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A pilot study was conducted at the Alexandria Sanitation Authority Wastewater Treatment Facility (ASA-AWTF) to understand the DEamMONification (DEMON) process control and performance. The DEMON process removes nitrogen using two biological processes. The first step, referred to as nitritation, is the biological conversion of ammonia to nitrite by ammonia oxidizing bacteria (AOBs). The second step is the biological conversion of ammonia and nitrite to nitrogen gas by anaerobic ammonia oxidation, referred to as the anammox process. The two steps in the DEMON process are achieved by carefully controlling the pH and dissolved oxygen (DO) concentration in the reactor in order to inhibit the nitrite oxidizing bacteria (NOB) and suppress the conversion of nitrite into nitrate while providing an optimal environment for the anammox organisms to thrive. In comparison to a conventional nitrification/denitrification process, the DEMON process is capable of achieving nitrogen removal using 60% less oxygen and 100% less COD which translates to reduced operating costs for chemicals and energy.

In this study the DEMON process was used to remove nitrogen from a high-ammonia recycle stream generated by dewatering anaerobically digested sludge. The study results show that the DEMON process can effectively treat centrate in a sequencing batch reactor (SBR) with a loading of between 0.50 – 0.65 kgN/m3/d and an HRT of 1.7 d without any chemical addition. Average removal efficiencies of 85% for ammonia and 63% for nitrogen were demonstrated under these loading and HRT conditions.

The stability of the DEMON process depended on controlling the feed rate, the pH and the DO in the reactor to control the nitritation and anammox reactions. The nitritation step of the DEMON process showed inhibition symptoms, leading to process instability. The nitritation inhibition was unique to ASA system as compared to a similar system in Strass, Austria. This inhibition was overcome purely by process control, through adjustment of dissolved oxygen. Operating at higher DO concentrations however had the effect of lowering the nitrogen removal efficiency of the system. The relatively brief demonstration study demonstrated the resilience of the anammox organisms when controlled by the Demon process control system.

Document Type: Research Article


Publication date: 2008-01-01

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