Nitrogen removal in anaerobic digestion liquors using the One-Step Anammox process

Driessen, W., Reitsma, G. and Hülsen, T., Paques bv, The Netherlands



There is an increasing interest in anaerobic digestion of sewage sludge, organic waste and industrial effluents. Dewatering liquors and effluents derived from anaerobic digestion processes contain significant amounts of nutrients. Although small in volume sludge dewatering liquors can represent up to 30% of the nitrogen and phosphorous load on the overall wastewater treatment works. Dedicated separate treatment of these sludge liquors by the so-called one-step ANAMMOX® process and PHOSPAQ® (struvite) process reduce energy consumption and allow nutrient recovery. These technologies can also effectively be applied on digestates from organics waste digesters and nutrient rich effluent streams from industry (e.g. fermentation industry, food industry). Long term operations have shown stable process performance of the One-Step Anammox® process achieving ammonia removal in excess of 90 %.

Key words: 

Anammox, Ammonia Removal, Sludge Liquor, Partial Nitritation, Anaerobic Digestion, Phospaq


The Anammox Conversion

The anammox (anaerobic ammonium oxidation) conversion is an elegant short cut in the natural nitrogen cycle (see figure 1 – left). The anammox process is characterized by removing ammonia (NH4+) using nitrite (NO2) rather than nitrate (NO3) requiring less oxygen (O2). The anammox conversion was discovered at a pilot plant of yeast and antibiotics producing company Gist Brocades (now DSM) in Delft, The Netherlands. The anammox process is a fully autotrophic process, meaning it does not require any carbon source. The anammox process was developed in partnership with the Technical University of Delft and the University of Nijmegen in The Netherlands.

The One-Step Anammox® Process

Paques bv from The Netherlands has developed the so called one-step-Anammox® reactor in which partial nitritation (equation 1) and the anammox reaction (equation 2) occurs simultaneously in one single process unit. It should be appreciated that in the one-step Anammox® only partial (50 %) nitritation is required to oxidized ammonia to nitrite to allow the reaction with the residual 50 % of ammonia (anammox reaction) to occur. The overall simplified conversions occurring in a one-step-Anammox® reactor can be described as follows:

Partial-Nitritation    :       NH3        +          O2             →           NO2                                                                                      (1)

Anammox                  :       NO2       +          NH4+         →           N2                                                                           (2)

Overall reaction        :       NH3       +      0.85O2          →           0.11NO3   +   0.44N2  +  0.14H+  +  1.43H2O (3)

Figure 1 schematically presents the anammox reaction as part of the nitrogen cycle (derived from Jetten et al, 1997) and the one-step Anammox® process combining partial nitritation with the anammox process.

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