Palatsi, J., Campos-Pozuelo, E., Torres, M., Porras, S., Flotats, X. (2005). Full-scale combination of anaerobic digestion and concentration by evaporation in Garrigues (Lleida, Spain): evaluation after 2 years of operation. In Sustainable Organic Waste Management for environmental Protection and Food Safety . Bernal, M.P., Moral, R., Clemente, R., Paredes, C. (Eds). ISBN: 84-689-0828-2. Volume II, pp 155-158. FULL-SCALE COMBINATION OF ANAEROBIC DIGESTION AND CONCENTRATION BY EVAPORATION IN GARRIGUES (LLEIDA, SPAIN): EVALUATION AFTER 2 YEARS OF OPERATION J. Palatsi 1 , E.Campos-Pozuelo 1 , M. Torres 2 , S. Porras 1 and X. Flotats 1 1 LEA-Centre UdL-IRTA. Rovira Roure 191, 25198 Lleida-Spain. 2 TRACJUSA treatment plant, Laboratory Dept., Camí de Juneda s/n, Juneda, Spain ABSTRACT Evaporation process is a reliable strategy to manage pig slurry, removing water and recovering nutrients by concentration. The described treatment plant, TRACJUSA, applies the VALPUREN TM process, which is based on the combination of anaerobic digestion and evaporation. The benefits of this combined process have been previously reported at laboratory scale. This paper studies the influence of anaerobic digestion on the general process after two years of full-scale operation. Biogas yield is highly correlated with the OLR of pig slurry and with the COD/VS ratio, which is a function of slurry characteristics and farm management practices. The key of the evaporation process is to concentrate nutrients what allows to obtain a high-quality condensate that can be reused. The influence of VFA content in the effluent of anaerobic digestion was studied together with the influence of acidification step, which occurs before evaporation. It can be concluded that farm management, stable anaerobic digestion, and acidification step prior evaporation, are the main factors that influence the successful performance of a centralized treatment plant of this kind. Keywords. Anaerobic digestion; pig slurry; post-treatment; evaporation. INTRODUCTION The northern part of Garrigues county (Lleida, Spain) presents a large nitrogen surplus from pig slurry. Redistribution of this slurry is limited by transport and spreading costs, due to its high water content and relatively low nutrient concentration. Based on waste management planning, it was concluded that centralized treatment plants were a need. The technology applied was the VALPUREN TM process (P9900761), which involves anaerobic digestion followed by phase separation, acidification and water evaporation of the liquid fraction, and solid fraction drying. The plant started operating in 2001 and currently serves more than 90 farms. The flow diagram of the plant is described in Burton and Turner (2003). Anaerobic digestion prior to evaporation presents several advantages as previously reported by Bonmatí and Flotats (2003): (1) to provide a part of the energy required, (2) to remove volatile organic matter, providing evaporation free condensates, or almost free, of organic matter. Another key process is the fall in pH in the acidification step prior to evaporation that ensures a low concentration of free ammonia in slurry, and prevents its volatilisation. The aims of this paper are: (1) to evaluate the combination of anaerobic digestion- evaporation processes at industrial plant scale, (2) to evaluate the influence of the plant inflow characteristics on the anaerobic digestion process, and (3) to evaluate the anaerobic digestion process of the framework plant’s general operation.