Low-temperature thermal hydrolysis of sludge prior to anaerobic digestion: Principal component analysis (PCA) of experimental data

Here, we report data of the principal component analysis (PCA) assessment and clustering analysis related to low-temperature thermal hydrolysis process (THP) for enhancing the anaerobic digestion (AD) of sludge in wastewater treatment plants (WWTPs) with primary sludge fermentation (Azizi et al., 2021). The PCA was examined to pinpoint the influence of different THP schemes on the variations of macromolecular compounds solubilization after low-temperature THP and the relative performances in enhancing methane potential in AD. We established 2 experimental setups with a total of 18 treatment conditions (3 exposure times, 30, 60, and 90 min at three temperature levels 50, 70 and 90 °C) in comparison to the untreated control samples. Scheme-1 comprises the THP of a mixture of (1:1 vol ratio) fermented primary sludge (FPS) and thickened waste activated sludge (TWAS); while scheme-2 comprised the THP of TWAS only. The factors employed in the assessment of the PCA encompassed the variations in the macromolecular compounds and other solubilization metrics. This included the variations in the levels of carbohydrates, lipids, proteins, and solubilization of chemical oxygen demand (COD) and volatile suspended solids (VSS). Furthermore, the evaluation considered the changes of volatile fatty acids (VFAs) and total ammonia nitrogen (TAN) with respect to time and temperature. The assessment of PCA classified the THP based on their differences and alterations that occurred after the treatment. The indices of the PCA assessments differed based on the factors of concern and the focus of each individual PCA assessment. In every individual PCA assessment, the respective contribution to the total variance in PCA analysis was calculated and manifested by the highest distribution of the principal components (PCs) axis PC1 and PC2. The differences in distributions of PCs after various PCA examinations can describe the relative influence of THP schemes and the most significant variables that can trigger major differences among THP conditions. The comparative differences demonstrated by PCA support the potential investigations of the efficiency of THPs conditions and their performance categories.