Bioremediation Of PAHs Coexisted With Heavy Metals In Soils By Immobilized Bacteria

Compound pollution is a common phenomenon in contaminated soil.PAHs and heavy metals usually deposit into soils simultaneously or successively.They constitute compound pollution soils and the existence of heavy metals perhaps have negative influence on bioremediation of PAHs.Unlike the previous remediation technique,immobilized-microorganism technique has obvious advantages,it can provide water,air and nutrient substance for the microorganism which it immobilized.And meanwhile it can protect the microorganism from the adverse competition through their micro-enviroment.Biochar has adsorption capacity for both PAHs and heavy metals,and can provide various nutrient elements for microorganism.In this paper,we use Chinese fir as raw materials to make biochar(600BC)at the temperature of 600 ?.Immobilized microorganism beads are made with biochar as adsorption carrier,and use sodium alginate as embedding medium.Then we inoculate the beads into liquid mineral salt medium to research the remediation effect of immobilized microorganism beads with the influence of cadmium.The medium has been added pyrene and different concentration of cadmium.Meanwhile,we inoculate the beads into contaminated soils through the artificial add of pyrene and cadmium,and the field soils contaminated by PAHs and heavy metals.At the same time,we use phospholipid fatty acids(PLFA)analyze the changes of structure of microbial community in soils before and after remediation.The main results are as follows:1.During the incubation time of 28 days,the degradation rate of pyrene by immobilized bacteria in mineral salt medium was 88%,the degradation rate of free bacteria was 99%;when the concentration of cadmium is lmg/L and 50 mg/L,neither of the bacteria in defferent forms had degraded pyrene.As a result,immobilized-microorganism technique by 600BC can not reduce the toxicity of cadmium on microorganism.2.Add pyrene and different concentration of cadmium ions into red soil and black soil artificially,then inoculate free bacteria(F)and immobilized bacteria(6BC)into the soils respectively culturing 90 days by avoiding light.The total contents of pyrene were extracted by ultrasonic extraction.When the soils were added pyrene alone,comparing with the blank control group(CK),the degradations of pyrene by free bacteria and immobilized bacteria in red soil were significant(p<0.05).The degradation rate were 80±0.03%and 55±0.09%respectively.The contents of pyrene in black soils adding free bacteria and immobilized bacteria were 1.82±0.05mg/kg.2.21±0.33mg/kg.They had no significant difference with the blank control group(p>0.05).When the content of cadmium of soils was 1mg/kg,the free bacteria in red soil still had capacity to degrade pyrene,the degradation rate were 72±0.06%,but immobilized bacteria did not degrade pryene.And neither of the bacteria in defferent forms had degraded pyrene in black soil.When the content of cadmium of soils was 50mg/kg,the contents of pyrene had not decreased in two soils.In red soils,immobilized-microorganism technique can not provide protection for bacteria from the toxicity of cadmium.Biochar might adsorb cadmium,increasing the toxicity of cadmium to bacteria and reduing the degradation of pyrene.When pyrene and cadmium coexist in black soil,the inoculation of immobilized bacteria has no effect of degradation on pyrene.3.Inoculate free bacteria(F)and immobilized bacteria(6BC)into three kinds of PAHs and heavy metals compound pollution field soils and culture 90 days by avoiding light.The results show that after culture experiment,the immobilized bacteria in yellow soil and yellow-brown soil had no degradation effect on PAHs,but the contents of total PAHs in in latosol soil had significant differences compared with the original soil.After 90 days,the available contents of PAHs in all of the groups in three field soils were lower than original soils(p<0.05).The available content of PAHs in F group in yellow-brown soil has significant difference from the rest of the three groups(p<0.05).After the experiment,the total PLFA contents and fatty acids contents of bacteria and actinomycetes in 6BC and BC groups in yellow-brown soil had significantly increased(p<0.05),but there is no different between the two groups(p>0.05).The total PLFA contents and fatty acids contents of bacteria and actinomycetes in yellow soil and latosol had significantly increased(p<0.05),the fatty acids content of fungi in 6BC and BC groups had increased(p<0.05),but CK and F groups had not(p>0.05).It could indicate that immobilized beads made by 600BC could enhance the grow of microrganism in soils.