Organic acids oxidation by Candida utilis: application to industrial waste water treatment

Abstract

A process including an anaerobic acidogenic reactor followed by a yeast reactor in series is proposed to treat highly concentrated effluents of the food industry. Candida utilis was selected and operated in batch or in a continuous stirred tank reactor with acetic acid or propionic acid or butyric acid or a mixture of these acids as the main carbon source while the pH was maintained at 3.5 to minimize bacterial contamination. The yeast growth kinetics was inhibited by the substrate when its concentration was higher than a critical value. A significant uncoupling between growth and substrate utilization was observed in the batch reactor and the transient state of the perfectly mixed reactor could not be predicted from batch data. If the continuous reactor was conveniently operated, the 97% TOC abatement obtained was independent of inlet concentration and space time provided that the space time was higher than the washout value. Such large loading rates as 30 kg TOC m −3 day could then be treated. Sludge production was of the same order of magnitude as in a conventional activated sludge reactor. The solids were easily flocculated and settled after neutralising the suspension. The same overall abatement was obtained with a pilot reactor treating on line the effluent of an acidogenic reactor fed with beet molasses. The organic acids were completely oxidised and the TOC abatement depended on the conversion of the initial compounds in acids. However, the liquid–solids separation required then a flocculation step with chitosan at low concentration.