The aim of the research was to study the treatability of tannery wastewater by a sequencing batch reactor (SBR) compared with a continuous flow full scale reactor. The experimental work presented in this paper was carried out on a laboratory scale anoxic-aerobic SBR fed with tannery wastewater coming from a full scale continuous flow treatment plant located in S. Miniato (Pisa, Italy). After a long acclimation period, a complete and stable nitrification has been developed. The denitrification was always performed without any additional carbon source with good results when influent COD/TKN ratio was higher than 8 and with a higher rate compared to that obtained in the continuous plant. When high effluent nitrate occurred, it was due only to stoichiometric (not kinetic) limitations. The organic substrate removal occurred mainly during the anoxic period and a high effluent COD (refractory) was often present at the end of the process. This research has shown the suitability of the industrial wastewater (particularly tannery wastewater) treatment by SBR because of its several advantages compared to the continuous reactors: i.e. a higher versatility and the possibility to work with higher loads (smaller volumes), by selecting, through the cyclic concentration gradients, a biomass resistant to the presence of inhibiting substances (often encountered in industrial wastewaters).

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