Achieving partial nitrification: A strategy for washing NOB out under high DO condition

Study on adsorption and desorption characteristics of lead pollution by biofilm in drinking water pipeline from multi-factor perspective

This study investigates lead adsorption and desorption behaviors in biofilms on drinking water pipeline materials (PVC, 304 stainless steel, copper) under varying flow rate, pH, and residual chlorine. Biofilms on stainless steel exhibited the highest adsorption capacity (450.81 μmol/m2), whereas PVC biofilms had the greatest desorption potential (25.30 μmol/m2). Optimal lead adsorption occurred at neutral pH (7.5), low flow velocity (0.10 m/s), and moderate chlorine concentration (0.3 mg/L). Optimal lead adsorption occurred at neutral pH (7.5), low flow velocity (0.10 m/s), and moderate chlorine concentration (0.3 mg/L). In contrast, higher flow velocities, acidic conditions, and elevated chlorine levels promoted desorption or inhibited interactions. PVC biofilms exhibited the highest biomass (1.58 × 106 CFU/cm2) and extracellular polymeric substances (EPS) (348 mg/m2), correlating with increased lead adsorption. Functional analysis revealed a higher abundance of ion-transport-related (functions associated with the movement of ions such as heavy metals across microbial cell membranes) functions in PVC biofilms, contributing to enhanced stability. The study offers valuable insights for optimizing pipe material selection and operational strategies to reduce lead contamination in water systems.

Increasing the light-dark ratio enhances nitrogen removal performance by altering the mechanism in photogranules

Photogranules provide a cost-effective solution for treating mariculture wastewater. The impact of light: dark ratios on nitrogen removal needs further study. We tested four photogranular reactors with different light: dark ratios and found that higher ratios increased total inorganic nitrogen (TIN) removal rate, achieved 99 % every 48 h at a 5.5 h:0.5 h ratio. Kinetic and metagenomic analyses showed that increased TIN removal was mainly due to a significant transformation in the nitrogen removal mechanism of photogranules. At 5.5 h:0.5 h, diatoms replaced the outer cyanobacteria, causing nitrifying bacteria to disappear via direct and indirect inhibition. In addition, the mechanisms by which photogranules remove nitrate nitrogen are diverse. Adjusting the light: dark ratio could change the nitrogen removal mechanism of photogranules in mariculture wastewater treatment and enhance their nitrogen removal performance. This offered insights into controlling light - related parameters of photogranules for practical engineering applications.

Optimization of AAO process for reduced N2O emissions and enhanced nitrogen removal in municipal wastewater treatment: Exploring carbon supplementation and DO control strategies

The anaerobic/anoxic/oxic (AAO) process remains a common nutrient removal process in municipal wastewater treatment, yet research focusing on concurrent optimization of process performance and N2O emissions reduction is scarce. This study aimed to investigate the mitigation of N2O emissions and enhance nitrogen removal efficiency in an AAO system treating low C/N domestic wastewater by establishing a fully enclosed gas-collecting continuous flow reactor and implementing carbon supplementation and dissolved oxygen (DO) control strategies. The results indicated that carbon supplementation in the anoxic zone effectively reduced nitrate concentrations and mitigated the accumulation of dissolved N2O below 0.1 mgN/L. The moderate DO control (1-2 mg/L) could ensure the nitrification efficiency while reducing the gaseous N2O emission rate to 63.48 mgN/d, and decreasing the dissolved N2O concentration in the effluent to below 0.01 mgN/L. Both too high and too low DO levels were detrimental to N2O emission mitigation. The optimized AAO process achieved a significant reduction in the N2O emission factor to 0.85 % and an increase in nitrogen removal efficiency to 81.81 %. Additionally, the enrichment of anammox bacteria, Candidatus brocadia (0.15 %), positively contributed to the improvement in nitrogen removal efficiency. In conclusion, this study provides valuable insights into optimizing AAO process to mitigate N2O emissions, enhance nitrogen removal, and lower carbon footprints associated with wastewater treatment.

Multi-stage anoxic/oxic sequencing batch reactor realizes shortcut nitrogen removal for anaerobically co-digested liquor of municipal sludge and urban organic wastes

Nitrogen removal from the combined anaerobic digestion dehydration liquor (CADDL) of municipal sludge and urban organic wastes is challenging due to high ammonium concentrations, low C/N ratio, and poor biodegradability. This study proposes a multi-stage anoxic/oxic (A/O) sequencing batch reactor with step feeding to realize partial nitrification and denitrification for shortcut nitrogen removal from the CADDL. We investigated the effects of external carbon source (acetate), dissolved oxygen (DO), A/O duration ratio, and A/O stage number on biological nitrogen removal. Moreover, we assessed the microbial community structure and nitrogen removal pathway. The results showed that the C/N consumption ratio for nitrite reduction to dinitrogen was 3.0 mg COD/mg N, and denitrifying bacteria yielded about 0.43. The optimal dosage of acetate was 2.2 mg COD/mg N. High DO concentration (1.5∼3.0 mg/L) in the aerobic stage improved the ammonia-oxidizing bacteria activity and nitrogen removal rather than worsening the nitritation. A high A/O duration ratio (50 min/60 min) was conducive to complete denitrification of nitrite. The three-stage A/O had an excellent nitrogen removal performance. Under optimal conditions, the nitrite accumulation ratio of nitritation and the total inorganic nitrogen removal reached 100% and 90.1%, respectively. The dominant ammonia-oxidizing bacteria was the genus Nitrosomonas (0.76% abundance), and the dominant denitrifying bacteria was Thauera (0.24% abundance). The nitrite-oxidizing bacteria were not detected, confirming that the biological nitrogen removal pathway was partial nitrification and denitrification. These findings provide a feasible option for the low-carbon nitrogen removal treatment for the CADDL of municipal sludge and urban organic wastes.

Engineering application on the combination of simultaneous partial nitrification and denitrification and anammox for advanced nitrogen removal from landfill leachate

The engineering application of continuous-flow process for advanced nitrogen removal from landfill leachate via anammox is at the forefront of landfill leachate treatment field. For the full-scale engineering renovation, the anaerobic + pre-aeration + anammox + MBR process was constructed for advanced nitrogen removal from landfill leachate of 150 m3/d. Under the strategy of aeration control and low reflux ratio, a stable operation of simultaneous partial nitrification and denitrification (SPND) and anammox was achieved. Without carbon sources addition, the nitrogen removal efficiency reached 94.07 ± 1.26 %, of which the nitrogen removal contribution of the SPND and anammox process reached 64.12 ± 0.92 % and 26.46 ± 1.10 %, respectively. The anammox bacteria mainly enriched in sponge biofilm and floc sludge with abundant reached 2.57 % and 2.17 %, respectively. Compared with the original process, the renovated process could significantly save 18.51 % of the treatment consumption. This study provided a practical and feasible approach for the renovation of the existing treatment process.

Achieving partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) by the inhibition of sulfide to accomplish stabilized nitrogen removal

The simultaneous partial nitrification, anammox, and denitrification (SNAD) process is widely applied for treating high-ammonia wastewater, but its application to low-ammonia organic wastewater has been scarcely explored. In this study, a partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) system was established to treat organic wastewater with low ammonia concentration. Experimental results revealed that sulfide at 5 mg/L selectively inhibited nitrite-oxidizing bacteria (NOB) but had little effect on ammonium-oxidizing bacteria (AOB). Finally, NOB was suppressed in PND system by intermittently adding sulfide to the PND system. The PND system provided nitrite and activated sludge enriched with AOB to the SNAD system during stable operation. The SNAD system demonstrated chemical oxygen demand (COD) and nitrogen removal efficiencies of 89.86 % and 86.45 %. Candidatus Brocadia and Nitrosomonas were the main ammonium oxidizing bacteria (AnAOB) and AOB. The contribution of AOB and denitrifying bacteria (DNB) to nitrogen transformation was 67.15 % and 25.33 % in the PND system. In the SNAD system, the contributions of AnAOB, AOB, and DNB were 34.40 %, 33.59 %, and 27.56 %, respectively. Overall, this study provided a new sustainable strategy for treating organic wastewater with low ammonia concentration.

Sludge enrichment and intermittent gradient aeration: Modulating microbial communities for start-up of partial nitrification in a sequencing batch reactor (SBR)

A novel approach has been proposed integrating sludge enrichment with intermittent gradient aeration to achieve partial nitrification (PN). Results indicated that this method suppressed nitrite-oxidizing bacteria (NOB) activity while maintained ammonia-oxidizing bacteria (AOB) activity, achieving an 82.87 % nitrite accumulation rate (NAR) during startup. During stable operation, specific ammonia oxidation rate and specific nitrite oxidation rate reached 18.44 and 2.67 mg N/g MLVSS/h, respectively. Shortening anoxic time from 30 to 20 min enhanced ammonia removal efficiency by 12.5 %, increasing NAR to 89.55 %. Further reduction to 5 min yielded 38.46 % and 91.88 %, respectively. AOB abundance enriched from 0.62 % to 22.28 %, with the AOB-to-NOB ratio jumping from 0.22 to 59.58. This research presented a rapid and effective strategy for achieving PN.

Genome-resolved metagenomics reveals the nitrifiers enrichment and species succession in activated sludge under extremely low dissolved oxygen

Nitrification, a process carried out by aerobic microorganisms that oxidizes ammonia to nitrate via nitrite, is an indispensable step in wastewater nitrogen removal. To facilitate energy and carbon savings, applying low dissolved oxygen (DO) is suggested to shortcut the conventional biological nitrogen removal pathway, however, the impact of low DO on nitrifying communities within activated sludge is not fully understood. This study used genome-resolved metagenomics to compare nitrifying communities under extremely low- and high-DO. Two bioreactors were parallelly operated to perform nitrification and DO was respectively provided by limited gas-liquid mass transfer from the atmosphere (AN reactor, DO < 0.1 mg/L) and by sufficient aeration (AE reactor, DO > 5.0 mg/L). Low DO was thought to limit nitrifiers growth; however, we demonstrated that complete nitrification could still be achieved under the extremely low-DO conditions, but with no nitrite accumulation observed. Kinetic analysis showed that after long-term exposure to low DO, nitrifiers had a higher oxygen affinity constant and could maintain a relatively high nitrification rate, particularly at low levels of DO (<0.2 mg/L). Community-level gene analysis indicated that low DO promoted enrichment of nitrifiers (the genera Nitrosomonas and Nitrospira, increased by 2.3- to 4.3-fold), and also harbored with 2.3 to 5.3 times higher of nitrification functional genes. Moreover, 46 high-quality (>90 % completeness and <5 % contamination) with 3 most abundant medium-quality metagenome-assembled genomes (MAGs) were retrieved using binning methods. Genome-level phylogenetic analysis revealed the species succession within nitrifying populations. Surprisingly, compared to DO-rich conditions, low-DO conditions were found to efficiently suppressed the ordinary heterotrophic microorganisms (e.g., the families Anaerolineales, Phycisphaerales, and Chitinophagales), but selected for the specific candidate denitrifiers (within phylum Bacteroidota). This study provides new microbial insights to demonstrate that low-DO favors the enrichment of autotrophic nitrifiers over heterotrophs with species-level successions, which would facilitate the optimization of energy and carbon management in wastewater treatment.

Start-up of pilot-scale ANAMMOX reactor for low-carbon nitrogen removal from anaerobic digestion effluent of kitchen waste

The pilot-scale simultaneous denitrification and methanation (SDM)-partial nitrification (PN)-anaerobic ammonia oxidation (Anammox) system was designed to treat anaerobic digestion effluent of kitchen waste (ADE-KW). The SDM-PN was first started to avoid the inhibition of high-concentration pollutants. Subsequently, Anammox was coupled to realize autotrophic nitrogen removal. Shortcut nitrification-denitrification achieved by the SDM-PN. The NO2--N accumulation (92 %) and NH4+-N conversion (60 %) were achieved by PN, and the removal of TN and COD from the SDM-PN was 70 % and 73 %, respectively. After coupling Anammox, the TN (95 %) was removed with a TN removal rate of 0.51 kg·m-3·d-1. Microbiological analyses showed a shift from dominance by Methanothermobacter to co-dominance by Methanothermobacter, Thermomonas, and Flavobacterium in SDM during the SDM-PN. While after coupling Anammox, Candidatus kuenenia was enriched in the Anammox zone, the SDM zone shifted back to being dominated by Methanothermobacter. Overall, this study provides new ideas for the treatment of ADE-KW.