The clear sugar liquid from the pretreatment section is used as the carbon source for fermentation. Qualified microbial strains are introduced, and sterile air is supplied. The temperature is controlled by cooling through internal and external coils in the fermentation tank, maintaining appropriate temperature and air volume for citric acid fermentation. After fermentation, the fermentation broth is temporarily stored in a transfer tank, then heated and sterilized through a heat exchanger. It is separated using a plate-and-frame filter press, with the liquid sent to the extraction section and the solid wet acid residue dried in a tube bundle dryer, cooled by air conveying, and packaged for external sale.

The citric acid fermentation clear liquid from the fermentation section is divided into two parts for TCC neutralization reaction and DCC neutralization reaction. One part of the clear liquid is mixed with dilute DCC acid and enters the TCC reaction unit to react with calcium carbonate, forming calcium citrate. The other part of the clear liquid reacts with calcium citrate produced from the DCC neutralization to form calcium hydrogen citrate. The slurry from both TCC and DCC neutralization reactions is separated using a vacuum belt filter. The calcium hydrogen citrate filter cake from the DCC neutralization is used in the acidolysis reaction unit, where it is mixed with concentrated sulfuric acid. The resulting reaction slurry is separated by a vacuum belt filter, and the filtrate undergoes further filtration through a two-stage plate-and-frame filter press to obtain refined acidolysis liquid. The calcium sulfate filter cake separated by the vacuum belt filter is transported to the calcium sulfate storage via a screw conveyor. The refined acidolysis liquid is passed through a decolorization column and anion-cation exchange devices before being sent to the refining section for concentration.

The refined acidolysis liquid from the extraction section is concentrated, then crystallized by cooling. It is separated using a centrifuge to obtain wet monohydrate citric acid crystals. The wet crystals are dried in a fluidized bed dryer, screened, and fed into a storage bin. After weighing, packaging, and metal detection, the final monohydrate citric acid product is obtained.