NOVELTY - Method (M1) for forming a low-metal biomass-derived pyrolysis oil, comprises: filtering a biomass-derived pyrolysis oil with a high flux rate filter arrangement having a flux rate of greater than or equal to 10 l/m2/hour to form a low-solids biomass-derived pyrolysis oil; filtering the low-solids biomass-derived pyrolysis oil with a fine filter arrangement having a pore diameter of less than or equal to 50 mu m to form an ultralow-solids biomass-derived pyrolysis oil; and contacting the ultralow-solids biomass-derived pyrolysis oil with an ion-exchange resin to remove metal ions and form the low-metal biomass-derived pyrolysis oil.    USE - The method is useful for forming low-metal biomass-derived pyrolysis oil (claimed), which is useful as a biofuel.    ADVANTAGE - The method utilizes the filtration steps that remove larger solid fragments of char including metals and other solubles from the biomass-derived pyrolysis oil to form ultra-low-solids biomass-derived pyrolysis oil with increased thermal stability, preferably without plugging or clogging the filter arrangement, thus providing the biomass-derived pyrolysis oil having very low metal content i.e. total metal content of less than or equal to 100 ppm.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method (M2) for forming a low-metal biomass-derived pyrolysis oil, comprising: filtering a biomass-derived pyrolysis oil to form an ultralow-solids biomass-derived pyrolysis oil; contacting a first portion of the ultralow-solids biomass derived pyrolysis oil with an acidic ion-exchange resin having sulfonic acid groups to form a first amount of the low-metal biomass-derived pyrolysis oil and a spent ion-exchange resin; regenerating the spent ion-exchange resin including contacting the spent ion-exchange resin with a solution containing sodium ions to exchange potassium ions, calcium ions, magnesium ions, strontium ions, titanium ions, vanadium ions, copper ions, iron ions, cobalt ions, chromium ions, lead ions, manganese ions, nickel ions, zinc ions and other mono-, divalent and/or trivalent metal ions present in the biomass-derived pyrolysis oil which are removed by ion exchange from the spent ion-exchange resin with the sodium ions from the solution to form a spent sodium-ion-containing exchange resin that is regenerated to form a regenerated ion-exchange resin; and contacting a second portion of the ultra-low-solids biomass derived pyrolysis oil with the regenerated ion-exchange resin to form a second amount of the low-metal biomass derived pyrolysis oil; and    (2) an apparatus (10) for forming a low-metal biomass-derived pyrolysis oil, comprising: a high flux rate filter arrangement (20) configured to receive and filter biomass-derived pyrolysis oil (12) to form a low-solids biomass-derived pyrolysis oil; a fine filter arrangement (28) in fluid communication with the high flux rate filter arrangement to receive the low-solids biomass-derived pyrolysis oil and configured to filter the low-solids biomass-derived pyrolysis oil to form an ultra-low-solids biomass-derived pyrolysis oil; and an ion-exchange unit (36) containing an ion-exchange resin and in fluid communication with the fine filter arrangement to receive the ultra-low-solids biomass-derived pyrolysis oil, where the ion-exchange unit is configured to contact the ultra-low-solids biomass-derived pyrolysis oil with the ion-exchange resin to remove metal ions and form the low-metal biomass-derived pyrolysis oil.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the apparatus for forming low-metal biomass-derived pyrolysis oil.    Apparatus (10)    Biomass-derived pyrolysis oil (12)    High flux rate filter arrangement (20)    Fine filter arrangement (28)    Ion-exchange unit (36)