Method for manufacturing a carboxylic acid comprising the steps of - subjecting a carbon source to a fermentation step to form a carboxylic acid, which fermentation step comprises the steps of fermenting a carbon source by means of a micro-organism in a fermentation broth to form carboxylic acid and neutralizing at least part of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate, - subjecting the magnesium carboxylate to an acidification step wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising carboxylic acid and magnesium chloride, - subjecting the aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step, to form an effluent comprising carboxylic acid and a magnesium chloride solution, - providing an aqueous solution comprising 5-25 wt.% of MgCl2 and optionally organic contaminants to an evaporation step, wherein water and, where present, organic components are evaporated, - withdrawing an aqueous solution with a MgCl2 concentration of 25-35 wt.% from the evaporation step and providing it to a preconcentrator where it is contacted with a HCl containing gas stream with a temperature of at least 300°C, - providing an aqueous solution with a MgCl2 concentration of 35-45 wt.% resulting from the preconcentrator to a thermohydrolysis reactor, the reactor being at a temperature of at least 300°C, - withdrawing MgO from the thermohydrolysis reactor in solid form, and withdrawing a HCl containing gas stream from the thermohydrolysis reactor, said HCl-containing gas stream having a temperature of at least 300°C, - providing the HCl-containing gas stream with a temperature of at least 300°C to the preconcentrator, - withdrawing a HCl-containing gas stream with a temperature of at most 150°C from the preconcentrator. - subjecting a carbon source to a fermentation step to form a carboxylic acid, which fermentation step comprises the steps of fermenting a carbon source by means of a micro-organism in a fermentation broth to form carboxylic acid and neutralizing at least part of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate, - subjecting the magnesium carboxylate to an acidification step wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising carboxylic acid and magnesium chloride, - subjecting the aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step, to form an effluent comprising carboxylic acid and a magnesium chloride solution, - providing an aqueous solution comprising 5-25 wt.% of MgCl2 and optionally organic contaminants to an evaporation step, wherein water and, where present, organic components are evaporated, - withdrawing an aqueous solution with a MgCl2 concentration of 25-35 wt.% from the evaporation step and providing it to a preconcentrator where it is contacted with a HCl containing gas stream with a temperature of at least 300°C, - providing an aqueous solution with a MgCl2 concentration of 35-45 wt.% resulting from the preconcentrator to a thermohydrolysis reactor, the reactor being at a temperature of at least 300°C, - withdrawing MgO from the thermohydrolysis reactor in solid form, and withdrawing a HCl containing gas stream from the thermohydrolysis reactor, said HCl-containing gas stream having a temperature of at least 300°C, - providing the HCl-containing gas stream with a temperature of at least 300°C to the preconcentrator, - withdrawing a HCl-containing gas stream with a temperature of at most 150°C from the preconcentrator.