Degradation Of Naphthalene In Groundwater By Microorganisms Under Sulfate Reduction

With the development and utilization of petroleum energy,the groundwater pollution caused by petroleum hydrocarbons is becoming more and more serious.Polycyclic aromatic hydrocarbons?PAHs?represent a class of widespread and persistent environment pollutants.Due to their carcinogenic,mutagenic,and teratogenic effects,PAHs pose a serious threat to human health and ecological environment.Biodegradation is an economical and environmental-friendly method of controlling organic pollutants,especially PAHs.The bacteria surviving under low temperature,anoxic or anaerobic conditions,were isolated from the site contaminated with petroleum hydrocarbons in Shenyang,China.The bacteria were identified by 16S rRNA.This study aimed to characterize physical and chemical properties of the bacterial community.The effects of environmental factors on biodegradation of naphthalene were investigated.The changes of mixed bacterial community structure were also analyzed.In addition,the degradation of naphthalene under sulfate reduction was further studied.The main experimental conclusions are as follows:?1?Screening,identification and characterization of naphthalene-degrading bacteria.The microbial community was mainly composed of Acinetobacter and Pseudomonas,using naphthalene as their sole carbon and energy source.The bacteria were able to automatically adjust the cell-surface hydrophobicity and auto-aggregation to adapt to the toxicity of naphthalene.They also exhibited high emulsification and strong tolerance to low concentrations of naphthalene,which played a great role in promoting biodegradation.?2?The influencing factors and kinetics of naphthalene biodegradation.The bacteria inoculation concentration of 5%was the appropriate value for the degradation of naphthalene.The optimum pH range of bacteria was 7.0⁸.0,and the alkali resistance was higher than the acid resistance.It had a high degradation efficiency at10³0?.The optimum culture temperature was 30?,but low temperature had no inhibition on biodegradation of naphthalene.With the increase of naphthalene concentration,the degradation efficiency and degradation rate of naphthalene also increased.It found that the degradation rate of naphthalene fit the GuassAmp equation well.The expression of the degradation kinetic equation with a high degree of fit was derived by MATLAB software.?3?Degradation of naphthalene by microorganisms under sulfate reduction.The reduction of sulfate was caused by the degradation of naphthalene.In the electron transfer process,sulfate acted as the electron acceptor and naphthalene was the electron donor.The degradation rate of naphthalene was linearly related to the reduction rate of sulfate.It could be observed that 4.29⁴.59 mol sulfate was consumed with 1mol of naphthalene degraded.However,the theoretical value of 6 that was expected assuming the complete reduction of naphthalene to CO₂,which implied the biodegradation of naphthalene could not convert naphthalene into CO₂ completely.In the coexistence of multiple electron acceptors,sulfate was the main electron acceptor and the effects of Fe³⁺and magnetite were limited in the degradation of naphthalene.After cultivation for30 days,the bacterial community had a larger diversity and lower abundance.It led to a decrease in the relative abundance of Acinetobacter and an increase in the relative abundance of Pseudomonas because of the effect of the degradation of naphthalene.In the system with electron acceptors,the abundance of community was smaller,and the diversity of community was greater.