NOVELTY - Pollution free, multistage transesterification processes with acid catalyst and base catalyst for the production of biodiesel and glycerin have now been found. Accordingly, one aspect of the present invention provides multistage processes for the transesterification of a mixture of triglycerides and fatty acids, comprising: (a) mixing said triglycerides and fatty acids, a low carbon alkyl alcohol, and an acid catalyst at a temperature that is less than the boiling temperature of said alcohol; said low carbon alkyl alcohol been selected from the group consisting of methanol, ethanol, propyl alcohol, and iso-propyl alcohol, or mixtures thereof, and the ratio of said low carbon alkyl alcohol to said triglycerides and fatty acids being in the range of 3:1 to 30:1; and maintaining the mixing in said first reactor for a period of residence time to effect acid-catalyzed transesterification of the fatty acids, and extracting mixture of glycerin and low carbon alkyl alcohol from reaction product of said first reactor by the first separation device continuously and partially recycling the reactants and products to said first reactor; (b) transporting the remaining reactants and products of said first reactor to the second reactor, mixing said reactants and products, said triglycerides and fatty acids, recycled mixture of glycerin and low carbon alkyl alcohol from the third separation device, additional low carbon alkyl alcohol, and a base catalyst in said second reactor at a temperature that is less than the boiling temperature of said additional low carbon alkyl alcohol, and the ratio of said additional low carbon alkyl alcohol to said triglycerides and fatty acids being in the range of 0:1 to 9:1; and maintaining the mixing in said second reactor for a period of residence time to effect base-catalyzed transesterification of the triglycerides, and extracting and transporting the mixture of glycerin and low carbon alkyl alcohol from said second reactor by the second separation device continuously to the said first reactor, and partially recycling the reactants and products to the said second reactor; (c)transporting the remaining reactants and products from said second reactor to the third reactor; mixing said reactants and products, additional low carbon alkyl alcohol, and additional base catalyst in said third reactor at a temperature that is less than the boiling temperature of said additional low carbon alkyl alcohol, and the ratio of said additional low carbon alkyl alcohol to said triglycerides and fatty acids being in the range of 0:1 to 9:1; and maintaining the mixing in said third reactor for a period of residence time to effect base-catalyzed transesterification of the triglycerides, and extracting and transporting the mixture of glycerin and low carbon alkyl alcohol from said third reactor by the third separation device to the said second reactor, and partially recycling the products to the said third reactor; (d) separating biodiesel from said third separation device; (e) processing the glycerin separated from said first separation device to produce crude glycerine; (f) processing the biodiesel separated from said third separation device to produce biodiesel. In the preferred embodiments of the invention, the preferred reaction pressure of said reactors is in the range from 0 bar to 15 bar. In the preferred embodiments of the invention, the preferred reaction temperature of said reactors are in the range from 60DEG C to 120DEG C, and lower than the boiling point of said low carbon alkyl alcohol at said preferred reaction pressure. In the preferred embodiments of the invention, the effluents from acid and base catalyzed reactions are blended and neutralized to produce fertilizer.