Evaluation of a Pilot Scale A/B Process Utilizing SND and Nitrite-Shunt With a Hydrocyclone for Improved Settleablilty

A pilot study to investigate the feasibility of converting Hampton Roads Sanitation District's (HRSD) Chesapeake-Elizabeth Wastewater Treatment Plant to an A/B process is currently underway. The A/B process is a two-sludge system utilizing a high rate activated sludge (HRAS) A-stage for carbon removal followed by a B-stage for biological nitrogen removal (BNR). By operating at very low DO and SRT (4-12 hours), the A-stage provides low cost carbon removal, with the reduced organic load resulting in lower volume requirements and aeration demand for the B-stage. To overcome carbon-limitation and ensure maximum denitrification, the pilot B-stage MLE has been equipped with an ammonia-based aeration control system designed to minimize aerobic heterotrophic COD oxidation as well as create conditions favorable for simultaneous nitrification-denitrification (SND) and nitrite shunt. The success of the aeration control system in achieving these objectives led to a modification of the MLE configuration. The new process, called NiDeMA (Nitritation-Denitritation through Modulating Aeration), is designed to enhance the SND and nitrite shunt afforded by the aeration control system. The NiDeMA process was able to sustain NOB suppression, with effluent total inorganic nitrogen (TIN) values in the range of 3-7 mg/L.