In order to investigate the effect of operating
conditions on P release or uptake rate of the sludge,
batch tests were adopted to simulate the anaerobic,
anoxic and aerobic processes. 5 L of the sludge from
the aerobic zone of the OD bioreactor was put into a
laboratory sequence batch reactor (SBR) for settling,
and then 4 L of the supernatant liquid was removed
from the SBR. Afterwards, the concentrated sludge
was washed with tap water to remove NO3− -N and
settled again. 4 L of the simulated wastewater containing
330 mg acetic acid and 15 mg SOP was added
for a total volume of 5 L mixed liquor in the SBR reactor.
The SBR was kept under anaerobic condition
for 2 h by stirring only, then the mixed liquor was divided
into two equal parts: one was exposed to aerobic
conditions for 4-5 h (aerobic period was initiated by
sparging compressed air though a diffuser at the bottom
of the reactor), and the other was exposed to anoxic
condition for 4-5 h after potassium nitrate was
added to obtain a concentration of 15 mg·L−1
NO3− -N
in the reactor (anoxic period was kept by stirring and
nitrogen gas injection to prevent oxygen penetration).
During the test process, samples were taken at certain
intervals for COD, 3
PO4− -P and NO3− -N analysis.