Alleviating the nitrite stress on anaerobic ammonium oxidation by pyrolytic biochar

Unveiling the mechanism of microbial nitrogen conversion by acclimating bioanode potential for enhancing ammonia removal and reducing N2O emission

The biodegradation mechanism of enhancing ammonia removal and reducing N2O emission by acclimating bioanode potential in bioelectrochemical systems (BES) was studied in this work. The BES was started up and optimized with different parameters (i.e., aeration volume, external resistance, and pH value). The cyclic voltammetry was then performed to determine the potential range for acclimating bioanode, suggesting that potentials of -0.3, -0.1, 0.1, 0.2, and 0.3 V were suitable for acclimation. The experimental results indicated that optimum total nitrogen removal was achieved at potential of 0.1 V with a removal efficiency of 83.7 %, which was 1.6 times higher than that of the control group, while the corresponding N2O emission of 1.3 mg-N/L was detected which reduced 2.8 times. The microbial community analysis indicated that the dominant genera for enhancing nitrogen conversion were Sphaerocheata, Petrimonas, and Lentimicrobium. The electrochemical tests suggested that potential acclimation could simultaneously enhance direct electron transfer and mediated electron transfer (MET), thereby increasing extracellular electron transfer, in which the proportion of MET process mediated by riboflavin played a decisive role. Meanwhile, the intracellular electron transfer process was also strengthened by the increase of the related enzyme activity and the corresponding electron transport system activity increased 3.4 times. Additionally, nitrogen conversion pathways were proposed, indicating that potential acclimation could regulate the ammonia degradation pathway, and reduce the intermediates accumulation. These findings provide new understanding of the nitrogen conversion mechanisms in BES for ammonia removal by acclimating bioanode potential.

Electrochemical synthesis of nitrosation compounds using CH3NO2 as a nitroso reagent

An electrochemical synthesis of various nitroso organic compounds (NOCs) from secondary amines was developed under metal-free and oxidant-free conditions. This method used commercially available nitromethane as the nitrosation reagent to provide various NOCs in good to excellent yields. Furthermore, the valuable drug molecule form desloratadine can be prepared by this method easily.

Influence of sludge biochar at different carbonization temperatures on anammox process

Adding biochar can expedite the establishment of the anaerobic ammonia oxidation (anammox) process and improve the nitrogen removal efficiency of the anammox reactor. However, the optimization research of biochar derived from dewatered sludge on anammox is relatively limited. In this study, four sequencing batch reactors (SBRs) were compared for the enrichment of anammox bacteria using synthetic wastewater with sludge biochar carbonized at temperatures of 300°C, 550°C, and 800°C, and without biochar (CK). The start-up and the nitrogen removal performance of anammox process were evaluated, as well as the effect of organic carbon on nitrogen removal. The results showed that the addition of sludge biochar at different pyrolysis temperatures all can accelerate the start-up of the anammox process, improve the nitrogen removal efficiency, and reduce the total nitrogen (TN) in the effluent. Although the reactor with biochar carbonized at 800°C showed the fastest increase in the nitrogen loading, the best TNRE occurred in the reactor with biochar carbonized at 300°C, which was 8.0% higher than those of the control (CK, p < 0.05). The predominant genus of anammox in SBRs differed between the sludge biochar reactor and the control reactor (without biochar), which were Candidatus Brocadia and Candidatus Jettenia, respectively. Additionally, the total abundances of anammox bacteria and denitrifiers increased with the addition of sludge biochar.

Biological carbon promotes the recovery of anammox granular sludge after starvation

This article adopts the strategy of adding biochar and increasing HRT to accelerate the performance and particle morphology recovery of anaerobic ammonia oxidation granular sludge stored at room temperature for 68 days. The results showed that biochar accelerated the death of heterotrophic bacteria, shortened the cell lysis and lag period of the recovery process by 4 days, and it only took 28 days for the nitrogen removal performance of the reactor to recover to the original level, and 56 days for re-granulation. Biochar promoted the secretion of EPS (56.96 mg gVSS^-1), and the sludge volume and nitrogen removal performance of the bioreactor remain stable. Biochar also accelerated the growth of Anammox bacteria. The abundance of Anammox bacteria in the biochar reactor reached 38.76% on the 28th day. The high abundance of functional bacteria and the optimized community structure of biochar made system (Candidatus_Kuenenia: 38.30%) more risk-resistant than control reactor.

Insights into the reaction of anammox to exogenous pyridine: Long-term performance and micro mechanisms

Some industrial wastewaters contain high amounts of toxic nitrogen-containing heterocyclic compounds, which may inhibit the efficiency of biological treatment. This work systematically investigated how exogenous pyridine affected the anaerobic ammonia oxidation (anammox) system and discussed the microscopic response mechanisms based on genes and enzymes. The anammox efficiency was not seriously inhibited by pyridine less than 50 mg/L. Bacteria secreted more extracellular polymeric substances to resist pyridine stress. After 6 days stress with 80 mg/L pyridine, the nitrogen removal rate of anammox system lost 47.7%. Long-term stress of pyridine reduced anammox bacteria by 7.26% and the expression of functional genes by 45%. Pyridine could actively bind to hydrazine synthase and ammonium transporter. This work fills a research gap in the ongoing threat of pyridines to anammox, and has guiding value for the application of anammox process in the treatment of ammonia-rich wastewater containing pyridine.

Iron-loaded sludge biochar alleviates the inhibitory effect of tetracycline on anammox bacteria: Performance and mechanism

The anaerobic ammonia oxidation (anammox) process is sensitive to environmental pollutants, such as antibiotics. In this study, the harmful effect of tetracycline (TC) on the performance of an anammox reactor and the mitigation of TC inhibition by iron-loaded sludge biochar (Fe-BC) were studied by analyzing extracellular polymeric substances (EPS), microbial community structure and functional genes. The total inorganic nitrogen (TIN) removal rate of the TC reactor was reduced by 5.86% compared to that of the control group, while that of the TC + Fe-BC reactor improved by 10.19% compared to that of the TC reactor. Adding Fe-BC increased the activity of anammox sludge by promoting the secretion of EPS (including protein, humic acids and c-Cyts). The results of the enzymolysis experiment showed that protein can improve the activity of anammox sludge, while the ability of polysaccharide to improve the activity of anammox was related to the treated enzymes. In addition, Fe-BC alleviated the inhibitory effect of TC by mediating the anammox electron transfer process. Furthermore, Fe-BC increased the absolute abundance of hdh and hzsB by 2.77 and 1.18 times compared to the TC reactor and improved the relative abundance of Candidatus Brocadia in the absence of TC. The addition of Fe-BC is an effective way to alleviate the inhibitory effect of TC on the anammox process.

A review of anammox metabolic response to environmental factors: Characteristics and mechanisms

Anaerobic ammonium oxidation (anammox) is a promising low carbon and economic biological nitrogen removal technology. Considering the anammox technology has been easily restricted by environmental factors in practical engineering applications, therefore, it is necessary to understand the metabolic response characteristics of anammox bacteria to different environmental factors, and then guide the application of the anammox process. This review presented the latest advances of the research progress of the effects of different environmental factors on the metabolic pathway of anammox bacteria. The effects as well as mechanisms of conventional environmental factors and emerging pollutants on the anammox metabolic processes were summarized. Also, the role of quorum sensing (QS) mediating the bacteria growth, gene expression and other metabolic process in the anammox system were also reviewed. Finally, interaction and cross-feeding mechanisms of microbial communities in the anammox system were discussed. This review systematically summarized the variations of metabolic mechanism response to the external environment and cross-feeding interactions in the anammox process, which would provide an in-depth understanding for the anammox metabolic process and a comprehensive guidance for future anammox-related metabolic studies and engineering applications.

Regulating performance of CANON process via adding external quorum sensing signal molecules in membrane bioreactor

In this study, the regulation effect of the external quorum sensing signals, N-dodecanoyl homoserine lactone (C12-HSL) on CANON process were investigated in a membrane bioreactor. C12-HSL significantly enhanced the aerobic ammonia-oxidizing bacteria and improved the ammonia monooxygenase activity to 0.134 from 0.076 μg NO₂^--N mg^-1 protein min^-1, while suppressed anaerobic ammonia-oxidizing bacteria and limited the TN removal to 0.07 from 0.22 kg m^-3 d^-1. Key enzymes synthesis were enhanced during the operation without C12-HSL addition, enabling the resistance of CANON system to high C12-HSL. As a result, the hydroxylamine oxidoreductase and nitrite reductase activity reached 35.9 EU g^-1 SS and 1.28 μg NO₂^--N mg^-1 protein min^-1, respectively; Nitrosomonas and Candidatus Kuenenia, with the abundance as 12.5 % and 22.9 %, cooperatively contributed to the TN removal, which maintained at 0.19 kg m^-3 d^-1. C12-HSL was profitable for aerobic ammonia oxidation, which could be adopted for regulating the nitrite production rate.

Large-scale (500 kg N/day) two-stage partial nitritation/anammox (PN/A) process for liquid-ammonia mercerization wastewater treatment: Rapid start-up and long-term operational performance

The nitrogen pollution control of liquid-ammonia mercerization wastewater (LMWW) is one of the typical obstacle restricting the sustainability of textile industry. In this study, a 500 kg N/day two-stage partial nitritation/anammox (PN/A) process containing PN reactor filled with zeolite and biofilm anammox reactors was successfully started up in 45 days and operated stably with high shock resistance over one year for LMWW treatment. The large-scale process achieved an average ammonium removal efficiency (94.3 ± 2.3%), total nitrogen removal efficiency (89.4 ± 2.7%) and nitrogen removal rate (1.003 ± 0.386 kg N/m³/day) during one year engineering operation. Simultaneous denitrification was revealed by the contribution of 5.2% total nitrogen removed. High-throughput sequencing results showed that Nitrosomonas was the most dominant genus in PN reactor, and Ca. Anammoxoglobus and Ca. Kuenenia were the functional bacteria for nitrogen removal in anammox reactors. Compared to traditional nitrification-denitrification process, the large-scale process reduced a total operational cost of 46.03 CNY/kg N for LMWW. This study revealed the proposed process was quite reliable with fast start-up and high impact resistance to overcome the obstacle of nitrogen pollution control for LMWW economically and conducive to the sustainable development for textile industry.

Effects of biochar on anaerobic treatment systems: Some perspectives

Many anaerobic activities involve carbon, nitrogen, iron, and sulfur cycles. As a well-developed porous material with abundant functional groups, pyrolytic biochar has been widely researched in efforts to promote microbial activities. However, the lack of consensus on the biochar mechanism has limited its practical application. This review summarizes the effects of different pyrolysis temperatures, particle sizes, and dosages of biochar on microbial activities and community in Fe(III) reduction, anaerobic digestion, nitrogen removal, and sulfate reduction systems. It was found that biochar could promote anaerobic activities by stimulating electron transfer, alleviating toxicity, and providing suitable habitats for microbes. However, it inhibits microbial activities by releasing heavy metal ions or persistent free radicals and adsorbing signaling molecules. Finding a balance between the promotion and inhibition of biochar is therefore essential. This review provides valuable perspectives on how to achieve efficient and stable use of biochar in anaerobic systems.

Anaerobic ammonium oxidation driven by dissimilatory iron reduction in autotrophic Anammox consortia

Feammox has been applied to wastewater biological nitrogen removal. However, few studies have reported that Fe(III)(hydr)oxides induced Anammox consortia to remove NH4+ via the Feammox pathway. In this study, Fe(OH)3 was added to Anammox systems to investigate its effect on nitrogen removal via Feammox. The specific Anammox activity increased by 39 % by Fe(OH)3. Ammonia oxidation was observed to occur along with Fe(III) reduction and Fe(II) generation, which was further confirmed by the isotope test with feeding 15NH4+-N to detect 30N2. The cyclic voltammetry test showed that electron-storage capacity of Anammox sludge increased with Fe(OH)3. In situ Fourier transform infrared spectroscopy suggested that Fe(OH)3 enhanced the polarization of functional groups of outer membrane cytochrome of Anammox consortia to benefit extracellular electron transfer. This study demonstrated that Fe(OH)3 could induce Anammox consortia to perform extracellular respiration to enhance NH4+-N removal in the Anammox sludge system.

Deciphering physicochemical properties and enhanced microbial electron transfer capacity by magnetic biochar

Magnetic biochar is important for improving the electron transfer capacity (ETC) of microorganisms in wastewater treatment. In this study, three magnetic biochar under different pyrolysis temperatures (300, 500 and 700 °C) were prepared by co-precipitation, and their characteristics and impacts on mediating microbial ETC were investigated. Results indicated that magnetic biochar had a higher capacitance and conductivity than pyrolytic biochar, with the largest specific capacitance of 14.7F/g for FCS700 (magnetic biochar prepared at 700 °C). The addition of magnetic biochar could improve the nitrogen removal efficiency of a sludge-biochar system. The electron transfer resistance (R_ct) of magnetic biochar was lower than pyrolytic biochar by 25.5 % (300 °C), 19.7 % (500 °C), and 11.6 % (700 °C), respectively. The structure of the microbial community in the sludge-biochar system differed significantly. Spearman correlation suggested that the electrochemical properties of biochar were an important factor affecting the structure of the microbial community.

A critical review of exogenous additives for improving the anammox process

Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.

Biochar enhances partial denitrification/anammox by sustaining high rates of nitrate to nitrite reduction

To examine the short-term effects of biochar on the partial-denitrification anammox (PD/A) process, the adsorption kinetics, nitrogen degradation, electron transfer properties, and microbial community succession of wastewater treatment systems with and without biochar added were monitored and characterized. The results showed that biochar increased nitrate reduction rates, which enhanced total nitrogen (TN) removal of the system by about 10%. The findings attributed improved TN removal to biochar's influence in accelerating electron transfer rather than its adsorption properties. Analysis of the nitrogen transfer pathway showed that when sufficient substrate was available, the anammox and denitrification reactions simultaneously removed nitrogen. When the nitrite supply was insufficient, the anammox reaction outcompeted the denitrification reaction for regenerated nitrite. Integrated microbial community and functional protein analyses indicated that biochar addition increased the abundance of Ca. Kuenenia and Pseudomonas. Meanwhile, biochar modulates denitrifying cellular metabolism by inducing protein changes.

Can nitrifiers from the sidestream deammonification process be a remedy for the N-overload of the mainstream reactor?

The combination of sidestream deammonification and bioaugmentation of the mainstream reactor using ammonia oxidizers from partial nitritation (PN) was not achieved before. This novel solution not only enables the efficient sidestream nitrogen removal, but also improves mainstream resistance to stress situations such as biomass washout or nitrogen overload. This feature is important for wastewater treatment plants (WWTPs) equipped with reject water deammonification as its implementation leads to lower nitrifier mass in the mainstream reactor and therefore diminish ability to cope with rapid increase in the loading rate (i.e. due to sidestream process failure). The proposed approach presents the use of the excess sludge from a modified PN process to boost the mainstream nitrification in unfavourable conditions. In a long-term laboratory experiment, the operation of an existing WWTP at low temperature was simulated in two reactors using real wastewater fluxes. One of them was augmented with the excess sludge from a PN reactor that treats reject water containing 20% of the WWTP N-load. The treatment efficiency in both reactors was tested under different nitrogen loading rates, as well as in the case of the of biomass loss. The bioaugmentation intensity was set according to the actual nitrogen load balance of the modelled WWTP, resulting in a daily seed volume only equal to 0.28% of the reactors' influent. Two incidents were simulated, where the nitrogen load increased by about 24.5% and 34%. In both cases, the nitrification efficiency in the non-augmented reactor dropped by about 45%, while the augmented reactor maintained efficient ammonium removal. The bioaugmentation effect was also noticeable during biomass washout - only in the non-augmented reactor nitrification was insufficient for over 60 days. These results undoubtedly show the possibility of combining two different approaches for sidestream nitrogen removal into one technology demonstrating the advantages of both component solutions.