Degrading Malonate Waste in a Membrane Bioreactor: Modeling and Experiments

Membrane bioreactors (MBRs) combine the advantages of biological treatment and microfiltration processes. MBRs have been successfully tested for many purposes including municipal and industrial wastewater. Although numerous research efforts involving MBRs have been performed, most have focused on the removal efficiency of the wastes being treated, rather than developing models that describe the biological and physical processes that occur in MBRs. The main objective of this research was to apply the standard biokinetic model used for conventional activated sludge to a MBR treating malonic acid, a short-chain organic acid contaminant found in industrial wastewater. A secondary objective was to test the MBR for its ability to degrade the same short-chain organic acid, since such organics can be difficult to degrade and are often intermediate products in the degradation of more complex compounds. The experimental values were fit to the standard biokinetic model for a conventional activated sludge process to obtain the biokinetic parameters: Y = 0.297 g active biomass/g malonic acid, kd = 0.331 d−1, Ks = 76.1 mg malonic acid / L, and k = 16.8 g malonic acid / g active biomass — d. The agreement between the model and experimental results suggests that the model (with its assumptions) is a reasonable description of the phenomena associated with a submerged MBR treating malonic acid. The removal efficiency of malonic acid in the MBR was always greater than 95%.