Spatio-temporal variation of the microbial community of the coast of Lebanon in response to petroleum hydrocarbon pollution

In this study, the coast of Lebanon was analyzed for the dynamic changes in sediment microbial communities in response to a major petroleum oil spill and tar contamination that occurred in the summer of 2021. Spatio-temporal variations in the microbial structure along the shores of Lebanon were assessed in comparison to baseline microbial structure determined in 2017. Microbial community structure and diversity were determined using Illumina MiSeq technology and DADA2 pipeline. The results show a significant diversity of microbial populations along the Lebanese shore, and a significant change in the sediment microbial structure within four years. Namely, Woeseia, Blastopirellula, and Muriicola were identified in sediment samples collected in year 2017, while a higher microbial diversity was observed in 2021 with Woeseia, Halogranum, Bacillus, and Vibrio prevailing in beach sediments. In addition, the results demonstrate a significant correlation between certain hydrocarbon degraders, such as Marinobacter and Vibrio, and measured hydrocarbon concentrations.

Ferric iron stimulation in marine SMFCs: Impact on the microbial structure evolution in contaminated sediments with low and high molecular weight PAHs

The impact of ferric iron stimulation on the evolution of microbial structure in marine sediment microbial fuel cells (SMFCs), operated for the bioremediation of a complex mixture of low and high molecular weight PAHs (naphthalene, fluorene, pyrene and benzo(a)pyrene), was assessed. Microbial evolution profiles showed high relative abundances of exoelectrogenic iron-reducing bacteria throughout the biodegradation, namely Geoalkalibacter, under ferric iron stimulation and anode reducing conditions, irrespective of sulfate reducing bacteria (SRB) inhibition. Highest PAHs removal was measured in the absence of anode reduction, under Fe stimulation and SRB inhibition, reaching 40.85% for benzo(a)pyrene, the most persistent PAH used in this study. Results suggest that amendment of contaminated sediment with ferric iron could constitute a better bioremediation strategy than using SMFCs. This becomes significant when considering the well-established and dominant indigenous SRB population in marine sediments that usually limits the performance of the anode as a terminal electron acceptor in marine SMFCs.

Microbial community evolution during the aerobic biodegradation of petroleum hydrocarbons in marine sediment microcosms: Effect of biostimulation and seasonal variations

Evolution of the microbial community structure in crude oil contaminated marine sediments was assessed under aerobic biodegradation during wet (18 °C) and dry (28 °C) seasons experiments, to account for seasonal variations in nutrients and temperature, under biostimulation and natural attenuation conditions. NMDS showed significant variation in the microbial communities between the wet and the dry season experiments, and between the biostimulation and the natural attenuation treatments in the dry season microcosms. No significant variation in the microbial community and oil biodegradation was observed during the wet season experiments due to high background nitrogen levels eliminating the effect of biostimulation. Larger variations were observed in the dry season experiments and were correlated to enhanced alkanes removal in the biostimulated microcosms, where Alphaproteobacteria dominated the total microbial community by the end of biodegradation (54%). Many hydrocarbonoclastic bacterial genera showed successive dominance during the operation affecting the ultimate performance of the microcosms.

Response of sediment microbial communities to crude oil contamination in marine sediment microbial fuel cells under ferric iron stimulation

In this study, response of the microbial communities associated with the bioremediation of crude oil contaminated marine sediments was addressed using sediment microbial fuel cells (SMFCs). Crude oil was spiked into marine sediments at 1 g/kg of dry sediment to simulate a heavily contaminated marine environment. Conventional SMFCs were used with carbon fiber brushes as the electrode components and were enhanced with ferric iron to stimulate electrochemically active bacteria. Controls were operated under open circuit with and without ferric iron stimulation, with the latter condition simulating natural attenuation. Crude oil removal in the Fe enhanced SMFCs reached 22.0 ± 5.5% and was comparable to the measured removal in the control treatments (19.2 ± 7.4% in natural attenuation SMFCs and 15.2 ± 2.7% in Fe stimulated open circuit SMFCs), indicating no major enhancement to biodegradation under the applied experimental conditions. The low removal efficiency could be due to limitations in the mass transfer of the electron donor to the microbes and the anodes. The microbial community structure showed similarity between the iron stimulated SMFCs operated under the open and closed circuit. Natural attenuation SMFCs showed a unique profile. All SMFCs showed high relative abundances of hydrocarbon degrading bacteria rather than anode reducers, such as Marinobacter and Arthrobacter in the case of the natural attenuation SMFCs, and Gordonia in the case of iron stimulated SMFCs. This indicated that the microbial structure during the bioremediation process was mainly determined by the presence of petroleum contamination and to a lesser extent the presence of the ferric iron, with no major involvement of the anode as a terminal electron acceptor. Under the adopted experimental conditions, the absence of electrochemically active microbes throughout the biodegradation process indicates that the use of SMFCs in crude oil bioremediation is not a successful approach. Further studies are required to optimize SMFCs systems for this aim.

Characterization of the microbial community diversity and composition of the coast of Lebanon: Potential for petroleum oil biodegradation

In this study, the shoreline of Lebanon, which extends over 225 km along the eastern side of the Mediterranean Sea, was characterized for its sediment microbial community diversity and composition using 16S rRNA gene sequencing with Illumina MiSeq technology. Non-metric multidimensional scaling (NMDS) analysis showed no clear grouping among nearby sampled sites along the shoreline. Insignificant diversion between the wet and dry season microbial communities was observed along the coast at each sampling site. A high variation at the genus level was observed, with several novel genera identified at high relative abundance in certain locations, such as JTB255 marine benthic groups OTU_4 (5.4%) and OTU_60 (3.2%), and BD7-8 marine group OTU_5 (2.9%).

Effect of algal surface area and species interactions in toxicity testing bioassays

Single and multispecies algal bioassays were assessed using copper toxicity with three green algae (Scenedesmus subspicatus, Scenedesmus quadricauda and Ankistrodesmus angustus) and one blue-green algae species (Oscillatoria prolifera). Single and multispecies toxicity tests were conducted based on cell density as per standard toxicity testing, and on equivalent surface area. A higher copper sulfate toxicity was registered for O. prolifera, followed by S. subspicatus, S. quadricauda, and A. angustus in single-species toxicity tests based on cell density. Single species toxicity tests based on surface area showed increased copper toxicity with increasing algal surface area except for A. angustus. In multispecies control bioassays, the growth of A. angustus was inhibited in the presence of other species in surface area-based tests. As compared to single species bioassays, O. prolifera, and S. quadricauda showed a decreased sensitivity to copper sulfate in both cell density and surface area based multispecies tests. However, for the algae species with the smallest surface area, S. subspicatus, 96h-EC₅₀ value decreased in multispecies bioassays based on surface area as compared to the single species test, while it increased in multispecies bioassays based on cell density. The difference in S. subspicatus sensitivity to copper between tests based on cell density and surface area supports the need to adopt multispecies toxicity testing based on surface area to avoid the confounding effect on copper toxicity of increased biomass for metal binding. 96h-EC₅₀ values for all species combined in the multispecies test based on cell density and on surface area were significantly different from 96h-EC₅₀ values obtained in single species bioassays. These results demonstrate that single-species bioassays may over- or underestimate metal toxicity in natural waters.

Assessment of crude oil bioremediation potential of seawater and sediments from the shore of Lebanon in laboratory microcosms

With the planned oil and gas exploration activities off the coast of Lebanon, the risk of shoreline contamination with crude oil spills has become a major concern. This study aimed at assessing the crude oil bioremediation potential of the chronically polluted Lebanese shores in light of the continuous discharge of nutrient-rich sewage into the Mediterranean Sea and the long-lasting absence of proper sewage treatment systems. It was anticipated that, with the high pollution levels of the coastline, background concentrations of nutrients would be sufficient to sustain high intrinsic biodegradation rates without human intervention. Biodegradation experiments were conducted using crude oil-spiked beach sediments and seawater under natural attenuation and biostimulation conditions. The experiments were conducted at 18 and 28 °C to account for seasonal variation in temperature, background nutrient levels, and microbial communities. The biodegradability of oil constituents - namely alkanes and polycyclic aromatic hydrocarbons (PAHs), was monitored over a 42-day period using gas chromatography-mass spectrometry (GC-MS). Under biostimulation conditions, significant enhancement in the overall biodegradation rates of alkanes and PAHs was observed in seawater at 18 and 28 °C, while little to no improvement was measured at both temperatures in sediments where background nutrient levels were sufficient to induce near maximum intrinsic biodegradation rates. Under both natural attenuation and biostimulation treatments, the increase in temperature increased the oil biodegradation rates in sediment and seawater microcosms. In both instances, the overall trend in the biodegradation of individual alkanes and PAHs suggested a typical decrease in biodegradation rates with the increase in carbon number/rings and alkyl groups.

Study on the catalytic performance of different crystal morphologies of HZSM-5 zeolites for the production of biodiesel: a strategy to increase catalyst effectiveness

Strategies to improve molecular transport and accessibility of ZSM-5 zeolites were investigated for the model reaction of esterification of linoleic acid with methanol for biodiesel production.

Preliminary economic assessment of the use of waste frying oils for biodiesel production in Beirut, Lebanon

In this study, a method for assessing the costs of biodiesel production from waste frying oils in Beirut, Lebanon, was investigated with the aim of developing an economic evaluation of this alternative. A hundred restaurant and hotel enterprises in Beirut were surveyed for promoting them in participating in the biodiesel supply chain, and for data collection on waste frying oils generation, disposal methods and frequency, and acquisition cost. Also, waste frying oils were collected and converted into biodiesel using a one-step base catalyzed transesterification process. Physicochemical characteristics of the produced biodiesel were conforming to international standards. Data produced from laboratory scale conversion of waste frying oils to biodiesel, as well as data collected from the only biodiesel plant in Lebanon was used to determine the production cost of biodiesel. Geographic Information System was used to propose a real-time vehicle routing model to establish the logistics costs associated with waste frying oils collection. Comparing scenarios of the configuration collection network of waste frying oils, and using medium-duty commercial vehicles for collection, a logistics cost of US$/L 0.08 was optimally reached. For the calculation of the total cost of biodiesel production, the minimum, average, and maximum values for the non-fixed cost variables were considered emerging 81 scenarios for possible biodiesel costs. These were compared with information on the commercialization of diesel in Lebanon for the years 2011 through 2017. Although competitive with petroleum diesel for years 2011 to 2014, the total biodiesel cost presented less tolerance to declining diesel prices in the recent years. Sensitivity analysis demonstrated that the acquisition cost of waste frying oils is the key factor affecting the overall cost of biodiesel production. The results of this study validate the economic feasibility of waste frying oils' biodiesel production in the studied urban area upon enforcement of low waste frying oils' acquisition costs, and can help spur food service enterprises to become suppliers of biodiesel production feedstock and support a healthy development of the biodiesel industry in Lebanon.

Evaluation of copper toxicity using site specific algae and water chemistry: Field validation of laboratory bioassays

Studies of metal toxicity to microalgae have predominantly been conducted using single non-target algae species and without due regard for the chemistry of the treated waters, leading to ineffective or excessive algaecide treatments. In this study, indigenous multi-algal species (Scenedesmus quadricauda, and Scenedesmus subspicatus and Oscillatoria agardhii) were used in laboratory toxicity bioassays under simulated field water chemistry (pH = 7.2, hardness = 196 mg L^-1 as CaCO₃, and alkalinity = 222 mg L^-1 as CaCO₃) to determine the optimum copper sulfate treatment dose to control algae growth in an irrigation canal. Toxicity bioassays were conducted using copper sulfate in chelated (with EDTA) and non-chelated (without EDTA) forms to assess the influence of the use of synthetic chelators in toxicity studies. Also, copper toxicity to the indigenous algae species was measured in the non-modified EPA test medium (pH = 7.5, hardness = 92 mg L^-1 as CaCO₃, alkalinity = 10 mg L^-1 as CaCO₃ and EDTA= 300 µg L^-1) to assess the impact of the water chemistry on algae inhibitory algal dosages. Under simulated water chemistry conditions, lower toxicity was measured in the test flasks with the chelated form of copper (96 h- EC₅₀= 386.67 µg L^-1 as Cu) as compared to those with the non-chelated metal (96 h-EC₅₀= 217.17 µg L^-1 as Cu). In addition, higher copper toxicity was measured in the test flasks prepared with the non-modified EPA medium using chelated copper (96 h-EC₅₀ = 65.93 µg L^-1 as Cu) as compared to their analogous microcosms with modified water chemistry (96 h-EC₅₀= 386.67 µg L^-1 as Cu), the increased water hardness and alkalinity in the latter case contributing to the decrease of the metal bioavailability. Results from laboratory experiments showed good correlation with copper dosages used in a small scale field testing to control algae growth, increasing confidence in laboratory bioassays.

Assessment of the performance of SMFCs in the bioremediation of PAHs in contaminated marine sediments under different redox conditions and analysis of the associated microbial communities

The biodegradation of naphthalene, 2-methylnaphthalene and phenanthrene was evaluated in marine sediment microbial fuel cells (SMFCs) under different biodegradation conditions, including sulfate reduction as a major biodegradation pathway, employment of anode as terminal electron acceptor (TEA) under inhibited sulfate reducing bacteria activity, and combined sulfate and anode usage as electron acceptors. A significant removal of naphthalene and 2-methylnaphthalene was observed at early stages of incubation in all treatments and was attributed to their high volatility. In the case of phenanthrene, a significant removal (93.83±1.68%) was measured in the closed circuit SMFCs with the anode acting as the main TEA and under combined anode and sulfate reduction conditions (88.51±1.3%). A much lower removal (40.37±3.24%) was achieved in the open circuit SMFCs operating with sulfate reduction as a major biodegradation pathway. Analysis of the anodic bacterial community using 16S rRNA gene pyrosequencing revealed the enrichment of genera with potential exoelectrogenic capability, namely Geoalkalibacter and Desulfuromonas, on the anode of the closed circuit SMFCs under inhibited SRB activity, while they were not detected on the anode of open circuit SMFCs. These results demonstrate the role of the anode in enhancing PAHs biodegradation in contaminated marine sediments and suggest a higher system efficiency in the absence of competition between microbial redox processes (under SRB inhibition), namely due to the anode enrichment with exoelectrogenic bacteria, which is a more energetically favorable mechanism for PAHs oxidation than sulfate.

Biodegradation and toxicity of vegetable oils in contaminated aquatic environments: Effect of antioxidants and oil composition

Antioxidants may affect the oxidative rate of vegetable oils determining their fate and impact in contaminated aquatic media. In previous studies, we demonstrated the effectiveness of butylated hydroxytoluene (BHT), one of the most used antioxidants in edible oils, in enhancing the biodegradation of glyceryl trilinoleate, a pure triacylglycerol of cis,cis-9,12-octadecadienoic acid (C18:2 delta), through retarding its oxidative polymerization relatively to the oil with no added antioxidant. In this study, the effect of BHT on the biodegradation and toxicity of purified canola oil, a mixed-acid triacylglycerol with high C18:1 content, was investigated in respirometric microcosms and by use of the Microtox® assay. Investigations were carried out in the absence and presence (200 mg kg(-1)) of the antioxidant, and at an oil loading of 0.31 L m(-2) (333 gal acre(-1)). Substantial oil mineralization was achieved after 16 weeks of incubation (>77%) and was not significantly different (p>0.05) between the two BHT treatments, demonstrating an important role of the oil fatty acid composition in determining the potency of antioxidants and, consequently, the fate of spilled vegetable oils. Furthermore, for both treatments, toxicity was measured at early stages of the experiments and disappeared at a later stage of incubation. The observed transient toxicity was associated with the combined effect of toxic biodegradation intermediates and autoxidation products. These results were supported by the gradual disappearance of BHT in the microcosms initially supplemented with the antioxidant, reaching negligible amounts after only 2 weeks of incubation.

Effect of butylated hydroxytoluene (BHT) on the aerobic biodegradation of a model vegetable oil in aquatic media

Antioxidants added to vegetable oils to prevent lipid oxidation significantly affect their biodegradation in impacted aquatic environments. In this study, the effect of butylated-hydroxytoluene (BHT) on the biodegradation of glyceryl trilinoleate, a model vegetable oil highly susceptible to autoxidation, was determined. Biodegradation experiments were conducted in respirometric microcosms at an oil loading of 333 gal acre(-1) (0.31 L m(-2)) and BHT concentrations ranging from 0 to 800 mg kg(-1) (0, 50, 100, 200, 400, and 800 mg kg(-1)). Competition between polymerization and biodegradation of the oil was observed at all BHT concentrations and was significant in the microcosms not supplemented with the antioxidant. In all microcosms, intractable rigid polymers unavailable for bacterial degradation were formed. Infrared analysis evidenced the advanced stages of the oil autoxidation. After 19 weeks of incubation, only about 41% of the oil was mineralized in the microcosms with no BHT. However, mineralization exceeded 67% in the microcosms with added antioxidant and did not significantly increase with increasing BHT concentrations. Biodegradation rate constants were calculated by nonlinear regression and were not significantly different in the microcosms with added BHT (k = 0.001 h(-1)). Higher k values were measured in the microcosms lacking the antioxidant (k = 0.0023 h(-1)), most likely due to the increased oxygen consumption associated with the autoxidation process in this case. No toxicity was detected in all biotic microcosms at the end of the incubation period, while high toxicity (EC(50) = 4.78%) was measured in the abiotic blanks with no antioxidant and was attributed to the accumulation of autoxidation products.

Assessment of aquatic toxicity and oxygen depletion during aerobic biodegradation of vegetable oil: effect of oil loading and mixing regime

The potential ecological impacts of aerobic biodegradation of vegetable oils on contaminated water columns was investigated in the laboratory at different oil loadings (100, 333, and 1,000 gal acre(-1)) and mixing regimes (fully, moderately, and nonmixed microcosms). The impacts were estimated by use of the Microtox assay and dissolved oxygen concentration measurements. The results of the Microtox assay showed no major toxicity at the 100 gal acre(-1) loading. Furthermore, oxygen was not completely depleted from the water column at this oil coverage. At higher oil loadings, oxygen was fully depleted from the mixed and nonmixed water columns. A transient toxicity in the aqueous phase was observed in the case of the moderately mixed microcosms at 333 gal acre(-1) and was maintained at moderate levels (EC(50) ∼ 30%) in the nonmixed microcosms. A substantial increase in toxicity (EC(50) ∼ 10%) was observed in both mixing conditions when the initial oil loading was increased to 1,000 gal acre(-1). At all oil loadings, significant toxicity (EC(50) < 2%) was found in the solid phase due to the strong partition of lipids to the biomass. Long and medium chains fatty acids associated with the measured toxicity were detected in both liquid and solid phases.