Abstract
Anaerobic lagoons are natural wastewater treatment systems suitable for swine farms in small communities due to its low operational and building costs, as well as for the environmental sustainability that these technologies enable. The local weather is one of the factors which greatly influences the efficiency of the organic matter degradation within anaerobic lagoons, since microbial growth is closely related to temperature. In this manuscript, we propose a mathematical model which involves the two-dimensional Stokes, advection–diffusion-reaction and heat transfer equations for an unstirred fluid flow. Furthermore, the Anaerobic Digestion Model No1 (ADM1), developed by the International Water Association (IWA), has been implemented in the model. The partial differential equations resulting from the model, which involve a large number of state variables that change according to the position and the time, are solved through the use of the Finite Element Method. The results of the simulations indicated that the methodology is capable of predicting reasonably well the steady-state of the concentrations for all processes that take place in the anaerobic digestion and for each one of the variables considered; cells, organic matter, nutrients, etc. In view of the results, it can be concluded that the model has significant potential for the design and the study of anaerobic cells’ behaviour within free flow systems.
Highlights
The aim of this work is to set-up a theoretical framework for wastewater treatment in unstirred flow anaerobic lagoons, by a model which allows the integration of fluid flow, heat transfer and cells behaviour, for the purpose of describing processes occurring in AL
In order to do this, an improved two dimensional mathematical model, based on the coupling of a set of parabolic partial differential equations (PDEs) and related to the phenomena associated to AL, has been developed
We have proposed and assessed a methodology for anaerobic cells performance for wastewater treatment, in AL, under the influence of the temperature
Summary
Its utilization is increasingly widely, due to its capacity for producing methane, which can be used afterwards as a heat source or for electricity generation, taking part within the low-carbon energy technologies and circular bio-economy [5]. In this context, anaerobic lagoons (AL) are natural wastewater treatment systems with a long hydraulic retention time, suitable for small communities due to the low energy demand and the operating costs [6,7,8,9]. AL offer a number of advantages, such as the establishment of concentration profiles along the reactor, a buffering capacity in cases of overloads and greater protection against acidification [10]
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