Experimental Research On Biodegradation Of Nitrobenzene In Groundwater And Soil

The accident at Jilin Petrochemical's nitrobenzene plant in November 13, 2005 caused a release of more than 100 tons of nitrobenzene into the Songhua River, resulted in a large extent of organic contamination of the watershed. In light of that where groundwater has close hydraulic relation with the surface water, nitrobenzene would readily seep into the adjacent aquifers, the relatively slow renewal rate of the groundwater and the long persistence of the organic pollutants, the potential harm of the recharge water from the contaminated rive to the subsurface environment cannot be neglected. To launch the research on the migration and transformation of nitrobenzene in groundwater and soil is of great importance to the water supply safety and the sustainable utilization of the groundwater resources in the areas along the Songhua River.As nitrobenzene cannot be hydrolyzed in general reaction conditions, the possibility of photolysis is low in subsurface environment and the volatilization can also be neglected when temperature lower than 20℃, biodegradation and adsorption make the main mechanisms of the migration and transformation of nitrobenzene in groundwater and soil. In this thesis, the biodegradation of low concentration nitrobenzene in groundwater and soil was studied by an experiment included a series of batch microcosms with uncontaminated groundwater, soils and aboriginal microbe as the main materials, and the culture condition set up according to the characteristics of the subsurface environment. The experiment can reflect the biodegradation processes in various groundwater and soils and the pollution trends, provide data for the prediction of numerical simulation and the security influence evaluation of nitrobenzene contamination. Furthermore, it also serves as a helpful experience for related researches on other organic pollutants.Based on the analyses and contrast of the experiment results, the following conclusions were obtained: (1) The aboriginal microbe in the subsurface environment could adapt themselves to the groundwater polluted by nitrobenzene and biodegrade nitrobenzene effectively in the temperature range of 8～10℃. In the aqueous systems, the degradation periods lasted about 4d, 5d and 6d when the initial concentration of nitrobenzene were 0.112mg/L, 0.504mg/L and 2.191mg/L, the degradabilities were 50.9%, 67.6% and 80.1% respectively within 4 days, the degradability reached 89.2% within 5d when the initial concentration of nitrobenzene was 2.191mg/L; In the biphasic systems of fine gravel, coarse sand, medium sand and groundwater, the degradation removal ratios were 93.7%, 100% and 100% within 8 days respectively when the initial concentration of nitrobenzene was 0.504mg/L, in the biphasic systems of silt and groundwater, the degradation removal ratio reached 98.81% within 4days. (2) At low concentration, the increase of substrate concentration could accelerate the degradation, resulting in a faster degradation rate without apparent inhibition; It also resulted in a higher kinetic threshold concentration, indicating a higher remaining concentration of nitrobenzene. (3) The variation of the concentration of nitrobenzene could incorporate different types of efficient degrading bacteria strains into the degradation process; The succession of the microbial communities could affect the efficiency of degradation. (4) The aquifer medium played an important role in the degradation process, in the biphasic systems of fine gravel, coarse sand, medium sand, silt and groundwater, the first-order reaction rate constant were 0.209 d^-1, 0.238 d^-1, 0.281 d^-1and 0.696d^-1 respectively. A trend could be deduced from the experiment that the degradation of nitrobenzene became faster as the granule size of aquifer medium grew finer.