Demonstration of Intermitttent On/Off Aeration at a Municipal Wastewater Treatment Plant for Denitrification and Energy Savings

Final Report

Intermittent On/Off Aeration

A 24 hour cycling monitoring

A 24 hour cycling samples from the oxidation ditches was analyzed for closely examining the activated sludge performance. Nitrate decreased down to 5 mg-N/L (Figure 3.6) with the intermittent operation. Without shutting off air, nitrate concentration will remain about 20 mg-N/L. Even though it is not possible to completely remove nitrate in ditch, phosphorus concentration slightly increased during the air-shut-off period (Figure 3.7). Poly-b-hydroxybutyrate (PHB) concentration also increased when air was shut-off, indicating the storage of intercellular energy at the anoxic stage. Both phosphorus increase and PHB storage in anaerobic stage are symptoms of occurrence of phosphorus accumulating organisms (PAOs).

Figure 3.6 Nitrate concentration for 24 hour cycle

Figure 3.7 Phosphorus concentration for 24 hour cycle

Though the PAOs seem to exist in the activated sludge, the biological phosphorus removal was not significant. The influent and effluent phosphorus concentration are shown in Figures 3.8 and 3.9. The effluent phosphorus concentrations were measured in the period while the Alum pump was shut off. Results indicated that phosphorus was removed only from 3 mg-P/L influent to 1.5 mg-P/L in the effluent, which is not sufficient to meet the effluent limit.

Figure 3.8 Influent total phosphorus concentration

Figure 3.9 Effluent phosphorus concentration

Therefore, even the PAOs seem to be exist in plant, its population may still not enough to remove phosphorus.

More information on this topic: Gerry Novotny