Abstract
Anaerobic co-digestion in wastewater treatment plants is looking increasingly like a straightforward solution to many issues arising from the operation of mono-digestion. Process modelling is relevant to predict plant behavior and its sensitivity to operational parameters, and to assess the feasibility of simultaneously feeding a digester with different organic wastes. Still, much work has to be completed to turn anaerobic digestion modelling into a reliable and practical tool. Indeed, the complex biochemical processes described in the ADM1 model require the identification of several parameters and many analytical determinations for substrate characterization. A combined protocol including batch Biochemical Methane Potential tests and analytical determinations is proposed and applied for substrate influent characterization to simulate a pilot-scale anaerobic digester where co-digestion of waste sludge and expired yogurt was operated. An iterative procedure was also developed to improve the fit of batch tests for kinetic parameter identification. The results are encouraging: the iterative procedure significantly reduced the Theil’s Inequality Coefficient (TIC), used to evaluate the goodness of fit of the model for alkalinity, total volatile fatty acids, pH, COD, volatile solids, and ammoniacal nitrogen. Improvements in the TIC values, compared to the first iteration, ranged between 30 and 58%.
Highlights
It is increasingly important for wastewater treatment plants (WWTPs) to recover as much energy and material as possible from waste sludge, turning WWTP into more energy-efficient and cost-effective facilities
Anaerobic co-digestion (AcoD) offers several potential advantages arising from optimized organic waste treatment [2], and overcomes two main issues related to the anaerobic digestion of waste sludge: the low organic load applied and the presence of spare capacity in WWTP
Since the development of the current state-of-the-art model for describing anaerobic digestion processes (Anaerobic Digestion Model No 1) [8], researchers have dealt with two key constraints for model application: (i) the wide range of variability of a large number of stoichiometric and kinetic parameters, requiring the estimation of the most sensitive ones, and (ii) the lack of generally accepted guidelines for influent substrate characterization according to model input variables [9]
Summary
It is increasingly important for wastewater treatment plants (WWTPs) to recover as much energy and material as possible from waste sludge, turning WWTP into more energy-efficient and cost-effective facilities. Stricter discharge limits on effluents and technology improvements in wastewater treatment processes are expected to increase the amounts of waste sludge to be treated and disposed [1]. In this context, anaerobic co-digestion (AcoD) offers several potential advantages arising from optimized organic waste treatment [2], and overcomes two main issues related to the anaerobic digestion of waste sludge: the low organic load applied and the presence of spare capacity in WWTP digesters, as much as 30% [3]. Since the development of the current state-of-the-art model for describing anaerobic digestion processes (Anaerobic Digestion Model No 1) [8], researchers have dealt with two key constraints for model application: (i) the wide range of variability of a large number of stoichiometric and kinetic parameters, requiring the estimation of the most sensitive ones, and (ii) the lack of generally accepted guidelines for influent substrate characterization according to model input variables [9]
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