Differences in the isotopic signature of activated sludge in four types of advanced treatment processes at a municipal wastewater treatment plant

The natural abundance of stable isotopes is a powerful tool for evaluating biological reactions and process conditions. However, there are few stable isotope studies on the wastewater treatment process. This study carried out the first investigation on variations in natural abundance of carbon and nitrogen stable isotope ratios (delta C-13 and (delta N-15) of activated sludge in four types of advanced treatment process (extended aeration activated sludge (EAAS), aerobic-anoxic-aerobic (A(2)O), recycled nitrification-denitrification (RND), and modified Bardenpho (MB)) at a municipal wastewater treatment plant. The (delta C-13 and (delta N-15 values of influent suspended solids settled in the primary sedimentation tank (i.e., primary sludge) ranged from -25.4 parts per thousand to -24.6 parts per thousand and 0.5 parts per thousand-2.9 parts per thousand respectively, during monitoring periods. The (delta C-13 values of the activated sludge were -24.6 parts per thousand to -23.6 parts per thousand (EAAS), -25.4 parts per thousand to -24.3 parts per thousand (A(2)O), -25.7 parts per thousand to -24.9 parts per thousand (RND), and -25.7 parts per thousand to -24.3 parts per thousand (MB). The (delta C-13 values of the activated sludge were similar to those of influent suspended solids. However, the (delta C-13 values of activated sludge in EAAS was significantly higher than in A(2)O, RND, and MB. Meanwhile, the (delta N-15 values of activated sludge were obviously higher than influent suspended solids; 5.8 parts per thousand-7.5 parts per thousand (EAAS), 6.6 parts per thousand-8.1 parts per thousand (A(2)O), 5.5 parts per thousand-7.5 parts per thousand (RND), and 5.3 parts per thousand-7.6 parts per thousand (MB). Changes in delta C-13 and delta N-15 values of the activated sludge within the treatment system were also found. These findings indicate that changes in delta C-13 and delta N-15 values of the activated sludge rely on important function for biological wastewater treatment such as nitrification, denitrification, and methane oxidation through wastewater treatment over time.