Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives

Diesel removal of contaminated soil by washing/flushing was enhanced with micro-bubbles and selected surfactants based on their solubilization properties and decontamination capacities. The influencing factors were studied to aim for increasing washing/flushing efficacy. The mixture solution of saponin and cyclodextrin increased the removal efficiency significantly compared to the single-agent solution flushing with an increasing range of 20%-31%. Meanwhile, micro-bubble enhancement increased over 20% of the diesel removal for the sandy soil flushing. As the flushing process may cause soil eroded, the TDS and soil solute in flushing solution were measured to evaluate the circulation time. The 90 min flushing time ensured the cleaning goal and reserved the soil solute by circulation flushing. The soil solute, especially the electron acceptor (NO₃^-) , was remained in the soil, which was highly demanded for residual diesel biodegradation of loam soil. It is concluded that mixed agents, circulation of flushing solution, and micro-bubbles increased the diesel removal, and the circulation flushing could be very promising in practical applications.

Metagenomics analysis identifies nitrogen metabolic pathway in bioremediation of diesel contaminated soil

Nitrogen amendment is known to effectively enhance the bioremediation of hydrocarbon-contaminated soil, but the nitrogen metabolism in this process is not well understood. To unravel the nitrogen metabolic pathway(s) of diesel contaminated soil, six types of nitrogen sources were added to the diesel contaminated soil. Changes in microbial community and soil enzyme genes were investigated by metagenomics analysis and chemical analysis through a 30-day incubation study. The results showed that ammonium based nitrogen sources significantly accelerated the degradation of total petroleum hydrocarbon (TPH) (79-81%) compared to the control treatment (38%) and other non-ammonium based nitrogen amendments (43-57%). Different types of nitrogen sources could dramatically change the microbial community structure and soil enzyme gene abundance. Proteobacteria and Actinobacteria were identified as the two dominant phyla in the remediation of diesel contaminated soil. Metagenomics analysis revealed that the preferred metabolic pathway of nitrogen was from ammonium to glutamate via glutamine, and the enzymes governing this transformation were glutamine synthetase and glutamate synthetase; while in nitrate based amendment, the conversion from nitrite to ammonium was restrained by the low abundance of nitrite reductase enzyme and therefore retarded the TPH degradation rate. It is concluded that during the process of nitrogen enhanced bioremediation, the most efficient nitrogen cycling direction was from ammonium to glutamine, then to glutamate, and finally joined with carbon metabolism after transforming to 2-oxoglutarate.

Bioremediation of diesel and gasoline-contaminated soil by co-vermicomposting amended with activated sludge: Diesel and gasoline degradation and kinetics

Present study aims to examine the efficiency of co-vermicomposting amended with activated sludge and E. fetida earthworm for bioremediation of diesel and gasoline from contaminated soil. The diesel and gasoline removal efficiency and degradation rates coefficients were estimated with gas chromatography (GC) analysis and first-order kinetics. The removal of gasoline and diesel in different co-vermicomposting processes with and without E. fetida ranged between 65-100% and 24.94-63.93%, respectively within 90- day experiment. Removal of gasoline and diesel increased in soil with addition of earthworm (E. fetida); higher degradation rate coefficients (k) were observed for co-vermicomposting with earthworm compared with co-vermicomposting processes. The highest k (0.014) for diesel degradation was estimated for microcosm reactor 4 (R4), where high numbers of E. fetida accelerate the less biodegradable organic contaminant from the soil matrices. The reasonable survival rates of earthworms in exposure to high concentration of petroleum-derivatives contaminated soils indicated increased activity of ligninolytic diesel-degrading earthworms and microorganisms. Therefore, co-vermicomposting amended with activated sludge is suggested as feasible and promising technologies for bioremediation of high content of organic contaminants from the soil matrices.

Enhancement of auxiliary agent for washing efficiency of diesel contaminated soil with surfactants

We used five types of surfactants assisted with sodium salts, including sodium tartrate (ST), sodium chloride (SC), and humic acid sodium (HAS) as auxiliary agents for soil washing to remove diesel from contaminated soil. Decontamination enhancement of diesel polluted soil washing with biosurfactant and H₂O₂ was examined, which showed higher effectiveness for newly contaminated soil. An increase in temperature and sodium salt addition exhibited a profound enhancement in diesel removal from aged contaminated soils. Compared to ST and SC, HAS exhibited a higher removal efficiency with saponin washing for aged diesel contaminated soil by lowering surface tension, shifting zeta potential, and increasing the number of micelles. Phytotoxicity experiments showed no significant inhibition of germination of lettuce, arugula, and cucumber with 0.2 g L^-1 saponin incubation. Conversely, there was a promotion on the root extension of lettuce and cucumber except for arugula. Similarly, the addition of 2% HAS (wight of saponin) improved on root growth of lettuce, arugula, and cucumber, increasing by 25%, 5%, and 22% at the period of 14 d, respectively. Because of excellent removal efficiency and non-toxicity, enhanced wash with saponin and HAS might be considered in the future design of full-scale remediation processes of diesel contaminated soil.

Optimization of aeration enhanced surfactant soil washing for remediation of diesel-contaminated soils using response surface methodology

Surfactant-enhanced soil washing has been used for remediation of organic pollutants for an extended period, but its effectiveness and wide application was limited by the high concentration of surfactants utilized. In this work, the efficiency of conventional soil washing performance was enhanced by 12-25% through the incorporation of air bubbles into the low concentration surfactant soil washing system. Surfactant selection pre-experiment using aerated and conventional soil washing reveals Brij 35 > TX100 > Tween 80 > Saponin in diesel oil removal. Optimization of the effect of time, surfactant concentration, pH, agitation speed, and airflow rate in five levels were undertaken using Response Surface Methodology and Central composite design. The optimum degree of variables achieved was 90 min of washing time, 370 mg/l of concentration, washing pH of 10,535 rpm of agitation speed and 7.2 l/min of airflow rate with 79.5% diesel removal. The high predicted R 2 value of 0.9517 showed that the model could efficiently be used to predict diesel removal efficiency. The variation in efficiency of aeration assisted and conventional soil washing was variable depending on the type of surfactant, organic matter content of the soil, particle size distribution and level of pollutant weathering. The difference in removal efficiency of the two methods increases when the level of organic matter increases and when the particle size and age of contamination decreases.