Proceedings

Abstract The Anammox® process is a biological treatment system for removal of ammoniacal nitrogen. The Anammox® process has been successfully applied on dewatering liquors from biosolids digesters and nutrient rich anaerobically treated industrial effluents (e.g. fermentation industry, food industry). Since the start-up of world’s first full scale Anammox® reactor in 2002 at Dokhaven WWTP in Rotterdam, 19 full-scale Anammox® plants have been built or are under construction representing a total installed capacity of over 65,000 kg N per day. The Anammox® process is characterised by removal of ammoniacal nitrogen without the need of an organic carbon source (COD). The Anammox® process is a continuously fed biological process using granular biomass. Long term operations have shown stable process performance of full-scale Anammox® reactors achieving ammoniacal nitrogen removal in excess of 90 % at various loading rates. Design considerations and long term operational experience are presented and discussed.

Keywords: Anammox, ammonia removal, anaerobic digestion, nutrient recovery, struvite, liquor treatment

Introduction In recent years there has been an increasing interest in anaerobic digestion of sewage sludge, organic solids and industrial effluents. Although anaerobic digestion is an effective method to remove organic substances (COD), the removal of nutrients (N, P) is very limited. As a result, liquors derived from anaerobic processes have reduced COD content, but often still contain relatively high concentrations of ammoniacal nitrogen (NH4 + + NH3) and ortho-phosphate (PO4).

Although small in volume sludge dewatering liquors of a sewage treatment work can represent up to 30% of the nitrogen and phosphorus load of the overall municipal wastewater treatment plant (WWTP). Returning untreated sludge dewatering liquors with high concentrations of ammonium (500-1500 mg/l) directly into the main wastewater treatment plant can adversely affect the overall capacity of the works as it will require a large amount of aeration capacity and decrease the sludge age. Especially when the WWTP’s capacity is limited this would require additional aeration capacity and additional aeration basin volumes (Driessen and Reitsma, 2011). Reduction of the nitrogen load in sludge dewatering liquors becomes even more important in case the main WWTP applies biological phosphorus removal (Shorrock et al, 2012).

Enhanced hydrolysis plants aim at extended degradation of biosolids, resulting in an increased release of nutrients. When biosolids are treated in thermal hydrolysis plants (THP), sludge dewatering liquors with elevated concentrations of ammonium (2000-3000 mg N/l) and phosphorus (150-350 mg P/l) are produced. Effective removal or recovery of nutrients from sludge dewatering liquors from anaerobic digesters involving THP treatment is crucial.

Dedicated separate treatment of sludge dewatering liquors can overcome the negative effects of returning untreated nutrient rich liquors to the main wastewater treatment plant. The Anammox® process is an effective way to remove ammoniacal nitrogen and phosphorus recovery is possible by precipitation of magnesium-ammonium-phosphate (MAP) by so called PhospaqTM reactors as demonstrated in full scale installations (Driessen et al, 2009). These processes can also effectively be applied on digestate dewatering liquors from organic solids digesters and nutrient-rich industrial effluents (e.g. food industry).