Optimization of thermo-chemical hydrolysis of kitchen wastes

Municipal Solid Wastes (MSWs) in Greece consist mainly of fermentable organic material such as food scraps (～50%) and paper residuals (～20%). The aim of this work was to study the thermo-chemical pretreatment of the kitchen waste (KW) fraction of MSW focusing on biotechnological exploitation of pretreated wastes for biofuel production. A representative sample of municipal food residues was derived by combining weighted amounts of each individual type of residue recognized in daily samples obtained from the University of Patras’ students restaurant located at the Students Residence Hall (Greece). Chemical pretreatment experiments of the representative KW sample were performed using several types of chemical solutions (i.e. H₂SO₄, HCl, NaOH, H₂SO₃) of different solute concentration (0.7%, 1.5%, 3%) at three temperatures (50, 75, 120 °C) and a range of residence times (30–120 min). Optimized results proved that chemical pretreatment of KW, using either 1.12% HCl for 94 min or 1.17% HCl for 86 min (at 100 °C), increased soluble sugars concentration by 120% compared to untreated KW. The increase of soluble sugars was mainly attributed to the mono-sugars glucose and fructose.