The release of PO4 3-P and TP accompanied by the simultaneous
release of K and Mg was observed in all samples during anaerobic
fermentation (Figs. 4A, B and S4), indicating most P in the fermentation
broth was mainly released from the polyphosphate in PAOs.
As shown in Fig. 4, the TP contents in the water phase of PGS-F and
PFS-F rapidly increased to 23.9 ± 0.3 mg/gVSS (26.6% of TP release
efficiency) and 34.4 ± 0.4 mg/gVSS (34.1% of TP release efficiency),
respectively, on the first day of anaerobic fermentation. They then
rose gradually from day 2 to day 7 at approximately 7.8 (R2 = 0.99)
and 6.7 mg/(gVSSd) (R2 = 0.99) for PGS-F and PFS-F, respectively.
The TP contents in the water phase of PGS-F and PFS-F on day 7
were 71.9 mg/gVSS (80.0% of TP release efficiency) and 74.6 mg/
gVSS (73.9% of TP release efficiency), respectively. The amount of
TP released from PFS-F was slightly greater than that from PGS-F
owing to the higher TP content in PFS-I (Table S1). Overall, the
TP-release capacities of PGS-F and PFS-F did not differ greatly. In
addition, the PO4 3-P and TP contents were almost at the same
levels in the water phases of PGS-F and PFS-F during anaerobic fermentation.
The average ratios of PO4 3-P/TP for PGS-F and PFS-F
were 0.96 and 0.97, respectively. Therefore, most TP in the fermentation
broth was composed of PO4 3-P, which has also been
observed by other researchers