Combined chemical and biological degradation of tannery wastewater by a periodic submerged filter (SBBR)

The paper reports on the results of an investigation aimed to evaluate the performances of an innovative tannery wastewater process based on the combining biological degradation, carried out in a sequencing batch biofilm reactor, with chemical oxidation, performed by ozone. The combined treatment was carried out at the laboratory scale on real primary effluent coming from a centralised plant treating the wastewater from a large tanning district in Northern Italy. SBBR performances with and without ozonation were compared resulting to be very satisfactory only in the latter instance where recorded COD, NH4–N and TSS average removals were 97%, 98% and 99.9%, respectively. Such efficiencies correspond to specific concentrations in treated effluent well below the limit values fixed by the in-force Italian regulations. Furthermore, it was proved that the combined process is characterised by a very low sludge production. In fact, the measured specific sludge production (0.03 kg TSS/kg CODremoved) resulted unexpectedly much more lower than the value reported for conventional biological systems (i.e., 0.3–0.5 kg TSS/kg CODremoved).