Partial nitritation of nitrogen-rich refinery wastewater (sour water) with different Ci/N molar ratios

In this study, a SHARON reactor was used to treat synthetic and real ammonium-rich refinery wastewater (sour water) with different inorganic carbon to nitrogen (Ci/N) molar ratios, in order to evaluate its possible implementation downstream of a steam stripping unit in a double-stage SHARON-ANAMMOX or SHARON-heterotrophic denitritation process. A synthetic influent containing NH4-N (2,000 mg/L) was initially fed to promote biomass acclimation, then real sour water containing also organic substrate, cyanides, sulphides and phenols was supplied. With both synthetic and real wastewater, the applied Ci/N molar ratio was progressively increased from 1 to 2 and the SHARON reactor produced an effluent suitable for further treatment by autotrophic ANAMMOX or heterotrophic denitritation, respectively. Acute toxicity assessments based on the specific measurement of nitritation activity confirmed that biomass acclimation to the toxic substances contained in the real wastewater occurred successfully. Moreover, high removal of organic matter (73%) suggested the absence of any competition between heterotrophic and autotrophic microorganisms. Controlling influent Ci/N molar ratio was shown to represent a key operating strategy to properly regulate SHARON performance, depending on the chosen downstream treatment, proving its actual feasibility under harsh operating conditions and providing useful indications for its implementation at full scale.