Effect Of Iron Minerals On Microbial Degradation Of Naphthalene

With the development of society and the progress of industry and agriculture,groundwater pollution is becoming more and more serious.Naphthalene,as a typical polycyclic aromatic hydrocarbon pollutant,has relatively high water solubility.Naphthalene has been detected in wastewater from petroleum,chemical and coal processing industries.Naphthalene pollution has attracted worldwide attention.Iron minerals exist widely in the nature with special pore distribution and surface charge characteristics,has a strong adsorption capacity of pollutants.Iron,as an important electron acceptor in microbial degradation of organic matter and a necessary nutrient for microbial survival,has an impact on the main reduction process in microbial degradation.However,there are relatively few studies on the adsorption and degradation of naphthalene in groundwater environment containing high iron minerals and high iron ions.Therefore,it is of great significance to study the degradation of naphthalene in shallow groundwater under the combined action of Iron minerals and microorganisms to reveal the degradation mechanism of naphthalene in groundwater.Based on the National Natural Fund's"Petroleum Hydrocarbon Biodegradation Environment in Shallow Porous Groundwater?41402207?",combined with site physical geography and hydrogeological conditions,the hydrochemical characteristics of groundwater were comprehensively analyzed;and through laboratory experiments,the effects of different Iron minerals on the microbial degradation of naphthalene were studied,so as to explore the microbial degradation mechanism of naphthalene in natural groundwater environment,and provide basis for preventing groundwater pollution and protecting water environment.In this paper,siderite and magnetite are selected as typical Iron minerals and quartz sand as blank samples.The effect of Iron minerals on the degradation of naphthalene is described by static adsorption batch experiments.The surface characteristics of minerals are analyzed by means of SEM and XRF,and the contents of iron ions and naphthalene in samples are tested.The purpose is to explore the interaction mechanism between Iron minerals and microbial degradation of naphthalene.The experimental results show that:?1?Both siderite and magnetite can adsorb naphthalene.The adsorption kinetics fits the quasi-second-order kinetics model.R² is between 0.9924 and 0.9967.Moreover,the adsorption of naphthalene by siderite and magnetite is non-linear,and the isothermal adsorption conforms to Langmuir adsorption model,R² is 0.9426 and 0.949,respectively.From the physical meaning of Langmuir isothermal adsorption,it can be judged that the adsorption of naphthalene by Iron minerals is attached to the monolayer adsorption,and the lower adsorption capacity is related to the weak interaction between naphthalene and minerals.?2?In the anaerobic environment of low temperature,the bacteria,the sterile group found that microorganisms can promote the occurrence of siderite mineral dissolution,resulting in the increase of Fe²⁺concentration,accompanied by decreased HCO₃^-content and pH value of solution.The increase of Fe²⁺concentration provided nutrients for microbial degradation and accelerated the reaction to sulfate reduction,promoted the microbial degradation of naphthalene,and sulfate reduction occurred in siderite bacteria group in 70 days.Magnetite is reduced by Fe?III?under the guidance of microorganisms,resulting in secondary minerals,which are wrapped on the surface of minerals,thus blocking the direct contact between microorganisms and naphthalene and magnetite,reducing adsorption and stopping microbial reduction.?3?The results of SEM and XRF showed that the microbial-chemical interaction occurred between Iron minerals and microorganisms.The iron ions in the solution are adsorbed,precipitated and dissolved,which promotes the formation of secondary minerals.The study of microbial-chemical interaction between Iron minerals and microorganisms plays an important role in the geochemical cycle of Iron minerals in groundwater.