Anaerobically Digesting Hazardous Waste Pichia pastoris Associated with Butyric Acid Cleaner Production

Recombinant Pichia pastoris semisolid hazardous waste treatment is difficult and traditional solid waste treatment is not applicable. However, P. pastoris wastes have features of high density and enriched proteins/polysaccharides, which could supply nitrogen/carbon sources for butyric acid production. The waste P. pastoris was first treated using NaOH to form a waste yeast suspension, and then the suspension was mixed with glucose to obtain a starting medium containing 5.6 g DCW/L (dry cell weight) yeast to initiate butyrate fermentation. The suspension was intermediately supplemented to bring the total waste yeast concentration to 26.3 g DCW/L while continuously feeding the concentrated glucose solution. With the proposed strategy, butyrate concentration reached high levels of 51.0-54.0 g/L using Clostridium tyrobutyricum as the strain. Amino acids/oligosaccharides/SO₄ ^2- in the suspension, raw material costs, complicated pretreatment process, and butyric acid cleaner production could be effectively utilized, reduced, eliminated, and realized. However, the apparent waste P. pastoris reduction rate was only 49% per batch, thus a "tanks in-series type's repeated waste treating system" model was developed to theoretically explore the possibility of increasing the waste yeast reduction rate R. The simulation results indicated that when setting the treatment unit numbers at 4, waste solid concentration could decrease from 26.3 to 3.37 g DCW/L and the hazardous waste yeast reduction rate R would increase from 49 to 97%.