Direct liquefaction of activated sludge from aerobic treatment of effluents from the cornstarch industry

Activated sludge from a cornstarch processing plant, a by-product of biological wastewater treatment, was converted directly into heavy oil by mixing with sodium carbonate of up to 20 wt%, and heating to temperatures ranging between 225 and 340°C with holding times of up to 120 min under a pressurized nitrogen atmosphere. Liquefaction was accomplished without a catalyst. The yields were influenced by the temperature and holding time. Heavy oil with heating value of 32 MJ kg⁻¹ was obtained with 30 wt% yield on a moisture- and ash-free basis at a temperature of 300°C and holding time of 60 min. The energy balance for this liquefaction process was estimated.