Alcaligenes faecalis No. 4 (No. 4) has the ability to carry out the following heterotrophic nitrification and aerobic denitrification, NH4+ → NH2OH → N2O → N2. Approximately, 40 and 60% of ammonium were converted to N2 gas and cell mass, respectively. Only a few percent of NO2− and NO3− were produced from ammonium. After brief explanation of significant properties of No. 4, several examples of application of No. 4 to treat ammonium, especially high‐strength ammonium in several wastewaters were presented. The ammonium removal rates in these examples showed several hundredfold higher than those in conventional ammonium treatment method. In wastewater treatment plants, the selection of handling of excess sludge after treatment is a problem to be solved. Some possibilities of utilization of the excess cells of No. 4 in agriculture or in cattle farming were also presented.
Part of the book: Nitrification and Denitrification