Effects of Heavy Metals on the Specific Ammonia and Nitrate Uptake Rates in Activated Sludge

Toxicity of heavy metals on activated sludge has already been considered as an important factor in the biological nutrient removal (BNR) system. This study identified the inhibition of nitrogen removal performance, including the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR), by adding different combinations of heavy metals [lead (Pb), nickel (Ni), cadmium (Cd), Pb+Ni, Ni+Cd, Pb+Cd, and Pb+Ni+Cd)] with seven concentration levels (0, 2, 5, 10, 15, 25, and 40 ppm) via batch experiments. This study investigated the interaction effect of these metal ions on both nitrification and denitrification, which had not been explored in previous studies. Experimental results showed that Ni had the highest inhibition on SAUR, whereas Cd had the highest inhibition on SNUR. In addition, no significant inhibition of SAUR or SNUR was observed upon adding even as high as 40 ppm of Pb into the activated sludge. Furthermore, no synergistic effect was found when different heavy metals were simultaneously added in different concentrations. It was also observed that first-order kinetic reaction could model the inhibition behaviors of both SAUR and SNUR of activated sludge with different combinations of heavy metals. In addition, the heavy metal biosorption ability by BNR activated sludge followed the order: Pb approximate to Cd > Ni. Finally, the specific biosorption capacity of heavy metals by activated sludge was found to increase upon increasing the heavy metal concentrations and decreasing mixed liquor suspended solids.