| Two-liquid-phase biofiltration technology is a new technology for hydrophobic and non-biodegradable volatile organic compounds?VOCs?.In this paper,two-liquid phase biofiltration system was applied to treat VOCs.The difference of removal performance between one-liquid phase and two-liquid phase biofilters were studied.In addition,bioaerosol emission and health risk assessment of exhausted gas from the biofilters were evaluated.It was expected that this study could provide technical support for the engineering application of two-liquid phase biofiltration technology.The removal performance of two-liquid phase filters?without biofilm?treating volatile organic compounds?VOCs?was firstly studied.The results showed that the two-liquid phase filter by adding 10%?v/v?of silicone oil demonstrated better removal efficiency of 53%.Various VOCs were used as the target compounds to be treated by the the two-liquid phase filter.And the dichloromethane presented the highest removal performance than other VOCs.When the gas-liquid ratio was 19:1,the average removal efficiency could achieve as high as 71%.The differences between one-liquid phase and two-liquid phase biofilters treating dichloromethane were compared.It was found that the two-liquid phase biofilter showed higher removal efficiency?81%?than that of non-liquid phase biofilter?66%?.Furthermore,the biomass accumulation inside the two-liquid phase biofilter was faster than the one-liquid phase bilfilter.The specific growth rates were 0.035 and0.026 g dry-biomass/?g-dry filter per day?for one and two-liquid phase biofilter,respectively.In addition,it was proven that higher extent of the removed dichloromethane was converted to CO2 by the microorganism in the two-liquid phase biofilter.However,the pressure drop and TOC value of the leachate from the two-liquid phase biofilter was much larger than that of one-liquid phase biofilter.The bioaerosol emissions from the two biofilters were studied.The results showed that increasing gas velocity in the biofilters led to the increase of bacteria and fungal aerosols concentrations.The concentration of bacteria in two-liquid phase and one-liquid phase was 268 cfu/m3 and 370 cfu/m3,and the fungal concentration was198 cfu/m3 and 331 cfu/m3,respectively.Further increase in gas velocity beyond 140m/h,the bioaerosol concentration declined.When the temperature was about 40?,the concentration of fungi aerosol in the both biofilters reached the maximum,namely108 cfu/m3 and 140 cfu/m3.While the temperature was about 50?,the aerosol concentrations of the two towers reached the maximum,152 cfu/m3 and 223 cfu/m3,respectively.Then as the temperature continued to rise,both bacteria and fungal concentrations were reduced.In addition,when the humidity of the packing layer was50%,the concentration of fungal aerosols reached 73 cfu/m3 and 104 cfu/m3 in two and one liquid phase biofilters.When the humidity reached 70%,the concentration of bacteria aerosols achieved as high as 253 cfu/m3?two-liquid phase?and 349 cfu/m3?one-liquid phase?,respectively.The value of HI in the both biofilters under the different conditions was much less than 1.0,suggesting that the exposure of bioaerosols was safe to human health at its present form. |
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