In the present study, the interactive effects of temperature and cultured bacteria on the performance of a biological treatment system of wastewater from a local yeast producing plant were investigated. The main objective of this study was to optimize the operating parameters that reduce organic load and colour. Biological treatment was conducted using a Central Composite Design (CCD) and optimised using Response Surface Methodology (RSM) on Design Expert 7 software. Two dependent variables namely, Chemical Oxygen Demand (COD) removal and colour reduction were studied. COD removal efficiency of 26% and decolourization efficiency of 44% were recorded for the wastewater treatment. The optimised conditions for the biological treatment were found to be at 16.37 g/l of bacterial powder at 25°C for COD removal and colour reduction. The optimised parameters can be used for biological treatment of yeast plant effluent for removal of organic load and colour.