Combined effect of adsorption and biodegradation of biological activated carbon on H_2S biotrickling filtration

摘要

In order to evaluate the combined effect of adsorption and biodegradation of H_2S 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 H_2S 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 recir-culation) differentiated. The last column (D) used 100% glass beads with liquid medium recirculation. Air streams containing 45 ppmv H_2S 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 H_2S. 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 H_2S 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 H_2S 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 H_2S 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 H_2S, compare to the systems with adsorption only.