BACKGROUNDEven though the nitrification process is inhibited in the presence of sulfide and organic matter, few efforts have been reported to overcome this weakness. The present work has the goal of determining the effect of zeolite (2.5, 5, 10 and 15 g L-1) as an improver of the nitrification process in the presence of sulfide and organic matter in a batch system. RESULTSThe inhibitory effect of both sulfide and organic matter on the nitrification process was decreased by 53% when using zeolite, with the best results at a zeolite concentration of 15 g L-1. No total ammonia nitrogen (TAN) adsorption on the zeolite was observed under these conditions, with TAN removal taking place mainly by biological oxidation. Specific nitrate production rate increased by 37.73% compared with the control. Sulfide was oxidized chemically in all the assays, with sulfate as the main product, while COD reduction and VSS production were not affected by zeolite. CONCLUSIONSZeolite can be used to improve nitrification in batch systems in the presence of sulfur and organic matter, obtaining a faster TAN removal rate and higher specific nitrate production compared with the controls. (c) 2018 Society of Chemical Industry