Water Research 36 (2002) 2205–2214 Combined chemical and biological degradation of tannery wastewater by a periodic submerged filter (SBBR) C. Di Iaconi a, *, A. Lopez a , R. Ramadori a , A.C. Di Pinto b , R. Passino b a Instituto di Ricerca Sulle Acque C.N.R.-Via F. De Blasio 5, 70123 Bari, Italy b Instituto di Ricerca Sulle Acque C.N.R.-Via Reno 1, 00198 Roma, Italy Received 1 February 2001; accepted 12 October 2001 Abstract 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, NH 4 –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 COD removed ) resulted unexpectedly much more lower than the value reported for conventional biological systems (i.e., 0.3–0.5kg TSS/kg COD removed ). r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Tannery wastewater; Integrated processes; SBBR; Ozonation 1. Introduction Tannery productive cycle includes a series of chemical treatments using a large number of chemicals (i.e., surfactants, acid and metallorganic dyes, natural or synthetic tanning agents sulphonated oils, salts, etc.) to transform animal skin into an unalterable and impu- trescible product [1]. Considering the large amount and the low biodegrad- ability of such chemicals, tannery wastewater treatment represents a serious environmental and technological problem. In fact, after conventional treatment (i.e., chromium precipitation-primary sedimentation-bio- logical oxidation-secondary sedimentation), effluents still do not meet the required limits at least for some parameters such as COD, salinity, ammonia and surfactants [2,3]. Referring to COD, at tannery wastewater treatment facilities, the concentration of biorefractory organics is usually reduced either by adding powder-activated carbon directly into the biological reactor or by expensive tertiary treatments among which the most frequent is the Fenton process. The main steps of such a process are: addition of iron salts (FeSO 4 or FeCl 2 ), wastewater acidification (H 2 SO 4 ), oxidation (H 2 O 2 ) and pH neutralisation [Ca(OH) 2 ]. The Fenton process is also effective for removing surfactants with efficiencies around 90% [2,4]. Large production of chemical sludge during the pH neutralisation step (about 1 kg TSS/m 3 ), significant consumption of chemicals [FeSO 4 or FeCl 2 , H 2 SO 4 ,H 2 O 2, Ca(OH) 2 ], corrosion problems due to the necessary acidic conditions and iron concentration in treated effluent often exceeding the limit of 2mg Fe n+ /L are the major drawbacks of such a process [5,6]. In some *Corresponding author. E-mail address: irsacd41@area.area.ba.cnr.it (C. Di Iaconi). 0043-1354/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0043-1354(01)00445-6