The use of yeasts to reduce the polluting potential of silage effluent

Abstract Silage effluent is one of the most potent agricultural wastes. The ability of yeast strains to grow on and purify silage effluent was investigated. Several strains of yeast were isolated from silage effluent in pure culture and their ability to grow on silage effluent was assessed in comparison with a strain of Candida utilis . Further studies were conducted with C. utilis and one of the isolates—strain T2B. This filamentous yeast was identified as a strain of Galactomyces geotrichum . Both strains were able to grow on three different samples of silage effluent of varying age and composition. Mean generation times varied from 4.5 to ca . 26 h. Removal of chemical oxygen demand (COD) and total organic carbon (TOC) was good. For the most dilute effluent studied 91–95% COD removal was obtained, while for the most concentrated effluent, 74–79% reductions were obtained. The greatest reduction in COD noted was from ca . 40,500 to 8500 mg l −1 . Very high reductions of phosphate concentration were obtained and some ammonia was removed. pH rose during treatment to 8.5–9 from initial values of 3.65–5.77. Strain T2B gave consistently higher yields of biomass than C. utilis , producing a maximum of 8.6 g dry weight l −1 on one effluent at 50% dilution. The prospects for using yeasts to treat silage effluent are discussed.