## 3 Factsage in the Environmental Sector
### Applications in the Field of Water Pollution  
In the area of water pollution, Factsage can be employed to model water quality in natural watersheds, forecast the efficiency of water treatment, and enhance the optimization of sludge treatment processes. Some of the study cases are shown in Table 7.  
Firstly, the EpH module can predict the stable presence of an element in an aqueous solution system at a specific potential and pH, thus enabling the prediction of heavy metal morphology and content in natural watersheds. [PERSON] et al. [115] employed the EpH module to simulate and predict the ionic morphology of lead (Pb) and nickel (Ni) in a 3 km stretch of a river. Several sampling points were set up in the river section, and in-situ temperature, pH, and electrode potential were measured and recorded while water samples were collected. The recorded environmental conditions and average surface water temperature were then input into the EpH module to obtain the Bubai diagrams of Pb and Ni at a given temperature, and the morphological scales at a given pH and electrode potential.  
Secondly, Factsage can be utilized to simulate the chemical reactions involved in wastewater treatment processes, as well as to predict the properties of wastewater before and after treatment. For instance, [PERSON] et al. [116] employed the EpH module to simulate  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Case Descriptions** & **Related Modules** & **Reference** \\ \hline Simulated and predicted the ionic forms of lead and nickel in surface water, explored & EpH & [115] \\ the impact of different environmental conditions on the forms of these heavy metal ions. & & \\ Simulated the settling behavior of various ions in brine to determine the optimal & & \\ conditions for the deposition of scale-forming ions. & & \\ \hline Investigated the selective capture of heavy metals Cr and As from solution using metal & & \\ polymers. & & \\ Simulated the chloride release characteristics after tail flue injection before and after & & \\ pretreatment of desulfurization wastewater. & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Application study of the field of water pollution of Factsage software.  
the precipitation process of scale-forming ions (Ca\({}^{2+}\) and Mg\({}^{2+}\)) in brine by passing CO\({}_{2}\), and to analyze the mineralogical characteristics of the resulting precipitation products. The optimal CO\({}_{2}\) pass time and pH value were ultimately determined. [PERSON] et al. [117] used the EpH module to investigate the trapping of heavy metal chromium and arsenic-oxygenated anions and to determine the suitable range of adsorption conditions by plotting the EpH of chromium under different conditions. Moreover, Factsage can predict the changes in wastewater properties before and after treatment. For example, [PERSON] et al. [118] utilized the Equilib module to simulate the Cl precipitation characteristics of a single chloride salt solution and pre-treatment FGD wastewater after tail flue injection and found that the precipitation of Cl-containing gas from FGD wastewater was significantly reduced after treatment.  
In summary, Factsage, although less used in the field of water pollution, still has excellent results and potential in modeling the morphology of heavy metals in water and predicting the chemical reactions of various inorganic pollutants in wastewater. Consequently, this software can be employed in the future for predicting the speciation of various ions in industrial wastewater, thus providing essential data for process optimization and pollutant reduction from the source. On the other hand, Factsage can also be utilized in responding to various unexpected water pollution incidents. The software enables the prediction of river pollution levels and, to some extent, the simulation of the effectiveness of different remediation measures, thereby offering theoretical support for addressing pollution in various watershed systems.