Studies On Remediation Of Nitrobenzene-aniline Contaminated Groundwater By Chemistry-biology Combinational Reaction Zone

With the progress of technology and agriculture, the social economy has been rapidly developing. However, lots of negative impacts emerge at the same time. The human activities lead to the serious pollution of soil and water. For example, the application of large amount of pesticide, the random deposit of waste without proper landfill, the accidental release of organic pollutants and the leak caused by oil extraction or irregular maintenance of transportation facilities.Nitrobenzene and aniline are important chemical materials, which are widely used in medicine, pesticide industry, printing, plastics and national defense construction. Nitrobenzene in the environment mainly comes from the effluent of chemical and dye works, especially the high content of nitrobenzene in the aniline dye effluent. The persistent organics threat the air, groundwater and soil environment which are inseparable for human. Especially, the serious pollution of nitrobenzene and aniline in the groundwater has caused grave damage to water resources. Therefore, how to control the nitrobenzene and aniline pollution has been an urgent problem all over the world.In the international field of groundwater purification, there have been lots of technologies for different types of pollutants. Among them, permeable reactive barrier (PRB), is a typical and widely used groundwater remediation technology. PRB shows excellent disposal effectiveness and can sustain a long time in-situ application. However, due to the limitation of hydro geologic condition, PRB is mostly applied in the shallow groundwater remediation. For deep aquifers, it would be quite difficult to construct, especially in the cities with serried underground pipes. Meanwhile, there are still problems aggravate the hardship of design and use for PRB, such as the suction of soil particles, the precipitation of chemical composition in groundwater and the accumulation of bioactive substances. These will cause blockage in walls and make it difficult to renew the medium. It increases the challenge of PRB in the application of in-situ remediation of groundwater.This research takes nitrobenzene-aniline combined contaminated groundwater as the research object, improves current PRB remediation technology, and proposes the chemistry-biology combinational reaction zone, which is more easily constructed, more widely applied, more flexibly installed and more easy to renew the reaction medium. The design concept of the technology is incarnated in two aspects. On the one hand, carbon-iron micro-electrolysis deoxidizes nitrobenzene to aniline in battery of wells to increase biodegradability; On the other hand, nitrobenzene and aniline are biodegraded in the bioreactor. The groundwater is purified ultimately.This technology can enrich the technology and index system of in-situ remediation of polluted groundwater. It has great social and environmental significance in improving quality of groundwater and ensuring safety of urban and rural residents'drinking water.This paper confirmed the reducing medium and the best processing condition of nitrobenzene. The nitrobenzene and aniline Psychrotrophs were cultivated, identified and immobilized. The chemistry-biology combinational reaction zone was built up and the efficiency was analyzed in the actual site. The conclusions are as follows:(1)Zero-valence iron is flexible and shows preferable degradation effects for persistent nitrobenzene. When it is in acidic condition, the temperature is about 100°C, the diameter of scrap iron is about 0.9~3mm, the proportion of iron and coconut shell charcoal is 1:1, the convert ratio of nitrobenzene can reach 87.2% at 90min and 96.8% at 120min.(2) Two efficient nitrobenzene and aniline Psychrotrophs named NB and AN were separated, which are both gram negative. Appraised by physiology and biochemistry and 16SrDNA complete sequence determination, NB is preliminarily identified as Pseudomonas sp, AN is Delftia sp. Degradation dynamics tests of nitrobenzene and aniline in individual and mixed bacterium indicates that in the low concentration (1.2mg/L of aniline, 0.7mg/L of nitrobenzene), the degradation speed is correspondingly low (aniline is 0.38mg/d , nitrobenzene is 0.2mg/d). While in the high concentration (60mg/L of aniline, 46mg/L of nitrobenzene), the degradation speed both exceed 15mg/d. When the concentration of aniline is 130mg/L, the degradation speed is 32.5mg/d. Meanwhile, the degradation rate of nitrobenzene by individual bacterium can reach above 90% in both high and low concentration. It illustrates that the two kinds of individual bacterium both have preferable adaptability to oligotrophic conditions and toleration to toxicity of nitrobenzene and aniline. Immobilization indicates that the immersion method for nitrobenzene and aniline is viable. The steady symbiont of NB and AN can degrade nitrobenzene and aniline effectively in groundwater environment. The most befitting condition is PH at 6, 4-day-long immobilization time, immobilization temperature at 10℃,revolving speed at 95rpm.(3)The simulation of chemistry-biology combinational reaction zone using seepage slot indicates that, at first, the concentration of nitrobenzene decreases obviously by the adsorption of activated carbon and the reduction of iron. As the reaction goes on, the saturation of activated carbon adsorption and the decreasing activity of iron bring down the degradation rate. The concentration of nitrobenzene and aniline in water both approach zero after disposed in the bioreaction wells. According to the variation trend of nitrobenzene and aniline in the effluent from chemistry-biology reaction zone, the efficiency and replaceablility are considered. The replacement cycle of biofilm module in the biological wells is 30 days, and it is 90 days for the reaction medium in the chemical wells(4)According to the experiment of raw water in the actual sites, chemical reaction zone can convert nitrobenzene to aniline rapidly and largely. The concentration of aniline in raw water increases from 66.75mg/L to 106.74mg/L within 20 days. Replacing biofilm module at 30 days during remediation process can maintain the optimum efficiency of chemistry-biology reaction zone. The result of 70 days continuous treatment indicates that the concentration of aniline in the final effluent approaches zero and the concentration of residual falls to about 0.2mg/L.