The invention relates to an apparatus for the heating of a biomass sludge, the apparatus comprising a first positive displacement pump (2), a second positive displacement pump (4), a first piping (6) connecting an outlet of the first positive displacement pump (2) to an inlet of the second positive displacement pump (4), a steam mixing device (8) provided in the first piping (6) between the first positive displacement pump (2) and the second positive displacement pump (4), and a steam source (10) which is in fluid communication with the steam mixing device (8) and configured to supply steam or a steam containing gas to the steam mixing device (8). The first positive displacement pump (2) and the second positive displacement pump (4) are configured so that, in operation of the apparatus, the flow rate of the first positive displacement pump (2) is smaller than the flow rate of the second positive displacement pump (4). The steam mixing device (8) is configured to mix the steam or steam containing gas supplied by the steam source (10) with a biomass sludge in the first piping (6). Further, the invention relates to an apparatus for the continuous preparation of a disintegrated biomass sludge, the apparatus comprising a first positive displacement pump (2), a first piping (6, 12) connecting an outlet of the first positive displacement pump (2) to an inlet of the first positive displacement pump (2) so as to form a closed loop, a first disintegration device (20) which is provided in the first piping (6, 12) and configured to disintegrate a biomass sludge supplied thereto, a second pump (14) and a third pump (16). An outlet of the second pump (14) is connected to the first piping (6, 12) and an inlet of the third pump (16) is connected to the first piping (6, 12) upstream of a position where the outlet of the second pump (14) is connected to the first piping (6, 12).
