The US annually produces 79 million dry tons of liquid organic waste including sewage sludge.Anaerobic digestion can only reduce the sludge volume by 50% in mass, leaving the other half as a growing waste management and hygienic problem. Hydrothermal Processing (HTP), a set of several chemical digestion processes, could be employed to convert sewage sludge into valuable products and minimize potential environmental pollution risks. Specifically, hydrothermal carbonization and hydrothermal liquefaction have been extensively studied to sustainably manage sludge. Two of the main reasons for this are the high upscaleability of HTP for public waste management and that it is estimated that HTP can recover eleven times more energy from waste products than landfilling. An integration of HTP with anaerobic digestion or recycling the soluble organics (in the HTP aqueous products) into the HTP process could lead to a higher overall rate of energy recovery for municipal sewage sludge.
In this work, leucine
and glucose were used as model molecules
to investigate the Maillard reaction between proteins and carbohydrates
during hydrothermal liquefaction (HTL) of microalgae. The main pathway
of the Maillard reaction between leucine and glucose via HTL was related
to the reaction of deaminated leucine with cyclic oxygenated compounds
from degraded glucose to produce pyrazine derivatives. Gas chromatography–mass
spectrometry results revealed that N and O heterocyclic compounds,
organic acids, and carbonyls/imine/amine were the main components
of both the biocrude oil and aqueous fraction. The optimal reaction
temperature, reaction time, leucine/glucose weight ratio, and solid
concentration for biocrude oil production are 320 °C, 60 min,
2:5, and 20 wt %, respectively. The obtained biocrude oil (higher
heating value of 38.07 MJ/kg), presenting a large amount of pyrazine
derivatives (84.2% peak area), yielded 47.6 wt % of leucine and glucose
feedstock.
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