Purification of waste water high in carbohydrates and simultaneous production of high protein feed product

A method for purifying waste water that is high in carbohydrates including starch while obtaining therefrom a high-protein feed product, comprising the steps of:

• inoculating said waste water at a pH of approximately 6, with yeast inoculant that converts starch, sugar and nutrients to more yeast, and in an amount sufficient to so convert substantially all the starch, sugar and yeast consumable nutrients in said waste water, said inoculant being at a pH such that a mixture of waste water and inoculant is adjusted to approximately 5,
• growing said inoculated yeast in said waste water while
• the pH in said water-inoculant mixture increases gradually from an initial value of approximately 5, toward neutrality as a by-product of the growth of the yeast without addition of further materials,
• circulating and recirculating the inoculated water with air in an amount that enhances the growth rate, and
• venting waste CO.sub.2 to atmosphere,
• separating out purified liquid waste from moist solids, at the time when the pH is about 7,
• harvesting a large proportion of moist solids, while selecting a smaller proportion for recycle,
• sending said smaller proportion to a treatment zone,
• treating it there with at least one antibiotic and lowering the pH there to about 3.5, by addition of acid, both to suppress a substantial portion of bacterial growth while the yeast grows, and then, after a suitable treatment time,
• recycling the treated material to said inoculating step as the inoculant yeast.