A full-scale compost biofilter system (CBS) was built to treat vapor losses emitted from three analogous vertical fixed roof p-xylene (p-X) liquid storage tanks of 7500 m(3) total working volume. The CBS showed a stable and efficient treatment of standing loss (L-s) and working loss (L-w) with an average removal efficiency of 95.4% through 18-month standing storage and filling operation of the tanks. The weight of activated carbon employed in the concentration buffer influences the CBS performance for Lw treatment under high organic loads. The daily average pressure drops across biofilter bed displayed very low with a maximum of 7.6 mm-H2O. This reflects that the CBS can be operated without stress and compression of biofilter bed and thus reduce maintenance frequency. No additional inputs of chemicals and fuels along with low electricity and water usage helped in its prolonged operation and increased its cost effectiveness. These advantages make the CSB become a promising control technology of vapor losses emitted from fixed roof organic liquid storage tanks. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.