Evaluating the Effects of Co-using Phytoremediation and Bioremediation in a Crude Oil Contaminated Soil

Crude oil is one of the most important sources of energy and its large scale production, transmission, consumption and disposal, making it one of the most important and common types of environmental pollution worldwide. Oil extraction and various oil products have led to spread of pollution in the soils around oil extraction and refining sites. During the production and transportation of crude oil, unsuitable operation and leakage may result in contamination of soil with petroleum hydrocarbons. Great concern in this case is the environmental risks of these pollutants. During the past decades, bioremediation of petroleum contaminated soil has been a hot issue in environmental research, and many bioremediation strategies have been developed and improved to clean up petroleum polluted soil. The aim of this study was to compare the effects of co-using of different bioremediation strategies on remediation of crude oil contaminated soil.

In order to investigate the effects of co-using phytoremediation and bioremediation in a crude oil contaminated soil, a factorial experiment in completely randomized design with three replications was conducted. The factors were three levels of crude oil contamination (0 wt% (C0), 2 wt% (C1) and 4 wt% (C2() and four treatments of remediation (Grass (B1), Alfalfa (B2), Grass + Pseudomonas Putida+ Phanerochaete Chrysosporium (B3), Alfalfa + Pseudomonas Putida+ Phanerochaete Chrysosporium (B4), control (B0)). For amendment of contaminated soil, soil samples were artificially contaminated with crude oil (from Tabriz Oil Refinery) and blended to soil (10% total quantity of soil spiked) then spiked soils were progressively mixed with unpolluted soil and homogenized. After preparation of the crude oil-spiked soil microbial inoculation were done and then the samples were packed into soil columns and then plants cultivation was done in soil columns (P.V.C pipes). At the end of growth period, some parameters were measured including residual Total Petroleum Hydrocarbons (TPHs) concentration, microbial basal respiration and dry weight of root and shoot. 

The results showed that TPHs concentration in C1 crude oil level by B3 and B4 remediation treatments decreased by 59% and 57%, respectively, and in C2 level B3 and B4 remediation treatments decreased TPHs content by 41% and 39%, respectively. B3 remediation treatment had the highest shoot and root dry weight and the lowest root and shoot dry weight observed from B2 remediation treatment. Shoot and root dry weight decreased with increasing crude oil contamination levels. The highest basal respiration rate was observed in B3 and B4 remediation treatments. In all of crude oil levels, there was not significant difference between B1 and B2 remediation treatments and control (B0) in basal respiration rate. In the highest crude oil contamination level (C2) the amount of carbon produced as CO2 increased because this level has higher concentration of oil pollutants and therefore has more required substrate for the activity of microorganisms, and consequently more microbial activities increased CO2 production. Compared to the control, the levels of crude oil contamination (C1 and C2) decreased dry weight of root by 46% and 61%, respectively and dry weight of shoot by 53% and 63%, respectively. Considering that the high concentrations of oil contaminants in the soil can lead to toxicity for plants and microorganisms and also hydrophilic properties of these compounds can decrease the availability of moisture and nutrients for plants root, therefore the growth of root decreased in oil contaminated soil. In lower level of crude contamination (C1), remediation treatments have more effective role in refining crude oil. This results from more plant growth and then more plant roots which increase the bioavailability of hydrocarbons by reducing the volume of soil micro pores. Also plants root release organic compounds which would increase the population and activity of soil microbes and these cause to increase of oil compounds degradation and elimination.

Experimental results showed that remediation treatments which contained bacteria and fungi with plants caused to more oil compounds elimination, microbial basal respiration and dry weight of root and shoot. Therefore, it can be found the importance of the presence of microorganisms and the microbial activity with plants in order to degrade and remove the soil oil compounds.
Keywords: Bioremediation, Oil pollution, Residual oil compounds, Microbial basal respiration