214 ©IWA Publishing 2012 water Science & Technology | 65.2 | 2012 Optimization of municipal sludge and grease co-digestion using disintegration technologies L. Bouchy, A. Pérez, P. Camacho, P. Rubio, G. Silvestre, B. Fernández, R. Cano, M. Polanco and N. Diaz ABSTRACT Many drivers tend to foster the development of renewable energy production in wastewater treatment plants as many expectations rely upon energy recovery from sewage sludge, for example through biogas use. This paper is focused on the assessment of grease waste (GW) as an adequate substrate for co-digestion with municipal sludge, as it has a methane potential of 479-710 LCH4/kg VS, as well as the evaluation of disintegration technologies as a method to optimize the co-digestion process. With this objective three different pre-treatments have been selected for evaluation: thermal hydrolysis, ultrasound and enzymatic treatment. Results have shown that co-digestion processes without pre-treatment had a maximum increment of 128% of the volumetric methane productivity when GW addition was 23% inlet (at 20 days of HRT and with an OLR of 3.0 kg COD/m^d), compared with conventional digestion of sewage sludge alone. Concerning the application of the selected disintegration technologies, all pre-treatments showed improvements in terms of methane yield (51.8, 89.5 and 57.6% more for thermal hydrolysis, ultrasound and enzymatic treatment, respectively, compared with non-pretreated wastes), thermal hydrolysis of GW and secondary sludge being the best configuration as it improved the solubilization of the organic matter and the hydrodynamic characteristics of digestates. Key words | co-digestion, disintegration, enzymatic treatment, grease, sewage sludge, thermal hydrolysis, ultrasound L. Bouchy (con'esponding auttior) A. Pérez CETaqua, water Technology Centre, Av Diagonal, 211 08018 Barcelona, Spain E-mail: Iboxhy9cetaqua.com P. Camacho Suez Environnement-Cirsee, 38 rue du Président Wilson, 78230 Le Pecq, France p. Rubio Agbar, Av Diagonal, 211 08018 Barcelona, Spain G. Silvestre B. Fernandez GIRO Centre Tecnolôgic, Rambla Pompeu Fabra 1, 08100 Mollet del Vallès, Spain R. Cano M. Polanco Facultad de Ciencias, Universidad de valladoiid. Prado de la Magdalena S/N, 47011 valladoiid, Spain N. Diaz SENER ingenieria y Sistemas S,A. c/Provença, 392, 5a planta, 08025 Barcelona, Spain INTRODUCTION I I At present, many drivers tend to foster the development of renewable energy production in wastewater treatment plants (WWTPs): for example strong incentives are being implemented at the European and national levels, and the aim for independence regarding energy providers. The final ambidon is energy self-sufficiency. In WWTPs several types of waste are produced and are usually disposed of, disregarding their energy potential: this is the case for grease. Furthermore, grease is a waste pro- duced by many other industries and economic activities (biofuel-producing industry, food industry, restaurants,...) and therefore it is an interesting market opportunity. On the other hand, grease is one of the most studied substrates to be co-treated with sewage sludge, but some limits have been detected for its application, such as degradadon limits for high grease addidons or inhibidon problems due to their degradadon products (Davidsson et al. 2007; Luos- tarinen et al. 2009). Within this context, amongst several approaches to be considered, many expectadons rely upon energy recovery from sludge, for example through biogas use. To date biogas producdon and use has not been opdmized, as in many cases it was designed and operated as a means of stabilizing sludge, and not recovering energy. Anaerobic co-digesdon is reported to offer several benefits over conven- tional digestion, such as increased cost efficiency and increased degradadon of the treated substrates due to poss- ible synergisdc effects (Luostarinen et al. 2009). doi; 10.2166/wst.2012.660