Post-treatment of effluents from anaerobic digesters by the Anammox process

The application of the Anammox process was studied under two different approaches for the post-treatment of anaerobic digester supernatants: two independent units, the combined SHARON-Anammox system, performed in a chemostate and a SBR, respectively, and, a single unit system composed by an air pulsing SBR to carry out the CANON process. The technology based on the combination of the SHARON-Anammox process was used to treat the effluent of an anaerobic digester from a fish canning industry. The presence of organic matter in the influent caused fluctuations in the efficiency of the SHARON unit and an optimal nitrite to ammonium ratio was not achieved in this system to feed the Anammox reactor. Nevertheless an overall percentage of nitrogen removal of 40-80% was obtained when the Anammox reactor operated at nitrite limited conditions. In those periods when the effluent from the SHARON unit contained a NO ₂^--N/NH₄⁺-N molar ratio higher than 1.3 the Anammox process lost its stability due to nitrite accumulation. The effluent from an anaerobic digester placed at a WWTP was treated by a CANON system operated at room temperature (20-24°C). This system was developed from a nitrifying air pulsing reactor working at limiting dissolved oxygen conditions which was inoculated with Anammox biomass. A quick start-up of the system was observed and the reactor reached a nitrogen removal rate of 0.25gN/(Ld) 40 days after inoculation. The maximum nitrogen removal rate reached 0.5gN/(Ld). These results indicate the feasibility of the treatment of effluents from psychrophilic anaerobic digesters using the Anammox process.