Simultaneous removal of nitrate and ammonium by hydrogen-based partial denitrification coupled with anammox in a membrane biofilm reactor

Selective genes expression and metabolites transformation drive a robust nitrite accumulation during nitrate reduction under alternating feast-famine condition

Nitrite production via denitrification has been regarded as a key approach for survival of anaerobic ammonium oxidation (anammox) bacteria. Despite the important carbon substrate, little is known about the role of differential genes expression and extracellular metabolite regulation among diverse microbial communities. In this study, a novel alternating feast-famine strategy was proposed and demonstrated to efficiently accumulate nitrite in a low-nitrogen loading rate (NLR) (0.2∼0.8 kg N/m3/d) denitrification system. Highly selective expression of denitrifying genes was revealed as key regulators. Interestingly, in absence of carbon source (ACS) condition, the expression of narG and narI/V genes responsible for reduction of nitrate to nitrite jumped to 2.5 and 5.1 times higher than that in presence of carbon source (PCS) condition with carbon to nitrate ratio of 3.0. This fortunately facilitated a rapid nitrite accumulation once acetate was added, despite a significantly down-regulated narG and narI/narV and up-regulated nirS/nirK. This strategy selected Thauera as the most dominant denitrifier (50.2 %) with the highest contribution to narG and narI/narV genes, responsible for the high nitrite accumulation. Additionally, extracellular xylose, pyruvate, and glucose jointly promoted carbon-central metabolic pathway of key denitrifiers in ACS stage, playing an important role in the process of self-growth and selective enrichment of functional bacteria. The relatively rapid establishment and robust performance obtained in this study shows an engineering-feasible and economically-favorable solution for the regulation of partial denitrification in practical application.

Exploring the potential of a novel alternating current stimulated iron‑carbon anammox process: A new horizon for nitrogen removal

This study explored a novel alternating current (AC) stimulation approach to enhance the nitrogen removal efficiency of an iron‑carbon based anammox (FeC anammox) system. In the preliminary experiment, the TN removal efficiency of the AC stimulated system was 8.06 % higher than that of a DC simulated system in same current densities of 0.25 mA/cm2. Gene expression analysis revealed that the AC-stimulated system, where, compared with the anammox system alone, the expression of HZS, HDH, NarG, NirS, NorB and NosZ increased by 1.81, 2.50, 1.64, 0.23, 1.15 and 1.27 times, respectively. In the continuous experiment, the TN removal rate increased from 60.13 % to 84.34 % after AC stimulation, and the working time of the FeC materials increased to 20 days. An analysis of the mechanism revealed that the parallel connection between the capacitive reactance and filler resistance in AC might reduce the internal resistance of the system, thereby improving the actual current density received by local microorganisms, and achieving a better strengthening effect.

Spatial difference in nitrogen removal pathways and microbial functional diversity in an EGSB reactor during the start-up of PD/Anammox

The start-up of a relatively high nitrogen load PD/Anammox in an EGSB reactor was achieved through strategies of bioaugmentation, mass transfer enhancement, and COD/NO3--N control, with NRR of 5.2 g N/L/d. Longitudinal heterogeneity in EGSB reactor induced divergent nitrogen conversion pathways and enriched different functional microorganisms between stratified sludge. Along the elevation of the reactor, the proportion of removed nitrogen through anammox increased continuously from bottom, middle and up, which were 65.0 %, 79.8 %, and 84.1 %, respectively, consistent with the trend of ex-situ activities calculated with Gompertz model. The bottom zone played a role in mixed nitrogen conversion to provide NO2--N accumulation and nitrogen removal, with higher abundance of Thauera, Denitratisoma and Ignavibacterium. The middle part was enriched Candidatus_Kuenenia (12.51 %), and up inhibited completed denitrification, together forming the anammox dominant zone. The proposed functional zones in the EGSB reactor provided approaches for the optimisation of high-load PD/Anammox systems.

Granulation of partial denitrification sludge: Advances in mechanism understanding, technologies development and perspectives

The high-rate and stably efficient nitrite generation is vital and still challenges the wide application of partial denitrification (PD) and anammox technology. Increasing attention has been drawn to the granulation of PD biomass. However, the knowledge of PD granular sludge is still limited in terms of granules characterization and mechanisms of biomass aggregation for high nitrite accumulation. This work reviewed the performance and granulation of PD biomass for high nitrite accumulation via nitrate reduction, including the system start-up, influential factors, granular characteristics, hypothetical mechanism, challenges and perspectives in future application. The physiochemical characterization and key influential factors were summarized in view of nitrite production, morphology analysis, extracellular polymer substance structure, as well as microbial mechanisms. The PD granules exhibit potential advantages of a high biomass density, good settleability, high hydraulic loading rates, and strong shock resistance. A novel granular sludge-based PD combined with anammox process was proposed to enhance the capability of nitrogen removal. In the future, PD granules utilizing different electron donors is a promising way to broaden the application of anammox technology in both municipal and industrial wastewater treatment.

Insight into biofilm formation of wastewater treatment processes: Nitrogen removal performance and biological mechanisms

Biofilm formation affects biological nitrogen (N) removal, and a sequencing batch biofilm reactor (SBBR) was set up to evaluate the changes in N removal and microbial characteristics during biofilm formation. The results indicated that the average effluent concentration of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total nitrogen (TN) in the SBBR were 27.48, 1.41, and 13.52 mg L-1, respectively after biofilm formation. Furthermore, this process increased microbial richness, but reduced microbial diversity. Patescibacteria, Proteobacteria, and Bacteroides were the dominant phyla that did not change after biofilm formation. After biofilm formation, Firmicutes was eliminated while Spirochaetes involved in the interspecies relationship. Biofilm increased the nitrification and denitrification relating coding genes abundance (hao, narG, narZ, nxrA, narH, narY, nxrB, napA, napB, norB, norC and nosZ), and enhanced the processes of N respiration and denitrification, carbohydrate metabolism, amino acid metabolism and membrane transport. Meanwhile, correlation analysis between genera and transcriptome reflected that Zooglea, Micropruina, Aeromonas and Tessaracoccus played essential roles in biofilm formation and N removal. The key enzyme abundance of EC:1.7.99.1, EC:1.7.2.4, and EC:1.1.1.42 of N and tricarboxylic acid (TCA) cycle increased after biofilm formation. This study can reveal the effect of biofilm formation on biological N removal and provide a theoretical foundation for the application of biofilm process.

Feasibility of anaerobic ammonium oxidation process for treatment of pretreated printed circuit board wastewater

The treatment of pretreated printed circuit board (PCB) wastewater by anaerobic ammonium oxidation (anammox) process has been rarely reported. This study sought to investigate the performance of the anammox process during various phases of pretreated PCB wastewater treatment. The nitrogen removal efficiency (NRE) reached 90 ± 10% at a Cu2+ concentration of 2.5 mg·L-1, but declined to 22 ± 11% as the Cu2+ level increased to 10.3  mg·L-1. During phase III, there was a 38% increase in the relative abundance of Candidatus Kuenenia compared to phase I. By adjusting the substrate concentration and introducing synthetic wastewater into the reactor, the anammox performance was nearly restored to that of phase I. These findings underscore the potential of the anammox process for treating pretreated PCB wastewater and expanding its practical applications to industrial wastewater treatment.

Effects of microplastics on denitrification and associated N2O emission in estuarine and coastal sediments: insights from interactions between sulfate reducers and denitrifiers

Global estuarine and coastal zones are facing severe microplastics (MPs) pollution. Sulfate reducers (SRB) and denitrifiers (DNB) are two key functional microorganisms in these zones, exhibiting intricate interactions. However, whether and how MPs modulate the interactions between SRB and DNB, with implications for denitrification and associated N2O emissions, remains poorly understood. Here, we simultaneously investigated the spatial response patterns of SRB-DNB interactions and denitrification and associated N2O emissions to different MPs exposure along an estuarine gradient in the Yangtze Estuary. Spatial responses of denitrification to polyvinyl chloride (PVC) and polyadipate/butylene terephthalate (PBAT) MPs exposure were heterogeneous, while those of N2O emissions were not. Gradient-boosted regression tree and multiple regression model analyses showed that sulfide, followed by nitrate (NO3-), controlled the response patterns of denitrification to MPs exposure. Further mechanistic investigation revealed that exposure to MPs resulted in a competitive and toxic (sulfide accumulation) inhibition of SRB on DNB, ultimately inhibiting denitrification at upstream zones with high sulfide but low NO3- levels. Conversely, MPs exposure induced a competitive inhibition of DNB on SRB, generally promoting denitrification at downstream zones with low sulfide but high NO3- levels. These findings advance the current understanding of the impacts of MPs on nitrogen cycle in estuarine and coastal zones, and provide a novel insight for future studies exploring the response of biogeochemical cycles to MPs in various ecosystems.

The impact of perfluorooctanoic acid shock on hydrogen-driven nitrate and arsenate removal

Perfluorooctanoic acid (PFOA) is a type of toxic per- and poly-fluoroalkyl substance (PFAS) commonly found in groundwater due to its use in firefighting and industrial applications. The main purpose of this study was to investigate the influence of PFOA shock on the biological performance of a hydrogen-driven bioreactor for nitrate and arsenate removal. Four hydrogen-driven removal reactors (HdBRs) used for the simultaneous removal of nitrate and arsenal were operated with concentrations of either 0, 1, 5, and 10 mg/L of PFOA to induce shock on the systems and examine the corresponding bacterial response. Our results showed that PFOA shock inhibited and decreased the maximum hydrogen-driven arsenate removal rate. Principal Component Analysis (PCA) confirmed that this performance decrease occurred due to a bacterial strike triggered by PFOA shock. PFOA toxicity also led to protein secretion and sludge density decreases. Bacterial analyses showed shifts in the community population due to PFOA shock. The dominant bacteria phylum Proteobacteria became more abundant, from 41.24% originally to 48.29% after exposure to 10 mg/L of PFOA. Other phyla, such as Euryarchaeota and Bacteroidetes, were more tolerant to PFOA shock. Although some of the predominant species within the sludge of each HdBR exhibited a decline, other species with similar functions persisted and assumed the functional responsibilities previously held by the dominant species.

An Advanced Synergy of Partial Denitrification-Anammox for Optimizing Nitrogen Removal from Wastewater: A Review

Anammox is a widely adopted process for energy-efficient removal of nitrogen from wastewater, but challenges with NOB suppression and NO₃^- accumulation have led to a deeper investigation of this process. To address these issues, the synergy of partial denitrification and anammox (PD-anammox) has emerged as a promising solution for sustainable nitrogen removal in wastewater. This paper presents a comprehensive review of recent developments in the PD-anammox system, including stable performance outcomes, operational parameters, and mathematical models. The review categorizes start-up and recovery strategies for PD-anammox and examines its contributions to sustainable development goals, such as reducing N₂O emissions and saving energy. Furthermore, it suggests future trends and perspectives for improving the efficiency and integration of PD-anammox into full-scale wastewater treatment system. Overall, this review provides valuable insights into optimizing PD-anammox in wastewater treatment, highlighting the potential of simultaneous processes and the importance of improving efficiency and integration into full-scale systems.