Abstract: A process is disclosed to improve the efficiency of nitrification in activated sludge systems. Supplemental ammonium nitrogen in the form of anhydrous ammonia or an aqueous solution of ammonia is added to the nitrification zone preferably during periods of low flow and low loadings of oxidizable nitrogenous compounds. The ammonium nitrogen addition is controlled by monitoring the ammonium nitrogen concentration of the activated sludge mixed liquor exiting the nitrification zone. The supplemental ammonium nitrogen causes an increase in the population of the nitrifying bacteria which results in an increased capacity for nitrification. The increased efficiency obtained will result in increased reliability of nitrification and lower effluent nitrogen concentrations.

Abstract: The tube settler of this invention is comprised of a plurality of long and narrow tubular passages inclined to the horizontal. The tubular passages have an approximate boomerang cross-sectional shape with the central apex directed upward. Rapid separation of settleable suspended material from a liquid is achieved because of the enforcement of laminar flow and a minimal settling distance within the tubular passages. Improved performance of this settler is attributed to enhanced conveyance of settled solids resulting from reduced upward liquid velocity in the vicinity of the countercurrent solids flow and the utilization of two solids discharge groves in each passageway.

Abstract: A nitrification process is disclosed wherein the population of the nitrifying bacteria in an activated sludge system may be increased by the addition of ammonium nitrogen to a return sludge reaeration zone. The increased nitrifying population results in increased reliability of nitrification and lower effluent ammonium nitrogen concentrations.