A Comparative Study of Immobilized Nitrifying and Co-Immobilized Nitrifying and Denitrifying Bacteria for Ammonia Removal from Sludge Digester Supernatant

摘要

Bench scale kinetic experiments were conducted to examine the use of cell immobilization in calcium alginate to remove ammonia in anaerobic sludge digester supernatant. Two systems, immobilized nitrifiers and co-immobilized nitrifiers and denitrifiers, were studied with and without the addition of methanol. Results indicated that partial nitrification (to nitrite) was achieved in both systems. The co-immobilized reactors did not exhibit the extent of nitrite accumulation observed in the solely nitrifying reactors. The nitrifying reactors were unable to buffer the hydrogen ion production, during the nitrification process, to the level the co-immobilized cell reactors achieved. Both of these differences suggested the occurrence of denitrification in the co-immobilized reactors. Scanning electron microscopic images of bacteria immobilized in the alginate spherical beads support the results of the kinetic experiments. Nitrifiers colonized in the 100-200 μm peripheral layer of the beads. Large voids caused by nitrogen gas due to denitrification were found in a number of co-immobilized bead samples.