Inhibition of the respiratory chain reactions in denitrifying EBPR biomass under simultaneous presence of acetate and electron acceptor

Effect of anaerobic duration on biological phosphorus removal in reversed AAO process (anoxic-anaerobic-oxic)

In this study, the effect of anaerobic duration on phosphorus (P) removal in reversed AAO (anoxic-anaerobic-oxic) process was investigated using synthetic wastewater (with different volatile fatty acid (VFA) ratios) and real wastewater. The P, poly-hydroxyalkanoates (PHAs), dehydrogenase activity (DHA), polyphosphate kinases (PPK), electron transfer system (ETS), and adenosine 5'-triphosphate (ATP) were determined as indicators. The highest P removal efficiencies were achieved at an anaerobic duration of 3, 4, and 6 h for 15, 30, and 60% VFA ratio in synthetic wastewater. The amount of the released P and stored PHAs can be manipulated by different anaerobic durations, but the P removal efficiency cannot be guaranteed with higher stored PHAs. Additionally, the energy metabolism confirmed the significance of anaerobic duration extension on microbial activity. The highest values of four indicators were all achieved at anaerobic duration of 4 h with 30% VFAs ratio which achieved the highest P removal efficiency. Real wastewater experiments also proved the reproductivity of these results. We defined this phenomenon as the "hunger response" where microorganisms responded to suppression (anaerobic duration extension) with higher activity after the end of the anaerobic condition. These results can provide references for better design and operation of biological phosphorus removal in RAAO process.

Nitrite and nitrate inhibition thresholds for a glutamate-fed bio-P sludge

Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater. A widely known cause of EBPR deterioration in wastewater treatment plants (WWTPs) is the presence of nitrate/nitrite or oxygen in the anaerobic reactor. Moreover, most existing studies on the effect of either permanent aerobic conditions or inhibition of EBPR by nitrate or free nitrous acid (FNA) have been conducted with a "Candidatus Accumulibacter" or Tetrasphaera-enriched sludge, which are the two major reported groups of polyphosphate accumulating organisms (PAO) with key roles in full-scale EBPR WWTPs. This work reports the denitrification capabilities of a bio-P microbial community developed using glutamate as the sole source of carbon and nitrogen. This bio-P sludge exhibited a high denitrifying PAO (DPAO) activity, in fact, 56% of the phosphorus was uptaken under anoxic conditions. Furthermore, this mixed culture was able to use nitrite and nitrate as electron acceptor for P-uptake, being 1.8 μg HNO₂-N·L^-1 the maximum FNA concentration at which P-uptake can occur. Net P-removal was observed under permanent aerobic conditions. However, this microbial culture was more sensitive to FNA and permanent aerobic conditions compared to "Ca. Accumulibacter"-enriched sludge.

Comparison of the dynamics, biokinetics and microbial diversity between activated sludge flocs and aerobic granular sludge

This work aimed to compare the dynamics, biokinetics, and microbial diversity between activated sludge flocs (ASF) and aerobic granular sludge (AGS) whose systems were operated under similar experimental conditions in terms of inoculum, feeding, substrate source, etc. Therefore, the kinetic parameters involved in the organic matter removal, nitrification, denitrification, and dephosphatation were determined, as well as the microbial changes were assessed by metagenomics analysis. Regarding the kinetic parameter yield coefficient (Y), values of 0.55 and 0.36 g VSS/g COD were found for ASF and AGS, respectively, showing a higher sludge production in ASF and the importance of feast/famine periods for lowering sludge production in AGS systems. AGS presented a lower sludge production and a higher endogenous consumption rate than ASF. The activity of phosphorus-accumulating bacteria was remarkably higher in AGS. Although both biomasses were aerobic, their kinetic parameters had significant differences.