Implications of full-scale implementation of an anammox- based process as post-treatment of a municipal anaerobic sludge digester operated with co-digestion J. R. Vázquez-Padín, N. Morales, R. Gutiérrez, R. Fernández, F. Rogalla, J. P. Barrio, J. L. Campos, A. Mosquera-Corral and R. Méndez ABSTRACT The feasibility of treating the supernatant of a municipal sludge digester supplemented with co- substrates by means of an anammox-based process (ELAN ® ) was tested in Guillarei (NW of Spain). Ammonia concentration measured in the supernatant of the sludge digester varied in the range 800– 1,500 g N/m 3 due to the fact that the sludge produced in the plant was co-digested with wastes coming from surrounding food industries. Treating this supernatant in the ELAN ® reactor, nitrogen removal rates up to 1.1 kg N/(m 3 d) were reached in experiments run in a pilot plant reactor operated in batch mode. No nitrite oxidation was registered after several months of operation despite the average dissolved oxygen (DO) concentrations being 1.5 g O 2 /m 3 and the temperature reaching values as low as 18 W C. By keeping the DO set point at 1–2gO 2 /m 3 and tuning the hydraulic retention time, the stability of the process was guaranteed and the presence of co-substrates in the anaerobic digester did not affect negatively the operation of the autotrophic nitrogen removal process. Due to the success of the pilot plant experiment, an upscale of the process to full scale is proposed. Mass balances applied to Guillarei wastewater treatment plant revealed that in the main stream line the average denitrification rate calculated with the data of year 2011 was 226 kg N/d. Since the nitrogen removal efficiency is limited by the amount of readily biodegradable organic matter available to carry out denitrification in the water line, the implementation of an anammox-based process to treat the supernatant seems the best option to improve the effluent quality in terms of nitrogen content. The nitrogen removal rate in the sludge line would be 30 times higher than the one in the water line. The implementation of the process would improve the energetic balance and the nitrogen removal performance of the plant. J. R. Vázquez-Padín (corresponding author) N. Morales R. Gutiérrez R. Fernández F. Rogalla Aqualia (FCC Group), Guillarei WWTP, Tui, Spain E-mail: jvazquezp@fcc.es J. P. Barrio Departamento de Explotación de la EPOSH, Administración Hidráulica de Galicia, Santiago de Compostela, Spain J. L. Campos A. Mosquera-Corral R. Méndez University of Santiago de Compostela, Department of Chemical Engineering, School of Engineering, Lope Gomez de Marzoa s/n, E-15782 Santiago de Compostela, Spain Key words | anaerobic digester supernatant, anammox, co-digestion, granular biomass, pilot scale, reject water INTRODUCTION Anammox-based processes arose in the 1990s as an alterna- tive to remove nitrogen from anaerobic digester supernatants. Several strategies have been tested to perform autotrophic nitrogen removal at the University of Santiago de Compostela: (a) two-step systems (partial nitrification and anammox take place in different reactors, the first one under aerobic conditions and the second one under anoxic conditions) with anammox reactors based on, e.g. granular reactors (Dapena-Mora et al. ) or membrane bio- reactors (Trigo et al. ); and (b) one-step systems (where both processes take place in the same reactor) based on, e.g. biofilms developed on zeolites (Fernandez et al. ) or granular reactors (Vázquez-Padín et al. ; Figueroa et al. ). Sequencing batch reactors (SBRs) are widely used due to their flexibility in both two-step and in one-step systems. The main advantages presented by the SBR are its efficient retention of the biomass and that it permits a homo- geneous distribution of substrates and biomass aggregates inside the reactor. SBRs have been successfully applied 1151 © IWA Publishing 2014 Water Science & Technology | 69.6 | 2014 doi: 10.2166/wst.2013.795 Downloaded from https://iwaponline.com/wst/article-pdf/69/6/1151/472293/1151.pdf by guest on 03 June 2020