Abiotic Loss Research Articles

The release, degradation, and distribution of PVC microplastic-originated phthalate and non-phthalate plasticizers in sediments

This study investigated the leaching of phthalate and non-phthalate plasticizers from polyvinyl chloride microplastics (MPs) into sediment and their degradation over a 30-d period via abiotic and biotic processes. The results showed that 3579% of plasticizers were released into the sediment from the MPs and > 99.9% degradation was achieved. Although a significantly higher degradation was found in plasticizer-added microcosms under biotic processes (overall, 94%), there was a noticeable abiotic loss (72%), suggesting that abiotic processes also play a role in plasticizer degradation. Interestingly, when compared with the initial sediment-water partitioning for plasticizers, the partition constants for low-molecular-weight compounds decreased in both microcosms, whereas those for high-molecular-weight compounds increased after abiotic degradation. Furthermore, changes in the bacterial community, abundance of plasticizer-degrading bacterial populations, and functional gene profiles were assessed. In all the microcosms, a decrease in bacterial community diversity and a notable shift in bacterial composition were observed. The enriched potential plasticizer-degrading bacteria were Arthrobacter, Bacillus, Desulfovibrio, Desulfuromonas, Devosia, Gordonia, Mycobacterium, and Sphingomonas, among which Bacillus was recognized as the key plasticizer degrader. Overall, these findings shed light on the factors affecting plasticizer degradation, the microbial communities potentially involved in biodegradation, and the fate of plasticizers in the environment.

Category-Based Toxicokinetic Evaluations of Data-Poor Per- and Polyfluoroalkyl Substances (PFAS) using Gas Chromatography Coupled with Mass Spectrometry.

Concern over per- and polyfluoroalkyl substances (PFAS) has increased as more is learned about their environmental presence, persistence, and bioaccumulative potential. The limited monitoring, toxicokinetic (TK), and toxicologic data available are inadequate to inform risk across this diverse domain. Here, 73 PFAS were selected for in vitro TK evaluation to expand knowledge across lesser-studied PFAS alcohols, amides, and acrylates. Targeted methods developed using gas chromatography-tandem mass spectrometry (GC-MS/MS) were used to measure human plasma protein binding and hepatocyte clearance. Forty-three PFAS were successfully evaluated in plasma, with fraction unbound (fup) values ranging from 0.004 to 1. With a median fup of 0.09 (i.e., 91% bound), these PFAS are highly bound but exhibit 10-fold lower binding than legacy perfluoroalkyl acids recently evaluated. Thirty PFAS evaluated in the hepatocyte clearance assay showed abiotic loss, with many exceeding 60% loss within 60 min. Metabolic clearance was noted for 11 of the 13 that were successfully evaluated, with rates up to 49.9 μL/(min × million cells). The chemical transformation simulator revealed potential (bio)transformation products to consider. This effort provides critical information to evaluate PFAS for which volatility, metabolism, and other routes of transformation are likely to modulate their environmental fates.

Measuring the photostability of agrochemicals on leaves: understanding the balance between loss processes and foliar uptake.

Photostability is an important property in agrochemicals, impacting their biological efficacy, environmental fate and registrability. As such, it is a property that is routinely measured during the development of new active ingredients and their formulations. To make these measurements, compounds are typically exposed to simulated sunlight after application to a glass substrate. While useful, these measurements neglect key factors that influence photostability under true field conditions. Most importantly, they neglect the fact that compounds are applied to living plant tissue, and that uptake and movement within this tissue provides a mechanism to protect compounds from photodegradation. In this work, we introduce a new photostability assay incorporating leaf tissue as a substrate, designed to run at medium throughput under standardized laboratory conditions. Using three test cases, we demonstrate that our leaf-disc-based assays provides quantitatively different photochemical loss profiles to an assay employing a glass substrate. And we also demonstrate that these different loss profiles are intimately linked to the physical properties of the compounds, the effect that those properties have on foliar uptake and, thereby, the availability of the active ingredient on the leaf surface. The method presented provides a quick and simple measure of the interplay between abiotic loss processes and foliar uptake, supplying additional information to facilitate the interpretation of biological efficacy data. The comparison of loss between glass slides and leaves also provides a better understanding of when intrinsic photodegradation is likely to be a good model for a compound's behaviour under field conditions. © 2023 Society of Chemical Industry.

Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean.

Sunlight chemically transforms marine plastics into a suite of products, with formulation—the specific mixture of polymers and additives—driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of ∼1% titanium dioxide (TiO2), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA’s average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO2, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO2 accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic’s environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.

Competitive superiority of N-fixing cyanobacteria when fixed N is scarce: Reconsiderations based on a model with heterocyst differentiation

Some cyanobacteria fix nitrogen (N) with specialized cells (heterocysts). Resource competition theory and some evidence suggest that such cyanobacteria can dominate when the supply of available dissolved N is low relative to that of phosphorus (P). To probe this notion, a recently introduced mathematical model of cyanobacteria that differentiate heterocysts was paired with a model of non-fixing algal competitors. With sufficiently low abiotic loss rates, dominance by cyanobacteria was predicted at low N:P supply ratios, coexistence for intermediate ratios, and dominance by algae at high ratios. Heterocysts do not reproduce, so differentiation is demographically costly, and at abiotic loss rates exceeding about 0.18 d − 1, cyanobacteria are predicted to be competitively excluded for all N:P supply ratios examined. The demographic cost of heterocyst production is also predicted to impact competitive dynamics in the presence of herbivores. Cyanobacteria are highly susceptible to apparent competition from algae, even when they are the less-preferred food of herbivores. Algae dominate at highest and lowest N:P supply ratios, and cyanobacteria at intermediate ratios, with two non-contiguous intervals of coexistence. In addition to these unexpected results, this study illustrates how planktonic community processes could determine whether nitrogen fixation contributes significantly to planktonic nitrogen supply.

Characterization of 4T Engine Oil Degrading Indigenous Bacteria Isolated From Semi Arid Zone of Rajasthan (Churu)

The biodegradation potential of petroleum hydrocarbons such as polycyclic aromatic hydrocarbons (PAHs) and n-branched alkanes etc. of 4T engine oil were evaluated in aqueous media using bacterial strain isolated from petroleum contaminated soil of semi Arid region (Churu) of Rajasthan (India). Out of 12 petroleum hydrocarbons degrading bacterial strain one of the most growing bacteria was identified as Achromobacter xylosoxidans M66 by morphological, physiological, biochemical and partial sequencing of 16s rDNA. This strain was capable to degrade 68 ± 2% of n-alkanes, 28 ± 4% PAHs, and the abiotic loss was 20 ± 2% during 28 days incubation period. 64 ± 3% of n-alkanes and 26 ± 3% PAHs were biodegraded and abiotic loss during this period was 21 ± 3% in 35 days of incubation. As expected abiotic losses were decreases with increasing long chain alkanes and PAH’s concentration. Correlation between cell number and biodegradation rate showed that as the number of cell increased the degradation rate is also increased. The hydrocarbon contents were measured by Gas chromatography Mass spectroscopy (GC-MS) QP-2010 plus Shimadzu) carriedColumn-Rtx-5 MS, 30-meter X 0.25 mm i.d. X 0.25 μm film thickness, 1 ml/min; pressure 72.6 kPa and split ratio 10%. The initial temperature was 60ºC kept for 6 minutes and final temperature for 260ºC was kept for 20 minutes with total running time of 50 minutes.

Evaluation and comparison of in vitro intrinsic clearance rates measured using cryopreserved hepatocytes from humans, rats, and rainbow trout

In vitro and in silico methods that can reduce the need for animal testing are being used with increasing frequency to assess chemical risks to human health and the environment. The rate of hepatic biotransformation is an important species-specific parameter for determining bioaccumulation potential and extrapolating in vitro bioactivity to in vivo effects. One approach to estimating hepatic biotransformation is to employ in vitro systems derived from liver tissue to measure chemical (substrate) depletion over time which can then be translated to a rate of intrinsic clearance (CLint). In the present study, cryopreserved hepatocytes from humans, rats, and rainbow trout were used to measure CLint values for 54 industrial and pesticidal chemicals at starting test concentrations of 0.1 and 1 μM. A data evaluation framework that emphasizes the behavior of Heat-Treated Controls (HTC) was developed to identify datasets suitable for rate reporting. Measured or estimated (“greater than” or “less than”) CLint values were determined for 124 of 226 (55 %) species-chemical-substrate concentration datasets with acceptable analytical chemistry. A large percentage of tested chemicals exhibited low HTC recovery values, indicating a substantial abiotic loss of test chemical over time. An evaluation of KOW values for individual chemicals suggested that in vitro test performance declined with increasing chemical hydrophobicity, although differences in testing devices for mammals and fish also likely played a role. The current findings emphasize the value of negative controls as part of a rigorous approach to data quality assessment for in vitro substrate depletion studies. Changes in current testing protocols can be expected to result in the collection of higher quality data. However, poorly soluble chemicals are likely to remain a challenge for CLint determination.

The mitochondrial NADH pool is involved in hydrogen sulfide signaling and stimulation of aerobic glycolysis

Hydrogen sulfide is synthesized by enzymes involved in sulfur metabolism and oxidized via a dedicated mitochondrial pathway that intersects with the electron transport chain at the level of complex III. Studies with H2S are challenging since it is volatile and also reacts with oxidized thiols in the culture medium, forming sulfane sulfur species. The half-life of exogenously added H2S to cultured cells is unknown. In this study, we first examined the half-life of exogenously added H2S to human colonic epithelial cells. In plate cultures, H2S disappeared with a t1/2 of 3 to 4 min at 37 °C with a small fraction being trapped as sulfane sulfur species. In suspension cultures, the rate of abiotic loss of H2S was slower, and we demonstrated that sulfide stimulated aerobic glycolysis, which was sensitive to the mitochondrial but not the cytoplasmic NADH pool. Oxidation of mitochondrial NADH using the genetically encoded mito-LbNOX tool blunted the cellular sensitivity to sulfide-stimulated aerobic glycolysis and enhanced its oxidation to thiosulfate. In contrast, sulfide did not affect flux through the oxidative pentose phosphate pathway or the TCA cycle. Knockdown of sulfide quinone oxidoreductase, which commits H2S to oxidation, sensitized cells to sulfide-stimulated aerobic glycolysis. Finally, we observed that sulfide decreased ATP levels in cells. The dual potential of H2S to activate oxidative phosphorylation at low concentrations, but inhibit it at high concentrations, suggests that it might play a role in tuning electron flux and, therefore, cellular energy metabolism, particularly during cell proliferation.

Shift of Soil Polycyclic Aromatic Hydrocarbons (PAHs) Dissipation Pattern and Microbial Community Composition due to Rhamnolipid Supplementation

Biosurfactants are promising substitutes for chemical surfactants during polycyclic aromatic hydrocarbon (PAH) bioremediation. However, recent studies have revealed contrasting findings and critical knowledge gaps regarding the impacts of biosurfactants on the soil PAH biodegradation efficiency and microbial community. Here, a laboratory study was conducted to evaluate the impact of rhamnolipid on the PAH dissipation efficiency and microbial community structure during the time-course incubation. The data showed that the contribution ratio of biotic loss and abiotic loss depended on the ring number of PAH. In the microcosms supplemented with 20 μg g−1 rhamnolipid, the biodegradation efficiencies of phenanthrene, fluoranthene, and pyrene increased by 10.1%, 12.3%, and 22.0%, respectively, compared to those in the rhamnolipid-free treatment after incubation for 7 days. In contrast, rhamnolipid either had no impact on or inhibited PAH degradation in the later time points (21–35 days). The abundance of bacterial 16S rRNA and phnAc genes showed significant increase in soil amended of both PAH and rhamnolipid. MiSeq sequencing results revealed that potential PAHs-degrading Massilia, Bacillus, Lysobacter, Archrobacter, and Phenylobacterium became dominant genera in PAH treatment, irrespective of the rhamnolipid added. Nevertheless, PAH addition in the presence of rhamnolipid also significantly stimulated the growth of Delftia, Brevundimonas, Tumebacillus, and Geobacillus. In contrast, the rhamnolipid altered the microbial community composition through the selection of Gaiella, Solirubrobacter, Nocardioides, and Bacillus. The results reveal the intensive selectivity effect of PAH and rhamnolipid on the soil microbes that are involved in bioremediation, and highlight the positive effect on PAHs biodegradation.

Characterization and genomic analysis of highly efficient thermotolerant oil-degrading bacterium Gordonia sp. 1D

A thermotolerant bacterial strain 1D isolated from refinery oil-contaminated soil was identified as Gordonia sp. based on the analysis of 16S rRNA and gyrB gene sequences. The strain was found to utilize crude oil, diesel fuel, and a wide spectrum of alkanes at temperatures up to 50°C. Strain 1D is the first representative of Gordonia amicalis capable of utilizing alkanes of chain length up to С36 at a temperature of 45-50°C. The degree of crude oil degradation by Gordonia sp. 1D at 45°C was 38% in liquid medium and 40% in soil (with regard to abiotic loss). There are no examples of so effective hydrocarbon-oxidizing thermotolerant Gordonia in the world literature. The 1D genome analysis revealed the presence of two alkane hydroxylase gene clusters, genes of dibenzothiophene cleavage, and the cleavage of salicylate and gentisate-naphthalene metabolism intermediates. The highly efficient thermotolerant strain Gordonia sp. 1D can be used in remediation of oil-contaminated soils in hot climates.

Natural attenuation of fluorene and pyrene in contaminated soils and assisted with hydroxypropyl-β-cyclodextrin. Effect of co-contamination

The objectives of this study were to investigate the mutual effect of the PAHs fluorene and pyrene on their respective biodegradation and dissipation processes in an agricultural soil, and to determine the effect of hydroxypropyl-β-cyclodextrin (HPBCD), used to increase the bioavailability of PAHs, on such processes. Fluorene dissipation was primarily due to abiotic processes, although a small contribution from biodegradation was also observed. Therefore, fluorene dissipation did not increase with HPBCD and its presence did not significantly alter the dehydrogenase activity. In contrast to fluorene, pyrene dissipation depended primarily on biotic factors, with endogenous soil microorganisms capable of degrading pyrene, with large increases in dehydrogenase activity. HPBCD increased biodegradation rate of pyrene. The co-contamination of soil with both PAHs did not affect fluorene evolution, but significantly inhibited pyrene biodegradation. The different abilities of soil bacterial consortia to catabolize these PAHs are discussed. Additionally, the possibility that the abiotic loss of fluorene through volatilization had a significant effect on the microbial community biodegradation of both fluorene and pyrene is examined.

Treatment of simulated biomass gasification wastewater of varying strength in a three stage rotating biological contactor

Abstract Wastewater generated during wet scrubbing of producer gas formed in biomass gasifiers consist mainly of phenolics, heterocyclics, mono and polynuclear aromatic hydrocarbons (PAHs). The concentration of organics in such wastewater is reported to vary over a wide range depending on gasifier operating conditions and water recycling practices. Such variations may impact the performance of biological treatment processes due to the toxic nature of constituents. Treatment of simulated biomass gasification wastewater of varying strength in a rotating biological contactor (RBC), bioaugmented with a novel bacteria, Exiguobacterium aurantiacum, and operated at constant hydraulic retention time (HRT) of 24 h revealed consistently high removal efficiency in the range of 91–92% for organic loading rate (OLR) of 6.7–16.1 g-COD/m2/d. Increase in OLR to 39.5 g-COD/m2/d caused a marked drop in COD removal efficiency (83%). Greater than 74% removal was observed for all the components although the influent concentration of phenolics and heterocyclics were much higher compared to the PAHs. Abiotic loss in absence of the biofilm was consistently low (12–20% COD removal). Treatment was accompanied by significant reduction in acute toxicity. The biofilm consisting of E. aurantiacum and mixed microbial consortium thus have a good potential for removal of these toxic constituents.

OsSUV3 functions in cadmium and zinc stress tolerance in rice (Oryza sativa L. cv IR64)

Protein of nuclear encoded SUV3 (suppressor of Var 3) gene is a DNA and RNA helicase, localized in mitochondria and is a subunit of the degradosome complex involved in regulation of RNA surveillance and turnover. To overcome the abiotic stress-induced loss of crop yield, a multi-stress tolerant trait is required. Beside salinity stress the heavy metals including cadmium and zinc also affect the yield and quality of food crops. Since rice is a one of the staple food therefore it is important to develop a multi-stress including salinity and metal tolerant variety. Recently we have reported the role of OsSUV3 in salinity stress tolerance in rice; however, its role in metal stress has not been studied so far. Here we report that in response to cadmium and zinc stress the OsSUV3 transcript level is induced in rice and its overexpression in transgenic IR64 rice plants confers the metal stress tolerance. In addition to its previously reported role in salinity stress tolerance, this study further shows the role of OsSUV3 helicase in cadmium and zinc stress tolerance suggesting its involvement in multi-stress tolerance.

Composting Study of Petroleum Contaminated Soil

Composting has been shown to be an effective bioremediation technique for the treatment of hydrocarbon-contaminated soil. In this research, the major objective of this research was to find the appropriate mix ratio of organic amendments for enhancing the degradation of petroleum hydrocarbons during diesel oil contaminated soil composting. The spent mushroom was added as an amendment for supplementing organic matter for composting of contaminated soil. The volumn ratios of contaminated soil to organic amendments were 1:1, 1.5:1 and 2:1. Target contaminant of this research was diesel oil, which was spiked at 16240 mg/kg sample on a dry weight basis. The degradation of diesel oil was significantly enhanced by the addition of these organic amendments relative to straight soil control. Degradation rates of total petroleum hydrocarbons (TPH) were the greatest at the ratio of 1:1 of contaminated soil to organic amendments on the volumn ratio. The abiotic loss of TPH was only about 6.83% of initial TPH.

Differential Microbial Transformation of Nitrosamines by an Inducible Propane Monooxygenase

The toxicity of N-nitrosamines, their presence in drinking and environmental water supplies, and poorly understood recalcitrance collectively necessitate a better understanding of their potential for bioattenuation. Here, we show that the bacterial strain Rhodococcus jostii RHA1 can biotransform N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPYR), and possibly N-nitrosomorpholine (NMOR) in addition to N-nitrosodimethylamine (NDMA). Growth of cells on propane as the sole carbon source greatly enhanced degradation rates when contrasted with cells grown on complex organics. Propane-induced rates in order of fastest to slowest were NDMA > NDEA > NDPA > NPYR > NMOR at concentrations <2000 μg/L. Removal rates for linear functional groups scaled inversely with mass and cyclic nitrosamines were more recalcitrant than linear nitrosamines. Controls demonstrated significant NDEA and NDPA losses independent of biomass, suggesting abiotic processes may play a role in attenuation of these two compounds under experimental conditions tested here. In contrast to NDMA, a transition from first to zero order kinetics was not observed for the other nitrosamines included in this study over a concentration range of 20-2000 μg/L. A genetic knockout for the propane monooxygenase enzyme (PrMO) confirmed the role of this enzyme in the biotransformation of NDEA and NPYR. This study furthers our understanding of environmental nitrosamine attenuation by revealing an enzymatic mechanism for the biotransformation of multiple nitrosamines, their relative recalcitrance to transformation, and potential for abiotic loss.

Characterization of 2T engine oil degrading indigenous bacteria, isolated from high altitude (Mussoorie), India

The biodegradability of petroleum hydrocarbons such as polycyclic aromatic hydrocarbons (PAHs) and n-branched alkanes etc. of 2T engine oil were studied in aqueous media using bacterial strain isolated from petroleum contaminated soil of high altitude. Out of five petroleum degrading bacterial strain one of the most growing bacteria was identified as Enterobacter strain by morphological, physiological, biochemical and partial sequencing of 16S rDNA. This strain was capable of degrading 75 ± 3% of n-alkanes, 32 ± 5% PAHs, and the abiotic loss was 24 ± 6% during 10 days incubation period. 85 ± 2% of n-alkanes and 51 ± 3% PAHs were biodegraded in 20 days. The abiotic loss during this period was 15 ± 3%. In 30 days of incubation period 98% ± 1% n-alkanes and 75 ± 3% PAHs were degraded. As expected abiotic losses were smaller with increasing long chain alkanes and PAH’s concentration. An increment in oil degradation was correlated to an increase in cell number indicating that the bacterial isolate was responsible for the oil degradation. The hydrocarbon contents were measured by Shimadzu QP-2000 Gas chromatography/mass spectrometry by ULBON HR-1 column.

The Removal and Remediation of Phenanthrene and Pyrene in Soil by Mixed Cropping of Alfalfa and Rape

The mechanisms and efficiencies of the removal and remediation of polycyclic aromatic hydrocarbons (PAHs) in soils by different planting patterns with rape ( Brassica campestris) and alfalfa ( Medicago sativa) were studied by pot experiments in a greenhouse. Results showed that the remediation efficiencies under mixed cropping of alfalfa and rape significantly exceeded those under single cropping when the initial concentrations of phenanthrene and pyrene were at 20.05-322.06 mg kg −1 and 20.24-321.42 mg kg −1, respectively. After 70 days plantation of crops, the contents of extractable PAHs in soils under mixed cropping were much lower than those under single cropping. About 65.17-83.52% of phenanthrene and 60.09%-75.34% of pyrene was removed from the soils under mixed cropping, respectively, which were averagely 43.26 and 40.38% for phenanthrene, and 11.03 and 16.29% for pyren higher than those under single cropping. Alfalfa or rape did absorb and accumulate PAHs from the soils apparently; the PAHs concentrations in plants monotonically increased with the increase of initial PAHs concentrations in soil; the accumulations of PAHs in plants showed following sequence as roots > above parts, phenanthrene > pyrene and single cropping > mixed cropping at same contamination level. Despite the presence of vegetation significantly enhanced the remediation of PAHs in soils, contributions of abiotic loss, plant uptake, accumulation and microbial degradation was much lower than those of plant-microbial interactions in the process of phytoremediation. Thus plant-microbial interactions are the main mechanisms for the remediation enhancement of soil PAHs pollution under mixed cropping models. Results suggested a feasibility of the establishment of multi-species phytoremediation for the improvement of remediation efficiencies of PAHs, which may decrease accumulations of PAHs in crops and thus reduce their risks.

Retention of Inactivated Bioaerosols and Ethene in a Rotating Bioreactor Constructed for Bioaerosol Activity Studies

AbstractAvailable literature raises the possibility that airborne microorganisms are not just passively transported through the air, but may be metabolically active while “in transit”. To investigate the metabolic activity of bacteria suspended in air enriched with volatile growth substrates, a rotating bioreactor system was developed and tested which allows prolonged suspension of bacteria in air. The bioreactors were 0.32 m3 stainless steel drums rotated at 1.3 revolutions per minute and equipped with on‐board pressure, temperature and humidity transducers with real‐time data collection. Bioreactors were tested for retention of a volatile organic compound, ethene, and for suspension of an inactivated laboratory‐generated Pseudomonas fluorescens bioaerosol. At an initial ethene concentration of 560 ppmv the first order abiotic loss of ethene was 0.051 ± 0.010 d–1 (average ± standard deviation) or a half life of 13.6 days. Inactivated airborne bacteria (size mode 0.5 to 0.7 μm) remained suspended with a half life of 8.5 days. Thus, the bioreactors maintained bacteria suspended in the presence of a volatile growth substrate for a time period theoretically sufficient to observe metabolic activity. Bioreactors will be used to test natural bioaerosols and active laboratory‐generated bioaerosols during enrichment with volatile organic compounds to assess growth and substrate biodegradation.

Slurry-phase biodegradation of weathered oily sludge waste

We assessed the biodegradation of a typical oily sludge waste (PB401) in Mexico using several regimes of indigenous microbial consortium and relevant bioremediation strategies in slurry-phase system. Abiotic loss of total petroleum hydrocarbons (TPH) in the PB401 was insignificant, and degradation rates under the various treatment conditions ranged between 666.9 and 2168.7 mg kg −1 day −1 over a 15 days reaction period, while viable cell count peaked at between log 10 5.7 and log 10 7.4 cfu g −1. Biostimulation with a commercial fertilizer resulted in 24% biodegradation of the TPH in the oily waste and a corresponding peak cell density of log 10 7.4 cfu g −1. Addition of non-indigenous adapted consortium did not appear to enhance the removal of TPH from the oily waste. It would appear that the complexities of the components of the alkylaromatic fraction of the waste limited biodegradation rate even in a slurry system.

Treatment of diesel fuel contaminated soil in jet–fluidized bed

Bioremediation of diesel-oil contaminated soil (4 wt%) was studied in a jet–fluidized reactor by the stimulation of indigenous oil micro-organisms. The experiments were carried out using different rates of aeration and/or jet air flow and consequently various mixing rates to investigate their influence on biodegradation and removal ratios. The diesel-oil content decreased rapidly in all experiments in the first 7 days, with different removal ratios. The presence of the jet favoured inter-particle exchanges, transfers between the various phases involved, and accelerated the diesel-oil removal process. Also, the influence of aeration seemed negligible compared with that of the jet. Removal and biodegradation ratios ranged from 69% to 99%, and 54% to 84%, respectively after 15 days of treatment. The best biodegradation ratio of 84% occurred in the case of an expanded bed with minimum fluidization, operating at a jet velocity of 37 m/s. The diesel-oil biodegradation was governed by first-order kinetics. Important air flows enhanced the efficiency of diesel-oil removal, and abiotic loss and hence decreased the biodegradation ratio.