Regeneration of a compost biofilter degrading high loads of ammonia by addition of gaseous methanol

The long-term stability of a bicifilter loaded with waste gases containing NH3 concentrations larger than 100 ppmv was studied in a laboratory-scale compost reactor. At an Empty bed residence time (T) of 21 sec, elimination capacities of more than 300 g NH3/m(3)/day were obtained at elimination efficiencies up to 87%. Because of absorption and nitrification, almost 80% of the NH3-N eliminated from the waste gas could be recovered in the compost as NH4-N or NO2-/NO3-N. The high elimination capacities could be maintained as long as the NH4+/NOx- concentration in the carrier material was less than 4 g NH4-/NOx--N/kg wet compost. Above this critical value, osmotic effects inhibited the nitrifying activity, and the elimination capacity for NH3 decreased. To restore the biofilter performance, a carbon source (methanol) was added to reduce NH4+/NOx- accumulated in the compost. Results indicate that methylotrophic microorganisms did convert NH4+/NOx- into biomass, as long as the NO3- content in the compost was larger than 0.1 g NO3--N/kg compost. Removal efficiencies of CH3OH of more than 90% were obtained at volumetric loads up to 11,000 g CH3OH/m(3)/day. It is shown that addition of CH3OH is a suitable technique for regenerating the compost material from osmotic inhibition as a result of high NH3 loading. The biofilter was operated for 4 months with alternating loading of NH3 and CH3OH.