Bread yeast is still produced by fermentation using molasses. As shown in Fig. 5, this process includes cultivation, separation, pressurized filtration, and the addition of baking powder. Wastewater derives mainly from centrifugal supernatant and the cell-washing process.
The estimated mass balance of this process is shown in Table 10 assuming that the yeast content is 2.4% of N and 0.36% of P, and the harvest vs. molasses is 75% and sugar content of molasses is 55%. The rate of loss to wastewater was estimated to be 8% for N and 3% for P. This factory in Hyogo Prefecture had sophisticated treatment systems for its wastewater. The fraction of high concentration was further concentrated and dried to make organic fertilizer. The removal rates of CODMn, TN, and TP are 99, 72, and 44%, respectively. The unit loading factor vs. product was around 3.3 kg of CODMn/t of yeast, 0.58 kg TN/t and 0.058 kg TP/t respectively.
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