The main source of ammonia in sewage originates from human urine, which typically contributes around 80% of the total nitrogen with only 1% of the total sewage volume. Therefore, decentralized treatment of source-separated urine could be a potential solution to remove nitrogen more efficiently through onsite urine nitrification and in-sewer denitrification than the centralized biological nitrogen removal (BNR) treatment, in a densely populated city like Hong Kong. Achieving effective nitrification of urine at high loading rate with high total ammonia nitrogen (TAN) concentration is the key issue to realize the concept above. Therefore, in this study, a lab-scale hydrostatically pressurized nitrifying bioreactor for source-separated urine nitrification was developed under 7 bars...[ Read more ]

The main source of ammonia in sewage originates from human urine, which typically contributes around 80% of the total nitrogen with only 1% of the total sewage volume. Therefore, decentralized treatment of source-separated urine could be a potential solution to remove nitrogen more efficiently through onsite urine nitrification and in-sewer denitrification than the centralized biological nitrogen removal (BNR) treatment, in a densely populated city like Hong Kong. Achieving effective nitrification of urine at high loading rate with high total ammonia nitrogen (TAN) concentration is the key issue to realize the concept above. Therefore, in this study, a lab-scale hydrostatically pressurized nitrifying bioreactor for source-separated urine nitrification was developed under 7 bars of pressure, which is to simulate natural pressurization condition if such a reactor is to be attached to the façade of a high-rise building, typically 200-400 m high, in Hong Kong. Such a high pressure may result in super-saturation of oxygen in the liquid phase, which could efficiently promote nitrification with high strength of ammonia in the influent.

Incomplete ammonia oxidation was observed with a nitrification potential of 99.7% of the influent ammonia while the daily loading rate at around 1.0 kg-TN m^-3d^-1 was achieved in this novel pressurized bioreactor. Besides, pressure promoted the formation of nitrifying granules providing an efficient liquid-solid separation for space saving. The proposed technology would provide a possible compact onsite urine nitrification system for potential application in Hong Kong.

Keywords: pressurized bioreactor; source-separated urine; nitrification; nitrifying granule.