Effects of surfactant and Zn (II) at various concentrations on microbial activity and ethylbenzene removal in biotricking filter

• Removal of ethylbenzene was enhanced significantly by Tween-20 and Zn (II).
• The metal ion Zn (II) improved dissolving of the surfactant Tween-20.
• The optimum dosages of the surfactant and zinc ion were evaluated.
• The toxicities of Tween-20 and Zn (II) to biofilms in the biofilter were examined.

The effects of Tween-20, a non-ionic surfactant, and Zn (II) on microbial activity and removal performance for ethylbenzene in a biotrickling filter (BTF) were evaluated. Batch experiments were conducted to evaluate the surfactant and Zn (II) at various concentrations for their toxicity to microorganisms, and results indicated that Tween-20 was beneficial to microbial activity at all the tested concentration, while Zn (II) affected adversely when the concentration overpassed 5.0 mg L−1. Then effects of the two additives on removal efficiency of ethylbenzene were evaluated in a BTF at an empty-bed retention time of 30 s and an ethylbenzene concentration of 1100 mg m−3. Results showed that the optimal concentrations of Tween-20 and Zn (II) were about 12 and 1.0 mg L−1, respectively. Compared to the results when neither of the two additives was added, Tween-20 improved ethylbenzene removal efficiency from 67% to 86% at the optimal condition, while on that basis, Zn (II) just increased the removal efficiency from 86% to 90%. The promoting effects of the two additives on recovering microbial activity and removing excessive biomass were also observed in this article.