Pretreatment of synthetic dairy wastewater using the sophorolipid-producing yeast Candida bombicola.

The presence of high strength fats and oils in dairy industry wastewaters poses serious challenges for biological treatment systems, and, therefore, its pretreatment is necessary in order to remove them. In the present study, synthetic dairy wastewater prepared in the laboratory was pretreated using the sophorolipid-producing yeast Candida bombicola in a laboratory-scale bioreactor under batch, fed-batch, and continuous modes of operation. To support the yeast growth, the wastewater was supplemented with sugarcane molasses (1% w/v) and yeast extract (0.1% w/v). Results from the batch operated fermentor revealed complete utilization of fats present in the wastewater within 96 h with more than 93% COD removal efficiency. The yeast was, however, able to pretreat the wastewater more quickly and efficiently under fed-batch mode of operation than under batch operated condition in the same fermentor. Continuous experiments were carried out with a wastewater retention time of 28 h in the reactor; results showed very good performance of the system in complete utilization of fats and COD removal efficiency of more than 90%. The study proved the excellent potential of the biosurfactant-producing yeast in pretreating high-fat- and oil-containing dairy industry wastewater.