Pulse Aeration of Secondary Aeration Tanks Holds Energy Saving Potential without Compromising Effluent Quality

Results showed no serious effluent quality deterioration when continuously air-mixed anaerobic and anoxic quadrants of the San Jose/ Santa Clara Water Pollution plant's secondary aeration systems were operated in pulse aeration mode. Ammonia concentrations in pulse aerated and continuously aerated tanks were, on average, 0.73 mg/l and 0.63 mg/l, respectively. Such a slight increase in ammonia concentration in pulse aerated tanks was inevitable with reduction in air flow to Quad 3, although the final effluent quality was never affected. Nitrite concentrations were on average 0.15 mg/l and 0.17 mg/l in the pulse aerated and non pulsed tanks, respectively. Nitrate was significantly reduced from an average concentration of 7.26 mg/l in continuously aerated tanks to 4.45 mg/l in the pulse aerated tanks. Phosphate levels in the effluents of pulse aerated experimental tanks were found to be higher than those in continuously aerated control tanks with averages of 2 mg/l and 1.5 mg/l, respectively. No significant difference was observed in mixed liquor suspended solids concentrations between pulse aerated and continuously aerated tanks, signifying that the chosen pulse aeration cycle of 1.5 min ON/10.5 min OFF was, indeed, sufficient to keep solids in suspension. Tanks with pulse aerated anaerobic and anoxic compartments produced final effluent as superior in quality to the NPDES permit requirements as those that were not pulse aerated. The study demonstrated implementation of pulse aeration in anaerobic and anoxic quadrants would result in 13% less total aeration demand with associated annual energy saving potential close to 430,000.