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

摘要

Bench scale kinetic experiments were conducted to examine the use of cell immobilization in calcium alginate to remove ammonia from the anaerobic sludge digester supernatant of the Moorhead Wastewater Treatment Facility. Two systems, immobilized nitrifiers and co-immobilized nitrifiers/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 nitrifier reactors. The nitrifier reactors were unable to buffer the hydrogen ion production, during the nitrification process, to the level the co-immobilized cells achieved. Both of these differences suggested the occurrence of denitrification in the co-immobilized reactors. The denitrification proceeded via the nitrite pathway due to the lack of nitrate present in the 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 im peripheral layer of the beads. Large voids caused by nitrogen gas due to denitrificaiton were found in a number of co-immobilized bead samples. The gas production and heterotrophic nature of the denitrifying bacteria caused a loss in bead integrity.