HANT process was developed in 1990’s targeting both nitrogen and phosphorus removal, which is the simplest BNR process known with only one internal mixed liquor recycle line. As shown in Fig. 1, deaeration tank is employed to reduce DO in mixed liquor before it is recycled to anoxic tank. Anaerobic tank is placed after anoxic tank, which is opposite from MLE process. Since denitrified mixed liquor proceeds to anaerobic tank, ORP in anaerobic tank can be readily kept low enough to encourage PAO to release phosphate. Other advantage is that the MLSS in anoxic tank is relatively high since the mixed liquor recycled to this tank is from membrane tank. Mixed liquor recycle rate (QRAS) ranges 2Q-4Q. TN and TP in the effluent are known to be 5-10 mg/L and 1-2 mg/L in municipal wastewater treatment without inorganic coagulant addition.
One drawback of this process is that the recycle rate to achieve optimum nitrogen removal cannot be independently decided since it is tied up with the recycle rate to maintain proper MLSS in membrane tank. For instance, reducing internal recycle rate to obtain a low enough ORP in anoxic and anaerobic tank is not always possible due to the solids accumulation in membrane tank. Therefore, the capability of managing the variations of influent characteristics season to season should be somewhat compromised.
Fig. 1. Process diagram of Hyundai Advanced Nutrient Treatment (HANT) process (Yoon, 2004).
© Seong Hoon Yoon