Biodegradation of a high-strength wastewater containing a mixture of ammonium, aromatic compounds and salts with simultaneous nitritation in an aerobic granular reactor

• Nitritation and biodegradation of aromatics were achieved in a granular reactor.
• Comamonas and Nitrosomonas were the main genera in the aerobic granules.
• Stable mature aerobic granules were maintained 390 days in a continuous reactor.
• Aerobic granular reactors are a promising technology for complex wastewaters.

Long-term operation (390 days) of a continuous airlift reactor with aerobic granular biomass was successfully applied to treat a highly complex wastewater composed of: ammonium (1000 mg N L−1), o-cresol (100 mg L−1), phenol (100 mg L−1), quinoline (50 mg L−1) and salts (16 g salts L−1). High nitrogen loading rate (1.1 g N L−1 d−1) and organic loading rate of 0.7 (g COD L−1 d−1) were achieved for the simultaneous nitritation and complete biodegradation of the aromatic compounds. The successful operation of the granular airlift reactor can be related to (i) the growth of specialized microorganisms in the aerobic granules and (ii) the continuous feeding regime. Aerobic granules were maintained stable in spite of the high salinity conditions. Dissolved oxygen (DO) concentration and DO/ammonium concentrations ratio were the key parameters to select a suitable effluent for anammox or heterotrophic denitrification via nitrite. Besides, nitrous oxide emissions were related to the DO concentration in the reactor.

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