Tranport And Removal Of P-nitrophenol In Bioaugmented Soil Aquifer Treatment (STA)

P-nitrophenol is an organic contaminant in high toxicity with low concentration in environment. It has remaind and been accumulated in environment over time due to its stable chemical structure and recalcitrance. For these characteristics, p-nitrophenol has posed a threat to human health and environment security. P-nitrophenol is widely produced in the process of manufacture and application of the fine chemical products such as pharmaceutical, pesticides, leather, dyestuff and explosive. It can be discharged into environment and contaminate soil and groundwater. Therefore, the transport and removal performance of p-nitrophenol in vadose zone is always a research focus.Soil aquifer treatment(SAT) is a widely used wastewater-soil infiltration treatment system with better efficiency and low cost, which removes contamination and improves water quality by physical-chemical-biological reaction in vadose zone or other infiltration media. The research on the transport and removal of p-nitrophenol in SAT simulated by lab-1D soil columns was carried out in this paper. Furthermore, bioaugmentation method was applied into SAT to improve the removal efficiency of p-nitrophenol, and the effect of p-nitrophenol initial concentration, flow rate and soil moisture content on removal efficiency. This paper was supported by the Doctoral Scientific Fund Project of the Ministry of Education of China(20130061110066). The study could provide a new natural method for the removal p-nitrophenol and other similar contamination. What’s more, the study can not only lay the theoretical foundation of underground pollution remediation, but provide engineering design parameters of artificial groundwater recharge and water reclamation technology.Through laboratory experiments and data analysis, the following findings were obtained:1. Adsorption kinetics experiments show that, the sorption processes of p-nitrophenol on medium-fine sand followed Lagergren pseudo second order kenetics equation, and the adsorption capacity of media was 208.68 μg/g. Isothermal adsorption experements show that, the adsorption isotherms are well represented by Freundlich isotherm model.2. A strain of aerobic bacterium capable of degrading p-nitrophenol was isolated from long-term pesticides polluted soil. It can take p-nitrophenol as sole carbon, nitrogen, and energy source, which can be used as augmented-bacterium in bioaugmented-SAT column tests. Biodegradation experiments show that, p-nitrophenol was completely removed by the augmented-bacterium within 60 h if the initial p-nitrophenol concentration was under 200 mg/L. However, when the concentration of p-nitrophenol was over 250mg/L, no significant degradation was observed due to its high toxicity in high concentration. The temperature of 30°C was favourable for the growth of augmented-bacterium. Additional inorganic nitrogen source had no effect on biodegradation. The molar ratio of p-nitrophenol reduced and nitrite produced was 1:1, so it can be speculated that the process of biodegradation was accompanied with the release of nitro group, and the degradation pathway may be hydroquinone pathway.3. Breakthrough experiments of abiotic SAT column show that, the breakthrough time of p-nitrophenol wastewater of three different concentrations(1, 10, 200 mg/L) at constant flow rate was identical. When the flow rates in the abiotic columns were 219 and 438 mL/d respectively, the breakthrough time during which the concentrations of p-nitrophenol in effluent increased from 0 to initial concentrations were 9 d and 5 d respectively. Above results indicated that the obstruction effective of p-nitrophenol transport in medium-fine sand was smaller.4. Bio-SAT column experiments show that, p-nitrophenol removal efficiency in SAT got well improved by the addition of bioaugmentation. The time when augmented-bacterium began to grow lagged and the removal capacity of SAT weakened with the increase of influent p-nitrophenol concentration. The removal efficiency of Bio-SAT supplied with low and medium concentration wastewater both reached 100%, and the removal efficiency of Bio-SAT supplied with high concentration wastewater was nearly 98%.5. The wastewater passed through Bio-SAT columns at different flow rates experiments show that, before the steady-state of remaining concentration in column effluent, removal rate and quantity reduced with the increase of flow rate. After the steady-state of remaining concentration in effluent, removal rate and quantity increased with the increase of flow rate, which indicated that the change of flow rate had no effect on the removal efficiency of Bio-SAT.6. The wastewater passed through Bio-SAT columns of different soil moisture content experiments show that, the column of low moisture content removed p-nitrophenol faster because that there was more dissolved oxygen for the growth of aerobic augmented-bacterium.