Effects of acetate and nitrite addition on fraction of denitrifying phosphate-accumulating organisms and nutrient removal efficiency in anaerobic/aerobic/anoxic process

Abstract

The effects of acetate and nitrite on the performance of sequencing batch reactors (SBRs) employing an anaerobic/aerobic/anoxic (AOA) process were investigated. Three types of SBR operations were used: sodium acetate addition at the start of anoxic condition for heterotrophic denitrification (Type 1); sodium acetate addition at the start of aerobic condition for anoxic phosphate removal by denitrifying phosphate-accumulating organisms (DNPAOs) (Type 2: conventional AOA process); and nitrite addition at the start of aerobic condition for inhibition of phosphate-accumulating organisms (PAOs) (Type 3). A track experiment shows that Type 2 led to the best performance of SBRs among the three types. An analysis by fluorescence in situ hybridization (FISH) revealed that nitrite addition decreased the ratio of PAOs with a decrease in phosphorus removal efficiency. The fraction of DNPAOs in Type 2 was the highest at 13%, indicating that Type 2 is suitable for the simultaneous nitrogen and phosphorus removal in the AOA process.

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

“…The residual phosphorus was removed in the final anoxic tank without oxygen. Especially in Phase 4, phosphorus was removed without a decrease in TOC concentration in the anoxic tank, indicating that phosphorus was accumulated by DNPAOs, like previous studies (Ahn et al, 2002a, b;Kuba et al, 1996Kuba et al, , 1997Soejima et al, 2006;Tsuneda et al, 2006). Therefore, it was suggested that DNPAOs contributed to not only phosphorus removal but also denitrification.…”

Modeling and experimental study on the anaerobic/aerobic/anoxic process for simultaneous nitrogen and phosphorus removal: The effect of acetate addition

“…On the contrary, Rieger et al have reported a model without the consideration of GAOs [36]. Furthermore, our previous research on the AOA process [18] has demonstrated that the fraction of GAOs is less than 5% in the AOA process during the entire operation period, thereby allowing GAOs to be neglected in the present study. Given these reports, neither glycogen nor GAOs were considered in the model.…”

“…Glycogenaccumulating organisms (GAOs) were not considered in this model following the report by Soejima et al [18] and Rieger et al [36]. Five dissolved components were considered relevant for the biological conversions and process stoichiometry: oxygen (S O 2 ), organic carbon (COD) (S C ), ammonium (S NH 4 ), nitrate (S NO 2 ), and phosphate (S PO 4 ).…”

“…The activated sludge obtained from a continuous EBPR process basin of a local municipal wastewater treatment plant was inoculated as the seed sludge for the AOA operation. The seed sludge was inoculated from a lab-scale AOA system [18]; thus, the high nitrogen and phosphorus removal efficiencies were achieved. The initial MLSS and mixed liquor volatile suspended solid (MLVSS) concentrations of the seed sludge were 2600 and 1700 mg l À1 , respectively.…”

“…This process, however, has a constraint to achieve such simultaneous removal: a strategy that leaves the phosphate for DNPAOs under the anoxic condition should not complete the phosphate uptake by PAOs under the preceding aerobic condition. Given that the phosphate release under a strictly aerobic condition is linked to an external COD uptake, i.e., in the presence of both the electron acceptor and donor [16,17], the addition of acetate at the beginning of the aerobic condition in the AOA process has already been investigated [15,18]. Although these studies have clearly indicated that the acetate addition contributes to the high nitrogen and phosphorus removal efficiencies in the AOA process, the prediction and optimization regarding the acetate addition is yet to be investigated.…”