Formaldehyde is a common gaseous pollutant affecting the indoor air quality and the health of occupants in buildings. Various technologies have been tried, such as adsorption, photocatalytic oxidization and botanical filtrations. However, the removal of indoor formaldehyde is still a challenging problem due to the low rate, byproduct formation and low efficiency of the above mentioned methods. Biological degradation technology with high removal efficiency has been successfully applied in industries for effluents and waste gas treatments. However, the potential biohazard risk from possible microorganism leakages of the biological system is the biggest concern of indoor air biofiltration systems. This study investigated the performance of a biological degradation system for formaldehyde removal at typical indoor condition. A microbial immobilization method was applied in the biofiltration system to reduce the potential biohazard risk. Bacterial strain of Pseudomonas putida was embedded in calcium alginate gel, which was then formed to a novel packing material called microbial granules. To investigate the operating performance of the biofilter in practical indoor environment, the concentrations of experimental inlet formaldehyde was controlled between 0.222 and 1.339 mg m-3, while the corresponding removal efficiency of the biofilter system varied from 68.6% to 93.5%. The pressure drop was maintained at 120 Pa with air flow rate increased up to 1.5 L min-1. The effect of inlet concentration, empty bed residence time, and nutrient feeding rate on the performance of the system was investigated as well. No microbial leakages were detected at air downstream during the experimental study, while the high microbial activity of bacteria entrapped in the packing material was observed. © 2012 Elsevier Ltd.
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