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The startup of anaerobic reactors is a very important issue for their application in the treatment of wastewaters and solid wastes. However, very limited information is available about the quantitative and dynamic modeling of anaerobic reactor startup in the literature. In this work, by introducing a linear phenomenological equation into the IWA Anaerobic Digestion Model No. 1 (ADM1), we developed a model to describe the dynamic behavior of the startup of anaerobic reactors. The model was calibrated and verified using the experimental results of two anaerobic reactors: an upflow anaerobic sludge blanket (UASB) reactor fed with soybean processing wastewater and a continuously stirred tank reactor (CSTR) system with simulated municipal solid wastes as the substrate. The simulation results matched with the experimental data well, and the model could capture the variation trends of the components. This agreement demonstrates the rationality and validity of the established model for describing the startup of anaerobic systems. [ABSTRACT FROM AUTHOR]

Microbial internal storage processes have been demonstrated to occur and play an important role in activated sludge systems under both aerobic and anoxic conditions when operating under dynamic conditions. High-rate anaerobic reactors are often operated at a high volumetric organic loading and a relatively dynamic profile, with large amounts of fermentable substrates. These dynamic operating conditions and high catabolic energy availability might also facilitate the formation of internal storage polymers by anaerobic microorganisms. However, so far information about storage under anaerobic conditions (e.g., anaerobic fermentation) as well as its consideration in anaerobic process modeling (e.g., IWA Anaerobic Digestion Model No. 1, ADM1) is still sparse. In this work, the accumulation of storage polymers during anaerobic fermentation was evaluated by batch experiments using anaerobic methanogenic sludge and based on mass balance analysis of carbon transformation. A new mathematical model was developed to describe microbial storage in anaerobic systems. The model was calibrated and validated by using independent data sets from two different anaerobic systems, with significant storage observed, and effectively simulated in both systems. The inclusion of the new anaerobic storage processes in the developed model allows for more successful simulation of transients due to lower accumulation of volatile fatty acids (correction for the overestimation of volatile fatty acids), which mitigates pH fluctuations. Current models such as the ADM1 cannot effectively simulate these dynamics due to a lack of anaerobic storage mechanisms.