THERMOPHILIC ANAEROBIC CO-DIGESTION OF AGRO-WASTE AND WASTE ACTIVATED SLUDGE: INFLUENCE OF THE ORGANIC LOADING RATE. Pavan P. 1, Bolzonella D. 2, Mata-Alvarez J. 3, Cecchi F. 2 1 Department of Environmental Sciences, University of Venice. Calle Larga S. Marta 2137, Venice, Italy. 2 Department of Science and Technology, University of Verona. Strada Le Grazie, Verona, Italy. 3 Department of Chemical Engineering. University of Barcelona. Martí i Franquès 1, plta.6; Barcelona This poster deals with the thermophilic anaerobic co-digestion of solid agro-waste (mainly fruit and vegetable residuals from markets) and waste activated sludge originated from the biological treatment of municipal wastewater. A pilot scale digestor of 200 l working volume was used. Treating only wasted sludge, the initial Organic Loading Rate (OLR) was 0,7 kgTVS/m 3 d; then it was increased up to 4 and then to 6 kgTVS/m 3. Increasing the amount of OFMSW in the feeding, the gas production rate (GPR) raised from 0.12 to 3,12 m 3 /m 3 d and the Specific Gas Production (SGP) from 0.16 to 0.51 m 3 /kgTVS. Regarding the process behaviour, its stability was showed also in critical operatif conditions. Considering the option of retrofitting the anaerobic digesters of the existing sludge line in WWTPs, the obtained data clearly show the process feasibility. The main aim of the project is to firmly establish biogas technology as an economically attractive energy production process for both on and off-site use. In particular this work investigates the thermophilic co-digestion of WAS and market waste, also in order to evaluate its feasibilty on existing WWPT so to exploit the already avaiable structures existing in wastewater treatment plants operating within the UE. Abstract The aim of the research project The work carried out is part of a research considered in the VI framework program financially supported by the European Union, the “Cropgen” project (contract n. SES6-CT ). Experimental The used digester was a CSTR type, fed semicontinuously once a day and maintained at 55 ± 1 °C. The substrates were acquired daily from the wastewater treatment plant of Treviso (sludge) and from the municipal collection from fruit and vegetables markets Table 2 Substrates characteristics. Table 3. Main results of the research. Results While GPR shows a linear trends increasing OLR, SGP reached a plateau when OLR approached to 6 kgTVS/m 3 d. This was supposed to be the process limit for these conditions Table 1. Operational conditions used in the research. Biogas production (GPR) increase linearly with OLR, while the specific production reached a plateau when OLR approached to 6 kgTVS/m 3 d. This could be the process limit for these conditions; The OLR range from 2 to 6 kgTVS/m 3 d was investigated, observing a completely stable situation in all the conditions studied. pH and alkalinity values were always in typical ranges. The addition of increasing amount of waste in the feed lead to an improvement in buffer capacity of the digester (from 2700 to 7000 mg CaCO 3 /l); The comparison with mesophilic process shows that, at very low OLR (<1 kgTVS/m 3 d), there are no big difference between the two processes. However, things may be different when higher loading rate are applied. Other experimental work has to be done to investigate this aspect. Only during the last experimental run, the higher OLR caused a slight decrease of pH. Anyway the process seems to be not inhibited. Conclusion The alkalinity and VFA trends showed not problematical values for the process behaviour. The main results of this work are: