Anaerobic Co-Digestion of olive oil wastewater with municipal solid and liquid waste: An Urban-Industrial symbiosis concept

The aim of this research was to explore the possibility for joint waste management from industry and municipality (Industrial-Urban Symbiosis (I-US)) through material and energy exchanges between municipality and industry and to improve the efficiency and environmental performance of biofuel production via such a combined waste valorization. In particular, the production of methane from three waste streams (Olive Industry Wastewater (OIWW), Liquid Fraction of Food Waste (LFFW) and Municipal Wastewater (MWW)), through anaerobic digestion under mesophilic conditions was carried out using a 40L CSTR. The CSTR was started up with synthetic wastewater and in the sequel the feed was replaced by a real wastewater mixture. A feed composition of 91.7% MWW, 3.3% LFFW, 5% OIWW was found to be appropriate as higher percentages of OIWW proved to be detrimental to the operation of the reactor. The mixture fed to the reactor had a COD concentration of approximately 10,000 g/L and NaHCO3 was added in order to maintain the reactor pH at approximately 7.5. The HRT was initially 40d and was progressively reduced to 30d and 20d (feed flow rate of 1, 1.34 and 2 L/d respectively). The VSS of the reactor stabilized at an average of 3.4 g/L. The biogas production rate stabilized at approximately 6.3 L/d, very close to the theoretically predicted based on COD removal and the methane content was 79%. A soluble COD removal of approximately 98% was attained.