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When Scheele discovered lactic acid, he recovered and purified the lactic acid from sour whey by saturation with lime, filtering off the crude calcium lactate, acidifying the crystal mass with “acid of sugar” (oxalic acid), filtering off the calcium oxalate, and evaporating to obtain a crude viscous lactic acid [12, 13]. Basically, this process with a calcium‐based neutralized fermentation and sulfuric acid instead of oxalic acid is the same process used in industry today for the production of crude lactic acid. Drawbacks are the continuously rising costs of lime/chalk, sulfuric acid, and other chemicals and the disposal of large quantities of gypsum (CaSO₄·2H₂O), as an unavoidable side product of this technology.

In such a process also the first downstream processing (DSP) step, biomass removal by filtration, can be accomplished relatively easily in a (mild) liming step, in essence quite similar to the traditional liming step to remove protein in sugar beet or sugarcane processing in sugar mills. A simplified block scheme of the traditional lactic acid production process including fermentation is shown in Figure 1.5.

TABLE 1.2 Summary of Lactic Acid Purification Methods

Lactic Acid Purification Method	Advantages	Disadvantages
Crystallization [27, 28]	Highly pure lactic acid product	Amount of mother liquor by‐product, scalability
Esterification/distillation [52]	Highly pure acid, scale‐up	Relatively high utility cost, amount of residue as by‐product
Lactic acid distillation [27, 28, 53]	Good splitting for heavy compounds	Amount of residue as by‐product
Extraction [54, 55]	Potentially high yield	Complex (e.g., for emulsion, entrainment issues), extractant cost