Biofiltration of xylene vapor by selected microorganisms

Abstract

Biofiltration of an air stream containing xylene vapor has been studied in a laboratory. The experimental study consisted of two parts. In the first part, xylene-degrading microorganisms were isolated from biofiltration system and performance study of selected microorganisms was completed in the second part. The biofilter column was 5.0 cm diameter and 200 cm long with gas sampling ports. For the first part, the biofilter medium in the experiment consisted of coconut husk 75%, manure compost 20% and wastewater sludge 5% v/v. Xylene-degrading microorganisms were isolated from the biofilter, which operated under a continuous loading of xylene vapor 8 h/day for 1 and 2 months. Four dominant species of xylene-degrading fungi in biofilter were identified. These dominant species were identified by phenotype and DNA sequencing techniques as Aspergillus flavus (M1), Aspergillus terreus (M2), Penicillium glabrum (M3) and Aspergillus niger (M4). For the second part, three microorganisms (M1, M2 and M3) were selected to individually inoculate biofilters for a performance study using a sterilized biofilter medium consisting of coconut husk and manure at a ratio of 70:30 v/v. Biofiltration of xylene vapor was carried out for 95 days at various concentrations and flow rate conditions. The initial moisture content of the biofilter medium was adjusted to 50% of dry weight. The pressure drop across the bed was 0.25 – 1 cm of H₂O. The pH and temperature were 5.5 to 8.5 and 28 – 33℃, respectively. The various inlet xylene concentrations (0.01 – 6.3 g.m⁻³) were tested with empty bed retention times of 705 s, 280 s and 140 s. The maximum elimination capacities of M1 and M2 (88 and 91 gm⁻³h⁻¹ respectively) were nearly the same, whereas M3 showed a better performance (115 gm⁻³h⁻¹).