Degradation Of Toluene And Hydrogen Sulfide In A Biotrickling Filter Under Different PH Conditions

Recently,biological treating process has become a new technology on treatment of waste gas.In this study,the removal performance and biological characteristics for toluene and hydrogen sulfide treatment were examined in two different biotrickling filters（BTF）with different pH condition（4.5 and 7.0）,which will provide some useful theoretical and practical information for industrial application.During the start-up time,the BTF was packed with ether-based polyurethane foam,toluene was used as the sole carbon source and single pollutant,and the toluene degradation performance,biomass concentration and pressure drop of were compared in two BTF system.It was found that the biofilm formation was completed within 6 d and 5 d at pH value of 4.5 and 7.0,respectively.Under the conditions of toluene inlet concentration of more than 400 mg/m3 and EBRT of 30 s,removal efficiency of toluene in BTF was about 900%at pH 4.5.Meanwhile,the removal efficiency was above 96%at pH 7.0.Scanning electron microscope revealed that bacilliform may be the dominant bacteria in BTF at pH 4.5 and spherical grew well in BTF at pH 7.0.The average well colour development（AWCD）was measured with BiologECO,which indicated that microorganism in upper and lower BTF at both pH 4.5 and pH 7.0 showed high biological activities,strong community growth capacity,abundant microbial community structure and strong ability to remove the target pollutants.After a period of stable operation,H₂S was supplied at an average concentration of 20¹50 ppm,and the long-term performance,metabolic activity of organisms,biological characteristic were examined to explore the effect of hydrogen sulfide on toluene biodegradation.It was found that Under the condition of EBRT of 30 s,H₂S had no effects on toluene removal efficiency in the both pH 4.5 and 7.0 BTF systems.Scanning electron microscope revealed that after the dominant bacteria were changed after H₂S supplying.The bacilliform bacteria was substituted by filamentous bacteria in BTF at pH 4.5,whereas the spherical bacteria was substituted by the bacilliform bacteria in BTF at pH 7.0.Furthermore,the microorganism in upper and lower BTF at pH 4.5 and 7.0 still showed high biological activity,strong community growth capacity,abundant microbial community structure and strong ability to remove the target pollutants after H₂S supply.The biomass in the system constantly accumulated as the reaction progresses.Biomass in BTF at pH 4.5 was slightly higher than that in BTF at pH 7.0,and the pressure drop in BTF at pH 4.5 was slightly higher than that in BTF at pH 7.0.In the BTF systems at pH 4.5 and 7.0,toluene-degrading and H₂S-degrading process were followed the Michaelis-Menten kinetic model.The R2 values for toluene at pH 4.5 and 7.0 were 0.9842 and 0.9778,and rmax values were 132.46 g/m3·h and 93.46 g/m3·h,respectively.Accordingly,KS values for toluene were 0.25 g/m3 and 0.075 g/m3,respectively.This result further indicated that the acidic environment had a certain effect on reinforcement of the performance of the biotrickling filter in the purification of toluene.The R2 values for H₂S at pH 4.5 and 7.0 were 0.9690 and 0.9717,and rmax,values were 60.24 g/m3·h and 51.55 g/m3·h,respectively.Accordingly,KS values for toluene were 0.06 g/m3 and 0.13 g/m3,respectively.Furthermore,The variation of elimination capacity and removal efficiency of toluene and hydrogen sulfide,CO₂ production rate were studied in condition of EBRT from 30 s to 10 s,toluene inlet concentrationfrom 400 mg/m3 to 600 mg/m3 and hydrogen sulfide inlet concentration from 140 ppm to 190 ppm.And the recovery of the BTFs after 30 days’starvation was also examined.It was found that the process parameters,such as inlet concentration,inlet loading and EBRT,had different effects on the toluene and H₂S removal efficiency.Under the condition that EBRT of 20 s,the BTFs had no effect on the removal efficiency of toluene and H₂S,but it could save the operating costs.The relatively CO₂ production capacity revealed that the mineralization rates were at 70.7%and 74.6%in BTF at pH 4.5 and pH 7.0,respectively.The fact that a neutral environment can promote the CO₂ production capacity in BTF was determined.For 30 d of starvation,when toluene and H₂S were re-introduced,the BTF at pH 4.5 was observed that 10 d was necessary to recover the removal efficiency of toluene,removal efficiency was 90%.While 6 d was necessary to recover the removal efficiency of H₂S,and removal efficiency was above 95%.In addition,the BTF at pH 7.0 was observed that 4 d was necessary to recover the removal efficiency of toluene,removal efficiency was 90%.And 7 d was necessary to recover the removal efficiency of H₂S,removal efficiency was above 95%.