Petroleum Hydrocarbon Contaminated Soil Bioremediation Research

There are high biological toxity and residue characteristics for oil pollutions. The oil pollution has therefore become a serious soil issue, which has attracted considerable public attentions. For the restoration of oil-contaminated soil, the bioremediation has low cost, high efficiency, no secondary pollution, more nature and other characteristics, and thus is one of the most promising soil remediation technologies. An exogenous microbe, Phanerochaete chrysosporium, was employed for bioremediation of oil-contaminated soil under laboratory conditions. This work has two objectives. The first one is to discuss how to make the pollutants and environmental conditions suitable for strain degradation, and the impact of affecting factors systematically. The second one is to preliminarily explore microbial-phytoremediation technique based on indigenous plants. To this end, the study was carried out as follows. Firstly, we investigate six factors affecting the degradation rate of oil, i.e. concentration, soil sample treatment, bacteria quantity, humidity, temperature and nutrient ratio. Secondly, the significant level and correlate relationship about influence factors were studied. Thirdly, according to multi-factors correlation analysis and orthogonal experiment, the optimal orthogonal test conditions were obtained. At last, we chose some indigenous plants and studied the degradation based on the microbial-phytoremediation. The main results of this thesis are as follows.(1) After 60d of treatment, the degradation rate of three concentration levels, i.e.low, medium and high concentrations (500mg/kg, 5000mg/kg, 10000mg/kg), were 58%, 70% and 72% respectively. The data above illustrate that in degradation bacterium tolerance range, the degradation increases with the concentration of oil pollution increasing. And the higher the concentration, the better the degradation is. The ploughing experimental results shown that when ploughing the oil-contaminated soil, the degradation rate of experimental group (5000mg/kg) and reference groups (500mg/kg, 10000mg/kg) were 18%, 14% and 30% respectively higher than non-ploughing groups. The consequence above illustrates that the ploughing strengthens the ventilated function which results in stronger microbe respiration, and thus improving the degradation rate. This effect is suitable for various concentrations. It is shown that the higher the concentration, the better the effect is. Adding exogenous microbe into contaminated soil, 8-28% higher than blank groups, has the significant promotion effect to remove TPHs. And the degradation rate of the amount of microbe, 0, 5, 10, 15, 20, 25 and 30mL, were 22, 46, 54, 60, 64, 74 and 70% respectively, illustrating that dosing and the degradation rate are not a simple direct proportion relationship, so it is important to determine the optimal dosing in the actual work which can improve degradation rate and save biological bacteria; The degradation rate of humidity, 5, 10, 15, 20 and 25%, were 12, 30, 48, 66 and 64% respectively, illustrating that the degradation rate increases with soil moisture content increasing in a certain range; The degradation rate of four groups, C: N: P=100:10:1, 120:10:1, 100:15:1, 50:2:1, were 64%, 44%, 60%, 52% respectively. The data analysis above from C/ N ratio perspective conclude that the degradation rate of groups (C: N≤10) are higher than groups(C: N>10), and exogenous microbe can keep high degradation activity in the conditions of C: N≤10; According to the annual average temperature in 18℃and summer temperature higher (special exception) in Chongqing area, design two kinds of temperatures tests (20℃and 35℃), and the degradation rate of two groups were 66% and 70% respectively, which illustrate that in certain temperature range, the higher temperature, the higher biological activity, and the final degradation rate is higher.(2) the texts of significance show that time, humidity, bacteria quantity and nutrient ratio have significant effects on degradation, and the orthogonal experiment L₉ (3⁴) based on multi-factors correlation analysis show that under the conditions of the temperature 35℃and ploughing, the best degradation combination were concentration 10000mg/kg, humidity 20%, the amount of microbe 20mL and nutrient ratio 100:10:1.(3) the single phytoremediation experiments show that Bracket-plant and Pink Reineckia both have effect on degradation of petroleum hydrocarbon, but Bracket-plant have high degradation effects, of which the degradation rate at different concentration levels were 29%, 35% and 33% respectively; The microbial-phytoremediation texts show that the degradation ability of the combination of Bracket-plant +microbe is the greatest and the degradation rate is the highest.This study has revealed the influence of different factors and environmental conditions on the microbial degradation, and proven preliminarily the potential advantages of two native Chongqing plants for microbe restoration. The results pave the way towards the on-site application of the restoration for oil contaminated soil.