Fig. 1. Carbon and nitrogen distribution (C to N ratio) in the fractions obtained by the fractionation of organic matter of wastewater sludges. W20, water-soluble fraction at 20°C; W20–100, water-soluble fraction from 20 to 100°C; W100, water-insoluble fraction at 100°C; SOL, soluble compounds; HEM, hemicellulose-like compounds; CEL, cellulose-like compounds; LIG, lignin-like compounds; AcS, acid-soluble fraction; AcIns, acid-insoluble fraction; Dist, distillable; NDist, nondistillable.