| The unorganized emission of volatile organic compounds?VOCs? has already been regarded one of the main causes of air pollution. Though biotrickling filters?BTF? has already been widely used to control of VOCs because of its advantages of high efficiency and environmental friendly, but the studies found that this technology can not provide a commendable performance when treating hydrophobic compounds,therefore, this study used surfactant enhanced biological technology to improve the removal efficiency?RE?. The application of surfactant can not only enhance the solubility of VOCs in water, which may reduce the mass transfer resistance between the gas phase and the biofilm phase, also can enhance the microbial activity, thereby improving the ability of using VOCs.n-Hexane was used as model VOC in this study, polyurethane foam was selected as the media, the sludge from the city sewage treatment plant as the seed sludge,saponins, a biosurfactant, Tween 20, a nonionic surfactant and its mixed surfactants was used as the additives, two separate while identical biotrickling filters, BTF 1 and BTF2 were carried out to examine the performance of the BTF on the n-hexane removal and the effect of the surfactant on its performance.At the BTFs system start-up period, both BTFs were operated under a continuous mode at an n-hexane inlet concentration of 250 mg m-3, gas flow rate of 0.55 m3h-1,corresponding to the gas EBCT of 30.0 s. Results indicated that the RE of BTF1 and BTF2 exceeded 90% on day 11 and day 13, respectively, and 95% of RE was observed consistently since day 18, Therefore, both BTFs were successfully started up and operated for 22 days.After the BTFs were successfully started up, we do the optimization experiment of surfactant concentration and mixing ratio. The BTFs were operated at an gas EBCT of 30.0 s, the n-hexane concentration in the incoming stream averaged 600 mg m-3,and a corresponding gas flow rate of 0.55 m3 h-1, The surfactants were added to the nutrient solution for BTF1, while was not for BTF2. Results indicated that the optimum concentration of saponins was 1.25 CMC, and a corresponding RE and EC was 88.4% and 63.4 g m-3 h-1, respectively. Compared with BTF2, When the concentration of saponins was increased from 0.1 to 0.5, 1.0, 1.25, 1.5CMC, the RE were increased 6.1% ? 12.1% ? 17.1% ? 27.0% and 20%, respectively. On that basis, theIX optimum additive concentration of 0.1CMC of Tween 20 was found out, and a corresponding RE and EC was 78.45% and 56.25 g m-3 h-1, respectively. Compared with BTF2, when the concentration of Tween 20 was increased from 0.05 to 0.1, 0.2,0.5, 1.0CMC, the RE were increased 7.33%, 15.79%, 8.07%, 5.65% and-3.53%,respectively. The optimum mixture ratio of saponins and Tween 20 was 3:1, and a corresponding RE and EC was 91.66% and 65.72 g m-3 h-1, respectively. Compared with BTF2, when the concentration of mixture ratio was increased from 3:1 to 2:1, 1:1,1:2, 1:3, the RE were increased 30.6%, 23.04%, 19.24%, 8.89% and 5.94%,respectively. The phenomenon of excessive biomass accumulation occurred two times throughout the entire process for BTF2, but not present for BTF1.Comparative experiments were carried out with BTF1 fed with optimum concentrations of saponins while BTF2?the control BTF? without it. When the inlet n-hexane concentration was increased from 400 to 600, 800 and 1000 mg m-3,corresponding to organic loading rates of 47.83, 71.74, 95.65 and 120.0 g m-3 h-1, the maximum average RE of BTF1 could reach 91.3%, 88.3%, 85.8% and 83.0%accordingly, the corresponding EC increased from 43.67 to 63.35, 82.07 and 99.6 g m-3h-1, while for BTF2, the final RE of it was just 62.8%, 61.4%, 60.8% and 56.8%,and the corresponding EC increased from 30.04 to 44.05, 58.16 and 68.16 g m-3 h-1.When subjecting both the BTFs to constant organic loading rate of 71.7 g m-3 h-1, an gas EBCTs of 30, 15, 10 and 7.5 s was examined. Results indicated that the REs of both BTFs dropped greatly when the gas EBCT was decreased. With the decreased EBCTs of 30, 15, 10 and 7.5 s the RE of BTF1 decreased from 88.4%, 84.4%, 75.6%to 64.5%, the corresponding EC also decreased from 63.4, 60.5, 54.2 to 46.2 g m-3 h-1,while for BTF2, the final RE of it was just 61.4%, 53.9%, 43.9% and 38.3%, and the corresponding EC decreased from 44.0, 38.6, 31.5 to 27.5 g m-3 h-1. Removal rates of BTF1 were higher than that of BTF2 under this two operation conditions, so its indicating that application of surfactant could enhance the BTF performance for n-hexane removal. |
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