Anaerobic biodegradation of vegetable oil and its metabolic intermediates in oil-enriched freshwater sediments

The degradation and toxicity of commercially traded vegetable oils following spills in aquatic environment

The production of commodity and specialty vegetable oils is increasing every year to fulfill the ever-increasing demand where the trading of oils occurs primarily via sea shipping. Spills of vegetable oil into the aquatic environment may result in detrimental effects on aquatic ecosystems. Environmental degradation of vegetable oil spills occurs mainly via microbial activity, chemical oxidation, wave and wind actions. However, the polymerization of oils can hinder their ability to naturally degrade. Thus, human intervention in the form of both short- and long-term remediation, is desirable to reduce the effects of vegetable oil spills on aquatic ecosystems. Studies have been conducted to determine how the type and concentration of the vegetable oil contamination influence its toxicity on various organisms. Some studies show that the effect of vegetable oil spills is found to be relatively short-lived and to a certain extent increase the survivability of certain organisms. However, the integrated effect of vegetable oil spills on aquatic organisms and their environment is still being researched. This review summarizes the existing knowledge on the reported occurrences of vegetable oil spills, their degradation, and their toxicity towards the surrounding aquatic environment which would be helpful in the knowledge transfer of remediation of vegetable oils.

Influence of the Intrinsic Characteristics of Cementitious Materials on Biofouling in the Marine Environment

Coastal marine ecosystems provide essential benefits and services to humanity, but many are rapidly degrading. Human activities are leading to significant land take along coastlines and to major changes in ecosystems. Ecological engineering tools capable of promoting large-scale restoration of coastal ecosystems are needed today in the face of intensifying climatic stress and human activities. Concrete is one of the materials most commonly used in the construction of coastal and marine infrastructure. Immersed in seawater, concretes are rapidly colonized by microorganisms and macroorganisms. Surface colonization and subsequent biofilm and biofouling formation provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. The new challenge of the 21st century is to develop innovative concretes that, in addition to their usual properties, provide improved bioreceptivity in order to enhance marine biodiversity. The aim of this study is to master and clarify the intrinsic parameters that influence the bioreceptivity (biocolonization) of cementitious materials in the marine environment. By coupling biofilm (culture-based methods) and biofouling (image-analysis-based method and wet-/dry-weight biomass measurement) quantification techniques, this study showed that the application of a curing compound to the concrete surface reduced the biocolonization of cementitious materials in seawater, whereas green formwork oil had the opposite effect. This study also found that certain surface conditions (faceted and patterned surface, rough surface) promote the bacterial and macroorganism colonization of cementitious materials. Among the parameters examined, surface roughness proved to be the factor that promotes biocolonization most effectively. These results could be taken up in future recommendations to enable engineers to eco-design more eco-friendly marine infrastructure and develop green-engineering projects.

Effect of Sub-Stoichiometric Fe(III) Amounts on LCFA Degradation by Methanogenic Communities

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H₂-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83-89%, 3-6%, and 0.2-10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

Insights on the criteria of selection of vegetable and mineral dielectric fluids used in power transformers on the basis of their biodegradability and toxicity assessments

Leakage of transformer dielectric fluids is a concern because it may pose a risk of environmental contamination. In this study, the deleterious effects of vegetable and mineral dielectric fluids in water bodies were investigated using biodegradability and acute toxicity tests with Danio rerio and Artemia salina. Regarding biodegradability, all four tested vegetable oils (soy, canola, sunflower and crambe) were considered as easily biodegradable, presenting degradation rates significantly higher than the Lubrax-type mineral fluid. Acute toxicity tests were performed in two separate experiments without solution renewal. In the first experiment, the organisms were exposed in direct contact to different concentrations of vegetable (soy) and mineral (Lubrax) oils. Total soy-type vegetable oil has a higher toxic effect than Lubrax-type mineral oil. In the second experiment, the organisms were exposed to increasing percentages of the water-soluble fraction (WSF) of both types of tested oils. The LC₅₀ values for the water-soluble fraction of the Lubrax-type mineral oil were about 5 and 8% for the Danio rerio and Artemia salina bioindicators, respectively, whereas the vegetable oil did not present toxic effect, regardless of its WSF. These results have shown that a strict selection of dielectric fluids and monitoring the leakage from power transformers is a serious duty of environmental protection agencies.

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.

Biodegradation of fat, oil and grease (FOG) deposits under various redox conditions relevant to sewer environment

Fat, oil and, grease (FOG) deposits are one primary cause of sanitary sewer overflows (SSOs). While numerous studies have examined the formation of FOG deposits in sewer pipes, little is known about their biodegradation under sewer environments. In this study, FOG deposit biodegradation potential was determined by studying the biodegradation of calcium palmitate in laboratory under aerobic, nitrate-reducing, sulfate-reducing, and methanogenic conditions. Over 110 days of observation, calcium palmitate was biodegraded to CO2 under aerobic and nitrate-reducing conditions. An approximate 13 times higher CO2 production rate was observed under aerobic condition than under nitrate-reducing condition. Under sulfate-reducing condition, calcium palmitate was recalcitrant to biodegradation as evidenced by small reduction in sulfate. No evidence was found to support calcium palmitate degradation under methanogenic condition in the simulated sewer environment. Dominant microbial populations in the aerobic and nitrate-reducing microcosms were identified by Illumina seqeuncing, which may contain the capability to degrade calcium palmitate under both aerobic and nitrate-reducing conditions. Further study on these populations and their functional genes could shed more light on this microbial process and eventually help develop engineering solutions for SSOs control in the future.

Bench-scale evaluation of aerosol delivery for biostimulation and bioaugmentation in the vadose zone

Aerosol delivery was evaluated for distributing biostimulation and bioaugmentation amendments in vadose zones. This technique involves transporting amendments as micron-scale aerosol droplets in injected gas. Microcosm experiments were designed to characterize reductive dechlorination of trichloroethene (TCE) under unsaturated conditions when delivering components as aerosols. Delivering amendments and/or microbes as aqueous aerosols resulted in complete dechlorination of TCE, similar to controls operated under saturated conditions. Reductive dechlorination was achieved with manual injection of a bioaugmentation culture suspended in soybean oil into microcosms. However, aerosol delivery of the culture in soybean oil induced little reductive dechlorination activity. Overall, the results indicate that delivery as aqueous aerosols may be a viable option for delivery of amendments to enhance vadose zone bioremediation at the field-scale.

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.

Effects of mixing energy on the sedimentation of vegetable oil spills by clay

The effects of clay dose and mixing energy on the efficiency of vegetable oil sedimentation by clay are investigated. The sedimentation efficiency increased with increasing clay dose to a maximum of about 80% of added oil. The maximum sedimentation efficiency was achieved at a lower clay dose, and the sedimentation efficiency was greater for a given clay dose when the oil was present as a thick oil film rather than as a thinner film. Sedimentation efficiency was relatively constant for mixing energies less than about 0.01 m2 s(-3) (0.01 W kg(-1)) but decreased dramatically at higher energy dissipation rates. Mixing energy may not be an important factor in determining the effectiveness of this response alternative because energy dissipation rates in natural surface water bodies under most typical conditions are less than 0.01 m2 s(-3). The effects of oil film thickness and mixing energy on the efficiency of vegetable oil sedimentation suggests that vegetable oil-mineral aggregates (VOMA) form through a different mechanism to that of petroleum oil-mineral aggregates (OMA). One consequence of the different formation mechanisms is that VOMA are much larger than petroleum OMA.

Remediation of groundwater contaminated with DNAPLs by biodegradable oil emulsion

Emulsion-based remediation with biodegradable vegetable oils was investigated as an alternative technology for the treatment of subsurface DNAPLs (dense non-aqueous phase liquids) such as TCE (trichloroethylene) and PCE (perchloroethylene). Corn and olive oil emulsions obtained by homogenization at 8000rpm for 15min were used. The emulsion droplets prepared with corn and olive oil gave a similar size distribution (1-10microm) and almost all of initially injected oil, >90%, remained in a dispersed state. In batch experiments, 2% (v/v) oil emulsion could adsorb up to 11,000ppm of TCE or 18,000ppm of PCE without creating a free phase. Results of one-dimensional column flushing studies indicated that contaminants with high aqueous solubility could be efficiently removed by flushing with vegetable oil emulsions. Removal efficiencies exceeded 98% for TCE and PCE with both corn and olive oil emulsions. The results of this study show that flushing with biodegradable oil emulsion can be used for the remediation of groundwater contaminated by DNAPLs.

Assessment of sediment toxicity during anaerobic biodegradation of vegetable oil using Microtox and Hyalella azteca bioassays

The potential ecological impacts of anaerobic degradation of vegetable oil on freshwater sediments were investigated. Sediment toxicity was evaluated using two regulatory biotests: the Microtox Solid Phase Test and an amphipod (Hyalella azteca) bioassay. The results of the Microtox test showed that the toxicity of the vegetable-oil-contaminated sediments (about 17-33 g oil/kg dry sediments) increased after 2 weeks incubation and then decreased to near background levels after incubation for 8 weeks under anaerobic conditions. The amphipod toxicity bioassay showed that the toxicity of fresh contaminated sediments decreased over time and returned to background levels within 8 weeks. These results suggest that the impact of vegetable oils on organisms within sediments may be limited. To account for the significance of environmental conditions, additional studies over a wide range of incubation conditions (e.g., temperature, nutrient concentration) and other test organisms at various trophic levels are recommended for both acute and chronic toxicity assessment.

Effects of ferric hydroxide on methanogenesis from lipids and long-chain fatty acids in anaerobic digestion

The addition of ferric hydroxide to sludge from a municipal anaerobic digester stimulated the rate of methanogenesis from canola oil when the initial oil concentration was high (4600 mg/L; P < 0.002), but not when it was low (920 mg/L; P > 0.05). Similar trends were observed when oleic acid, a fatty acid that is a major component of canola oil triglycerides, was provided, but the effects were statistically significant only when the initial concentration of ferric hydroxide was also high (18 g/L; P = 0.015). Iron reduction occurred when ferric hydroxide was added to microcosms containing anaerobic digester sludge, but the extent of ferrous iron production was much less in acetate-amended microcosms than in those that were provided with canola oil or oleic acid. Methanogenesis and acetate consumption were completely inhibited when the initial acetate concentration was approximately 5000 mg/L, regardless of the initial ferric hydroxide concentration. The main effect of ferric hydroxide in this system appears to have been a result of stimulation of the rate of fatty acid oxidation.

Effect of iron on the sensitivity of hydrogen, acetate, and butyrate metabolism to inhibition by long-chain fatty acids in vegetable-oil-enriched freshwater sediments

Freshwater sediment microbial communities enriched by growth on vegetable oil in the presence of a substoichiometric amount of ferric hydroxide (sufficient to accept about 12% of the vegetable-oil-derived electrons) degrade vegetable oil to methane faster than similar microbial communities that develop when sediments are enriched by growth on vegetable oil in the absence of ferric hydroxide. This study examined the effects of enrichment in the presence of Fe(III) on the fatty-acid sensitivity of several important members of anaerobic triglyceride-degrading microbial communities in freshwater sediments. The fatty-acid sensitivity of three groups of microorganisms-hydrogenotrophic methanogens, acetate consumers, and hydrogen-producing acetogens-were investigated by comparing the rates of hydrogen, acetate, or butyrate consumption in the presence and absence of oleic acid. Methanogenesis from hydrogen was not affected by sediment enrichment conditions or by the presence of oleic acid, suggesting that hydrogenotrophic methanogens were insensitive to fatty acid inhibition in these sediments. Oleic acid inhibited the anaerobic degradation rates of acetate and butyrate by 38% and 63%, respectively, but enrichment in the presence of Fe(III) eliminated the fatty-acid sensitivity of acetate degradation and reduced the sensitivity of butyrate degradation by about half. These results suggest that iron-reducing bacteria may provide an alternative pathway through which vegetable oil can be converted to methane in anaerobic freshwater sediments.

Solubilization of Oleic Acid by Myrj 59 Surfactant

Palm oil mill effluent (POME) is one of the sources of contamination in effluent that leads to problems such asclogging in drainpipes and sewer lines. POME discharge consists of high content of free fatty acids (FFAs) aswell as high concentration of biochemical oxygen demand (BOD), chemical oxygen demand and suspendedsolids. FFAs in effluent are not favorable due to low water solubility and resistant to biodegradation whenprecipitated from effluent and binds to soil limiting their bioavailability to microorganisms for biodegradation.Nonionic surfactants are favorable as hydrocarbon or oil solubilizer because they can perform at lowtemperatures, has low-foaming characteristics and relatively stable at high temperatures and under harshchemical conditions. Therefore, there is a need for the usage of surfactant that is biodegradable and at the sametime effective at solubilizing FFAs in POME before being released to streams. Thus, FFAs will be keptmobilized and readily available for biodegradation by microorganisms. Oleic acid is a long chain free fatty acidpresents as the major fatty acid component (40-52 %w/w) in palm oil. Oleic acid was selected for solubilizationby biodegradable nonionic surfactant polyoxyethylene (100) stearate with the commercial name Myrj 59. Thesolubilizations were conducted with various concentrations of Myrj 59; below, at and above the critical micelleconcentration (CMC). The amount solubilized was determined by gas chromatography (GC) using flameionization detector (FID) technique. The solubilization process was confirmed by characterizing the solubilizedoil using Fourier Transform infrared (FTIR) to observe changes in chemical bonds. Highest solubilization wasachieved with Myrj 59 solution at above its CMC, solubilizing 516.31 ppm oleic acid. The FTIR spectra showedstrong peak at 2927 cm-1 with high intensity suggesting intermolecular hydrogen bonding between oleic acid andethylene oxide (EO) groups of surfactant.