Distribution of C and N in soluble fractionations for characterizing the respective biodegradation of sludge and bulking agents

This study utilized C and N distribution in different soluble fractionations instead of the routine C/N ratio to characterize the respective biodegradation of sludge and bulking agents in bio-drying or composting. For sludge, C was mainly distributed (31.8%) in the neutral detergent soluble and water insoluble fraction (SOL), whereas it was mainly distributed in the cellulose-like fraction (CEL) for straw (39.5%) and sawdust (45.8%). A large proportion of N was in the 35 °C water-soluble fraction (W35 °C) for sludge (34.0%) and straw (52.5%), while for sawdust it was in the lignin-like fraction (LIG; 49.4%). For sludge, the C and N loss were mainly contributed by W35 °C (36.9% and 52.4%). The other fractions also contributed a lot. For straw, 22.4% of C and 89.8% of N lose in W35 °C. The hemicellulose-like (HEM) and CEL fraction also gave a large contribution to C loss (28.5% and 40.1%), while contributing little to N loss.