Nutrient removal and phosphorus recovery in the anaerobic/oxic/anoxic process combined with sludge ozonation and phosphorus adsorption

摘要

A continuous A/O/A (anaerobic/oxic/anoxic) process with sludge ozonation and phosphorus adsorption was operated under various ozonation conditions to meet increasingly stringent requirements for environmental protection and phosphorus resource recovery. In this system, excess sludge was withdrawn from the anoxic tank and was ozonated. The supernatant of ozonated sludge flowed into a phosphorus adsorption column packed with zirconium-ferrite adsorbent. The effluent of the column and the settlings of the ozonated sludge were recirculated to the A/O/A system. Although adequate sludge reduction was observed, deterioration of nitrification was confirmed when the sludge amount for ozonation was set at 16% of total MLSS per day. The decrease in the sludge amount for ozonation (9.4% of total MLSS per day) resulted in efficient nitrogen removal while MLSS concentration was gradually increased. Under this condition, no excess sludge was withdrawn during at least 2 months operation. The phosphorus concentration in each tanks indicated that phosphorus was removed by both oxygen utilizing PAOs (polyphosphate-accumulating organisms) and nitrateitrate utilizing PAOs. Phosphorus in sludge was solubilized by ozonation and a large part of the solubilized phosphorus consisted of PO4-P. Then, over 90% of PO4-P was recovered in the phosphorus adsorption column.