Environmental Molecular Diagnosis Of The Ammonium Affecting Petroleum Contaminants Degradation Mechanisms

Ammonium is generally considered to be the optimal nitrogen source for petroleumdegrading microorganisms.However,our previous research and a few literatures found that the addition of ammonium as a nitrogen source under certain conditions may hinder the degradation of certain petroleum pollutants.For both ammonium and petroleum hydrocarbons are reducing substances,the question that whether the existence of ammonium has effects on the utilization of electron acceptors in the petroleum hydrocarbons degradation has no clear answer.The mechanism of ammonium affected petroleum substances degradation under different redox conditions is still unclear.Environmental Molecular Diagnostics(EMDSs)is an important means to understand the mechanism.To solve the problem,based on the principle of Natural Attenuation,a variety of EMDSs techniques such as isotope,microbial diversity sequencing,gene quantification,and metagenomic sequencing was used,micro-ecospace experiments with different redox conditions including aerobic condition,anaerobic condition,and aerobic-anaerobic sequential condition were carried out,a petroleum contaminanted aquifer was investigated.Then big data mathematical statistical analyses were put into use to recognize the mechanism of petroleum degradation affected by ammonium.Through the above research,the following understandings are obtained:The results show that ammonium has different effects on petroleum hydrocarbon degradation in different REDOX environments.In the laboratory microcosm scale: In the aerobic environment,generally,the ammonium shows the promotion effect to hydrocarbon degradation.Ammonium stimulates the growth of Alkanindiges and other ammonium-derived hydrocarbon-degrading microorganisms rapidly,following the oxidation of ammonium.After the nitrate was formed,there were nitrate dissimilatory reduction and denitrification,which may promote the degradation of hydrocarbons.Under the anaerobic environment and in the denitrification condition,there would be nitrification and anaerobic ammonium oxidation the presence of ammonium,which couldn't promote the petroleum biodegradation caused by denitrification,but might inhibite the denitrification by preliminary analysis.In the aerobicanaerobic sequential condition,ammonium can significantly promote aerobic hydrocarbondegrading microorganisms such as Cupriavidus and Acidovorax under the initial aerobic conditions.After the environment transited to anaerobic condition,ammonium inhibited the growth of denitrifying microorganisms such as Pseudomonas,thereby inhibiting the degradation of petroleum hydrocarbons.At the oil-contaminated aquifer scale: In the nitrate reduction and sulfate reduction dominated groundwater environment,ammonium may promote or inhibit the growth of a few microorganisms.However,these microorganisms are not the dominant population in the aquifer and cannot significantly affect the population structure.For the key genes of denitrification and sulfate reduction have no significant correlation with ammonium,as well as the genes of ammonium assimilation and ammonium oxidation have no significant correlation with denitrification and sulfate reduction genes,it is speculated that ammonium has no significant effect on the degradation of petroleum pollutants at the aquifer scale.In summary,under different redox conditions,ammonium has different effects on the degradation of petroleum hydrocarbon.Ammonium is not an optimal nitrogen source all the time when remediation the contaminated sites.It depends on the redox conditions.In aerobic environment,ammonium could be a good option,but ammonium is easy to be nitrificatd and loss.In anaerobic environment,ammonium could not be a good choice,for it may inhibits the degradation of petroleum hydrocarbons in some extent.Therefore,it is suggested that the redox conditions should be fully considered when choose nitrogen source for oil contaminated site remediation.