NOVELTY - Producing biodiesel fuel involves: subjecting feed of glycerides (G1) and free fatty acids (A1) to enzymatic (trans)esterification, with alcohol to produce intermediate stream (S1) comprising fatty acid alkyl esters (E1), water, and glycerin; introducing portion of (S1) to a separator to remove glycerin, water, and alcohol, to produce a second intermediate stream (S2) comprising (E1) and unreacted free fatty acids; and introducing (S2) and a base to a fatty acid alkyl ester recovery unit to produce a fatty acid-base complex, that is separated from (E1).    USE - For producing biodiesel fuel (claimed).    ADVANTAGE - The present process converts 100 to 10000 (preferably 1000) gallons per hour of stream to biodiesel fuel; is energy self-sufficient; doesn't require external utilities; and avoids direct discharge of wastewater. The present process includes selecting unit operation and flow configuration that enables the efficient use of enzymes. The process is mobile and feedstock-flexible, so that it can be effectively deployed in a distributed and dynamic way.    DETAILED DESCRIPTION - Producing (P1) biodiesel fuel involves: a) providing a feed stream comprising glycerides and free fatty acids; b) optionally filtering out at least a portion of solids contained in the feed stream; c) introducing the feed stream and an alcohol into a first reactor, operated at effective first reaction conditions and including a first effective esterification and transesterification catalyst, or mixture of such catalysts, to react at least a portion of the free fatty acids with the alcohol to produce fatty acid alkyl esters and water, and to react at least a portion of the glycerides with the alcohol to produce fatty acid alkyl esters and glycerin, thereby producing a first intermediate stream comprising fatty acid alkyl esters, glycerin, water, and alcohol; d) introducing at least a portion of the first intermediate stream to a first separator operated to remove at least some glycerin, water, and alcohol, thereby producing a second intermediate stream comprising fatty acid alkyl esters and unreacted free fatty acids; e) optionally further reacting, separating, or treating the second intermediate stream; and f) introducing the second intermediate stream and a base to a fatty acid alkyl ester recovery unit operated to contact the base with the unreacted free fatty acids to produce a fatty acid-base complex, and separate the fatty acid-base complex from the fatty acid alkyl esters, thereby generating a crude product stream comprising the fatty acid alkyl esters. INDEPENDENT CLAIMS are included for the following:    (1) producing (P2) biodiesel fuel from free fatty acids involving a1) providing a feed stream comprising free fatty acids; b1) introducing the free fatty acids and an alcohol into a first reactor, operated at effective first reaction conditions and including a first effective esterification catalyst, to react at least a portion of the free fatty acids with the alcohol to produce fatty acid alkyl esters and water, thereby producing a first intermediate stream comprising fatty acid alkyl esters, water, and alcohol; c1) introducing at least a portion of the first intermediate stream to a first separator operated to remove at least some water and alcohol, thereby producing a second intermediate stream comprising fatty acid alkyl esters and unreacted free fatty acids; d1) optionally introducing the second intermediate stream and an alcohol to a second reactor, operated at effective second reaction conditions and including a second effective esterification catalyst, to react free fatty acids contained in that with the alcohol to produce fatty acid alkyl esters and water, thereby producing a third intermediate stream comprising fatty acid alkyl esters, water, and alcohol; e1) optionally introducing at least a portion of the third intermediate stream, if produced by step d1), to a second separator operated to remove at least some water and alcohol, thereby producing a fourth intermediate stream comprising fatty acid alkyl esters and unreacted free fatty acids; and f1) introducing the second intermediate stream and/or the fourth intermediate stream, if the fourth stream is produced by steps d1)-e1), and a base to a fatty acid alkyl ester recovery unit operated to contact the base with the unreacted free fatty acids to produce a fatty acid-base complex, and separate the fatty acid-base complex from the fatty acid alkyl esters, thereby generating a crude product stream comprising the fatty acid alkyl esters;    (2) a system configured for carrying out the process (P1) and (P2); and    (3) a biodiesel fuel composition produced by the process (P1) and (P2).