Carbon source fate in lysozyme-assistant anaerobic fermentation process of excess sludge: interphase carbon migration, recovery and extraction

Lysozyme has been regarded as promising approach to enhance anaerobic fermentation of excess sludge. However, little investigation has revealed the specific patterns of interphase carbon source migration and recovery. This study demonstrated that the rising lysozyme dosages greatly improved the kinetics and performances of endogenous carbon source release and biotransformation, which mainly occurred within 48-h treatment. Considerable 146.66 mg C/g VSS particulate carbon sources were solubilized from sludge solid, composing of proteins, humic acids and metabolic intermediates. Meanwhile, almost 57.48 % of the originally released carbon sources were bio-transformed into short-chain fatty acids with accelerated sludge acidification, which were regarded as the recoverable carbon source. Correspondingly, considerable carbon recovery of 103.18 mg C/g VSS was achievable by lysozyme assistance in 96-h anaerobic fermentation. Such lysozyme catalysis strategy improved carbon migration and recovery by 5.38 and 6.21 times, respectively. The fermented sludge was easily dewatered after chemical conditioning, thereby the effective carbon source extraction was implemented by solid-liquid separation. Approximately 65.99–87.02 % of the recoverable carbon sources were remained in fermentative liquid. The high ratios of carbon sources to nutrients (nitrogen and phosphorus) suggested favorable bio-availability and utilizability of the recoverable carbon sources. The overall carbon flow and migration pathways in lysozyme-driven patterns were illustrated to directly clarify the carbon source fate in anaerobic fermentation process and carbon recovery benefits from excess sludge.