Evaluation of a Gravity Flow Membrane Bioreactor for Treating Municipal Wastewater.

The biomass concentrator reactor (BCR), a gravity flow membrane bioreactor (MBR) design, was evaluated for use in treating a municipal wastewater stream. The BCR operates with less than 2.5 cm of pressure head and uses a 3 to 4 mm thick tortuous path membrane with pore size ranging from 18 to 28 µm to achieve solids separation. A two-stage, aerobic/anoxic reactor was evaluated for the removal of chemical oxygen demand (COD), ammonia, total nitrogen, and solids separation. The reactor was fed 72 L/day, with a hydraulic retention time of 9.3 hours, and had a solids retention time of 20 days. The influent COD was reduced by 93%, whereas, influent ammonia was reduced below 0.1 mg/L and total nitrogen was reduced by 53.7%. A lack of readily biodegradable COD limited denitrification and thus total nitrogen removal. The reactor solids were retained completely in the reactor by the membrane for the duration of testing.

Anaerobic biodegradation of soybean biodiesel and diesel blends under sulfate-reducing conditions.

Biotransformation of soybean biodiesel and its biodiesel/petrodiesel blends were investigated under sulfate-reducing conditions. Three blends of biodiesel, B100, B50, and B0, were treated using microbial cultures pre-acclimated to B100 (biodiesel only) and B80 (80% biodiesel and 20% petrodiesel). Results indicate that the biodiesel could be effectively biodegraded in the presence or absence of petrodiesel, whereas petrodiesel could not be biodegraded at all under sulfate-reducing conditions. The kinetics of biodegradation of individual Fatty Acid Methyl Ester (FAME) compounds and their accompanying sulfate-reduction rates were studied using a serum bottle test. As for the biodegradation of individual FAME compounds, the biodegradation rates for the saturated FAMEs decreased with increasing carbon chain length. For unsaturated FAMEs, biodegradation rates increased with increasing number of double bonds. The presence of petrodiesel had a greater effect on the rate of biodegradation of biodiesel than on the extent of removal.

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 dispersants on the biodegradation of South Louisiana crude oil at 5 and 25 °C.

This article reports biodegradation rates for a commercial dispersant, JD-2000, South Louisiana crude oil (SLC) alone, and SLC dispersed with JD-2000 at 5 and 25 °C. Results from the biodegradation experiments revealed that Component X, a chemical marker for JD-2000, rapidly degraded at both temperatures. The application of JD-2000 decreased by half the overall biodegradation rate of aliphatic compounds at 25 °C. At 5 °C, a residual fraction consisting of iso- and n-alkanes (C29-C35) persisted after 56 d. The combination of dispersant and higher temperature resulted in faster removal rates for 2- and 3-ring polycyclic aromatic hydrocarbons. When compared with Corexit 9500, our results suggest that the chemistry of the surfactant (or surfactants) in JD-2000 might have favored oil dissolution (substrate transport to the aqueous phase) as an uptake mechanism over adhesion, which requires direct contact of the biomass with the oil.

Characterization of solidifiers used for oil spill remediation.

The physical characteristics and chemical composition of oil spill solidifiers were studied, and correlation of these properties with product effectiveness enabled determination of characteristics that are desirable in a good solidifier. The analyses revealed that the commercial products were primarily comprised of organic polymers and a few trace elements. A natural sorbent, which was composed entirely of plant based matter, was also evaluated, and it had the highest oil removal capacity, but it did not produce a solid mat-like final product. Generally, solidifiers with a carbonate group, pore size greater than 5 µm, and bulk densities lower than 0.3 g cm(-3) were found to have better efficiency and produced a cohesive rubbery final product that facilitated removal compared to sorbents. The importance of bulk density and pore size in the performance of the solidifier suggest that the primary mechanism of action was likely physical sorption.

Anaerobic biodegradation of soybean biodiesel and diesel blends under methanogenic conditions.

Biotransformation of soybean biodiesel and the inhibitory effect of petrodiesel were studied under methanogenic conditions. Biodiesel removal efficiency of more than 95% was achieved in a chemostat with influent biodiesel concentrations up to 2.45 g/L. The kinetics of anaerobic biodegradation of soybean biodiesel B100 (biodiesel only) with different petrodiesel loads was studied using biomass pre-acclimated to B100 and B80 (80% biodiesel and 20% petrodiesel). The results indicated that the biodiesel fraction of the blend could be effectively biodegraded, whereas petrodiesel was not biodegraded at all under methanogenic conditions. The presence of petrodiesel in blends with biodiesel had a greater inhibitory effect on the rate of biodegradation than the biodegradation efficiency (defined as the efficiency of methane production). Both the biodegradation rate coefficient and the methane production efficiency increased almost linearly with the increasing fraction of biodiesel. With the increasing fraction of petrodiesel, the biodegradation rate and efficiency were correlated with the concentration of soluble FAMEs in the water.

Parametric study to determine the effect of temperature on oil solidifier performance and the development of a new empirical correlation for predicting effectiveness.

Temperature can play a significant role in the efficacy of solidifiers in removing oil slicks on water. We studied and quantified the effect of temperature on the performance of several solidifiers using 5 different types of oils under a newly developed testing protocol by conducting experiments in constant temperature rooms set at 22°C and 5°C. The results indicated that solidifier efficiency decreased substantially at the lower temperature, especially at lower application rates. The removal efficiency of the solidifier was in general directly proportional to temperature, except for the heavier oils, where removal by attachment was observed. Solidifier products with lower powder bulk density exhibited the best removal effectiveness. Analysis of experimental data yielded empirical correlations involving certain operational variables such as application rate, temperature, solidifier property (bulk density), and oil property (viscosity). Regression analysis was used to fit a mathematical model to the experimental solidifier effectiveness data.

Aerobic biodegradation kinetics and mineralization of six petrodiesel/soybean-biodiesel blends.

The aerobic biodegradation kinetics and mineralization of six petrodiesel/soybean-biodiesel blends (B0, B20, B40, B60, B80, and B100), where B100 is 100% biodiesel, were investigated by acclimated cultures. The fatty acid methyl esters (FAMEs) of biodiesel were found to undergo rapid abiotic transformation in all experiments. The C10-C21 n-alkanes of petrodiesel were metabolized at significantly higher microbial utilization rates in the presence of biodiesel. The rates of mineralization of the blends were also enhanced in the presence of biodiesel; yet a similar enhancement in the extent of mineralization was not observed. Abiotic fuel-blends/aqueous-phase equilibration experiments revealed that the FAMEs of biodiesel were capable of cosolubilizing the n-alkanes of petrodiesel, a mechanism that fully explains the faster utilization and mineralization kinetics of petrodiesel in the presence of biodiesel without necessarily enhancing the extent of biomineralization. The biodegradation of six targeted aromatic compounds present in petrodiesel was also influenced by the amount of biodiesel in a blend. While toluene, o-xylene, and tetralin were not degraded in the B0 and B20 treatments, all of the targeted aromatic compounds were degraded to below detection limits in the B40 and B80 treatments. Biomass acclimated to B60, however, was unable to degrade most of the aromatic compounds. These results indicate that the amount of biodiesel in a blend significantly affects the absolute and relative abundance of the dissolved and bioavailable constituents of biodiesel and petrodiesel in a way that can considerably alter the biodegrading capacity of microbial cultures.

Biodegradability of Corexit 9500 and dispersed South Louisiana crude oil at 5 and 25 °C.

The reported persistence of the dioctyl sodium sulfosuccinate (DOSS) surfactant in Corexit 9500 in the oil plumes formed during the Deepwater Horizon oil spill has contributed to concerns regarding the biodegradability and bioavailability of dispersed oil and dispersants used as an oil spill countermeasure in the Gulf of Mexico. We studied the biodegradation of DOSS and dispersed South Louisiana crude oil (SLC) in laboratory microcosms. Two oil-degrading cultures from the Gulf of Mexico were isolated, one from the surface (meso) and one from close to the area of the Macondo well (cryo). Each was enriched on SLC, the former at 25 °C, the latter at 5 °C. Results indicated that the meso culture rapidly and completely degraded DOSS, alkanes, and aromatics. The cryo culture metabolized the same compounds but with a lag of 28 d and a remaining residual of iso-alkanes, n-C(30-35), and the 4-ring PAHs.

Microbial kinetic model for the degradation of poorly soluble organic materials.

A novel mechanistic model is presented that describes the aerobic biodegradation kinetics of soybean biodiesel and petroleum diesel in batch experiments. The model was built on the assumptions that biodegradation takes place in the aqueous phase according to Monod kinetics, and that the substrate dissolution kinetics at the oil/water interface is intrinsically fast compared to biodegradation kinetics. Further, due to the very low aqueous solubility of these compounds, the change in the substrate aqueous-phase concentration over time was assumed to approaches zero, and that substrate aqueous concentration remains close to the saturation level while the non-aqueous phase liquid (NAPL) is still significant. No former knowledge of the saturation substrate concentration (S(sat)) and the Monod half-saturation constant (K(s)) was required, as the term S(sat)/(K(s) + S(sat)) in the Monod equation remained constant during this phase. The n-alkanes C10-C24 of petroleum diesel were all utilized at a relatively constant actual specific utilization rate of 0.01-0.02 mg-alkane/mg-biomass-hr, while the fatty acid methyl esters (FAMEs) of biodiesel were utilized at actual specific rates significantly higher with increasing carbon chain length and lower with increasing number of double bonds. The results were found to be in agreement with kinetic, genetic, and metabolic evidence reported in the literature pertaining to microbial decay rates, uptake mechanisms, and the metabolic pathway by which these compounds are assimilated into microorganisms. The presented model can be applied, without major modifications, to estimate meaningful kinetic parameters from batch experiments, as well as near source zone field application. We suggest the estimated actual microbial specific utilization rate (kC) of such materials to be a better measure of the degradation rate when compared to the maximum specific utilization rate (k), which might be orders of magnitude higher than kC and might never be observed in reality.

Biodegradation of alkylates under less agitated aquifer conditions.

The biodegradability of three alkylates (2,3-dimethylpentane, 2,4-dimethylpentane and 2,2,4-trimethylpentane) under less agitated aquifer conditions was investigated in this study. All three alkylates biodegraded completely under these conditions regardless of the presence or absence of ethanol or benzene, toluene, ethylbenzene, and xylenes (BTEX) in the feed. In the presence of ethanol, alkylates degradation was not inhibited by ethanol. However, alkylates degraded more slowly in the presence of BTEX suggesting competitive inhibition to microbial utilization of alkylates. In the sterile controls, alkylates concentrations remained unchanged throughout the experiments.

Biological nitrogen and carbon removal in a gravity flow biomass concentrator reactor for municipal sewage treatment.

A novel membrane system, the Biomass Concentrator Reactor (BCR), was evaluated as an alternative technology for the treatment of municipal wastewater. Because the BCR is equipped with a membrane whose average poresize is 20 µm (18-28 µm), the reactor requires low-pressure differential to operate (gravity). The effectiveness of this system was evaluated for the removal of carbon and nitrogen using two identical BCRs, identified as conventional and hybrid, that were operated in parallel. The conventional reactor was operated under full aerobic conditions (i.e., organic carbon and ammonia oxidation), while the hybrid reactor incorporated an anoxic zone for nitrate reduction as well as an aerobic zone for organic carbon and ammonia oxidation. Both reactors were fed synthetic wastewater at a flow rate of 71 L d(-1), which resulted in a hydraulic retention time of 9 h. In the case of the hybrid reactor, the recycle flow from the aerobic zone to the anoxic zone was twice the feed flow rate. Reactor performance was evaluated under two solids retention times (6 and 15 d). Under these conditions, the BCRs achieved nearly 100% mixed liquor solids separation with a hydraulic head differential of less than 2.5 cm. The COD removal efficiency was over 90%. Essentially complete nitrification was achieved in both systems, and nitrogen removal in the hybrid reactor was close to the expected value (67%).

Determining the dispersibility of South Louisiana crude oil by eight oil dispersant products listed on the NCP Product Schedule.

We recently conducted a laboratory study to measure the dispersion effectiveness of eight dispersants currently listed on the National Contingency Plan Product Schedule. Results are useful in determining how many commercial dispersant products would have been effective for use on South Louisiana crude oil in the Deepwater Horizon oil spill. The test used was a modification of the Baffled Flask Test (BFT), which is being proposed to replace the current Swirling Flask Test (SFT). The modifications of the BFT in this study included use of one oil rather than two, increasing replication from 4 runs to 6, and testing at two temperatures, 5 °C and 25 °C. Results indicated that temperature was not as critical a variable as the literature suggested, likely because of the low viscosity and light weight of the SLC. Of the eight dispersants tested, only three gave satisfactory results in the laboratory flasks at both temperatures.

Microtox aquatic toxicity of petrodiesel and biodiesel blends: the role of biodiesel's autoxidation products.

The acute Microtox toxicity of the water accommodated fraction (WAF) of six commercial soybean biodiesel/petrodiesel blends was investigated at different oil loads. We analyzed five fatty acid methyl esters (FAMEs), C10-C24 n-alkanes, four aromatics, methanol, and total organic carbon (TOC) content. At high oil loads, the WAFs' toxicity was significantly higher for blends containing biodiesel. At the lowest load, the WAFs' toxicity decreased almost linearly with decreasing biodiesel in the blend. At intermediate loads, the WAFs of all the blends appeared to have a similar toxicity. Analysis of WAFs confirmed the presence of autoxidation byproducts of FAMEs at high oil loads. Pure unsaturated FAMEs and n-alkanes were nontoxic when present in water at their reported solubility limits. However, 24-h equilibrated WAFs of pure FAMEs were highly toxic for C18:1 and C18:3, but not for C18:2. The authors concluded that at high oil loads, the acute toxicity of the WAFs was caused by FAMEs' autoxidation byproducts, whereas at low oil loads, the toxicity appeared to be caused primarily by the aromatic compounds present in petrodiesel. The addition of a synthetic antioxidant in biodiesel did not appear to affect the concentration of autoxidation byproducts in the WAF but resulted in a slight decrease in its toxicity. The major autoxidation byproducts identified in the WAF of commercial biodiesel were present neither in the WAFs of pure unsaturated FAMEs nor in the WAF of a different soybean biodiesel that was transesterified in our laboratory, which was nontoxic. We concluded that the process of transesterification of biodiesel might be a more critical factor in determining the aquatic toxicity of the fuel than the source of feedstock itself.

Partitioning behavior of petrodiesel/biodiesel blends in water.

The partitioning behavior of six petrodiesel/soybean-biodiesel blends (B0, B20, B40, B60, B80, and B100, where B100 is 100% unblended biodiesel) in water was investigated at various oil loads by the 10-fold dilution method. Five fatty acid methyl esters (FAMEs), C10-C20 n-alkanes, and four monoaromatic compounds were targeted for analysis. Only the aromatic compounds were partitioned according to Raoult's law at all oil loads. The partitioning of the FAMEs and n-alkanes at higher oil loads was found to be orders of magnitude higher than the reported aqueous solubilities of these compounds, and directly correlated with the amount of oil load applied. Depth filtration of the water-accommodated fractions (WAFs) significantly reduced the observed concentrations of the FAMEs and n-alkanes, but did not appreciably affect the aromatic compounds. The FAMEs and n-alkanes concentrations in the filtered WAFs agreed with the aqueous solubilities of those compounds reported in the literature, but the n-alkanes showed progressive deviations from those solubilities with the increase in the amount of biodiesel in the blends. Further dilution experiments on pure n-hexadecane confirmed the presence of a metastable colloidal phase that seems to be controlled by hydrophobic interactions and surface phenomena. The addition of biodiesel to the oil blend appeared to have a positive impact on the dissolved concentrations and the colloidal accommodation of the n-alkanes. Autoxidation of the biodiesel constituents was found to be significant, and increased with increasing oil loads. Chemical products such as hexanal, n-butyl acetate, diethylene glycol monobutyl ether, and diethylene glycol monobutyl ether acetate were positively identified among the FAMEs' autoxidation byproducts. Our data suggest a positive enhancement for biodiesel on the formation of the oil in water colloidal phase, possibly by forming a surfactant-cosurfactant-like pair of the FAMEs and their autoxidation byproducts.

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.

Effect of environmental factors on the effectiveness of ammoniated bagasse in wicking oil from contaminated wetlands.

Ammoniated bagasse is a plant-derived organic sorbent that can be used for capturing oil and for supplying slow-release nutrients to oil-degrading microorganisms. We investigated the oil-wicking behavior of this sorbent under various conditions for its effectiveness in remediating oil-contaminated wetlands. Abiotic microcosms simulating a wetland environment were used to assess the influence of sand particle sizes (20 x 30 and 60 x 80 U.S. mesh), degrees of oil saturation (25% and 75%), water table levels (on top of the clean sand layer, oiled-sand layer, and sorbent layer), and the presence of sorbent. Results indicated that oil wicking favors higher oil contamination, larger sand particle size, and low water coverage. Water coverage was the predominant factor limiting the effectiveness of sorbent. The most plausible explanation for this limitation was that sorbent captured more water than oil at higher water coverage.

Application of entropy analysis of in situ droplet-size spectra in evaluation of oil chemical dispersion efficacy.

In situ droplet-size distributions were measured using a laser in situ scattering and transmissiometry (LISST-100X) particle size analyzer during the evaluation of natural and chemical dispersion efficiency of crude oils under different wave and current conditions. An entropy grouping of the in situ dispersed oil droplet-size spectra has classified the multi-modal droplet-size distributions into different groups based on similar droplet-size spectra characteristics within groups and distinction between groups. A generalized linear logistic regression model was fitted to analyze the effects of a number of factors and their interactions on the grouping of oil droplet-size spectra. The grouped results corresponded to the oil dispersion efficiency at different levels. This new method for droplet-size distribution data analysis can have significant implication in field evaluation of natural and chemical dispersion efficiency of oil.

Biodegradability of lingering crude oil 19 years after the Exxon Valdez oil spill.

In 2001 and 2003, geospatial surveys of lingering oil were conducted in Prince William Sound (PWS) resulting in a prediction of significant acreage being contaminated with substantial subsurface oil from the 1989 Exxon Valdez oil spill (EVOS). In 2007, other researchers developed a mass weathering index (MWI) based on the degree of weathering of PAHs normalized to conserved biomarkers: if the degree of weathering of oil is 70% or more, further attempts at bioremediation would be unjustified. The objective of our study was to measure the biodegradability of the 19-year lingering oil in laboratory microcosms. Samples of beach substrate were collected from representative sites in PWS contaminated with oil residues of varying weathering states according to the MWI model. Enough sacrificial microcosms were set up to accommodate two treatments for each site (natural attenuation and biostimulation). Results indicated that lingering oil is biodegradable. Nutrient addition stimulated biodegradation compared to natural attenuation in all treatments regardless of the degree of weathering. The most weathered oil according to the MWI was the most biodegradable. Substantial biodegradation occurred in the natural attenuation microcosms due to the high sediment Total Kjeldahl Nitrogen (TKN), which served as a nitrogen source for biodegradation. Most of the observed biodegradation was due to the presence of dissolved oxygen. Nitrogen was a limiting factor but oxygen was the predominant one.