TORULA YEAST WASTE-WATER TREATMENT BY DOWNFLOW ANAEROBIC FILTERS

The by-products, molasses, of the sugar industry are used as a source of biomass. Torula yeast is obtained from molasses fermentation and used as animal food. After the separation of the yeast, a highly concentrated wastewater is produced. At present, the wastewater is spread on the land or discharged to streams, causing serious pollution problems. More than 30 000 m3 of wastewater from the torula yeast industry are daily produced with an average COD concentration of 20 g/litre and a pH around 4.5 (Travieso et al., 1988, Report to Sugar Industry Ministry, Havana, Cuba). Considering the advantages of the anaerobic downflow filter for the treatment of acidic waste-waters a study of this system for the treatment of torula yeast wastewaters was developed. The effects of the support media, the hydraulic retention time, the organic loading and the effluent recirculation on the filter efficiency were studied. Among gravel media, polystyrene media and ceramic media, it was demonstrated that ceramic media were the most effective. For the operational parameters studied, a hydraulic retention time of 3 days, organic volumetric loading of 6 kg COD/m3 day and the use of an effluent recirculation ratio of 1:1 were considered the optimum.