The optimum substrate to biomass ratio to reduce net biomass yields and inert compounds in biological leachate treatment under pure-oxygen conditions

To investigate the effect of both initially present soluble inert COD (S-I) and soluble inert COD formed by microbial activities (S-PM) on the effluen t soluble residual COD (S-R) and to determine biokinetic constants, the pur e-oxygen was employed for the batch assays of biological leachate treatment . The results of this work showed that the effluent residual soluble COD wa s entirely composed of SI and SPM, therefore, could not be reduced below 7- 10% of total influent soluble COD (S-T0.inf), corresponding to the organics removal efficiency of 93-90%. The value of SI of leachate, which is associ ated with the types of wastewaters, was determined as approximately 7.84% o f S-T0.inf and the soluble inert COD by microbial activities was assessed b y means of the coefficient f(PM) Of 0.0474. These results mean that signifi cant amount of feed leachate COD may pass the biological system without any change. On the basis of the concept that microorganisms must satisfy their maintenance energy requirements prior to synthesizing new biomass, a set o f batch assays with various ratios of S-T0.inf /X-0 were carried out to eva luate their effects on the excess biomass production. Decreasing the supply of substrate per unit biomass resulted in gradual decrease in the biomass yields, but, at the same time, it resulted in gradual increase in the bacte ria mediated inert COD as a side effect. The optimum ratios of S-T0.inf /X- 0 were concluded as 0.2-0.6 according to the careful consideration of both aspects on the reduction of net sludge yields and inert COD from microbial activities.