TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The plant oil is selected from rapeseed oil, corn oil, colza oil, canola oil, tall oil, sunflower oil, soybean oil, hempseed oil, olive oil, linseed oil, mustard oil, palm oil, peanut oil, castor oil, coconut oil, jatropha oil, camelina oil, salicornia oil, pennycress oil and/or algal oil.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The contaminant is an alkali metal, alkaline earth metal, transition metal, or non-metal other than C, H, or O (preferably Ca, Fe, Mg, Na, P, and K).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The fatty acid or triglyceride-containing component is an animal fat and/or plant oil. The animal fat is selected from lard, tallow, train oil, milk fat, fish oil, grease and/or sewage sludge. The treated feedstock has a total concentration of Ca, Fe, Mg, Na, P, and K contaminants that is reduced by at least 35 (preferably at least 70)% relative to the feedstock. The hydroprocessed biofuel is a hydroprocessed diesel biofuel or a hydroprocessed aviation biofuel. In the method (M2), the cation exchange resin is in the hydrogen form.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The ion exchange resin is a strong base or weak base anion exchange resin and/or strong acid cation exchange resin. The strong base anion exchange resin has quaternary ammonium functional groups. The weak base anion exchange resin has amine functional groups. The strong acid cation exchange resin has sulfonic acid functional groups. Preferred Method: The method (M1) further involves: contacting the treated feedstock with hydrogen under catalytic hydroprocessing conditions to provide a hydroprocessed product; fractionating the hydroprocessed product to recover a hydroprocessed biofuel. The contacting with hydrogen under catalytic hydroprocessing conditions results in both hydrotreating and hydrocracking reactions. The method (M2) further involves: blending the hydroprocessed biofuel with petroleum-derived fuel (1-99 wt.%). EXAMPLE - No suitable example given.