Combined effect of adsorption and biodegradation of biological activated carbon on H2S biotrickling filtration

In order to evaluate the combined effect of adsorption and biodegradation of H2S on activated carbon surface in biotrickling filtration, four laboratory-scale biofiltration columns were operated simultaneously for 120 h to investigate the mechanisms involved in treating synthetic H2S streams using biological activated carbon (BAC). The first three columns (A, B, C) contained a mixture of activated carbon and glass beads, with the carbons (BAC or virgin activated carbon (VAC)) and conditions (with or without liquid medium recirculation) differentiated. The last column (D) used 100% glass beads with liquid medium recirculation. Air streams containing 45 ppmv H2S were passed through the columns at 4 s of gas retention time (GRT) and liquid flow rate was set at 0.71 ml min−1. Column D got its breakthrough in 3 min of operation, indicating a negligible contribution of glass beads to the adsorption of H2S. The removal efficiency (RE) of Columns B and C using VAC dropped quickly to 30% within the first 8 h, and afterwards continued to drop further but slowly. Column A using BAC stayed at 25% of RE throughout the operation time. A thorough investigation of the H2S oxidation products, i.e., various S species in both aqueous (recirculation media) and solid phases (BAC and VAC), was conducted using ICP-OES, IC, XRF, and CHNS elemental analyzer. BAC demonstrated a better performance than columns with adsorption only. Water film was found to enhance H2S removal. The percentage of sulphate in the total sulphur of the BAC system improved to twice of that of VAC system, indicating sulphate is the main product of H2S biofiltration. The observed pH drop in BAC system double confirmed that the presence of biodegradation in the biofilm over carbon surface did profound effect on the oxidation of H2S, compare to the systems with adsorption only.