1 Pilot-scale ELAN ® process applied to treat primary 1 settled urban wastewater at low temperature via partial 2 nitritation-anammox processes 3 Alba Pedrouso a,* , Irati Aiartza a , Nicolás Morales b , Jose R. Vázquez-Padín b , Frank Rogalla b , Jose L. Campos c , Anuska Mosquera-Corral a and Ángeles Val del Río a , a Department of Chemical Engineering, School of Engineering, Universidade de Santiago de Compostela. E- 15705. Santiago de Compostela, Spain. E-mail: alba.pedrouso@usc.es; iratiaiartzam@gmail.com; anuska.mosquera@usc.es; mangeles.val@usc.es. b Aqualia,Guillarei WWTP, Camino de la Veiga s/n, E-36720 Tui, Spain. E-mail: nicolas.morales.pereira@fcc.es; jvazquez@fcc.es; Frogalla@fcc.es c Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Avda. Padre Hurtado 750, 2503500, Viña del Mar. Chile. E-mail: jluis.campos@uai.cl. * Corresponding author Abstract 4 A single stage partial nitritation and anammox granular pilot scale reactor (600 L) was 5 operated to treat primary settled sewage in an urban wastewater treatment plant. The fed 6 wastewater contained low total nitrogen concentrations of 6 - 25 mg TN/L and the 7 system operated without temperature control ranging from 18 to 12 ºC. A control 8 strategy, based on the pH value, was applied to stop the aeration supply. The pH set- 9 point was fixed at 6.0 and allowed obtaining a total nitrogen removal efficiency 10 approximately of 50% treating a load of 67 mg TN/(L·d) without the addition of any 11 chemicals. Although nitrite oxidizing bacteria were present in the inoculated sludge, 12 when the pH-based control was implemented (day 30) the ammonium oxidation was 13 favored compared to the nitrite oxidation activity. Then, the system operated stable the 14 rest of the operational period (days 30-94) despite the presence of organic matter in the 15 wastewater and the high variability of nitrogen load and temperature during the 16 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/