Integrating anaerobic digestion and hydrothermal liquefaction for renewable energy production: An experimental investigation

The combination of anaerobic digestion and hydrothermal liquefaction can provide enhanced energy production from animal wastes such as cow manure. Hydrothermal liquefaction (HTL) of anaerobic digestate is a novel approach for waste management to recover residual carbon Anaerobic digestion of cow manure was conducted at room temperature with different hydraulic retention times (HRT) viz. 10, 18, 28, 38, 50 and 60 days. The digested cow manure (16%w/w dry weight solids) obtained from various HRTs was subjected to hydrothermal liquefaction at 350 degrees C, 18MPa for a fixed reaction time of 30 min in the presence of 5 wt % Na2CO3. The results showed cumulative biogas production in the range of 3.9-22.6 m(3)/kgVS(added). HTL of the resultant digestates led to approximate to 20-42 wt % biocrude yield. The biocrude has a higher heating value (HHV) of 28.4-31.2 MJ/kg. About 76% energy, approximate to 51-83% carbon and approximate to 2-4% nitrogen was recovered in the biocrude following HTL of the digestates. A positive energy balance was achieved for the products derived from the combination of anaerobic digestion and hydrothermal liquefaction. (c) 2015 American Institute of Chemical Engineers Environ Prog, 34: 1662-1673, 2015