosan (0.062 day^?1) being slightly more effective as an amendment than Osmocote (0.051 day^?1). Loss of pyrene in a control sediment (i.e., pyrene, without additives) was 66.6% over a 63-day period. The concurrent application of additives yielded the greatest biodegradation rates (0.072day^?1), resulting in a 98.2% loss of pyrene over 63 days. The treatment of oil contaminated beach sediments with both osmocote (1%) and chitosan (0.1%) is therefore recommended as an effective treatment for the intrinsic biodegradation of recalcitrant PAHs in oil-contaminated beach sediments.     

Increased Capacity for Polycyclic Aromatic Hydrocarbon Mineralization in Bioirrigated Coastal Marine Sediments

Bioirrigation of marine sediments by benthic infauna has the potential to increase both the rate and depth of bacterial mineralization of polycyclic aromatic hydrocarbons (PAHs) by recirculating oxygenated bottom water into sediment burrows. Rates of heterotrophic bacterial production and mineralization of PAHs (naphthalene, phenanthrene, and fluoranthene) were measured in sections of sediment cores sampled from stations in San Diego Bay. Data suggest that rates of PAH biodegradation and bacterial heterotrophy were influenced by bioirrigation by benthic infauna. PAH mineralization and heterotrophic production were higher in core sections where sulfide was not detected relative to core sections containing sulfide. Depth-integrated capacity of the upper 17 cm of sediment to mineralize PAHs was 4 to 10 times higher at the station with bioirrigation coefficients that increased with depth. Remedial dredging of sediments to remove contaminant mass (and presumable lower ecological risk) will also remove benthic infauna. Removal of infauna and the subsequent lowering of bioirrigation in surface sediments would be expected to lower the capacity of intrinsic PAH bioremediation. This could cause local increases in ambient PAH concentration and consequently increase the ecological risk at the site and potentially degrade the health of the ecosystem by removing a sink for PAHs.     

Biodegradation and proton exchange using natural rubber in microbial fuel cells

Microbial fuel cells (MFCs) generate electricity from waste but to date the technology’s development and scale-up has been held-up by the need to incorporate expensive materials. A costly but vital component is the ion exchange membrane (IEM) which conducts protons between the anode and cathode electrodes. The current study compares natural rubber as an alternative material to two commercially available IEMs. Initially, the material proved impermeable to protons, but gradually a working voltage was generated that improved with time. After 6 months, MFCs with natural rubber membrane outperformed those with anion exchange membrane (AEM) but cation exchange membrane (CEM) produced 109 % higher power and 16 % higher current. After 11 months, polarisation experiments showed a decline in performance for both commercially available membranes while natural rubber continued to improve and generated 12 % higher power and 54 % higher current than CEM MFC. Scanning electron microscope images revealed distinct structural changes and the formation of micropores in natural latex samples that had been employed as IEM for 9 months. It is proposed that the channels and micropores formed as a result of biodegradation were providing pathways for proton transfer, reflected by the steady increase in power generation over time. These improvements may also be aided by the establishment of biofilms that, in contrast, caused declining performance in the CEM. The research demonstrates for the first time that the biodegradation of a ubiquitous waste material operating as IEM can benefit MFC performance while also improving the reactor’s lifetime compared to commercially available membranes.     

In situ phytoremediation of PAH- and PCB-contaminated marine sediments with eelgrass (Zostera marina)

In view of the fact that there are presently no cost-effective in situ treatment technologies for contaminated sediments, a 60-week-long phytoremediation feasibility study was conducted in seawater-supplied outdoor ponds to determine whether eelgrass (Zostera marina) is capable of removing polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) from submerged marine sediments. It was determined that all PAHs and PCBs, independent of the number of aromatic rings and degree of chlorination, respectively, were removed to a much larger extent in planted sediments compared to unplanted controls. After 60 weeks of treatment, the concentration of total PAHs decreased by 73% in planted sediments but only 25% in unplanted controls. Similarly, total PCBs declined by 60% in the presence of plants while none were removed in the unplanted sediment. Overall, the apparent PAH and PCB biodegradation was greatest in the sediment layer that contained most of the eelgrass roots. Abiotic desorption tests conducted at week 32 confirmed that the phytoremediation process was not controlled by mass-transfer or bioavailability limitations since all PAHs and PCBs desorbed rapidly and to a large extent from the sediment. PAHs were detected in both roots and shoots, with root and shoot bioaccumulation factors for total PAHs amounting to approximately 3 and 1, respectively, after 60 weeks of phytoremediation treatment. Similarly, the root bioaccumulation factor for total PCBs was around 4, while no PCBs were detected in the eelgrass leaves at the end of the experiment. The total mass fraction of PAHs and PCBs absorbed and translocated by plant biomass during the 60-week period was insignificant, amounting to less than 0.5% of the total mass of PAHs and PCBs which was initially present in the sediment. Finally, the number of total heterotrophic bacteria and hydrocarbon degraders was slightly but not statistically significantly greater in planted sediments than in unplanted controls. After ruling out contaminant loss to the water column or absorption and transformation within plant cells, it is most likely that the presence of eelgrass stimulated the microbial biodegradation of PAHs and PCBs in the rhizosphere by releasing root exudates, plant enzymes, or even oxygen. Additional research is needed to further elucidate these potential phytoremediation mechanisms.     

Distribution,Sources Identification,and Ecological Risk of PAHs and PCBs in Coastal Surface Sediments from the Northern Persian Gulf

Hormozgan Province plays a vital role in fishery, petroleum, and industrial activities in southern Iran. However, no comprehensive studies on organic pollution have been performed. PCBs and PAHs were analyzed in surface sediments from areas receiving industrial (nine sites), river (one site), and urban (two sites) effluents. The sediment samples were collected in March and September 2010 (in dry and wet seasons) at the highest tidal time. The overall pollution level of PCBs ranged from 2.5 ± 0.8 to 462.0 ± 206.7 ng/g dry weight. CB153 congener dominated in most of the sediment samples. Congener profiles of PCBs showed close similarity with formulations of commercial products such as Aroclor 1260 and 1254 g. A wide range of 55.3 to 1231.6 ng/g dry weight was detected for ∑PAHs. Results of PCA and PCA-MLR tests confirmed both petrogenic and pyrogenic origins for PAH pollution. The higher means of ∑PAHs and ∑PCBs in industrial and urban wastewaters were found near the shore, evidencing the role of these wastewaters in the PAH and PCB contamination in Hormozgan sediment. The concentrations of PAHs and PCBs in detected hotspots exceed the U.S. NOAA sediment quality guidelines.     

Aerobic MTBE biodegradation in the presence of BTEX by two consortia under batch and semi-batch conditions

This study explores the effect of microbial consortium composition and reactor configuration on methyl tert-butyl ether (MTBE) biodegradation in the presence of benzene, toluene, ethylbenzene and p-xylenes(BTEX). MTBE biodegradation was monitored in the presence and absence of BTEX in duplicate batch reactors inoculated with distinct enrichment cultures: MTBE only (MO—originally enriched on MTBE) and/or MTBE BTEX (MB—originally enriched on MTBE and BTEX). The MO culture was also applied in a semi-batch reactor which received both MTBE and BTEX periodically in fresh medium after allowing cells to settle. The composition of the microbial consortia was explored using a combination of 16S rRNA gene cloning and quantitative polymerase chain reaction targeting the known MTBE-degrading strain PM1^T. MTBE biodegradation was completely inhibited by BTEX in the batch reactors inoculated with the MB culture, and severely retarded in those inoculated with the MO culture (0.18 ± 0.04 mg/L-day). In the semi-batch reactor, however, the MTBE biodegradation rate in the presence of BTEX was almost three times as high as in the batch reactors (0.48 ± 0.2 mg/L-day), but still slower than MTBE biodegradation in the absence of BTEX in the MO-inoculated batch reactors (1.47 ± 0.47 mg/L-day). A long lag phase in MTBE biodegradation was observed in batch reactors inoculated with the MB culture (20 days), but the ultimate rate was comparable to the MO culture (0.95 ± 0.44 mg/L-day). Analysis of the cultures revealed that strain PM1^T concentrations were lower in cultures that successfully biodegraded MTBE in the presence of BTEX. Also, other MTBE degraders, such as Leptothrix sp. and Hydrogenophaga sp. were found in these cultures. These results demonstrate that MTBE bioremediation in the presence of BTEX is feasible, and that culture composition and reactor configuration are key factors.     

Basic examinations on chemical pre-oxidation by ozone for enhancing bioremediation of phenanthrene contaminated soils

Biological treatment of polycyclic aromatic hydrocarbons (PAH) has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the clean-up of contaminated soils. Because bioavailability of the contaminants is of great importance for a successful bioremediation, a chemical pre-oxidation step by ozone was tested to enhance the subsequent biodegradation steps. Oxidation of PAH by ozone should result in reaction products that have a better solubility in water and thus a better bioavailability. A major part of this work was done by examinations of the model substance phenanthrene as a typical compound of PAH. After initial ozonation of phenanthrene, analysis by GC-MS showed at least seven identified conversion-products of phenanthrene. In comparison with phenanthrene these conversion products were more efficiently biodegraded by Sphingomonas yanoikuyae or mixed cultures when the ozonation process resulted in monoaromatic compounds. Primary ozonation products with biphenylic structures were found not to be biodegradable. Investigations into the toxicity of contaminated and ozonated soils were carried out by well-established toxicity assays using Bacillus subtilis and garden cress. The ozonated soils surprisingly showed higher toxic or inhibitory effects towards different organisms than the phenanthrene or PAH itself. The microbial degradation of phenanthrene in slurry reactors by S. yanoikuyae was not enhanced significantly by preozonation of the contaminated soil.     

Naphthalene biodegradation in temperate and arctic marine microcosms

Naphthalene, the smallest polycyclic aromatic hydrocarbon (PAH), is found in abundance in crude oil, its major source in marine environments. PAH removal occurs via biodegradation, a key process determining their fate in the sea. Adequate estimation of PAH biodegradation rates is essential for environmental risk assessment and response planning using numerical models such as the oil spill contingency and response (OSCAR) model. Using naphthalene as a model compound, biodegradation rate, temperature response and bacterial community composition of seawaters from two climatically different areas (North Sea and Arctic Ocean) were studied and compared. Naphthalene degradation was followed by measuring oxygen consumption in closed bottles using the OxiTop^® system. Microbial communities of untreated and naphthalene exposed samples were analysed by polymerase chain reaction denaturing gradient gel electrophoresis (PCR–DGGE) and pyrosequencing. Three times higher naphthalene degradation rate coefficients were observed in arctic seawater samples compared to temperate, at all incubation temperatures. Rate coefficients at in situ temperatures were however, similar (0.048 day^?1 for temperate and 0.068 day^?1 for arctic). Naphthalene biodegradation rates decreased with similar Q₁₀ ratios (3.3 and 3.5) in both seawaters. Using the temperature compensation method implemented in the OSCAR model, Q₁₀ = 2, biodegradation in arctic seawater was underestimated when calculated from the measured temperate k₁ value, showing that temperature difference alone could not predict biodegradation rates adequately. Temperate and arctic untreated seawater communities were different as revealed by pyrosequencing. Geographic origin of seawater affected the community composition of exposed samples.     

Enhancing the intrinsic bioremediation of PAH-contaminated anoxic estuarine sediments with biostimulating agents

Estuarine sediments are frequently polluted with hydrocarbons from fuel spills and industrial wastes. Polycyclic aromatic hydrocarbons (PAHs) are components of these contaminants that tend to accumulate in the sediment due to their low aqueous solubility, low volatility, and high affinity for particulate matter. The toxic, recalcitrant, mutagenic, and carcinogenic nature of these compounds may require aggressive treatment to remediate polluted sites effectively. In petroleum-contaminated sediments near a petrochemical industry in Gwangyang Bay, Korea, in situ PAH concentrations ranged from 10 to 2,900 microg/kg dry sediment. To enhance the biodegradation rate of PAHs under anaerobic conditions, sediment samples were amended with biostimulating agents alone or in combination: nitrogen and phosphorus in the form of slow-release fertilizer (SRF), lactate, yeast extract (YE), and Tween 80. When added to the sediment individually, all tested agents enhanced the degradation of PAHs, including naphthalene, acenaphthene, anthracene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, and benzo[a]pyrene. Moreover, the combination of SRF, Tween 80, and lactate increased the PAH degradation rate 1.2-8.2 times above that of untreated sediment (0.01-10 microg PAH/kg dry sediment/day). Our results indicated that in situ contaminant PAHs in anoxic sediment, including high molecular weight PAHs, were degraded biologically and that the addition of stimulators increased the biodegradation potential of the intrinsic microbial populations. Our results will contribute to the development of new strategies for in situ treatment of PAH-contaminated anoxic sediments.     

Evaluation of 4-bromophenol biodegradation in mixed pollutants system by Arthrobacter chlorophenolicus A6 in an upflow packed bed reactor

Bromophenol is listed as priority pollutant by U.S. EPA, however, there is no report so far on its removal in mixed pollutants system by any biological reactor operated in continuous mode. Furthermore, bromophenol along with chlorophenol and nitrophenol are usually the major constituents of paper pulp and pesticide industrial effluent. The present study investigated simultaneous biodegradation of these three pollutants with specially emphasis on substrate competition and crossed inhibition by Arthrobacter chlorophenolicus A6 in an upflow packed bed reactor (UPBR). A 2³ full factorial design was employed with these pollutants at two different levels by varying their influent concentration in the range of 250–450 mg l^?1. Almost complete removal of all these pollutants and 97 % effluent toxicity removal were achieved in the UPBR at a pollutant loading rate of 1707 mg l^?1 day^?1 or lesser. However, at higher loading rates, the reactor performance deteriorated due to transient accumulation of toxic intermediates. Statistical analysis of the results revealed a strong negative interaction of 4-CP on 4-NP biodegradation. On the other hand, interaction effect between 4-CP and 4-BP was found to be insignificant. Among these three pollutants 4-NP preferentially degraded, however, 4-CP exerted more inhibitory effect on 4-NP biodegradation. This study demonstrated the potential of A. chlorophenolicus A6 for biodegradation of 4-BP in mixed pollutants system by a flow through UPBR system.     

Distribution characteristics,sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in sediments from Haizhou Bay,China

Sixteen USEPA priority polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography–mass spectrometry. Twenty samples were collected from the surface sediments of Haizhou Bay in this survey. This research aimed to identify the PAHs' contamination level, composition pattern, pollution sources, and assess the ecological risk of PAHs. The results showed that the sum of PAH concentrations ranged from 116.6 ng g^?1 to 2414.9 ng g^?1 (mean: 662.42 ng g^?1), which is higher than the reported values for different wetlands worldwide. Three- and four-ring PAHs (accounts for more than 70% of the total PAH content) were predominant in the wetland sediment. The PAHs source distribution in the surface sediments were determined using diagnostic ratio and PCA/MLR. Consequently, multiple PAHs sources were found. Of the total PAH, 79.25% was derived from vehicular emission, 20.75% from coal combustion. The effect range low/effect range median (ERL/ERM) values indicated a low toxicity risk level. However, the fluoranthene concentrations exceeded the ERL level, and even the ERM level, in some stations. The mean effects range–median quotient (M-ERM-Q) suggests a low ecological risk for the PAHs in the sediments.     

Monitoring nutrient impact on bacterial community composition during bioremediation of anoxic PAH-contaminated sediment

Marine harbor sediments are frequently polluted with significant amount of polycyclic aromatic hydrocarbons (PAHs) some of which are naturally toxic, recalcitrant, mutagenic, and carcinogenic. To stimulate biodegradation of PAHs in PAH-contaminated sediments collected from near Gwangyang Bay, Korea, lactate was chosen as a supplementary carbonaceous substrate. Sediment packed into 600 ml air-tight jar was either under no treatment condition or lactate amended condition (1%, w/v). Microbial community composition was monitored by bacteria-specific and archaea-specific PCR-terminal restriction fragment length polymorphism (T-RFLP), in addition to measuring the residual PAH concentration. Results showed that lactate amendment enhanced biodegradation rate of PAHs in the sediment by 4 to 8 times, and caused a significant shift in archaebacterial community in terms of structure and diversity with time. Phylogenetic analysis of 23 archaeal clones with distinctive RFLP patterns among 288 archaeal clones indicated that majority of the archaeal members were closest to unculturable environmental rDNA clones from hydrocarbon-contaminated and/or methanogenesis-bearing sediments. Lactate amendment led to the enrichment of some clones that were most closely related to PAH-degrading Methanosarcina species. These results suggest a possible contribution of methanogenic community to PAH degradation and give us more insights on how to effectively remediate PAH-contaminated sediments.     

Domestic wastewater treatment using multi-electrode continuous flow MFCs with a separator electrode assembly design

Treatment of domestic wastewater using microbial fuel cells (MFCs) will require reactors with multiple electrodes, but this presents unique challenges under continuous flow conditions due to large changes in the chemical oxygen demand (COD) concentration within the reactor. Domestic wastewater treatment was examined using a single-chamber MFC (130 mL) with multiple graphite fiber brush anodes wired together and a single air cathode (cathode specific area of 27 m²/m³). In fed-batch operation, where the COD concentration was spatially uniform in the reactor but changed over time, the maximum current density was 148?±?8 mA/m² (1,000 Ω), the maximum power density was 120 mW/m², and the overall COD removal was >90 %. However, in continuous flow operation (8 h hydraulic retention time, HRT), there was a 57 % change in the COD concentration across the reactor (influent versus effluent) and the current density was only 20?±?13 mA/m². Two approaches were used to increase performance under continuous flow conditions. First, the anodes were separately wired to the cathode, which increased the current density to 55?±?15 mA/m². Second, two MFCs were hydraulically connected in series (each with half the original HRT) to avoid large changes in COD among the anodes in the same reactor. The second approach improved current density to 73?±?13 mA/m². These results show that current generation from wastewaters in MFCs with multiple anodes, under continuous flow conditions, can be improved using multiple reactors in series, as this minimizes changes in COD in each reactor.     

Differences in Sediment Organic Matter Composition and PAH Weathering between Non-Vegetated and Recently Vegetated Fuel Oiled Sediments

We examined polycyclic aromatic hydrocarbon (PAH) attenuation in contaminated field sediments after only 2 years of plant growth. We collected sediments from vegetated and non-vegetated areas at the Indiana Harbor Canal (IHC), an industrialized area with historic petroleum contamination of soils and sediments. PAH concentrations, PAH weathering indices, and organic matter composition in sediments colonized by Phragmites, cattails, or willow trees were compared to the same indices for non-vegetated sediments. We hypothesized that bulk sediment and humin fractions with measurable increases in plant organic matter content would show measurable changes to PAH attenuation as indicated by more weathered PAH diagnostic ratios or reduced PAH concentrations. Carbon-normalized PAH concentrations were lower in vegetated bulk sediments but higher in vegetated humin fractions relative to non-vegetated sediment fractions. Total organic carbon content was not indicative of more weathered N₃/P₂ ratios or reduced PAH concentrations in vegetated sediment fractions. More weathered N₃/P₂ ratios were observed with increased modern carbon (plant carbon) content of vegetated sediment fractions. Phragmites sediments contained more modern carbon (plant carbon) and more weathered PAH ratios [C₃-naphthalenes and C₂-phenanthrenes (N₃/P₂)] than willow, cattail, and non-vegetated sediments.     

Open circuit versus closed circuit enrichment of anodic biofilms in MFC: effect on performance and anodic communities

The influence of various carbon anodes; graphite, sponge, paper, cloth, felt, fiber, foam and reticulated vitreous carbon (RVC); on microbial fuel cell (MFC) performance is reported. The feed was brewery wastewater diluted in domestic wastewater. Biofilms were grown at open circuit or under an external load. Microbial diversity was analysed as a function of current and anode material. The bacterial community formed at open circuit was influenced by the anode material. However at closed circuit its role in determining the bacterial consortia formed was less important than the passage of current. The rate and extent of organic matter removal were similar for all materials: over 95% under closed circuit. The biofilm in MFCs working at open circuit and in the control reactors, increased COD removal by up to a factor of nine compared with that for baseline reactors. The average voltage output was 0.6 V at closed circuit, with an external resistor of 300 kΩ and 0.75 V at open circuit for all materials except RVC. The poor performance of this material might be related to the surface area available and concentration polarizations caused by the morphology of the material and the structure of the biofilm. Peak power varied from 1.3 mW m^?2 for RVC to 568 mW m^?2 for graphite with biofilm grown at closed circuit.     

Dissolved Oxygen Saturation Controls PAH Biodegradation in Freshwater Estuary Sediments

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in terrestrial and aquatic environments and can represent a significant constituent of the carbon pool in coastal sediments. We report here the results of an 18-month seasonal study of PAH biodegradation and heterotrophic bacterial production and their controlling biogeochemical factors from 186 sediment samples taken in a tidally influenced freshwater estuary. For each sampling event, measurements were averaged from 25–45 stations covering ∼250 km². There was a clear relationship between bacterial production and ambient temperature, but none between production and bottom water dissolved oxygen (DO) % saturation or PAH concentrations. In contrast with other studies, we found no effect of temperature on the biodegradation of naphthalene, phenanthrene, or fluoranthene. PAH mineralization correlated with bottom water DO saturation above 70% (r² > 0.99). These results suggest that the proportional utilization of PAH carbon to natural organic carbon is as much as three orders of magnitude higher during cooler months, when water temperatures are lower and DO % saturation is higher. Infusion of cooler, well-oxygenated water to the water column overlying contaminated sediments during the summer months may stimulate PAH metabolism preferentially over non-PAH organic matter.