Investigating the Concomitant Removal of Hydrocarbons and Heavy Metals by highly adapted Bacillus and Pseudomonas strains

This study investigates the concomitant removal of hydrocarbons and heavy metals by highly adapted Bacillus and Pseudomonas strains. In regions characterized by harsh conditions such as Qatar, the weathering processes would affect the content, status, and distribution of these contaminants. It was shown in the weathered soil from Dukhan oil wastes dumpsite that 14 heavy metals exceeded the EPA limits. Moreover, it was demonstrated that soil organics did not affect the distribution of the metals in the soil. However, most of the heavy metals were strongly bonded to the residual and the iron-manganese oxide fractions. Eighteen bacterial strains isolated from highly weathered oily soils were able to grow with heavy metal concentrations up to 3 mM and above for some. Seven selected strains (4 Bacillus and 3 Pseudomonas) showed the ability to remove almost 60 to 70% of most of the heavy metals when used at 1 mM. Moreover, they removed up to 75% of the diesel range organics. These results are of interest for selecting bacterial strains, which can overcome the toxicity of hydrocarbons and heavy metals and remove them concomitantly.

Effects of Ramp Rate and Starting Temperature on Gas Chromatography-Mass Spectrometric Analyses of Petroleum Hydrocarbons

The quest for better GC-MS/FID starting temperature and ramping conditions for the quantification of hydrocarbons in our environment necessitated this study. A surrogate n-alkane standard was screened using nine GC-MS conditions involving the alteration of ramp rates and/or initial temperatures. There was observed increase in the TIC chromatogram or ionic mass unit as the ramp rate or initial temperatures were increased. The peak areas of the analytes were significantly affected. The R2 and response factor values of the eight standard calibration curves (each for a modified method) varied from 0.9224 – 0.9971 and 0.0034 – 0.0045 respectively. Consequently, the quantification of the diesel concentration in diesel spiked water and soil by using the eight methods was different from each other and from the standard method. Average differences of 11.5 and 15 % from the theoretical values were observed for the water and soil analyses respectively. Increasing ramp rates or initial temperatures led to shorter throughput but less data accuracy. The use of 60 oC as starting temperature and ramp at 5 oC/minute was better for quantification of the diesel range organics.

Can the sensitivity of soil-dwelling organisms to landfarmed soils contribute to asess the sustainablity of landfarming of oil refinery waste?

Beneficial soil organisms inhabiting healthy soils participate in providing soil ecosystem sevices. Oil refineries generate large quantities of solid waste containing several classes of hydrocarbons as well as metals, which are ploughed into the soil during landfarming to utilise the biodegradation capabilities of the ecosystem of the soil. The contaminants may be toxic to these organisms. For the sustainable use of the services of the ecosystem of the soil, it is crucial to know whether remediation had been sufficient for the intended land use. Indicators are needed to assess the degree of recovery. This study aimed to analyse landfarmed soil at an oil refinery chemically and to assess the toxicity and recovery by using a variety of standardised bioassays with the vermicomposting species Eisenia andrei (Oligochaeta) and the springtail Folsomia candida (Collembola). The results showed that soil from the landfarming site, despite remediation, still contained several hazardous chemicals such as diesel range organics, but that the soil mixture was not acutely toxic to the exposed test organisms. It did cause a loss in earthworm (E. andrei) biomass, inhibited cocoon production and also decreased juvenile production of the springtail F. candida. The results suggested the site still needs remediation before landfarming should continue. Bioassays provide a more ecologically relevant assessment of the remediation status of the soil and its toxicity than chemical analysis alone. This finding supports the use of bioassays as an ecotoxicological tool for assessment of landfarmed soils.