Characteristics of anoxic phosphors removal in sequence batch reactor
WANG Ya-yi , PAN Mian-li , YAN Min , PENG Yong-zhen , WANG Shu-ying
DOI:
Received September 06, 2006,Revised December 17, 2006, Accepted , Available online
Volume 19,2007,Pages 776-782
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The characteristics of anaerobic phosphorus release and anoxic phosphorus uptake were investigated in sequencing batch reactors
using denitrifying phosphorus removing bacteria (DPB) sludge. The lab-scale experiments were accomplished under conditions of
various nitrite concentrations (5.5, 9.5, and 15 mg/L) and mixed liquor suspended solids (MLSS) (1844, 3231, and 6730 mg/L). The
results obtained confirmed that nitrite, MLSS, and pH were key factors, which had a significant impact on anaerobic phosphorus
release and anoxic phosphorus uptake in the biological phosphorous removal process. The nitrites were able to successfully act as
electron acceptors for phosphorous uptake at a limited concentration between 5.5 and 9.5 mg/L. The denitrification and dephosphorous
were inhibited when the nitrite concentration reached 15 mg/L. This observation indicated that the nitrite would not inhibit phosphorus
uptake before it exceeded a threshold concentration. It was assumed that an increase of MLSS concentration from 1844 mg/L to 6730
mg/L led to the increase of denitrification and anoxic P-uptake rate. On the contrary, the average P-uptake/N denitrifying reduced
from 2.10 to 1.57 mg PO4
3??-P/mg NO3??-N. Therefore, it could be concluded that increasing MLSS of the DEPHANOX system might
shorten the reaction time of phosphorus release and anoxic phosphorus uptake. However, excessive MLSS might reduce the specific
denitrifying rate. Meanwhile, a rapid pH increase occurred at the beginning of the anoxic conditions as a result of denitrification
and anoxic phosphate uptake. Anaerobic P release rate increased with an increase in pH. Moreover, when pH exceeded a relatively
high value of 8.0, the dissolved P concentration decreased in the liquid phase, because of chemical precipitation. This observation
suggested that pH should be strictly controlled below 8.0 to avoid chemical precipitation if the biological denitrifying phosphorus
removal capability is to be studied accurately.
