Citric acid wastewater treatment
The production of citric acid is carried out through fermentation process. The wastewater discharged contains high concentration of biodegradable organics, which are mainly carbohydrates and their degradation products. The wastewater discharged from citric acid production can be divided into high concentration wastewater and low concentration wastewater. In the production and fermentation process of citric acid, the main sources of wastewater are as follows.
Saccharification filter cloth washing water; In the saccharification process, the saccharification liquid must be filtered to remove corn residue. The filter cloth of the filter needs to be cleaned regularly to produce saccharified filter cloth washing water, which contains starch, protein, cellulose, corn fat and sodium ions.
The sugar liquid is fermented to obtain the fermentation liquid, the mycelium is removed by the filter press, and the fermentation clear liquid is sent to the extraction workshop after filtration. At this time, the filter cloth of the filter press needs to be cleaned regularly to produce secondary pressure washing filter cloth water, which contains citric acid, residual sugar, protein and cellulose.
After the fermentation broth is discharged from the fermentation tank, the fermentation tank shall be washed with clean water before the next feeding, so as to produce tank brushing water, which contains citric acid, residual sugar, protein, vitamins, polyether, etc.
The fermentation supernatant is neutralized with CaCO 3 to produce calcium citrate precipitation. The upper mother liquor is “concentrated sugar water”, which contains citric acid, calcium citrate, residual sugar, oil, protein, trace sodium salt, polyether and organic pigment.
The solid-phase calcium citrate obtained in the neutralization process is sent to the filter after slurry mixing, and the residual sugar and soluble impurities are further washed with 80 ~ 90 ℃ hot water. After suction filtration, the sugar washing water is discharged, which contains calcium sulfate, calcium citrate, residual sugar, oil, protein, inorganic calcium and organic pigment.
The first step of refinement is to remove solid substances in the sand filter. The sand column should be washed regularly to form sand column flushing water, which contains calcium sulfate, citric acid and other solids forming filter cake.
Ion exchange light acid water is produced at four positions: sand column, carbon column, anion column and cation column. Before regeneration of the ion exchange column, the dilute acid solution is discharged into the rear column, and then the residual acid is washed to the rear column with clean water. The generated wastewater is ion exchange dilute acid water.
The regeneration flushing water of exchange column comes from carbon column, cation column and anion column. After the regeneration of the exchange column (soaking) is completed and the regenerated wastewater is discharged, wash the residual regenerated wastewater with deionized water.