Q2. What is the effect of adding carbon source in anaerobic phase?
By addition of carbon source in anaerobic phase, more readily biodegradable compounds are available to PAO/DNPAO for synthesis internal PHB; thereby the N and P removal efficiencies can be promoted simultaneously.
Q3. What was the phosphorus concentration at the beginning of the anoxic phase?
At the beginning of anoxic phase, phosphorus concentration was normally 42 mg/L on average, and then decreased to 20.8 mg/L at the end of anoxic phase as a result of the denitrifying phosphorus uptake.
Q4. How much phosphorus removal efficiency was achieved in Run 3?
The phosphorus concentrations of influent and effluent in Run 3 both declined to 6.9 and 0.3 mg/L, respectively, with the increased phosphorus removal efficiency of 97%.
Q5. What was the effect of adding NH3-N ions on the biofilm?
The biofilm N-SBR performed well throughout the experimental period with NH3-N ions almost completely converting to NO3- or NO2-.
Q6. What is the effect of the post-aeration phase on the phosphorus removal?
This finding revealed that the post-aeration phase was indispensable to A2N-SBR process for polishing the effluent, as the post aerobic phosphorus uptake accounted for approximately 45% of the phosphorus removal when electron acceptors as NO3--N were not available.
Q7. What is the effect of the HRT on the final nitrogen and phosphorus removal?
the tests of HRT effect indicated that the duration for the anaerobic and anoxic reactions significantly affected the final nitrogen and phosphorus removals especially for the P removal that is prone to occur “second phosphorus” release in the absence of electron donors (e.g. COD) and acceptors (e.g. O2 or NOx-N),thereby lowering the final phosphorus removal efficiency.
Q8. What was the effect of the pH increase in the A2N-SBR process?
In A2-SBR, an immediate and sharp increase in pH ranging from 7.06 to a peak of 7.21 (shown with point A in Fig. 2) was observed at the initial 15 min of anaerobic phase which was attributable to the VFAs uptake by DNPAO/PAO.
Q9. What is the effect of COD/P on phosphorus removal?
In general, high COD/P favors the improvement of phosphorus removal (Fig. 4); however, in the A2N-SBR process that based on the denitrifying phosphorus removal, the final P-uptake capacity also greatly depends on the amount of electron acceptors (NOx-N), i.e. the influent N/P ratios.
Q10. What was the effect of the addition of KNO3 to the initial anoxic phase?
As the mean influent NH4+-N concentration during the spring semester was found to be approximately 25 mg/L lower than that of the autumn semester, a spike of nitrate (KNO3) of 10mg/L NO3--N was added to the initial anoxic phase to ensure there was no limitation of electron acceptors for a complete phosphorus uptake.
Q11. What is the effect of low COD/TN on phosphorus removal?
As a result, the electron donors (COD) available to DNPAO are reduced, finally leading to the deterioration of phosphorus removal capacity.
Q12. What was the average concentration of NH4+-N in the influent wastewater?
The average concentrations of COD, Biochemical oxygen demand (BOD5), total nitrogen (TN), NH4+-N and phosphorus in the influent wastewater over the experimental period were 237±58 mg/L, 145±98 mg/L, 37±21 mg/L, 35±20 mg/L and 12±5 mg/L, respectively.
Q13. Why was the end of the P-uptake not pointed out by DO or pH?
it is worthy noting that on day 241 the end of the P-uptake was not pointed out by DO or pH variations (Figs. 1 and 2), probably due to the fact that the 2h post-aeration reaction was not sufficient for complete phosphorus uptake.
Q14. What is the average phosphorus removal efficiency?
Table 3 Performance of A2N-SBR process for removal of COD, NH4+-N, TN and P (aaverage data are in parenthesis)For the phosphorus removal, as the influent phosphorus concentration was adjusted in a broad range to gain the different COD/P, this subsequently caused a significant fluctuation of phosphorus removal efficiency even though the average phosphorus removal efficiency had reached 89% (Table 3).