Assessment of aeration system performance efficiency: Frequent sampling for damage detection

A study of oxygen transfer efficiency (OTE) in aeration basins, using measu rements of oxygen depletion in offgas collected from them, was carried out over a period of several years by collaborations between the University of California, Los Angeles and the Bureau of Sanitation Research Group of the City of Los Angeles. Measurements were taken of dissolved oxygen (DO), wate r temperature, oxygen depletion, and air flux at each sampling location as part of the process to obtain standardized OTE. Field instruments, permanen tly located near the tanks and galleries, are connected to the control room that automatically records return activated-sludge flow, influent flow, ta nk DO sensor readings, and air flow. Data from the control room and field i nstruments were collected for the times of the samples to provide context a nd some degree of quality control for the samples obtained by the measureme nt team. The combined air flux and OTE measurements not only agree with the familiar inverse relationship between OTE and air flux but have allowed detection o f strong evidence that serious leakage has developed in a few weeks in the air distribution systems of tanks 4 and 5, which was indirectly confirmed b y observation of water ejection from the air release valves on the tanks. H owever, the detail provided by OTE measurements allows more specific unders tanding of the magnitude of the problem and its significance for the operat ion of these tanks. Analysis of the OTE measurements made at the site since 1991 also indicates that the diffusers in some of the tanks may now be in need of cleaning or replacement.