Fig. 2: Comparing molecular characteristics of DOM between PD and SD sludge samples.
Molecular composition is shown based on (a) elements and elemental combinations and (b) compound classes, calculated based on relative intensity weights. Elemental ratios (e.g., H/C, O/C) and mass averages were obtained using intensity-weighted averages (IWA). Each value represents the mean of seven biologically independent replicates. In panel (a), error bars represent standard deviation (SD). In panel (b), the bar + data overlap plot shows the mean (bar), median (center line), whiskers representing 1.5 × the interquartile range (IQR), and outliers as points beyond the whiskers. Significance was evaluated by pair-sample t-test: *** represents p ≤ 0.001, ** represents p ≤ 0.01, * represents p ≤ 0.05, and no asterisk indicates p > 0.05; exact p-values are provide in the Source Data File. Mass and relative intensity (RI) distribution are shown for (c) total, (d) lignin, (e) lipid and (f) protein compounds. The density plots of mass-RI were generated using a 2D Kernel density plot, with the mass range from 100 to 1000 m/z and RI from 0 to 1, using a 1000 1000 grid. The mass-RI distribution of additional compound classes including unsatHC, ConHC, AminoSugar, Tannin and Carb was provided in Supplementary Fig. 7. g Principal component analysis (PCA) of the relationship between molecular composition and structural factors: H/C ratio, double bond equivalent (DBE), aromaticity index (AImod) and other relevant parameters. h C-C single-bond distribution of lignin, lipid and protein compounds. The C-1-DBE was used to represent C-C single bonds, while non-C = C bonds (e.g., C = O, C = N) were excluded from the calculations; distributions of other compound classes was provided in Supplementary Fig. 11. AImod distribution of (i) lipid and (j) protein molecules of PD and SD DOM samples.
