SBBGR technology for minimising excess sludge production in biological processes Claudio Di Iaconi a, *, Marco De Sanctis b , Simona Rossetti b , Roberto Ramadori b a Istituto di Ricerca Sulle Acque C.N.R., Via F. De Blasio 5, 70123 Bari, Italy b Istituto di Ricerca Sulle Acque C.N.R., Via Salaria Km 29300, 00016 Monterotondo, Italy article info Article history: Received 12 May 2009 Received in revised form 24 November 2009 Accepted 5 December 2009 Available online 11 January 2010 Keywords: Municipal wastewater treatment Periodic biofilter Sludge production Granular biomass FISH analysis abstract This paper reports the results of an investigation aimed at evaluating the performance of an innovative technology (SBBGR system – Sequencing Batch Biofilter Granular Reactor), characterised by a low sludge production, for treating municipal wastewater at demon- strative scale. The results have shown that even at the maximum investigated organic load (i.e., 2.5 kg COD/m 3 d), the plant removed 80% of COD, total suspended solids and nitrogen content with relative residual concentrations lower than the Italian limits for discharge into soil. The process was characterised by a very low sludge production (i.e., 0.12–0.14 kg TSS/kg COD removed ) ascribable to the high sludge age in the system (qc >120 d). Molecular in situ detection methods and microscopy staining procedures were employed in combination with the traditional measurements (oxygen uptake rate and total protein content) to evaluate both the microbial activity and composition, and the structure of the biomass. A stable presence of active bacterial populations (mainly Proteobacteria) was found within compact and dense aggregates. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction It is a well established fact that the heart of a wastewater treatment plant is its biological process. Excess sludge produced in this process (roughly 50% of influent organic load) must be treated and disposed of, and may account for as much as 60% of total plant operating costs (Horan, 1990). In Europe, not only has sludge production continuously increased over recent decades (from 5.5 million tonnes dry solids in 1992 to 8 million in 1998 and 10 million in 2007; Ginestet, 2007; Laturnus et al., 2007) but so also have disposal costs (now estimated at between 350 and 750 Euros per tonne of dry solids; Ginestet, 2007). Unfortunately, these figures are expected to increase further as a result of progressively more stringent effluent regulation criteria together with the growing number of wastewater treatment plants. Therefore, in the near future, reducing excess sludge production will be one of the most challenging tasks involved in wastewater treatment. In the past, different strategies have been applied for reducing the production of excess biomass in aerobic biological treatment (Canales et al., 1994; Chen et al., 2002; Lee and Welander, 1996; Low and Chase, 1999; Yasui and Shibata, 1994; Ratsak et al., 1994). Most of these strategies attempt to shift the metabolism of organic pollutants from an anabolic to a cata- bolic pathway. An interesting strategy that goes in this direc- tion is the enhancing of biomass retention. In fact, it is widely accepted that net biomass growth rate is equal to the difference between growth due to substrate consumption, via the true yield factor (Y ), and decay due to endogenous metabolism, death, predation and lysis (b), via the biomass concentration (X ). Thus, the larger the biomass concentration, the smaller * Corresponding author. Tel.: þ39 0805820511. E-mail address: claudio.diiaconi@ba.irsa.cnr.it (C. Di Iaconi). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 44 (2010) 1825–1832 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.12.007