SPHAUL - Integrated modeling of anaerobic digestion with SPH

Project: SPHAUL - Integrated modeling of anaerobic digestion with SPH 
Funding organisation: FFG - Die Österreichische Forschungsförderungsgesellschaft 
Funding: BRIDGE: 21. Ausschreibung BRIDGE 1

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Project leader: Wolfgang RAUCH
Project staff: Daniel WINKLER, Michael MEISTER, Massoud REZAVAND
Project duration: 01.10.2015 - 31.03.2018 
Project number: 850738

Partners:

  • University of Innsbruck (scientific)
  • hydro-IT GmbH (industrial)
  • BioTreaT GmbH (industrial)

Abstract:

Anaerobic digestion (AD) is a common and widely applied technology for advanced treatment of biodegradable materials such as domestic sewage, agricultural manure, food waste and the biodegradable fraction of solid waste. Due to the biological processes in the digester, biogas (containing up to 2/3 methane) is formed under anaerobic conditions from the biological residues and subsequently utilised to generate both heat and energy (see e.g. Ward et al., 2008). The environmental and economic benefits of applying AD both in advanced wastewater treatment and treatment of organic waste is undisputed and the process is widely applied in Europe (see e.g. Bidlingmaier et al., 2004). Due to the importance of the process not only fundamental aspects (e.g. Tafdrup, 1995) but also modelling (e.g. Lauwers et al., 2013) and monitoring (e.g. Madsen et al., 2011) have been extensively researched and reported. In a current review Appels et al. (2011) identify the mathematical description as one of the limitations in the exploitation of AD process. Especially the connection of models describing the physical processes (flow and mixing) with biokinetic models is still missing, which is a limitation in design and management of the AD process. Consequently a novel model concept – capable of such refined process description - has a huge potential in practical applications, both as a computational software tool and also as an instrument for AD consultancy.
The project SPHAUL addresses this issue and proposes to link the novel Lagrangian smoothed particle hydrodynamics (SPH) method together with the standard biokinetic anaerobic digestion model (ADM). It is expected that this novel approach is breaking grounds in the mathematical description of AD technology and could lead a computational software tool for industry.

Based on the problem statement above, in this project we will develop a novel software concept for integrated AD simulation. We suggest the novel fully Lagrangian SPH method as alternative, meshless CFD method for simulating the physical processes in AD. Particularly important for this project in terms of modelling biochemical processes are good simulation properties for multiphase flow (Colagrossi et al., 2003; Aristodemo et al., 2010), concentration rates (Aristodemo et al., 2010) and transport phenomena (Tartakovsky et al., 2007) and well as the natural way to implement moving objects (mixing devices) (Adami et al., 2012 and Baraff, 1997). In the framework of this project the numerical concept and implementation of a SPH software specified to AD simulations is developed. The key innovation of this project is the extension of SPH to allow for both fluid flow modelling and spatial discretised AD kinetics, which has not been previously attempted. The research aim of SPHAUL is to develop the numerical methods of SPH further so that the simulation of biophysical and biochemical processes in environmental engineering is possible, with the focus on anaerobic digestion.
For this purpose two-phase water-particle flow is studied in SPH. We will apply two approaches that is a) a multi fluid algorithm where inert sediments are seen as a second phase and b) the rigid body method for the simulation of larger objects in the flow field. The substrate biomass is assumed as a pseudo-Newtonian fluid with specific density and viscosity but with spatially varying concentrations. The inert matter (sediments and objects) is an important component in the digester tanks and hence is essential in coupling the local hydrodynamics to the biological kinetics. The ADM biokinetic model is included in the developed SPH software and the associated differential equations are coupled to the SPH simulation results.
In this project simulation results are validated with physical experiments, field measurements and data from available software packages. After extension of the software to a GPU version with enhanced processing power, a series of simulations with varying reactor geometries and mixer types is performed to assess its influence on the biophysical processes.
This Bridge project is classified as a translational research project and the results are of great importance for the industry working in the field of anaerobic digestion – both in software development and design, management and consultancy.