Batch biological treatment of nitrogen deficient synthetic wastewater using Azotobacter supplemented activated sludge

Biological treatment of nitrogen deficient wastewaters are usually accomplished by external addition of nitrogen sources to the wastewater which is an extra cost item. As an alternative for effective biological treatment of nitrogen deficient wastewaters, the nitrogen fixing bacterium, Azotobacter vinelandii, was used in activated sludge and also in pure culture. Total organic carbon (TOC) removal performances of Azotobacter-added and free activated sludge cultures were compared at different initial TN/TOC ratios. The rate and extent of TOC removal were comparable for all cultures when initial TN/TOC ratio was larger than 0.12; however, both the rate and extent of TOC removal from nitrogen deficient (TN/TOC<12%) synthetic wastewater were improved by using Azotobacter-added activated sludge as compared to the Azotobacter-free activated sludge culture. More than 90% TOC removal was obtained with pure Azotobacter or Azotobacter-added activated sludge culture from a nitrogen deficient synthetic wastewater.