Case study of aeration performance under changing process conditions

Off gas analyses of oxygen transfer efficiency (OTE) at Terminal Island Treatment Plant of Los Angeles document changing performance of fine-pore diffusers in an activated sludge plant from 1991 to 1998. Although the plant treats a challenging waste stream, the aeration tanks are little different from other plants. Recent sessions provided improved time and space resolution, compared to previous work. Samples were more closely spaced, and some samples were taken in the intervals between the aeration grids, at the ends of the tanks, and near the edges of the grids. Very short term fluctuations in the data were assessed by leaving the hood in the same position for 1-2 h. The 1998 efficiencies were low. Analysis of the measurements since 1991 shows effects expected from fouling, and there was also extensive deterioration of the air distribution system that has now been remedied by a refurbishment program. These measurements show the degree to which efficiency losses may grow unrecognized if OTE measurements are not done. Hence. this study may serve as a prototype for similar measurement programs at other plants.