A novel biofiltration technology for odour treatment

Abstract

Hydrogen sulphide (H2S) and ammonia (NH3) are often simultaneously emitted from various industrial processes. Biofiltration has been well known as an effective odour control technology for these compounds which are associated with environmental problems and health risks. However, there have been little studies of the mechanisms for simultaneous removal of H2S and NH3. In this two-stage study, a novel system was developed for the elimination of contaminated air loaded with H2S and NH3 mixture. In the first stage, a preliminary study was conducted to investigate the feasibility of using waste materials from coal power plants (i.e. coal slag) and landscapes (i.e. wood chip and compost) as packing media in biofiltration systems for odour control. Coal slag and the trickling operation mode were selected for further in-depth study based on their best removal efficiency. In the second stage, the optimized biotrickling system packed with coal slag was employed to investigate the effects of operating parameters on the treatment performance of H2S and NH3 removal. Superior single H2S removal efficiency (over 99%) at concentrations of up to 100 ppm was achieved at an EBRT of as low as 5 s, which is shorter than most previously reported removal efficiencies for biofiltration systems. For individual H2S removal without pH control, the critical loading significantly decreased from 153 g/m3/h to 40 g/m3/h. Excellent NH3 removal efficiency was achieved at the loading below 108.4 g/m3/h (i.e. 350 ppm). For simultaneous removal, outstanding H2S (98.5%) and NH3 (99.9%) removal efficiencies were obtained at loadings of up to 120 gH2S/m3/h and 80 gNH3/m3/h, respectively. The results of products analysis revealed that the metabolic products of sulphide and ammonia oxidation were dependent on inlet loadings. In sulphide oxidation, elemental sulphur and sulphate were the most abundant by-products at high and low inlet loadings, respectively. For ammonia removal, half of the introduced NH3 was oxidized to nitrate and the rest was converted to ammonium ion at low loadings, while nitrite and ammonium ion were predominant at high loadings. However, for the simultaneous elimination of H2S and NH3, the main metabolic end-products were elemental sulphur and nitrite at most studied cases under the relatively high H2S (> 100 g/m3/h) andNH3 (> 80 g/m3/h) loadings. The reactor size could be estimated using kinetics parameters that were determined from the modified Michaelis-Menten model. The result demonstrated that less than 10 s were required for excellent removal of H2S and NH3. Microbial community dynamics were investigated using both culture- and molecular-based methods. The occurrence and predominance of specific bacterial species varied with the operating conditions in the system. The optimized biotrickling filter was demonstrated to be a feasible and economical alternative for the simultaneous odour removal. There were no common operating problems, such as clogging and compaction, in the operation for more than two years. The results of this study could be used as a guide for the further improvement in the design and operation of industrial-scale odour treatment systems. In the meantime, the disposal burden of waste residues from coal power plants could be alleviated by recycling the coal slag as packing materials for odour control purposes.