Effect of mineral salts addition on the behaviour of an ethanol biofilter.

Ethanol biofiltration was studied in a 0.1651 packed bed reactor filled with sugar cane bagasse complemented with mineral medium and inoculated with Candida utilis. The main objective was to improve the elimination capacity of the system by adding salts to the solid medium. The biofilter was operated for one month, varying both the inlet ethanol concentration (7.6-16.5 g m(-3) and the airflow rate (1.61-2.50 x 10(-3) m3 h(-1)). Removal efficiency (RE) of 100% was attained at ethanol loads ranging from 74.2 to 250 g h(-1) m(-3). When the RE decreased, acetaldehyde and ethyl acetate appeared in the outlet stream; adding mineral salts restored a 100% RE. Both ammonium sulfate and ammonia were assimilated by the yeast (conversion yield of nitrogen from the N-source to biomass of 75%), but only ammonia restored the pH of the medium to a value adequate for efficient biofiltration (7.7). Fifty seven percent of the carbon from ethanol was converted into CO2, and 8.7% into biomass. Final yeast population was 7 x 10(9) cells g(-1) dry matter, corresponding to 56 mg protein g(-1) dry matter, which offers potential to also use the protein enriched bagasse as feed.