A novel denitrifying phosphorus removal and partial nitrification, anammox (DPR-PNA) process for advanced nutrients removal from high-strength wastewater.

This study developed a novel DPR-PNA (denitrifying phosphorus removal, partial nitrification and anammox) process for sustaining high-strength wastewater treatment in a modified continuous flow reactor without external carbon source. After 259-days operation, a synchronous highly-efficient total inorganic nitrogen, PO43--P and CODcr removal efficiencies of 88.5%, 89.5% and 90.1% were obtained, respectively even influent nitrogen loading rate up to 3.2 kg m-3 d-1. Batch tests revealed that denitrifying phosphorus accumulating organisms (DPAOs) using NO3--N as electron acceptors significantly enriched (74% in total PAOs), which emerged remarkable positive impacts on deep-level nutrient removal as the key limiting factor. Furthermore, the NO2--N inhibitory threshold value (∼20.0 mg L-1) for DPAOs was identified, which demonstrated as an inhibitory component in excessive recycling NOx--N. From the molecular biology perspective, Dechloromonas-DPAOs group (18.59%) dominated the excellent dephosphatation performance, while Nitrosomonas-AOB (ammonia oxidizing bacteria) group (16.26%) and Candidatus_Brocadia-AnAOB (anammox bacteria) group (15.12%) were responsible for the desirable nitrogen loss process. Overall, the present work highlighted the novel DPR-PNA process for nutrients removal is a promising alternation for wastewater of high nitrogen but low carbon.

Enhancement of nitrite production via addition of hydroxylamine to partial denitrification (PD) biomass: Functional genes dynamics and enzymatic activities.

This study investigated the activity of partial denitrification (PD) biomass/key enzymes, functional gene expressions in response to 0 ~ 50 mg/L hydroxylamine (NH2OH) addition. Results indicated that NH2OH contributed to nitrite (NO2--N) production, facilitating the maximum increase of nitrate (NO3--N) to NO2--N transformation ratio to 80.47 ± 2.82%, leading to 2.56-fold NO2--N higher than those of control. The observed transient inhibitory effect on NO3--N reduction process was attributed by high-level NH2OH (35 ~ 50 mg/L). Enzymatic assays revealed the enhanced activity of both NO3--N and NO2--N reductase while the former showed obvious superiority which led to high NO2--N accumulation. These results were further confirmed by the corresponding functional genes (narG, napA, nirS and nirK). Besides, negative influence of NH2OH addition was limited to PD aggregates, due to the increasing secretion of extracellular polymeric substances (EPS) as well as proteins/polysaccharides ratios in tightly-bound structure of EPS.