A dynamic model of an anaerobic biofilm reactor for wastewater treatment applications

MUSSATI, MIGUEL; AGUIRRE, PÍO; SCENNA, NICOLÁS; FUENTES MORA, MAUREN

Santiago de Chile, Chile

Simposio; 12th Internacional Biotechnology Symposium and Exhibition (Biotechnology 2004); 2004

CONICYT, Chile

The former biological methods developed to clean wastewaters were the aerobic processes. However, these systems demand high-energy consumption for aeration and pumping and generate a large amount of waste sludge for disposal. The increasing energy prices and decreasing available land for sludge disposal have motivated the use of anaerobic processes, which also provide methane (biogas) as a valuable product. In addition, anaerobic microorganisms are quite resistant to toxics. However, they exhibit some disadvantages. The slow cellular growth rate is the most important one. This fact has imposed to operate the conventional anaerobic systems at long hydraulic retention time to achieve relatively high cleaning efficiency. However, this disadvantage has been overcome by accumulating large amount of active biomass within the bioreactor as attached or flocculated biomass. Nevertheless, the prolonged start up period required by the anaerobic biofilm systems is still a critical aspect. Besides the slow growth rate of the anaerobic bacteria, the formation of a stable and well-balanced biofilm is crucial to achieve high cleaning efficiencies and stable operation. The application of inappropriate start up policies caused the initial bad reputation of the high-rate anaerobic processes. Despite of that and due to energy savings and conservation, recycling, minimization of sludge production and a progress towards sustainability, anaerobic processes have become more common. In this context, computer-aided modeling and simulation are important tools to gain both insight into the anaerobic degradation process itself and skills to design, control and operate efficiently high-rate anaerobic processes. In this paper, a dynamic model of methanogenic biofilm reactors for degrading complex substrates is presented. Biological interactions of the anaerobic consortium, physicochemical equilibria, biofilm process dynamics, and reactor system are integrated in a reactor-module model. The model of the anaerobic degradation process considers product and pH inhibitions of each bacterial group. The model of the physicochemical system involves all ionic and non-dissociated species of the main acid-base systems present in the anaerobic degradation liquor. The biofilm model accounts for biomass detachment process rate as a function of the biomass concentration in the film and the biofilm thickness. The gas phase model involves methane, carbon dioxide and water vapor dynamics. The reactor-module model consists of a continuous stirred tank reactor type, in which an inert support is placed to facilitate the biofilm formation and growth. Unlike the previous models, this model includes the balance equations of the non-active biomass in the liquid phase and biofilm. The model parameters were estimated from measurements from our lab-scale dynamic experiments and experimental data reported in literature. Pilot and full-scale plant data taken from literature were used to validate the steady sate model. *Abstract aceptado, pero no hubo participación por carecer de solvencia económica.