Conversion of sewage sludge to heavy oil by direct thermochemical liquefaction

To investigate optimum starting materials and catalyst loading for conversion of sewage sludge to heavy oil, various kinds of sewage sludges were liquefied at a temperature of 300°C, a pressure of 12 MPa, and a catalyst (sodium carbonate) loading of 0-20 wt %. The optimum kind of sewage sludge was found to be either raw primary sludge or raw mixed sludge because average oil yields of these sludges reached 43 %-higher than those of other kinds of sludges. For most sewage sludges, oil production proceeded satisfactorily without the addition of any catalyst.