Eliminació autotròfica en línia principal (Anmmox mainstream)

Abstract

Mainstream autotrophic Anammox nitrogen removal from wastewaters combined with a partial nitritation process (PN-A) is a system that presents several advantages. Despite its efficiency has been studied mainly for currents with high ammonium concentration and high temperatures, nowadays it is also being studied for urban wastewaters treatment, which are at environmental temperature and have low ammonium concentration. In this study PN-A process is analysed in one-stage piston flow reactor treating synthetic water at environmental temperature and with a NH4+ influent concentration of 75 mg-N/L. In order to enable Anammox to oxidize nitrogen anaerobically it needs nitrite as electron acceptor, which is formed during partial nitritation by aerobic ammonium oxidizing bacteria (AOB). Both sequential reactions are carried in biomass granules that have an aerobic environment in the external part and anaerobic in the internal. For this reason, aeration is not homogeneous all along the reactor, hence different zones with or without oxygen are differentiated to enchance one process or another. A tracking of the process is done analysing important parameters for the development of the system, which are pH, temperature, dissolved oxygen and inorganic carbon concentration, alkalinity, conductivity and salinity. In addition, nitrogen species concentrations in the influent and the effluent are analysed to describe nitrogen loading rate (NLR), nitrogen removal rate (NRR) and NO3-produced/NH4-removed ratio, in order to study PN-A process efficiency. With regard to the process efficiency throughout the study, positive results has not been achieved due to nitrite oxidizing bacteria (NOB). NOB presence is confirmed by the biomass activity tests depending on its diameter. Granules with <500 μm diameter are more abundant and present AOB and NOB activity, whereas Anammox activity is not detected since they are inhibited by oxygen that reach all the granule due to oxygen diffusion. However, in granules with >500 μm diameter AOB and Anammox activity is detected because oxygen diffusion only reaches to a maximum of 200 μm