Materials and Methods
Biofilter set up
A bench-scale, three-stage upflow biofilter was made from an acrylic cylinder with an effective column height of 160 cm and an internal diameter of 10 cm (Fig. 1). The column was divided into three 50-cm stages (referred to as bottom, middle and top stage) by a stainless steel mesh in order to support media and to enhance uniform distribution of the inlet gas. Each stage was filled to a height of 40 cm with equal amount of the filter-bed materials. Hydrogen sulfide was generated by mixing hydrochloric acid (HCl) with sodium sulfide (Na2S). The airflow supplied by an air compressor was allowed to bubble through the HCl solution containers for better mixing. The experiment was conducted at ambient temperature (30-36 °C) .