NOVELTY - An arrangement for filtrating a rough-filtrated sludge comprises a filter body (5') is configured to be arranged with the filter surface member extending in a vertical plane, where the gravitation is utilized for obtaining passing of the liquid substance of the sludge through the filter surface member into a space (42); unit (44) configured to direct jet (52) of gas onto the second side of the filter surface member to promote passing of the liquid substance through it; and unit (47) configured to move the impact area of the jet over the second side of the filter surface member.    USE - For filtrating rough-filtrated sludge emanating from cattle droppings and sewage sludge, such as in connection with dwelling houses (claimed).    ADVANTAGE - The arrangement is remarkably simple to the construction; is low cost and have a very reliable function; and is suited to be used in plants for production of biogas or in water cleaning plants.    DETAILED DESCRIPTION - An arrangement for filtrating a rough-filtrated sludge comprises a filter body having at least one filter surface member (5') configured to filter a the sludge by retaining particles of the sludge onto its first side and letting liquid substance of the sludge pass through; and unit (9) configured to feed a the sludge to be filtered onto the first side of the filter surface member, where the filter body is configured to be arranged with the filter surface member extending in a vertical plane, the gravitation is utilized for obtaining passing of the liquid substance of the sludge through the filter surface member into a space (42) on a second side (46) of the member opposite to the first side, and the arrangement comprises unit (44) configured to direct at least one jet (52) of gas onto the second side of the filter surface member to promote passing of the liquid substance through it from the first to its second side, and unit (47) configured to move the impact area of the jet over the second side of the filter surface member. An INDEPENDENT CLAIM is included for filtrating a rough-filtrated sludge involving feeding the rough-filtrated sludge onto a first side of at least one filter surface member of a filter body and making liquid substance of the sludge to pass through the filter surface member while retaining particles of the sludge onto its first side, where the filter body is kept with the filter surface member extending in vertical plane and the gravitation is utilized for obtaining passing of the liquid substance of the sludge through the filter surface member into a space on a second side of the member opposite to the first side, that at least one jet of gas is directed onto the second side of the filter surface member to promote passing of the liquid substance through it from the first to its second side, and that the impact area of the jet is moved over the second side of the filter surface member.    DESCRIPTION OF DRAWING(S) - The figure shows view of arrangement.    Filter surface member (5')    Unit configured to feed (9)    Space (42)    Unit configured to direct jet of gas (44)    Jet (52)