The short SRT nitrification process/flowsheet was developed to provide an inexpensive alternative for plants in the northern climates which need to upgrade their activated sludge process for year-round nitrification or nitrogen removal. In this process/flowsheet supplemental nitrifiers are added daily to the activated sludge process to replenish nitrifiers removed with the wasted activated sludge. The supplemental nitrifiers are grown in a separate small side-stream aeration tank using ammonia available in the digested sludge dewatering liquid or in the digester supernatant. Paper presents description of this flowsheet, the theoretical background and results of modeling. Modeling of this process/flowsheet showed that the addition of the supplemental nitrifiers allows the main stream activated sludge process to nitrify during low winter temperatures at very low SRT values. For example an SRT of 7 to 10 days at 10°C is required, instead of 13 to 18 days for conventional nitrification. Thus this process/flowsheet can provide nitrification in a substantially smaller aeration tank than required for the conventional nitrification.

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