A novel green production process of citric acid on the pilot scale by directly recycling its extraction effluent

Abstract Citric acid effluent (CAE) treatment, the bottleneck of cleaner production of CA, has attracted intense attention. To solve pollution problems starting from the extraction process, a novel approach to directly recycle the effluent was proposed. First, a novel adaptive evolutionary method with morphology control was established to domesticate the CA-producing strain Aspergillus niger in the CAE. Based on this constructed strategy, an adaptive A. niger strain that could tolerate the effluent inhibition was obtained. Next, CAE was directly recycled without pretreatment to make mash for subsequent CA fermentation. Then, the whole CAE recycling-system including liquefaction, fermentation and extraction performance was assessed at laboratory and pilot scale. Here, the recycling process ran steadily on the pilot scale in 12 successive batches. The nutrients in the CAE were effectively utilized without inhibiting the CA fermentation. The proposed strategy for the CAE recycling was simple with low investment and operation cost, which made it appropriate for industrial-scale applications. It also provides inspiration for the effluent recycling in other submerged fermentations which are dominated by the filamentous fungi.