Assisted bioremediation tests on three natural soils contaminated with benzene

Abstract

Bioremediation is an attractive and useful method of remediation of soils contaminated with petroleum hydrocarbons because it is simple to maintain, applicable in large areas, is economic and enables an effective destruction of the contaminant. Usually, the autochthone microorganisms have no ability to degrade these compounds, and otherwise, the contaminated sites have inappropriate environmental conditions for microorganism's development. These problems can be overcome by assisted bioremediation (bioaugmentation and/or biostimulation). In this study the assisted bioremediation capacity on the rehabilitation of three natural sub-soils (granite, limestone and schist) contaminated with benzene was evaluated. Two different types of assisted bioremediation were used: without and with ventilation (bioventing). The bioaugmentation was held by inoculating the soil with a consortium of microorganisms collected from the protection area of crude oil storage tanks in a refinery. In unventilated trials, biostimulation was accomplished by the addition of a nutrient mineral media, while in bioventing oxygen was also added. The tests were carried out at controlled temperature of 25 ºC in stainless steel columns where the moist soil contaminated with benzene (200 mg per kg of soil) occupied about 40% of the column's volume. The processes were daily monitored in discontinued mode. Benzene concentration in the gas phase was quantified by gas chromatography (GC-FID), oxygen and carbon dioxide concentrations were monitored by respirometry. The results revealed that the three contaminated soils were remediated using both technologies, nevertheless, the bioventing showed faster rates. With this work it was proved that respirometric analysis is an appropriate instrument for monitoring the biological activity.

Importance of soil physical characteristics for petroleum hydrocarbons phytoremediation: A review

“…In an experiment Carvalho et al (2015) reported higher (≥99.3%) remediation rates in bioventing technique (comparing to no ventilation -bioventing), confirming the importance role of oxygen on remediation. This effect was more pronounced for granite (comparing to limestone and schist) with biggest difference in remediation time, when compared to techniques of no ventilation (Carvalho et al, 2015). Furthermore, anaerobic bioremediation can be used for deep soil layers since the process does not require oxygen.…”

“…In another study, limestone and granite with specific clay minerals showed higher duration for achieving the target remediation efficiency but schist with the highest fine fraction and no clay minerals, resulted in the lowest time necessary for remediation (Carvalho et al, 2015). Yanai et al (2006) showed that along with coarser textural particles, low pH (between 5 and 6) and high concentrations, resulted in more Cd uptake by Thalaspi caerulescens plant.…”

“…They also reported that, sandy soils are more effective for surfactant remediation than clay soils because the clay surface adsorption reduce surfactant effectiveness. Not only the diversity and abundance of the clay, minerals is an important factor in the remediation processes, but sometimes the fractions of fine particles in one specific texture control the procedure (Carvalho et al, 2015). Falciglia et al (2011) investigated soil textural behavior (coarse, medium, fine sand, silt and clay size aggregate fractions) involved with artificially polluted diesel fuel, and thermally treated at different temperatures.…”

“…Many of the plant-bacteria interaction are dependent upon soil aeration porosity (Tang et al, 2010a). In Soil contaminant bioavailability, the composition of root exudates, and nutrient levels are all directly depend on aeration porosity (Carvalho et al, 2015). These processes would be inversely affected by entering and presenting hydrocarbons into soil, but not in all soils and situations.…”

The Effects of Enrichment Nutrients on the Growth of Indigenous Bacteria Species in Spent Lubricating Oil Contaminated Water

“…The percentages obtained were relatively low. This could be attributed to the prolonged disposal of the hydrocarbons on the surrounding soils, which have compacted the soil and affected the soil texture and by extension the oxygen and water holding capacity of the soil [28].…”