Sulfided, phosphorus-added NiMo/Al2O3 catalyst was used for hydrodenitrogenation (HDN) of bio-oil derived from sewage sludge. The as-received bio-oil samples contained approximately 6% nitrogen. The bio-oil was dissolved in various solvents prior to hydrotreatment and the removal of nitrogen compounds was evaluated. The HDN of bio-oil dissolved in xylene at 350 degrees C over phosphorus added NiMo/Al2O3 resulted in a complete denitrogenation of bio-oil and high yield of aliphatic hydrocarbon containing product with moderate heating value. Bio-oil dissolved in non-polaric solvent (xylene) showed 2-3 times higher nitrogen removal than that of protic solvents due to the competition between denitrogenation and deoxygenation. This study reveals that sulfided NiMo/Al2O3 catalyst is an efficient approach to remove nitrogen heteroatom compounds prior to further upgrading bio-oil derived from sewage sludge. (C) 2012 Elsevier B.V. All rights reserved.