The present invention relates to a method for reducing an amount of dissolved impurities in an oxygen containing renewable feedstock, the dissolved impurities being selected from impurities comprising phosphorus and impurities comprising at least one metal. The method comprises obtaining a net elementary charge of a first feedstock; mixing the first feedstock with an elementary charge balancing component to obtain the feedstock to be treated, whereby the feedstock to be treated has a net elementary charge which is closer to zero net elementary charge than the net elementary charge of the first feedstock; and subjecting the feedstock to be treated to a heat treatment at a temperature of 180-400 C. in order to precipitate compounds containing said phosphorus and said at least one metal.

Embodiments described herein provide a method, comprising routing a bio-oil to a mixing device; routing a wash material to the mixing device; using the mixing device to form a mixture from the bio-oil and the wash material; routing the mixture to an electrostatic separator; and applying an electric field to the mixture, in the electrostatic separator, to separate the wash material from the bio-oil.