Upcycling of nutrients from kitchen waste: Integration of anaerobic digestion system and microbial protein production system

To upcycle the nutrients from kitchen waste (KW), an integrated system consisting of anaerobic digestion (AD) reactor and microbial protein (MP) production reactor was established in this study. The subsystem I (AD system) demonstrated an efficient bio-energy production (282.37 mL CH4/g VS), with 553.54 mg/L of NH4+-N remained in the digestate. The subsystem II (MP production system) utilized the nitrogenous constituents of the digestate, with 2.04 g/L MP production. In order to further enhance the recovery efficiency, C/N ratio in the subsystem II was studied. NH4+-N recovery efficiency was 23.08% higher after C/N ratio optimization along with 0.24 g/L increment on MP production. Over 0.7 g/L of essential amino acids was obtained, according with the qualitative necessary for the feeds. Also, the key enzyme abundance of CO2 releasing and amino acid biosynthesis was obviously increased with max. 55.21%. Meanwhile, the integrated system was profitable via a simplified economic assessment. [Display omitted] •Methane production reached 282.37 mL/g VS in anaerobic digestion subsystem.•2.04 g/L microbial protein (MP) production was obtained with 98.60% NH4+-N recovery.•Increment of 23% N recovery and 0.24 g/L MP were gained with optimized C/N ratio.•The abundance of key enzymes was increased (Max. 55.21%) by optimizing C/N ratio.•The comprehensive profit of the integrated system was assessed of 201.18 €/t MP.