Factors affecting the fate of heavy metals in the activated sludge process

Important factors that control the fate of heavy metals in the activated sludge process were studied in laboratory reactors. Because heavy metal adsorption by activated sludge results from the interaction between bacterial cell surfaces and metals in the aqueous solution phase, both phases were characterized and controlled to the extent possible. Activated sludge bacteria were cultured on a soluble wastewater substrate under constant growth-rate conditions, whereas important inorganic or organic complexing ligands in the solution phase were either measured or estimated. An equilibrium chemical model incorporating conditional adsorption constants was successfully used to predict the distribution of metals between soluble chemical species and "surface complexes." Biological solids retention time $(\theta _{c})$ and system pH are factors that could be used to control the distribution of metals between solution and solid phases.