## 3 Results
### Dynamic Biogas Process Modeling
#### 3.4.1 White Box Biogas Process Models  
The very popular IWA Anaerobic Digestion No 1 (ADM1) was published in 2002 [31] to model and simulate sewage sludge processes. As an AD process model, it includes both biochemical and physicochemical reactions in a detailed manner. Regarding biochemical reactions, the model consists of an enzymatic disintegration step as an elemental dissociation step of complex organic substrates into their basic components: Carbohydrates, proteins, fats and inert components. The further bacterial degradation of these basic components is modeled as a four-stage system of anaerobic degradation: hydrolysis, acidogenesis, acetogenesis and methanogenesis. Regarding physicochemical reactions, liquid-liquid reactions and gas-liquid exchanges are included. The ADM1 includes 19 reactions with 24 species and more than 100 parameters. By knowing the characteristics of the input waste or feedstock input, the ADM1 can be applied to calculate representative results for biogas production for different types of feedstock and under different conditions by varying its parameters [72; 73]. The ADM1 was widely discussed in several studies with different types of aspects and was reviewed briefly, for example, in [20; 74]. Based on its high impact as a white box model to calculate the precise system state of AD and under the influence of rising model predictions for different kinds of research fields, the ADM1 was configured as a software code on different software environments to model and examine the behavior of different input feedstock on the AD process. An ADM1 code included in a graphical programming software environment is presented with SIMBA#(r). SIMBA#(r) is based on MATLAB(r) Simulink in its initial design. Further development led to an independent commercial software environment based on C# code [75]. SIMBA#(r) was used in [76] to model a four-chamber biogas digester fed with pig manure and achieved high pH stability of the fermentation substrate inside the digester as a simulation result. AQUASIM, an open source software published in 2013 and using C++ compiler, was created for mathematical modeling and parameter identification of aquatic systems [77]. The implementation of an ADM1 code was successfully used for different research topics, including the performance simulation of a full-scale sludge digester and the validation of its experimental data of about 200 days operated at mesophilic conditions [78]. Using AQUASIM for an ADM1 parameter estimation to predict experimental data (20 days) of a lab-scale digester for the aquatic plants species _Hydrilla verticillata_ (water thyme) [79] led to a well predictable biogas production rate, provided that a parameter optimization of reaction rates was performed. The possibility of integrating an ADM1 program code inside the modeling environment of MATLAB(r) Simulink led [80] to publish a C code-based ADM1 program code as a possibility of using this code as an S-function (as a graphical coding function block) in Simulink. Reference [81] built a graphical user interface (GUI) inside the programming environment Python as an easy-to-use possibility for changing model input parameters of the ADM1. The ADM1 itself was implemented as MATLAB(r) code. Both the GUI modeled in Python and the ADM1 implemented as MATLAB(r) code resulted in a software tool called the \"Anaerobic Digestion Model Simulator v1.0\" (ADMS 1.0) that was validated with AQUASIM by a variation of the ADM1 input parameters. A MATLAB(r) code of the ADM1 was published by the authors of [82] to evaluate the stability of AD and an optimum mixture of different input feedstock. The MATLAB(r) code incorporates the ADM1 model implementation description in [83]. A GUI was built to run the model without extensive programming skills for the purpose of usability. The different studies show that the ADM1 is applicable to model and simulate the AD process with different types of feedstock under the use of different types of programming environments.