Development And Application Of Evaluation Model For In-situ Bioremediation Techniques Of Petroleum Hydrocarbon Contaminated Sites

Currently,petroleum hydrocarbon pollution has become a global environmental problem,not only destroying the ecological balance,but also causing great harm to human health.In situ bioremediation has become a hotspot technology for the remediation of oil contaminated sites due to its ecological,environmental,and cost-effective characteristics.However,the complexity of underground media causes great uncertainty in remediation technology.Modeling in situ bioremediation can help assess the transportation and degradation of petroleum hydrocarbons,design cleanup operations and the duration of remediation techniques.This article systematically reviews the concepts,simulation mechanisms,and practical applications of relevant model studies.It is found that traditional bioremediation technology evaluation models have shortcomings such as unclear soil media characteristics,overly simplified adsorption,and simplified space.In this study,an in-situ remediation technology evaluation model for petroleum hydrocarbon contaminated soil was developed to address the above issues,and the visualization,parameter source acquisition and senario simulation of the model were completed through experiments and simulations.The main research conclusions are as follows:(1)The chemical extraction of petroleum hydrocarbon contaminated soil aged for 0,30,and 90 days was carried out by mixing hydroxypropyl beta-cyclodextrin(HPCD)with different concentrations of surfactants and low molecular organic acids.The correlation between the extraction results and the total petroleum hydrocarbons(TPH)bioaccumulation of earthworms was analyzed for total fractions and fractions with different carbon chain ranges.The analysis results showed that 0.5 mmol/L rhamnolipid and 50 mmol/L HPCD could effectively extract the bioavailability concentration of petroleum hydrocarbon contaminated soil.The slope of correlation between chemical extraction methods and biomass was 1.1797,and R~2was 0.9792.(2)A 90 day closed static incubation experiment and isothermal remediation experiments with two treatment methods,including natural attenuation and biological enhanced remediation,were conducted.The experimental results show that bioremediation can promote the desorption of weak adsorption phase into the dissolved phase,and the soil water partition coefficients for natural attenuation and bioremediation are 0.153 L/g and 0.092L/g,respectively.Static incubation experimental data and isothermal adsorption experimental data were processed using sensitivity analysis,parametric scanning and Bayesian inversion methods to obtain the conversion rates of dissolved phases and adsorbed phases under natural attenuation and bioaugmentation.According to the experimental results and parameter fitting results,it is proved that bioenhanced remediation can promote biodegradation,as well as the formation of strong adsorption phase and non extractable phase.(3)A 120 day indoor sand tank validation experiment was conducted,and the experiment was divided into two repair groups including natural attenuation and biological enhanced remediation.The experimental results show that temperature and oxygen concentration can inhibit the degradation of petroleum hydrocarbons in soil,the same layer of the sand tank has the same level of degradation,and the lower the degradation ability of the sand tank from top to bottom.The bioremediation technology evaluation model was also used to numerically simulate the sand tank scale,and the simulation results were well correlated with experimental data.The linear slopes of natural attenuation and bioenhanced remediation are between 0.9718-1.0317 and 0.9954-1.0271,respectively,and the corresponding R~2is between 0.8994-0.9915 and 0.7181-0.9605,respectively.The developed assessment model for in-situ remediation of petroleum hydrocarbons in soil has considerable simulation results.(4)The simulation of a polluted site in Gongshu District,Hangzhou City was conducted at a demonstration site scale for a period of 3 years.The simulation scenarios were natural attenuation remediation and bioaugmentation remediation,taking into account changes in environmental factors such as soil temperature,soil humidity,and oxygen concentration.The simulation results show that after the restoration reaches a stable period,the naturally attenuated residual TPH concentration is around 1000 to 3700 mg/kg,and the concentration of residual TPH in bioremediation is around 880-1700 mg/kg.Relying solely on indigenous microbial degradation in contaminated sites,it is difficult to achieve remediation goals without adding exogenous irritants and microorganisms.At the same time,further auxiliary remediation measures,such as secondary bacterial agent addition or soil oxygenation,are recommended for bioenhanced remediation.Auxiliary remediation measures are recommended before the formation of anaerobic zones to maintain the remediation function of the site and inhibit the generation of adsorbed phases.