Process for the production of an organic acid from a lignocellulosic feedstock. The process is integrated with a pulp mill and comprises: a) pre-treating a lignocellulosic feedstock with an alkaline liquor from the pulp, thereby obtaining a pretreated cellulosic feed and a black liquor; b) subjecting the pretreated cellulosic feed from step a) to enzymatic hydrolysis, thereby obtaining a saccharide feed; c) subjecting the saccharide feed from step b) to microbial fermentation using calcium oxide from the pulp mill as a neutralising agent, thereby obtaining an organic acid calcium salt; d) treating the organic acid calcium salt with sulfuric acid, thereby obtaining the organic acid; e) optionally isolating lignin from the black liquor obtained in step a), thereby obtaining lignin and weak black liquor; and f) returning the black liquor from step a) and/or the weak black liquor from step e) to the pulp mill chemical recovery process.