Impact of nitrite on aerobic phosphorus uptake by poly-phosphate accumulating organisms in enhanced biological phosphorus removal sludges

Distinctive species interaction patterns under high nitrite stress shape inefficient denitrifying phosphorus removal performance

Denitrifying phosphorus removal using nitrite as an electron acceptor is an innovative, resource-efficient approach for nitrogen and phosphorus removal. However, the inhibitory effects of nitrite on anoxic phosphorus uptake and process stability are unclear. This study investigated the total phosphorus removal performance under nitrite stress and analyzed microbiome responses in 186 sludge samples. The results indicated that the total phosphorus removal rates and dominant taxon abundance were highly similar under nitrite stress. High nitrite stress induced a community-state shift, leading to unstable dynamics and decreased total phosphorus removal. This shift resulted from increased species cooperation. Notably, the shared genera OLB8 and Zoogloea under non-inhibitory nitrite stress, suggesting their vital roles in mitigating nitrite stress by enhancing carbon and energy metabolism. The response patterns of these bacterial communities to high nitrite stress can guide the design and optimization of high-nitrogen wastewater reactors.

Nitrite-resistance mechanisms on wastewater treatment in denitrifying phosphorus removal process revealed by machine learning, co-occurrence, and metagenomics analysis

Nitrite is a key intermediate in nitrogen metabolism that determines microbial transformations of N and P, greenhouse gas (N₂O) emissions, and system nutrient removal efficiency. However, nitrite also exerts toxic effects on microorganisms. A lack of understanding of high nitrite-resistance mechanisms at community- and genome-scale resolutions hinders the optimization for robustness of wastewater treatment systems. Here, we established nitrite-dependent denitrifying and phosphorus removal (DPR) systems under a gradient concentration of nitrite (0, 5, 10, 15, 20, and 25 mg N/L), relying on 16S rRNA gene amplicon and metagenomics to explore high nitrite-resistance mechanism. The results demonstrated that specific taxa were adopted to change the metabolic relationship of the community through phenotypic evolution to resist toxic nitrite contributing to the enhancement of denitrification and inhibition of nitrification and phosphorus removal. The key specific species, Thauera enhanced denitrification, whereas Candidatus Nitrotoga decreased in abundance to maintain partial nitrification. The extinction of Candidatus Nitrotoga induced a simpler restructuring-community, forcing high nitrite-stimulating microbiome to establish a more focused denitrification rather than nitrification or P metabolism in response to nitrite toxicity. Our work provides insights for understanding microbiome adaptation to toxic nitrite and giving theoretical support for operation strategy of nitrite-based wastewater treatment technology.

Correlating bacterial and archaeal community with efficiency of a coking wastewater treatment plant employing anaerobic-anoxic-oxic process in coal industry

Coking wastewater (CWW) contains various complex pollutants, and biological treatment processes are frequently applied in the coking wastewater treatment plants (CWWTPs). The present work is to evaluate the contaminants removal of a full-scale CWWTP with an anaerobic-anoxic-oxic process (A/A/O), to reveal function of bacterial and archaeal community involved in different bioreactors, and to clarify the relationship between the performance and microbial community. Illumina Miseq sequencing of bacteria showed that β-proteobacteria dominated in three bioreactors with relative abundance of 60.2%~81.7%. 75.2% of sequences were assigned to Petrobacter in the bioreactor A1, while Thiobacillus dominated in A2 and O with relative abundance of 31.8% and 38.7%, respectively. Illumina Miseq sequencing of archaea revealed a high diversity of methanogens existed in A1 and A2 activated sludge. Moreover, Halostagnicola was the dominant archaea in A1 and A2 activated sludge with relative abundance of 41.8% and 66.5%, respectively. Function predicted analysis explored that function of bacteria was similar to that of archaea but the relative abundance differed from each other. A putative biodegradation model of CWW treatment in A/A/O process indicated that A1 and A2 activated sludge mainly reduced carbohydrate, protein, TN, phenol and cyanide, as well as methane production. Bacteria in the bioreactor O were responsible for aerobic biotransformation of residual carbohydrates, refractory organics and nitrification. The redundancy analysis (RDA) further revealed that removal of COD, TN, and NO₃^--N, phenol and cyanides were highly correlated with some anaerobic bacteria and archaea, whereas the transformation of NH₄⁺-N was positively correlated with some aerobic bacteria.

Ameliorating effect of nitrate on nitrite inhibition for denitrifying P-accumulating organisms

Lowered air supply and organic carbon need are the key factors to reduce wastewater treatment costs and thereby, avoid eutrophication. Denitrifying PO₄^3-- removal (DPR) process using nitrate instead of oxygen for PO₄^3- uptake was started up in the sequencing batch reactor (SBR) at a nitrate dosing rate of 20-25 mg N L^-1 d^-1. Operation with a real municipal wastewater supplied with CH₃COONa, K₂HPO₄ and KNO₃ succeeded in the cultivation of biomass containing denitrifying polyphosphate accumulating organisms (DPAOs). The durations of SBR process anaerobic/anoxic/oxic cycles were 1.5 h, 3.5 h and 1 h, respectively. SBR operation resulted in a maximum PO₄^3--P uptake of 17 mg PO₄^3--P g^-1 MLSS. The highest TN and PO₄^3- removal efficiencies were observed during the first half of reactor operation at 77 (±10) % and 71 (±5) %, respectively. An average COD removal rate of 172 (±98) mg g^-1 MLSS and a high average removal efficiency of 89 (±4) % were achieved. Nitrite effect with/without nitrate as DPR electron acceptor was investigated in batch-scale to show possibilities to use high nitrite and nitrate contents simultaneously as electron acceptors for the anoxic phosphate uptake. Nitrate attenuation against nitrite toxicity can be economically justified in full-scale treatment applications in which wastewater has a high nitrogen content. Nitrate attenuated nitrite toxicity (caused by nitrite content at 5-100 mg NO₂^--N L^-1) when using supplemental additions of nitrate (at concentrations of 45-200 mg NO₃^--N L^-1) in batch tests. Illumina sequencing emphasized that during biomass adaption microbial community changed by lowered aerobic cycle length and by lowered nitrate dosing towards representation of key DPAO/PAO- organisms, such as Candidatus Accumulibacter, Xanthomonadaceae, Comomonadaceae, Saprospiraceae and Rhodocyclaceae. This study showed that DPAO biomass adaption to nitrate maintained an efficient COD, nitrogen and phosphorus removal and the biomass can be applied for treatment of wastewater containing high nitrite and nitrate content.

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.

Interaction between β-lactam antibiotic and phosphorus-accumulating organisms

β-Lactam antibiotics have been widely used in clinic due to strong antibacterial activity with mild adverse side effects and have been detected in the environment. In the enhanced biological phosphorus removal (EBPR) process, phosphorus-accumulating organisms (PAOs) play a major role. In this study, amoxicillin, aztreonam, and cefoperazone are the selected antibiotics that applied in investigating the interaction mechanism of β-lactam antibiotics and PAO. The effects of β-lactam antibiotics on PAOs were analyzed comprehensively from the aspects of antibiotic impacts on phosphorus removal rate, intracellular polymer, their toxicity to PAOs, and PAO impacts on the fate of β-lactam antibiotics. It was found that the phosphorus removal rate of PAO increased by 19.21% and 15.75%, respectively at 10 mg/L amoxicillin and aztreonam, while cefoperazone had certain inhibition effect on phosphorus removal efficiency. Quantitative analysis shows that in the aerobic stage, three kinds of β-lactam antibiotics could promote the synthesis of polyphosphates (poly-P). The degradation rates of three antibiotics were as follows: amoxicillin > aztreonam > cefoperazone. The fate characteristics of antibiotics provide a theoretical basis for environmental risk assessment. The toxic effects of three antibiotics were as follows: cefoperazone > aztreonam > amoxicillin according to the bacteriostatic test. It provided a scientific theoretical basis for systematically evaluating the biological toxicity of antibiotic pollutants.

Efficient phosphate accumulation in the newly isolated Acinetobacter junii strain LH4

Phosphate (PO₄^3-) accumulation associated with bacteria contributes to efficient remediation of eutrophic waters and has attracted attention due to its low cost, high removal efficiency and environmental friendliness. In the present study, we isolated six strains from sludge with high concentrations of chemical oxygen demand, total nitrogen and total phosphorus levels. Among them, strain LH4 exhibited the greatest PO₄^3- removal ability. Strain LH4 is typical of Acinetobacter junii based on physiological, biochemical, and molecular analyses and is a PO₄^3--accumulating organism (PAO) based on toluidine blue staining. The strain grew quickly when subjected to aerobic medium after pre-incubation under anaerobic condition, with a maximum OD₆₀₀ of 1.429 after 8 h and PO₄^3- removal efficiency of 99%. Our data also indicated that this strain preferred utilizing the carbon (C) sources sodium formate and sodium acetate and the nitrogen (N) sources NH₄Cl and (NH₄)₂SO₄ over other compounds. To achieve optimal PO₄^3- removal efficiency, a C:N ratio of 5:1, inoculation concentration of 3%, solution pH of 6, incubation temperature of 30 °C, and shaking speed of 100 rpm were recommended for A. junii strain LH4. By incubating this strain with different concentrations of PO₄^3-, we calculated that its relative PO₄^3- removal capacity ranged from 0.67 to 3.84 mg L^-1 h^-1, ranking in the top three among reported PAOs. Our study provided a new PO₄^3--accumulating bacterial strain that holds promise for remediating eutrophic waters, and its potential for large-scale use warrants further investigation.

Biological Phosphorus Removal During High-Rate, Low-Temperature, Anaerobic Digestion of Wastewater

We report, for the first time, extensive biologically mediated phosphate removal from wastewater during high-rate anaerobic digestion (AD). A hybrid sludge bed/fixed-film (packed pumice stone) reactor was employed for low-temperature (12°C) anaerobic treatment of synthetic sewage wastewater. Successful phosphate removal from the wastewater (up to 78% of influent phosphate) was observed, mediated by biofilms in the reactor. Scanning electron microscopy and energy dispersive X-ray analysis revealed the accumulation of elemental phosphorus (∼2%) within the sludge bed and fixed-film biofilms. 4′, 6-diamidino-2-phenylindole (DAPI) staining indicated phosphorus accumulation was biological in nature and mediated through the formation of intracellular inorganic polyphosphate (polyP) granules within these biofilms. DAPI staining further indicated that polyP accumulation was rarely associated with free cells. Efficient and consistent chemical oxygen demand (COD) removal was recorded, throughout the 732-day trial, at applied organic loading rates between 0.4 and 1.5 kg COD m^-3 d^-1 and hydraulic retention times of 8–24 h, while phosphate removal efficiency ranged from 28 to 78% on average per phase. Analysis of protein hydrolysis kinetics and the methanogenic activity profiles of the biomass revealed the development, at 12°C, of active hydrolytic and methanogenic populations. Temporal microbial changes were monitored using Illumina MiSeq analysis of bacterial and archaeal 16S rRNA gene sequences. The dominant bacterial phyla present in the biomass at the conclusion of the trial were the Proteobacteria and Firmicutes and the dominant archaeal genus was Methanosaeta. Trichococcus and Flavobacterium populations, previously associated with low temperature protein degradation, developed in the reactor biomass. The presence of previously characterized polyphosphate accumulating organisms (PAOs) such as Rhodocyclus, Chromatiales, Actinobacter, and Acinetobacter was recorded at low numbers. However, it is unknown as yet if these were responsible for the luxury polyP uptake observed in this system. The possibility of efficient phosphate removal and recovery from wastewater during AD would represent a major advance in the scope for widespread application of anaerobic wastewater treatment technologies.

Nitrification and denitrifying phosphorus removal in an upright continuous flow reactor

Simultaneous nitrification and denitrifying phosphorus removal was achieved in a single-sludge continuous flow bioreactor. The upright bioreactor was aligned with a biomass fermenter (BF) and operated continuously for over 350 days. This study revealed that unknown bacteria of the Saprospiraceae class may have been responsible for the successful nutrient removal in this bioreactor. The successive anoxic-aerobic stages of the bioreactor with upright alignment along with a 60 L BF created a unique ecosystem for the growth of nitrifier, denitrifiers, phosphorus accumulating organisms and denitrifying phosphorus accumulating organisms. Furthermore, total nitrogen to chemical oxygen demand (COD) ratio and total phosphorus to COD ratio of 0.6 and 0.034, respectively, confirmed the comparative advantages of this advanced nutrient removal process relative to both sequencing batch reactors and activated sludge processes. The process yielded 95% nitrogen removal and over 90% phosphorus removal efficiencies.