Performances And Biofilm Characteristics Of Biotrickling Filters For High Concentration Ethylbenzene Removal At Present Of Saponins

In the recent,the environmental problems caused by the emission of volatile organic compounds(VOCs)have already attracted extensive attention worldwide.And,some new laws and regulations against the pollutant of VOCs have been promulgated.Biotrickling filter(BTF)based on microbial metabolism has been accepted as an effectively alternative for controlling VOC emissions due to its cost-effectiveness,handiness and environmental friendliness.However,this biological technology has a poor removal for hydrophobic VOCs.The application of surfactant into biofilters which can effectively enhance the BTFs performance was is turning into a promising solution.Based on the above reasons,ethyl benzene was chosen as target pollutant in this work,and the biosurfactant saponin was used as the additives.Two identical bioreactors,BTF1 and BTF2,were run in parallel to investigate the effects of saponin on the BTF performance for controlling ethylbenzene.Additionally,in order to investigate the mechanisms of surfactant,the effect of saponins on the alterations of biofilm characteristic including the component and chemical structure of EPS,relative hydrophobicity and surface charge was also investigatedAt the start-up stage,when an average ethylbenzene inlet concentration of 250mg/m~3,with a corresponding gas empty bed residence time of 30 s was introduced into the BTF systems,97%of removal efficiency(RE)in both BTFs was observed since day 16,both BTFs were counted as the achievement of start-up on day 21.After successful start-up of BTF1 and BTF2,comparative experiments were carried out to evaluate the effects of saponins concentration on the biofilter performance.The BTF1 as the experimental group was fed with optimum concentrations of saponins,while BTF2 as the control group was evaluated.Both BTFs were operated at an average ethylbenzene influent concentration of 1300 mg/m~3,gas EBRT of 30 s.When saponin concentration was increased from 20 to 48 mg/L,the BTF1 performance was higher than BTF2.The optimum concentration of saponins was40 mg/L and a maximum RE of ethylbezene reached 84.3%,the corresponding elimination capacity(EC)reached 131.9 g/(m~3 h).Results showed that Saponins could be applied to enhance the removal performance of ethylbenzene in biofilters.The removal performance of ethylbenzene using BTF1 and BTF2 for comparison was investigated under 40 mg/L of saponins.When the inlet ethylbenzene concentration increased,ranging from 750 to 2300 mg/m~3,gas empty bed residence time of 30 s,the RE and EC of BTF1 were higher than BTF2.When the empty bed residence time was decreased ranging from 45 to 15 s at the concentration of 1300mg/m~3,the introduction of saponin can enhance the RE of ethylbenzene significantly.When gas empty bed residence time was decreased to 7.5 s,there is no difference with BTF1 and BTF2.Results showed that the surface characteristic of biofilms could be altered by the introduction of saponin,and the uptake rates of biofilms to VOCs could be enhanced due to surfactant.The result of FTIR showed that the chemical structure of biofilms was changed.