| The nitrobenzene(NB)and 3,4-dichloroaniline(DCA)are a type of aromatic compounds that is widely used in the manufacture of organic products,such as dyes,drugs,synthetic resin,and pesticides.The halogenated aromatic compounds have been contaminating the environment by transport,accidental discharge and the disposal through industrial effluents,and the degradation of several herbicides.The study on the treatment problem of chemical wastewater under high salinity condition is the present focus of environmental science and engineering fields in world.Due to scarce information on the degradation of aromatic hydrocarbons in high salinity,we believe that the problem of salt-tolerant bacteria to degrade it has not been adequately investigated.This study is to isolate pure salt-tolerant strain(s)able to degrade aromatic hydrocarbons from the farm field of Chongqing,forest soil of Chongqing and active sludge of Henan Chemistry Factory.The study is to reveal the optimum condition of degradation of aromatic hydrocarbons through analysis of culture pH,temperature,cells growth and concentration of aromatic hydrocarbons.The dynamical equation of degradation is to be derived by quadratic regression.The optimum technological parameter is to be established by Orthogonal experiment,defined as a technique for improvement of the degradable capacity of aromatic hydrocarbons by introduction of the community structure of the salt-tolerant consortium.The study is to disclose the rule of the degradation of aromatic hydrocarbons in high salinity by salt-tolerant bacteria,and thus provide a new idea for the treatment of saline wastewater by salt-tolerant microbial consortium.With systematically summarizing the development of research at home and abroad on high-salinity wastewater containing aromatic compounds,the study focused on the following five research works:(1)The two halophilic microbial strains were isolated from the farm field and the activated sludge.A Gram-negative bacterium strain Y6,capable of growing aerobically on 3,4-dichloroaniline(DCA)as the sole carbon and energy source,and capable of degrading nitrobenzene(NB),was identified as Myroides odoratimimus strain by morphological,physiological,and biochemical characteristics as well as 16S rDNA sequence.The other Gram-negative bacterium strain YX2,was identified as Bacillus licheniformis strain by morphological,physiological,and biochemical characteristics as well as 16S rDNA sequence.(2)Analysis of culture pH,temperature,cells growth,and DCA concentration demonstrated that strain Y6 could effectively degrade DCAwithout a lag phase.The kinetics of DCA degradation was well described using the Andrews equation,and the kinetic parameters were as follows:qmax=1.74 h-,Ks=43.5 mg·L-1,and Ki=230.3 mg·L-1.In addition,strain Y6 was found to be moderately halophilic and showed the highest power of DCA degradation in 5%NaCl(w/w,%).With initial concentrations of 30,100,and 200 mg·L-1,100%,80.4%,and 33.2%of DCA were transformed after 96 h in 5%NaCl,respectively.With initial concentrations of 30,100,and 200 mg·L-1,76%,52.3%,and 15.3%of DCA were transformed after 120 h in 10%NaCl,respectively.These results suggest that strain Y6 has the potential to degrade DCA in saline wastewater.To date,this is the first report on the degradation of DCA by a M.odoratimimus strain with moderate salinity tolerance.(3)Aimed at efficiently remedying nitrobenzene-contaminated saline wastewater,the nitrobenzene-degrading characteristic of a Myroides odoratimimus strain Y6 was studied and analyzed.To evaluate the nitrobenzene-degrading ability of Strain Y6,the concentration of nitrobenzene was detected by high performance liquid chromatography.The effects of temperature,pH,initial concentration of nitrobenzene,inoculum concentration and culture type on the biodegradation of nitrobenzene by Strain Y6 under saline conditions were studied.Strain Y6 showed the highest power of nitrobenzene degradation in 7%NaCl(w/w%).The optimal conditions for the biodegradation of nitrobenzene by Strain Y6 were at pH 6.0,28? and D600=1.With initial concentrations of 100 and 200 mg·L-1,97.5%and 65.7%of nitrobenzene were transformed after 168 h in 7%NaCl,respectively.There kinds of additional compounds,glucose,starch and glycerin were tested to choose a favorite carbon source for the cometabolism of Strain Y6.The results showed that they could promote nitrobenzene biodegradation and cell growth.And the rate of degradation could enhance to 93.3%,when adding in 800 mg·L-1 glucose as primary substrate.The study shows that Strain Y6 could be an excellent candidate for the bio-treatment of nitrobenzene-contaminated wastewater with high salinity.To date,this is the only study on the degradation of nitrobenzene by M.odoratimimus strain.(4)The strain YX2 was capable of utilizing nitrobenzene as the sole carbon,sulfur and energy source,but degradation rate of nitrobenzene was affected by the concentration of compound.Only 33.1%NB degradation was observed after 3 d in the presence of basal salts medium with initial concentration of 200 mg·L-1.The goal of this study was to select a kind of carbon/nitrogen source as co-substrate from 11 kinds of compounds that could be most effective in enhancing the biodegradation.The result showed that the strainYX2 in LB medium has the strongest power on the biodegradation of NB.With initial concentrations of 50,100,200,and 600 mg·L-1,NB was completely degraded by the strain YX2 after 36,36,72 and 156 h,respectively.About 99%NB with initial concentration of 200mg·L-1 was removed by the strain YX2 in the presence of LB medium with initial concentration of 500 mg·L-1 benzene,500 mg·L-1 phenol,and 500 mg·L-1 aniline,respectively;Strain YX2 degraded more than 80%nitrobenzene of initial concentration of 600 mg·L-1 with co-substrate of 500 mg·L-1 benzene,500 mg·L-1 phenol,and 500 mg·L-1 aniline,respectively.In 5%NaCl,the strain completely degraded 200 mg·L-1 and 600 mg·L-1 nitrobenzene after 72 h and 168 h.The experiment showed that Strain YX2 is so far the most effective to degrade NB.These results demonstrate that the strain YX2 has a high application potential in the treatment of nitrobenzene wastewater with high salinity.(5)The treatment performance of halophilic microbial consortium consisting of different mixture ratio of two aromatic compound(DCA and NB)in saline wastewater was investigated and compared.In 0%NaCl,98.9%NB and 90.5%DCA was removed after 72 h by the halophilic consortium with the initial NB concentration of 200 mg·L-1 and DCA 30mg·L-1.With the initial NB concentration of 600 mg·L-1 and DCA 100mg·L-1,the halophilic consortium degraded more than 70%NB and 70%DCA.In 5%NaCl,the halophilic consortium completely degraded NB and DCA after 216 h with the initial of concentration 600 mg·L-1 and 100mg·L-1,respectively.These results demonstrate that both Strain Y6 and Strain YX2 have a high application potential in the treatment of nitrobenzene wastewater with high salinity. |
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