Novel Laboratory Biofilter for Rigorous Control of the Unsaturated Porous Medium for Improved Biofilter Operation
Water content of the unsaturated biofilter medium is one of the most important parameters in the treatment of contaminated air by biofiltration. Many biofilter failures are traced to too much or not enough water in the biofilter medium. Most bacteria demonstrate reduced metabolic activity at reduced water content. High water contents improve microbiological activity, although if too wet, reduced mass transfer of the contaminant and oxygen into the biofilm lowers activity. Our novel reactor combined water content control of the solid phase and headspace mixing of the gas phase to produce a differential reactor. The differential reactor exposes all the solid phase to the same environmental parameters (water content, contaminant concentration, temperature, etc.). This compares to the traditional long column (integral) laboratory biofilter where most of the parameters change along the length of the reactor. Water content was controlled using the suction cell principle between -5 to -300 cm H2O. Air recirculation or direct agitation provided gas phase mixing. A 7 to 20 ml/min flow of 100 ppm of toluene in air at 30 0C was continuously introduced through a humidifier (RH > 98%) into a reactor with 1.5 g of loosely packed compost and a 1 L headspace. The EC has varied approximately 50% over the water content range. The EC averaged about 10 g/m3h. Although the EC’s (20 - 4 g/m3h) were lower than most reports for toluene removal, they were still in the general range reported.