Dairy wastewater treatment in a moving bed biofilm reactor G. Andreottola, P. Foladori, M. Ragazzi and R. Villa Dept. Civil and Environmental Engineering, University of Trento, Via Mesiano, 77, 38050 Trento, Italy (E- mail: lisa@ing.unitn.it) Abstract Dairy raw wastewater is characterised by high concentrations and fluctuations of organic matter and nutrient loads related to the discontinuity in the cheese production cycle and machinery washing. The applicability of a Moving Bed Biofilm Reactor (MBBR) filled with FLOCOR-RMP ® plastic media to the treatment of dairy wastewater was evaluated in a pilot-plant. COD fractionation of influent wastewater, MBBR performance on COD and nutrient removal were investigated. A removal efficiency of total COD over 80% was obtained with an applied load up to 52.7 gCOD m –2 d –1 (corresponding to 5 kgCOD m –3 d –1 ). The COD removal kinetics for the MBBR system was assessed. The order of the kinetics resulted very close to half-order in the case of a biofilm partially penetrated by the substrate. The nitrogen removal efficiency varied widely between 13.3 and 96.2% due to the bacterial synthesis requirement. The application of a MBBR system to dairy wastewater treatment may be appropriate when upgrading overloaded activated sludge plants or in order to minimise reactor volumes in a pre-treatment. Keywords Biofilm process; dairy wastewater; moving bed biofilm reactor; organic carbon removal Introduction Wastewater stream effluent from dairy factories is characterised by high organic loads and strong fluctuations of flow rates related to discontinuity in the cheese production cycle. Furthermore, the use of nitric acid or phosphoric acid for cleaning and washing machinery and storage tanks can have a relevant influence on discharged levels of nutrients. These aspects together increase the complexity of dairy wastewater treatment, especially in relation to the stringent limits recently introduced for nitrogen and phosphorus discharge into surface water bodies. Physico-chemical characterisation of dairy wastewater and the alternatives for its treatment have been outlined by many authors on both pilot-scale and full-scale plants with the aim of finding technologies with high removal efficiency and easy management. Conventional activated sludge plants, aerobic or anaerobic SBR systems (Hung 1984; Hamoda and Al-Awadi, 1995), UASB reactors (Öztürk et al., 1993) and biofilm systems as RBC (Surampalli and Baumann, 1986) are cited as the most applied systems. Although activated sludge plants have been widely applied in the treatment of dairy wastewater, they are related to periodical occurrence of bulking and foaming as referred to by several authors in recent decades (Radick, 1981; Rensink and Donker, 1990). In order to minimise bulking problems and to simplify plant management, biofilm systems, and in particular the MBBR (Moving Bed Biofilm Reactor) configuration, represent a promising option for the treat- ment of dairy wastewater rather than the conventional activated sludge plants (Rusten et al., 1992). Since biomass grows on plastic media, the suspended solid load reaching the final settler is lower than the one in the activated sludge systems, as it is made up only of biomass detached from the carrier elements. In the case of a high SVI it is possible to improve settling through polyelectrolyte dosage without undesired effects because sludge does not have to be recycled. Compared to conventional biofilm systems (such as RBC or trickling filters), MBBR offers larger specific surface for the attachment of biomass and it Water Science and Technology Vol 45 No 12 pp 321–328 © IWA Publishing 2002 321 Downloaded from http://iwaponline.com/wst/article-pdf/45/12/321/424865/321.pdf by guest on 21 April 2021