Effect of aqueous phase recirculation on product characteristics from hydrothermal carbonation of kitchen waste and the migration of O

Hydrothermal carbonization (HTC) is considered as a promising method for treating kitchen waste (KW), as the main by-product of HTC, the aqueous phase (AP) contains rich organic matter, and its effective utilization is very necessary. Therefore, this work investigated the effect of AP cycle on gas, hydrochar, bio-oil and AP obtained from HTC of KW. The results showed that CO2 was the main component of gas, bio-oil mainly included organic acids, ketones, furans and aromatic compounds, etc. And the organic acids was the main organic matter in AP, accounting for more than 70 %. With the increase of AP cycles, the yields of hydrochar increased from 47.28 % to 54.91 %, while the atomic ratio of H/C and O/C decreased gradually. The results of Fourier transform infrared spectrum (FT-IR), X-ray photoelectron spectroscopy (XPS) and elemental analysis showed that AP cycles promoted the decarboxylation and aromatization of KW. According to the results of gas chromatography-mass spectrometry (GC-MS), during the AP cycle, organic acids participated in HTC process and promoted protein decomposition and polycondensation between macromolecules, thus promoting the increase of aromatic compounds and N-containing compounds in bio-oils and AP. And the migration path of O according to the existence form of O in different products was speculated.