The start-up of an anammox reactor as the second step for the treatment of ammonium rich refinery (IGCC) wastewater with high C org /N ratio

In this study, the refinery wastewater produced by the integrated gasification combined cycle (IGCC) and pre-treated in a lab-scale partial nitritation chemostat was fed to a granular anammox reactor, in order to evaluate its feasibility as the final treatment step. The IGCC wastewater was characterized by high NH4-N concentration (540±82 mg L-1), high organic carbon to nitrogen ratio (Corg/N), and by the presence of toxic substances. A conservative exponential law was adopted to progressively replace the synthetic influent with the pre-treated IGCC wastewater, in order to avoid any stressful conditions which could hinder the process. An increase in specific anammox activity (SAA) up to 0.104 gNO2-N gVSS-1 d-1 was initially observed, suggesting that stimulation may occur if pre-treated IGCC wastewater dilution is sufficiently high. A system malfunction caused a worsening of process performance, which was partially restored: when only pre-treated IGCC wastewater was fed, the nitrogen removal efficiency and SAA were 71±3% and 0.045±0.002 gNO2-N gVSS-1 d-1, respectively, and the removal of organic matter due to denitrification was negligible. As to physical/morphological properties of anammox granules, they did not change significantly during the whole experimental campaign. Results showed that the anammox process can be successfully applied to treat complex industrial wastewaters with high Corg/N ratio, if a conservative start-up strategy is adopted and the preliminary partial nitritation step guarantees an efficient removal of readily degradable organic matter.