START-UP AND THE EFFECT OF GASEOUS AMMONIA ADDITIONS ON A BIOFILTER FOR THE ELIMINATION OF TOLUENE VAPORS

Biotechnological techniques, including biofilters and biotrickling fil ters are increasingly used to treat air polluted with VOCs (Volatile O rganic Compounds). In this work, the start-up, the effect of the gaseo us ammonia addition on the toluene removal rate, and the problems of t he heat accumulation on the performance of a laboratory scale biofilte r were studied. The packing material was sterilized peat enriched with a mineral medium and inoculated with an adapted consortium (two yeast and five bacteria). Start-up showed a short adaptation period and an increased toluene elimination capacity (EC) up to a maximum of 190 g/m (3)/h. This was related to increased CO, outlet concentration and temp erature gradients between the packed bed and the inlet (Tm-Tin). These events were associated with the growth of the microbial population. T he biofilter EC decreased thereafter, to attain a steady state of 8 g/ m(3)/h. At this point, gaseous ammonia was added. EC increased up to 8 0 g/m(3)/h, with simultaneous increases on the CO, concentration and ( Tm-Tin). Two weeks after the ammonia addition, the new steady state wa s 30 g/m(3)/h. In a second ammonia addition, the maximum EC attained w as 40 g/m(3)/h, and the biofilter was in steady state at 25 g/m(3)/h. Carbon, heat, and water balances were made through 88 d of biofilter o peration. Emitted CO2 was about 44.5% of the theoretical value relativ e to the total toluene oxidation, but accumulated carbon was found as biomass, easily biodegradable material, and carbonates. Heat and water balances showed strong variations depending on EC. For 88 d the total metabolic heat was -181.2 x 10(3) Kcal/m(3), and water evaporation wa s found to be 56.5 kg/m(3). Evidence of nitrogen limitation, drying, a nd heterogeneities were found in this study. (C) 1998 John Wiley & Son s, Inc.