Abatement of High Concentrated Ammonia Loaded Waste Gases in Compost Biofilters

The performance of lab-scale compostbiofilters for the purification of waste gasescontaining high (>70 mg m-3) ammoniaconcentrations was studied. When using fresh compostmaterial, no effect of inoculating the compostmaterial with a nitrifying culture was observed sincehigh elimination capacities (up to 350 gNH3 m-3 d-1) were obtained in both theinoculated and the non-inoculated biofilter. Due tothe physico-chemical interaction of NH3 with thecompost material at the start of the experiment, nomicrobiological start-up period was observed and highremoval efficiencies were obtained from the first dayon. Next to this, no NH3-toxicity was observedeven at concentrations up to 550 mg NH3 m-3.About 50% of the NH3-removal was found to benitrified, while the other 50% remained in thebiofilter as NH4+. As a result of this, noacidification of the carrier material was observed andNH4NO3 accumulated in the biofilter. Due toosmotic effects, however, a complete inhibition innitrification and NH3-removal was obtained at ameasured NH4NO3-concentration in the compostmaterial of 6–7 g N kg-1, corresponding to acumulative NH3-removal in the biofilter of ±6000 g m-3. Finally, it was illustrated that theremoval of the odorant dimethyl sulfide (Me2S) ina Hyphomicrobium MS3-inoculated compostbiofilter is completely inhibited due toNH3-toxicity at a waste gas concentration of 100 mg NH3 m-3. Next to this, theNH4+- and NO3−-concentrations inthe compost material that were shown to inhibit thenitrification, also strongly affected theMe2S-degrading activity of Hyphomicrobium MS3.