A sewage treatment machine comprising: a closed container into which the liquid to be treated is brought to boil; a vacuum-generating apparatus which is adapted to maintain the inside of the closed container at a given pressure having a value lower than the environmental/ external pressure; a supply line for the liquid to be treated, which is adapted to channel the liquid to be treated to the inside of the closed container; a heat-pump assembly which is associated to the closed container so as to be able to transfer heat to the liquid present on the bottom of the closed container thus to bring said liquid to boil, and simultaneously remove heat from the vapours that reach the top of the closed container thus to condense the vapour and obtain a distilled liquid; a first drain line that branches off/departs from the bottom part of the closed container and is adapted to channel/transfer, outside of the closed container, the liquid that accumulates/stagnates on the bottom of the closed container; and a second drain line that branches off/departs from the upper part of the closed container and is adapted to channel/transfer, outside of the closed container, the vapours that form inside the closed container and/or the distilled liquid resulting from condensation of said vapours; said sewage treatment machine being characterised in that said heat-pump assembly contains a refrigerant fluid comprising one or more gases of the family of the hydro-fluoro-olefins in a percentage greater than 3%; in that said second drain line comprises a tank adapted to contain the vapour and/or the distilled liquid arriving from the closed container; and in that said heat-pump assembly comprises: a first heat-exchanger adapted to heat up the liquid that stagnates on the bottom of the closed container; a second heat-exchanger adapted to cool down/condense the vapour that forms inside the closed container; a first expansion member which is interposed between the first and the second heat-exchanger and is adapted to cause the rapid expansion of the refrigerant fluid directed towards the second heat-exchanger; a third heat-exchanger which is located inside the tank of the second drain line, so as to be able to cool down the distilled liquid and/or vapour located inside the same tank, and is connected in parallel to the second heat-exchanger; and a second expansion member which is interposed between the first and the third heat-exchanger and is adapted to cause the rapid expansion of the refrigerant fluid directed towards the third heat-exchanger. said sewage treatment machine being characterised in that said heat-pump assembly contains a refrigerant fluid comprising one or more gases of the family of the hydro-fluoro-olefins in a percentage greater than 3%; in that said second drain line comprises a tank adapted to contain the vapour and/or the distilled liquid arriving from the closed container; and in that said heat-pump assembly comprises: a first heat-exchanger adapted to heat up the liquid that stagnates on the bottom of the closed container; a second heat-exchanger adapted to cool down/condense the vapour that forms inside the closed container; a first expansion member which is interposed between the first and the second heat-exchanger and is adapted to cause the rapid expansion of the refrigerant fluid directed towards the second heat-exchanger; a third heat-exchanger which is located inside the tank of the second drain line, so as to be able to cool down the distilled liquid and/or vapour located inside the same tank, and is connected in parallel to the second heat-exchanger; and a second expansion member which is interposed between the first and the third heat-exchanger and is adapted to cause the rapid expansion of the refrigerant fluid directed towards the third heat-exchanger.