Tannery wastewater treatment by sequencing batch biofilm reactor

The paper reports the results of an investigation aimed to evaluate the performances of an innovative process for treating tannery wastewater. In such a process biological degradation, carried out in a sequencing batch biofilm reactor (SBBR), is combined with chemical oxidation by ozone. The treatment was carried out at laboratory scale on a real primary effluent coming from a centralized plant treating the wastewater of a large tannery district in Northern Italy. SBBR performances without and with ozonation were compared with very satisfactory results particularly in the latter instance when the recorded COD, TKN, and TSS average removals, (96%), (92%), and (98%), respectively, permitted to achieve the fixed limits enforced by Italian regulation without needing any additional polishing step. With or without ozonation, the process that resulted was characterized by a specific sludge production (0.1 kgVSS/kg CODremoved) significantly lower than the values featuring conventional biological systems (i.e., 0.3-0.5 VSS/kg CODremoved). Moreover, as in the reactor the biomass density results were very high, i.e., 98 gVSS/Lsludge, it was possible to achieve and maintain biomass concentration as high as 20 gVSS/L.