Pilot-scale ELAN® process applied to treat primary settled urban wastewater at low temperature via partial nitritation-anammox processes

A single stage partial nitritation and anammox granular pilot scale reactor (600 L) was operated to treat primary settled sewage in an urban wastewater treatment plant. The fed wastewater contained low total nitrogen concentrations of 6–25 mg TN/L and the system operated without temperature control ranging from 18 to 12 °C. A control strategy, based on the pH value, was applied to stop the aeration supply. The pH set-point was fixed at 6.0 and allowed obtaining a total nitrogen removal efficiency approximately of 50% treating a load of 67 mg TN/(L·d) without the addition of any chemicals. Although nitrite oxidizing bacteria were present in the inoculated sludge, when the pH-based control was implemented (day 30) the ammonium oxidation was favored compared to the nitrite oxidation activity. Then, the system operated stable the rest of the operational period (days 30–94) despite the presence of organic matter in the wastewater and the high variability of nitrogen load and temperature during the operation. Nitrogen was autotrophically removed accomplishing the stringent discharge limits (10 mg TN/L) and nitrate concentrations in the effluent lower than 3 mg NO3−-N/L. Both biomass concentration and granules size increased during the operational period indicating the growth of the biomass inside the reactor and therefore the potential treatment capacity.Authors want to thank the Pioneer_STP (ID 199) project funded by the WaterWorks2014 Cofunded Call (Water JPI/Horizon 2020). This work was also funded by the Spanish Government through FISHPOL (CTQ2014-55021-R) and GRANDSEA (CTM2014-55397-JIN) projects and by Galician Government by the MEDRAR (IN852A 2016) project. The authors from the USC belong to CRETUS (AGRUP2015/02) and the Galician Competitive Research Group (GRC ED431C 2017/29). All these programs are co-funded by FEDER. This work was as well funded by the Chilean Government through the Project FONDECYT 1150285 and CONICYT/FONDAP/15130015S