Terrestrial microcosms in a feasibility study on the remediation of diesel-contaminated soils

Bacterial community dynamics and associated genes in hydrocarbon contaminated soil during bioremediation using brewery spent grain

Brewery spent grain (BSG) has previously been exploited in bioremediation. However, detailed knowledge of the associated bacterial community dynamics and changes in relevant metabolites and genes over time is limited. This study investigated the bioremediation of diesel contaminated soil amended with BSG. We observed complete degradation of three total petroleum hydrocarbon (TPH C10-C28) fractions in amended treatments as compared to one fraction in the unamended, natural attenuation treatments. The biodegradation rate constant (k) was higher in amended treatments (0.1021k) than in unamended (0.059k), and bacterial colony forming units increased significantly in amended treatments. The degradation compounds observed fitted into the elucidated diesel degradation pathways and quantitative PCR results showed that the gene copy numbers of all three associated degradation genes, alkB, catA and xylE, were significantly higher in amended treatments. High-throughput sequencing of 16S rRNA gene amplicons showed that amendment with BSG enriched autochthonous hydrocarbon degraders. Also, community shifts of the genera Acinetobacter and Pseudomonas correlated with the abundance of catabolic genes and degradation compounds observed. This study showed that these two genera are present in BSG and thus may be associated with the enhanced biodegradation observed in amended treatments. The results suggest that the combined evaluation of TPH, microbiological, metabolite and genetic analysis provides a useful holistic approach to assessing bioremediation.

Bioremediation of hydrocarbon contaminated soil using local organic materials and earthworms

Bioremediation technologies have demonstrated significant success on biological quality recovery of hydrocarbon contaminated soils, employing techniques among which composting and vermiremediation stand out. The aim of this study was to evaluate the efficiency of these processes to remediate diesel-contaminated soil, employing local organic materials and earthworms. During the initial composting stage (75 days), the substrate was made up using contaminated soil, lombricompost, rice hulls and wheat stubbles (60:20:15:5% w/w). Diesel concentration in the contaminated substrate was about 5 g kg^-1, equivalent to a Total Petroleum Hidrocarbons (TPH) experimental concentration of 3425 ± 50 mg kg^-1. During the later vermiremediation stage (60 days), the earthworm species Eisenia fetida and Amynthas morrisi were evaluated for their hydrocarbon degradation capacity. Physicochemical and biological assays were measured at different times of each stage and ecotoxicity assays were performed at the end of the experiments. TPH concentration reduced 10.91% after composting and from 45.2 to 60.81% in the different treatments after vermiremediation. Compared with TPH degradation in the treatment without earthworms (16.05%), results indicate that earthworms, along with indigenous microorganisms, accelerate the remediation process. Vermiremediation treatments did not present phytotoxicity and reflected high substrate maturity values (>80% Germination Index) although toxic effects were observed due to E. fetida and A morrisi exposure to diesel. Vermiremediation was an efficient technology for the recovery of substrate biological quality after diesel contamination in a short period. The addition of organic materials and suitable food sources aided earthworm subsistence, promoted the decontamination process and improved the substrate quality for future productive applications.

Bioremediation assessment, hematological, and biochemical responses of the earthworm (Allolobophora caliginosa) in soil contaminated with crude oil

Soil contamination with crude oil is a major environmental problem. The aim of this study was to assess whether the earthworm Allolobophora caliginosa could improve the degradation of petroleum hydrocarbons while enriching soils that were contaminated with crude oil. In addition, the toxic effects of crude oil on earthworms during bioremediation will be assessed. The soil samples were experimentally contaminated with two different quantities of light crude oil 5 or 7.5 ml for 60 days. Activities of A. caliginosa resulted in 33.56% and 54.98% total petroleum hydrocarbon (TPH) losses from the soil contaminated with 5 ml of crude oil after 22 and 60 days; respectively. While in 7.5 ml crude oil-contaminated soil, there was a loss of 32.24% and 71.05% of TPH over the same period of time. During the experiment, however, there were no signs of improvement in soil physicochemical properties. Earthworm tissue analyses at the end of the experiment showed significant bioaccumulation of petroleum hydrocarbons in their tissues and changes in their metabolic and hematological parameters. Earthworms exposed to crude oil showed a significant increase in protein, malondialdehyde, and glutathione but decreased in catalase levels and total antioxidant capacity compared to control earthworm after 60 days of exposure. There was a significant decrease in the Hgb, RBC_S, Hct, MCV, MCH, platelet count, and WBCs. As a result, the earthworm Allolobophora caliginosa has been shown to be good bioremediator for oil-contaminated soils and also has potential as a bioindicator for contamination.

Application of sulphate and cytokinin in assisted arsenic phytoextraction by industrial Cannabis sativa L

Phytoextraction is currently investigated to effectively remediate soil contaminated by metals and provide highly competitive biomass for energy production. This research aimed to increase arsenic (As) removal from contaminated soil using industrial Cannabis sativa L., a suitable energy crop for biofuel production. Assisted phytoextraction experiments were conducted on a microcosm scale to explore the ability of two friendly treatments, sodium sulphate (SO₄) and exogenous cytokinin (CK), in increasing As phytoextraction efficiency. The results showed that the treatments significantly increased As phytoextraction. Cytokinin was the most effective agent for effectively increasing translocation and the amount of As in aerial parts of C. sativa. In fact, the concentration of As in the shoots of CK-treated plants increased by 172% and 44% compared to untreated and SO₄-treated plants, respectively. However, the increased As amount accumulated in C. sativa tissues due to the two treatments negatively affected plant growth. Arsenic toxicity caused a significant decrease in aerial C. sativa biomass treated with CK and SO₄ of about 32.7% and 29.8% compared to untreated plants, respectively. However, for our research purposes, biomass reduction has been counterbalanced by an increase in As phytoextraction, such as to consider C. sativa and CK an effective combination for the remediation of As-contaminated soils. Considering that C. sativa has the suitable characteristics to provide valuable resources for bioenergy production, our work can help improve the implementation of a sustainable management model for As contaminated areas, such as phytoremediation coupled with bioenergy generation.

Insights into the mechanisms underlying the remediation potential of earthworms in contaminated soil: A critical review of research progress and prospects

In recent years, soil pollution is a major global concern drawing worldwide attention. Earthworms can resist high concentrations of soil pollutants and play a vital role in removing them effectively. Vermiremediation, using earthworms to remove contaminants from soil or help to degrade non-recyclable chemicals, is proved to be an alternative, low-cost technology for treating contaminated soil. However, knowledge about the mechanisms and framework of the vermiremediation various organic and inorganic contaminants is still limited. Therefore, we reviewed the research progress of effects of soil contaminants on earthworms and potential of earthworm used for remediation soil contaminated with heavy metals, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pesticides, as well as crude oil. Especially, the possible processes, mechanisms, advantages and limitations, and how to boost the efficiency of vermiremediation are well addressed in this review. Finally, future prospects of vermiremediation soil contamination are listed to promote further studies and application of vermiremediation in contaminated soils.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in a diesel oil-contaminated mangrove by plant growth-promoting rhizobacteria

In this study, Rhizophora mangle L. mangrove plants and plant growth-promoting bacteria were evaluated for their ability to degrade polycyclic aromatic hydrocarbons in diesel oil-contaminated sediment. The diesel-contaminated soil was sown with plant growth-promoting bacteria in the R. mangle L. rhizosphere and monitored for 120 days in a greenhouse. The plant growth-promoting bacteria Pseudomonas aeruginosa and Bacillus sp. were analyzed for their ability to degrade eight priority polycyclic aromatic hydrocarbons, achieving a removal rate for naphthalene (80%), acenaphthene (> 60%), anthracene (> 50%), benzo(a)anthracene (> 60%), benzo(a)pyrene (> 50%) and dibenzo(a,h)anthracene (> 90%) in the treatments with and without plants. R. mangle L. demonstrated a removal rate above 50% for acenaphthene and fluoranthene. The bacterial strains promoted the development of the plant propagule in 55% of sediment contaminated with diesel. Scanning electron microscopy revealed the formation of biofilms by the strains in the roots of the plants in contact with the diesel. Thus, the interaction between Rhizophora mangle L. and the bacterial strains (Bacillus sp. and P. aeruginosa) demonstrated the potential of the strains to degrade diesel and bioremediate mangroves impacted by diesel oil.

Toxicity assessment of fresh and weathered petroleum hydrocarbons in contaminated soil- a review

Soil contamination with total petroleum hydrocarbons (TPH) is widespread throughout the globe due to the massive production of TPH anthropogenically and its occurrence in the soil. TPH is toxic to beneficial soil organisms and humans and thus has become a serious concern among the public. Traditionally TPH toxicity in the soil is estimated based on chemical fractions and a range of bioassays including plants, invertebrates and microorganisms. There is a large inconsistency among ecotoxicology data using these assays due to the nature of TPH and their weathering. Therefore, in this article, we critically reviewed the weathered conditions of TPH, the potential fate in soil and the bioindicators for the assessment of the ecotoxicity. Based on the current research and the state-of-the-art problem, we also highlighted key recommendations for future research scope for the real-world solution of the ecotoxicological studies of hydrocarbons.

Phytoremediation of contaminated soils containing gasoline using Ludwigia octovalvis (Jacq.) in greenhouse pots

Greenhouse experiments were carried out to determine the phytotoxic effects on the plant Ludwigia octovalvis in order to assess its applicability for phytoremediation gasoline-contaminated soils. Using plants to degrade hydrocarbons is a challenging task. In this study, different spiked concentrations of hydrocarbons in soil (1, 2, and 3 g/kg) were tested. The results showed that the mean efficiency of total petroleum hydrocarbon (TPH) removal over a 72-day culture period was rather high. The maximum removal of 79.8 % occurred for the 2 g/kg concentration, while the removal rate by the corresponding unplanted controls was only (48.6 %). The impact of gasoline on plants included visual symptoms of stress, yellowing, growth reduction, and perturbations in the developmental parameters. The dry weight and wet weight of the plant slightly increased upon exposure to gasoline until day 42. Scanning electron microscopy (SEM) indicated change to the root and stem structure in plant tissue due to the direct attachment with gasoline contaminated compared to the control sample. The population of living microorganisms in the contaminated soil was found to be able to adapt to different gasoline concentrations. The results showed that L. octovalvis and rhizobacteria in gasoline-contaminated soil have the potential to degrade organic pollutants.

Earthworms, pesticides and sustainable agriculture: a review

The aim of this review is to generate awareness and understand the importance of earthworms in sustainable agriculture and effect of pesticides on their action. The natural resources are finite and highly prone to degradation by the misuse of land and mismanagement of soil. The world is in utter need of a healthy ecosystem that provides with fertile soil, clean water, food and other natural resources. Anthropogenic activities have led to an increased contamination of land. The intensification of industrial and agricultural practices chiefly the utilization of pesticides has in almost every way made our natural resources concave. Earthworms help in a number of tasks that support many ecosystem services that favor agrosystem sustainability but are degraded by exhaustive practices such as the use of pesticides. The present review assesses the response of earthworm toward the pesticides and also evaluates the relationship between earthworm activity and plant growth. We strictly need to refresh and rethink on the policies and norms devised by us on sustainable ecology. In an equivalent way, the natural resources should be utilized and further, essential ways for betterment of present and future livelihood should be sought.

Lab-scale investigation on remediation of diesel-contaminated aquifer using microwave energy

Aquifer contamination with diesel fuel is a worldwide environmental problem, and related available remediation technologies may not be adequately efficient, especially for the simultaneous treatment of both solid and water phases. In this paper, a lab-scale 2.45 GHz microwave (MW) treatment of an artificially diesel-contaminated aquifer was applied to investigate the effects of operating power (160, 350 and 500 W) and time on temperature profiles and contaminant removal from both solid and water phases. Results suggest that in diesel-contaminated aquifer MW remediation, power significantly influences the final reachable temperature and, consequently, contaminant removal kinetics. A maximum temperature of about 120 °C was reached at 500 W. Observed temperature values depended on the simultaneous irradiation of both aquifer grains and groundwater. In this case, solid phase heating is limited by the maximum temperature that interstitial water can reach before evaporation. A minimal residual diesel concentration of about 100 mg kg(-1) or 100 mg L(-1) was achieved by applying a power of 500 W for a time of 60 min for the solid or water phase, respectively. Measured residual TPH fractions showed that MW heating resulted in preferential effects of the removal of different TPH molecular weight fractions and that the evaporation-stripping phenomena plays a major role in final contaminant removal processes. The power low kinetic equation shows an excellent fit (r(2) > 0.993) with the solid phase residual concentration observed for all the powers investigated. A maximum diesel removal of 88 or 80% was observed for the MW treatment of the solid or water phase, respectively, highlighting the possibility to successfully and simultaneously remediate both the aquifer phases. Consequently, MW, compared to other biological or chemical-physical treatments, appears to be a better choice for the fast remediation of diesel-contaminated aquifers.

Remediation of hydrocarbon-contaminated soils by ex situ microwave treatment: technical, energy and economic considerations

In this study, the remediation of diesel-polluted soils was investigated by simulating an ex situ microwave (MW) heating treatment under different conditions, including soil moisture, operating power and heating duration. Based on experimental data, a technical, energy and economic assessment for the optimization of full-scale remediation activities was carried out. Main results show that the operating power applied significantly influences the contaminant removal kinetics and the moisture content in soil has a major effect on the final temperature reachable during MW heating. The first-order kinetic model showed an excellent correlation (r2 > 0.976) with the experimental data for residual concentration at all operating powers and for all soil moistures tested. Excellent contaminant removal values up to 94.8% were observed for wet soils at power higher than 600 W for heating duration longer than 30 min. The use of MW heating with respect to a conventional ex situ thermal desorption treatment could significantly decrease the energy consumption needed for the removal of hydrocarbon contaminants from soils. Therefore, the MW treatment could represent a suitable cost-effective alternative to the conventional thermal treatment for the remediation of hydrocarbon-polluted soil.

Influence of inocula with prior hydrocarbon exposure on biodegradation rates of diesel, synthetic diesel, and fish-biodiesel in soil

To achieve effective bioremediation within short warm seasons of cold climates, microbial adaptation periods to the contaminant should be brief. The current study investigated growth phases for soil spiked with diesel, Syntroleum, or fish biodiesel, using microbial inocula adapted to the specific substrates. For modeling hydrocarbon degradation, multi-phase first order kinetics was assumed, comparing linear regression with nonlinear parameter optimization of rate constants and phase durations. Lag phase periods of 5 to >28d were followed by short and intense exponential growth phases with high rate constants (e.g. from kFish=0.0013±0.0002 to kSyntr=0.015±0.001d(-1)). Hydrocarbon mineralization was highest for Syntroleum contamination, where up to three times higher cumulative CO2 production was achieved than for diesel fuel, with fish biodiesel showing initially the slowest degradation. The amount of hydrocarbons recovered from the soil by GC-MS decreased in the order fish biodiesel>diesel>Syntroleum. During initial weeks, biodegradation was higher for microbial inocula adapted to a specific fuel type, whereby the main effect of the inoculum was to shorten the lag phase duration; however, the inoculum's importance diminished after daily respiration peaked. In conclusion, addition of an inoculum to increase biodegradation rates was not necessary.

Comparative performance of free surface and sub-surface flow systems in the phytoremediation of hydrocarbons using Scirpus grossus

Two types of flow system, free surface flow (FSF) and sub-surface flow (SSF), were examined to select a better way to remove total petroleum hydrocarbons (TPH) using diesel as a hydrocarbon model in a phytotoxicity test to Scirpus grossus. The removal efficiencies of TPH for the two flow systems were compared. Several wastewater parameters, including temperature (T, °C), dissolved oxygen (DO, mgL(-1)), oxidation-reduction potential (ORP, mV), and pH were recorded during the experimental runs. In addition, overall plant lengths, wet weights, and dry weights were also monitored. The phytotoxicity test using the bulrush plant S. grossus was run for 72 days with different diesel concentrations (1%, 2%, and 3%) (Vdiesel/Vwater). A comparison between the two flow systems showed that the SSF system was more efficient than the FSF system in removing TPH from the synthetic wastewater, with average removal efficiencies of 91.5% and 80.2%, respectively. The SSF system was able to tolerate higher diesel concentrations than was the FSF system.

A phytotoxicity test of bulrush (Scirpus grossus) grown with diesel contamination in a free-flow reed bed system

In this study, bulrush (Scirpus grossus) was subjected to a 72 day phytotoxicity test to assess its ability to phytoremediate diesel contamination in simulated wastewater at different concentrations (0, 8700, 17,400 and 26,100mg/L). Diesel degradation by S. grossus was measured in terms of total petroleum hydrocarbon (TPH-D). The TPH-D concentration in the synthetic wastewater was determined with the liquid-liquid extraction method and gas chromatography. S. grossus was found to reduce TPH-D by 70.0 and 80.2% for concentrations of 8700 mg/L and 17,400mg/L, respectively. At a diesel concentration of 26,100mg/L, S. grossus died after 14 days. Additionally, the biomass of S. grossus plants was found to increase throughout the phytotoxicity test, confirming the ability of the plant to survive in water contaminated with diesel at rates of less than 17,400mg/L.

Plant-bacteria partnerships for the remediation of hydrocarbon contaminated soils

Plant-bacteria partnerships have been extensively studied and applied to improve crop yield. In addition to their application in agriculture, a promising field to exploit plant-bacteria partnerships is the remediation of soil and water polluted with hydrocarbons. Application of effective plant-bacteria partnerships for the remediation of hydrocarbons depend mainly on the presence and metabolic activities of plant associated rhizo- and endophytic bacteria possessing specific genes required for the degradation of hydrocarbon pollutants. Plants and their associated bacteria interact with each other whereby plant supplies the bacteria with a special carbon source that stimulates the bacteria to degrade organic contaminants in the soil. In return, plant associated-bacteria can support their host plant to overcome contaminated-induced stress responses, and improve plant growth and development. In addition, plants further get benefits from their associated-bacteria possessing hydrocarbon-degradation potential, leading to enhanced hydrocarbon mineralization and lowering of both phytotoxicity and evapotranspiration of volatile hydrocarbons. A better understanding of plant-bacteria partnerships could be exploited to enhance the remediation of hydrocarbon contaminated soils in conjunction with sustainable production of non-food crops for biomass and biofuel production.