The partitioning of copper in the activated sludge process as a function of pH

The uptake of metal onto the biomass in the activated sludge system has been reported to be a function of pH, metal concentration, organic ligand concentration and time of contact. All of the previous studies were carried out under batch conditions by adjusting a sample biomass to the desired pH and adding the copper. The test results indicated that as the pH increased more copper was adsorbed per unit of biomass.

In this study, complete mix continuous flow biological reactors, under steady state conditions, were used to observe the effect of pH on the partitioning of copper in the activated sludge system. The pH values studied, 6.3, 7.4, 8.4, and 8.9, were obtained using phosphate buffers. The copper concentrations were used 176 ppb and 17.5 ppb.

At the influent copper concentration of 176 ppb, the amount of copper adsorbed per unit of biomass increased from .33 ug Cu/mg MLVSS at pH 6.4 to .42 ug CU/mg MLVSS at a pH of 8.9. At 17.5 ppb influent copper, the copper adsorbed increased from .08 μg Cu/mg MLvss at pH 6.4 to .1l μg Cu/mg MLVSS at pH 8.9. The free ionic form remained less than 10-7 moles per liter at all conditions. The concentration of soluble copper did not vary appreciably as a function of pH but was controlled by the concentration of solids in the mixed liquor.