Long-term results of ammonia removal and transformation by biofiltration

In this paper, long-term (>8 month) results of ammonia removal in biofilter s was studied. Compost was used as the biofilter medium and activated carbo n as an added material. The ammonia removal was normally >95% at influent a mmonia concentrations of 20-500 ppmv. According to the test results, the in fluent ammonia concentration should be < 200 ppmv (0.1570 g-ammonia/kg-medi a per day) so that the effluent concentration of ammonia is (1.0 mg/m(3) (t he emission standard of China), and the biofiltration system can achieve go od long-term performance. In the biofiltration system utilized in this stud y, the shortest retention time that the system could attain was 0.532 min. However, the retention time can be decreased further without decreasing the ammonia removal efficiency. Countercurrent flow is favorable, as it enhanc es the moisture retention ability of the media. In the bioreactors, ammonia can be converted into the nitrate. The bioreactors have a stratification p henomenon for ammonia removal over the biofiltration depth, which implies t hat different parts of the bioreactor play different roles in the ammonia r emoving process. (C) 2000 Elsevier Science B.V. All rights reserved.