Organic acids oxidation by Candida utilis: application to industrial wastewater treatment

A process including an anaerobic acidogenic reactor followed by a yeast rea ctor in series is proposed to treat highly concentrated effluents of the fo od industry. Candida utilis was selected and operated in batch or in a cont inuous stirred tank reactor with acetic acid or propionic acid or butyric a cid 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 kin etics was inhibited by the substrate when its concentration was higher than a critical value. A significant uncoupling between growth and substrate ut ilization was observed in the batch reactor and the transient state of the perfectly mixed reactor could not be predicted from batch data. If the cont inuous reactor was conveniently operated, the 97% TOC abatement obtained wa s 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 orde r of magnitude as in a conventional activated sludge reactor. The solids we re easily flocculated and settled after neutralising the suspension. The sa me overall abatement was obtained with a pilot reactor treating on line the effluent of an acidogenic reactor fed with beet molasses. The organic acid s were completely oxidised and the TOC abatement depended on the conversion of the initial compounds in acids. However, the liquid-solids separation r equired then a flocculation step with chitosan at low concentration. (C) 20 00 Elsevier Science Ltd. All rights reserved.