Total Nitrogen Removal Efficiency Research Articles

Deciphering anammox response characteristics and potential mechanisms to polyethylene terephthalate microplastic exposure

Microplastics (MPs) are frequently detected in the wastewater. Herein, the short-term and long-term effects of polyethylene terephthalate (PET) MPs on anammox granular sludge were investigated and the potential response mechanisms were analyzed. Results showed that although short-term exposure of anammox granular sludge to PET-MPs induced a stress response, the nitrogen removal performance was not significantly affected. By contrast, long-term exposure to PET-MPs inhibited nitrogen removal performance with increased exposure time and PET-MP concentration. The total nitrogen removal efficiency (TNRE) decreased by 28.7% when sludge was exposed to 200mg/L of PET-MPs. However, the anammox activity recovered with prolonged operation time, and approximately 87% of the initial TNRE was recovered after three months. Microbial community evolution and metabolic exchange variations were the potential response mechanisms of anammox granular sludge to PET-MP exposure, with PET-MP exposure decreasing the anammox bacteria growth rate and relative symbiotic bacterial abundance in the anammox consortia and hindering cross-feeding pathways. The findings of this study provide novel insight into anammox behavior when treating wastewater containing PET-MPs.

Unveiling the mechanism underlying in−situ enhancement on anammox system by sulfide: Integration of biological and isotope analysis

The in−situ utilization of sulfide to remove the nitrate produced during the anaerobic ammonium oxidation (anammox) process can avoid prolonged sludge acclimatization, facilitating the rapid initiation of coupled nitrogen removal processes. However, the understanding of in−situ enhancement on anammox system by sulfide remains unclear. Herein, sulfide (Na2S) was introduced as an additional electron donor to remove the nitrate derived from the anammox under varying sulfide/nitrogen (S/N, S2−-S/NO3–-N, molar ratio) ratios (0.004–4.375). The underlying mechanisms were elucidated by molecular biology techniques including flow cytometry, quantitative polymerase chain reaction, and 16S rRNA amplicon sequencing, alongside isotope tracer analysis. Results revealed that anammox reactors, when operated with in−situ sulfide addition, exhibited a significant enhancement in total nitrogen removal efficiency (NRE) ranging from 11.5%−41.7% (achieved 96%), with the optimal S/N ratios of 0.01−0.8. Isotope tracer analysis indicated the successful coupling of the anammox, sulfur autotrophic denitrification (SADN), and dissimilatory nitrate reduction to ammonium (DNRA) processes within the system, with their contributions to nitrogen removal being 46%−50%, 24%−30%, and 20%−22%, respectively. Moreover, a notable increase in the abundance of sulfur–oxidizing bacteria (SOB) (20%−40% increase) and DNRA bacteria (10%−20% increase) were observed. Effective collaboration was further supported by the sustained viability of microbial communities. It is speculated that the heightened presence of SOB and DNRA bacteria created a low toxicity environment by converting sulfide to biogenic sulfur, thereby promoting the well−being of anammox bacteria. However, the excessive dosage of sulfide (S/N=1.8) intensified the DNRA process (contribution>35%) and weakened the anammox process, leading to an increase in effluent NH4+-N concentration and a decline in NRE. This study confirms that the in−situ adding an appropriate amount of sulfide favors achieving complete nitrogen removal in anammox system, which provides a novel avenue to resolve the issue of the residual nitrate in anammox process.

Investigation of nitrogen conversion in ditch-treated greywater: Contributions of biochar and aeration

This study aimed to assess the contribution of different combinations of uninterrupted aeration and tidal flow modes, as well as shallow and deep biochar landfill methods, to nitrogen removal pathways in ditches. Compared to natural ditches, the addition of biochar and aeration resulted in higher water pollution removal rates, lower Greenhouse Gas (GHG) emissions, and reduced sediment leaching. The nitrogen mass balance revealed that Total Nitrogen removal efficiency of each ditch group was 25.33% for CA-C, 43.75% for DBT-C, 49.08% for UBT-C, 30.75% for DBA-C, and 45.16% for UBA-C. Compared to the control group (CA-C), the tidal flow group with deep biochar landfill (DBT-C)demonstrated the highest efficiency in total nitrogen removal. To elucidate the fate of nitrogen elements, potential transformation processes of unexplained nitrogen were explored. The primary outflow pathway of nitrogen pollution in ditches is through liquids. The nitrogen composition in the liquid of each ditch indicated that for shallow biochar configurations (UBT-C/UBA-C), denitrification might be the main factor limiting TN removal efficiency. In contrast, for deep biochar configurations (DBT-C/DBA-C), hydrolysis and nitrification of organic nitrogen were identified as limiting factors, with tidal flow alleviating these limitations. Overall, the combination of shallow biochar and tidal flow aeration in a ditch is the most effective method for removing rural greywater, providing valuable insights for the development of design parameters in greywater removal systems.

A novel Zobellella endophytica W14 strain for nitrogen removal from hypersaline wastewater through simultaneous nitrification and denitrification.

To address the challenges associated with biological treatment of high-salinity wastewater, a novel salt-tolerant strain, Zobellella endophytica W14, was isolated. This strain exhibited heterotrophic nitrification-aerobic denitrification (HN-AD) capabilities. Strain W14 could grow and remove ammonium in high-salinity environments with salinity levels ranging from 0 to 11% (w/v). At 5% salinity, strain W14 demonstrated high removal efficiencies for nitrite, ammonium, and nitrate (100%, 99.58%, and 98.85%, respectively), when these compounds were provided as the single source of nitrogen. In cases of mixed nitrogen sources, total nitrogen removal efficiency of strain reached 95.22%. The nitrogen balance analysis confirmed the utilization of nitrogen sources by strain W14 through both assimilation and dissimilation. Through the amplification of functional genes involved in nitrogen metabolism (i.e., hao, napA, nirS, and nosZ), the nitrogen metabolism pathway of strain W14 was predicted to be: NH₄⁺ → NH₂OH → NO₂⁻ → NO₃⁻ → NO₂⁻ → NO → N₂O → N₂. The study reveals that the novel W14 strain can efficiently remove total nitrogen from high-salinity wastewater and has significant potential for biological treatment of such wastewater.

Slaughterhouse wastewater remediation using carbonized sawdust followed by textile filtration

Slaughterhouse wastewater (SWW) is considered an industrial wastewater, which seriously harms the environment due to the high concentration of contaminants such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS). Additionally, the wastewater from slaughterhouses contains harmful bacteria. This study used a lap-scale model to treat SWW from a local private slaughterhouse. The treatment process involves three stages: adsorption using activated carbon, which is derived from sawdust, followed by sedimentation, and finally, a slow sand filter with a modified layer of woven textile cotton. The first two steps were tested to obtain the ideal operation condition of the treatment system. After the final step of treatment, we evaluated the overall process using a modified slow sand filter (MSSF). We used a Jar test to determine the optimal dosage of activated carbon from sawdust (ACS). The monitored parameters were physicochemical, such as turbidity, total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN). The bacteriological examination included both total coliform count (TCC) and fecal coliform count (FCC). The results of the jar test revealed that the optimal ACS dose was 2.0 g/l. After adjusting the contact time and pH levels for the adsorption process, we discovered that the ideal contact time was 100 min and the ideal pH level was 4.0. Finally, we evaluated the entire treatment system by applying the MSSF after the sedimentation process, and found that the removal efficiencies of turbidity, BOD, COD, TSS, TDS, TP, and TN were 97.14, 94.80, 91.80, 98.96, 81.17, 81.12, and 82.50%, respectively. This is in addition to the filter's ability to remove bacteria counts at a rate of up to 98.93 and 99.13% of TCC and FCC, respectively.

Revealing the size effect mechanisms of micro(nano)plastics on nitrogen removal performance of constructed wetland

Micro(nano)plastics (MPs) in aquatic environments can disrupt wastewater treatment, particularly nitrogen removal in constructed wetlands (CWs). However, their broader effects on microbial and plant nitrogen metabolism remain unclear. This study investigated the effects of different-sized MPs (4 mm, 100 µm, and 100 nm) on nitrogen transformation in CWs. Results revealed that 4 mm- and 100 µm-MPs did not significantly affect total nitrogen (TN) removal, although 100 µm-MPs significantly increased leaf antioxidant enzyme activities and reduced plant uptake of nitrogen by 12.95 % (p < 0.05). In contrast, 100 nm-MPs decreased the TN removal efficiency by 7.97 % via inhibiting both nitrification and denitrification, since 100 nm-MPs penetrated cell membranes, disrupted reactive oxygen species balance, and reduced bacterial viability, thus suppressing microbial nitrogen degradation by 8.07 % (p < 0.05). Additionally, 100 nm-MPs significantly inhibited plant growth and reduced plant nitrogen uptake by 16.05 % (p < 0.05). Furthermore, 100 µm-MPs increased the abundance of nitrifiers but reduced denitrifiers and functional genes, whereas 100 nm-MPs reduced the abundance of both nitrifiers and denitrifiers along with their functional genes (p < 0.05). These findings highlight the need to improve waste management to mitigate the adverse effects of MPs on nitrogen removal.

Analysis on pollutants removal and sludge characteristics of a novel two-phase anaerobic/aerobic/integrated deoxygenated and anoxic reactor associated with membrane process for treating pesticide wastewater

Most frequently used biological method was improved anaerobic/anoxic/aerobic (A/A/O) process for treating actual pesticide wastewater presently. However, the effluent results were far away from what the national standard expects due to pesticide wastewater characteristics of high COD concentration, high total nitrogen (TN) concentration and high toxicity. In this study, a novel two-phase anaerobic/aerobic/integrated deoxygenated and anoxic reactor associated with membrane process (P1) were regarded as excellent candidates for the treatment of pesticide wastewater, compared the removal efficiency of pollutants with improved A/A/O process (P2) under different hydraulic retention times (HRTs). Effluent ethylene thiourea (ETU) concentration was reduced effectively by 67.1 % in P1. The average cyanide (CN−) effluent concentration in P1 and P2 was 0.40 mg/L and 6.67 mg/L, respectively. During the entire HRT change period, P1 significantly increased the biological oxygen demand (BOD5) removal efficiency by 12.98 %. The average effluent COD concentration of P1 was 36.41 mg/L, while that of P2 was 984.42 mg/L. In addition, TN removal efficiency of P1 exhibited distinct superiority. When HRT was 72 h, the average TN effluent concentration of P1 and P2 was 12.67 mg/L and 67.66 mg/L. The sludge performance indicators have been determined and results showed that the sludge viscosity of the membrane reactor in P1 had merely 32.6 % higher than that of the secondary sedimentation tank in P2, and the average vertical displacement of sludge settleability in P1 was 23.0 % slight lower than that of P2. The overall sludge performance proved that higher sludge concentration was allowed in P1. Moreover, experiment improved nitrite reductase (NIR) and nitrate reductase (NAR) in P1 were less susceptible to be suppressed by ETU and CN− increase compared with P2. Finally, the positive correlation relationship of sludge settleability with ETU and CN− has been identified successfully in P1.

Efficient removal of nitrate and ammonium by strain Pseudomonas poae EH-E3 under acidic pH and low-temperature conditions

The combined effect of low temperature and an acidic environment may restrict the growth and metabolic activity of microorganisms involved in nitrogen removal. To overcome poor biological nitrogen removal efficiency during low-temperature treatment of acidic wastewater, a novel pure strain of Pseudomonas poae EH-E3 was successfully isolated and screened based on its strong heterotrophic nitrification and aerobic denitrification capacity. Strain EH-E3 could completely eliminate inorganic nitrogen sources of nitrate within 30h and ammonium within 20h at 15 °C and pH 5.0, with corresponding removal efficiencies for total nitrogen of 95.13% and 91.35%, respectively. Nitrogen balance testing indicated that strain EH-E3 removed 43.25% of ammonium, 45.72% of nitrate, and 51.20% of nitrite in the form of gaseous products. Enzyme activity assays revealed that the specific activities of ammonia monooxygenase, nitrate reductase, and nitrite reductase were 0.533, 0.956, and 0.011 U/mg proteins, respectively. These findings suggest that strain EH-E3 has strong potential for use in low-temperature treatment of acidic wastewater.

Synergistic electro-thermal enhancement of nitrogen removal in an iron-based Anammox system at low temperatures

In this study, a novel AC-stimulation technology was explored by synergistic electro-thermal enhancement for nitrogen removal in a Fe-based Anammox at low temperatures. Highest total nitrogen (TN) removal efficiency achieved by the AC-stimulated Anammox system was 73.59 % at 0.45 mA/cm2 AC densities, compared to 45.72 % TN removal efficiency realized in the control (non-AC-stimulated) Anammox system, both conducted at 13 °C. Additionally, the Anammox enzymes HZS and HDH exhibited the highest copy numbers at the same current density. Results from response surface methodology (RSM) analysis indicated that the optimal conditions included electrode spacings of 3.89 cm, 4.11 cm, and 3.78 cm, and AC densities of 0.43 mA/cm2, 0.46 mA/cm2, and 0.39 mA/cm2 at temperatures of 13 °C, 16 °C, and 19 °C, respectively. Mechanism analysis revealed that the electrons provided by AC could stimulate biological processes while simultaneously heating the material.

Formate-facilitated recovery of wastewater anammox granular sludge from oxygen inhibition: Effects and mechanisms

Oxygen leakage due to poor reactor sealing or accidental aeration can have detrimental impacts on the performance of wastewater anammox processes. Strategies of restoring functionality of anammox consortia are scarce, and providing appropriate chemical reducing reagents may help reduce oxidative damage. This study characterized the responses of anammox granular sludge (AnGS) to oxygen inhibition, and identified formate as an effective promoter capable of facilitating activity recovery, while other organics (acetate, glucose, methanol) were less effective. Upon 12 h of air exposure (DO: 1.2 ± 0.1 mg/L), the total nitrogen removal efficiency of a lab-scale AnGS reactor decreased from 85.15 % to 45.46 %. Compared with natural recovery (without chemical addition), potassium formate at 10 mg COD/L for 3 days significantly increased the total nitrogen removal efficiency, both in the short-term (66.68 % vs 57.09 %, 3 days post inhibition) and long-term (82.34 % vs 72.88 %, 30 days post inhibition). By examining sludge morphology, metagenome and transcriptome, the following potential mechanisms were proposed: 1) rapidly decreasing intracellular ROS; 2) enhancing nitrite turnover; 3) maintaining granular sludge integrity; 4) facilitating interspecies metabolic interactions. The ability of formate to facilitate sludge recovery from oxygen inhibition also implies its potential in mitigating other oxidative stresses in wastewater anammox reactors.

Synchronised removal of nitrogen and sulphate from rubber industrial wastewater by coupling of Sulfammox and sulphide-driven autotrophic denitrification in anaerobic membrane bioreactor.

Global rubber industry, growing 4-6 % annually with 13.76 million Mt of rubber produced in 2019, significantly impacts the economy. This study explores coupling sulfate-dependent ammonium oxidation (Sulfammox) and sulfide-driven autotrophic denitrification (SDAD) within an anaerobic membrane bioreactor (AnMBR) to treat high-strength natural rubber wastewater. Over 225 days, the AnMBR system achieved maximal chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4+-N), and sulfate sulfur (SO42--S) removal efficiencies of 58 %, 31 %, 13 %, and 45 %, respectively. TN is predominantly removed through Sulfammox (accounting for 49 % of NH4+-N removal), SDAD, and conventional denitrification pathways. Sulfate removal is achieved via Sulfammox (responsible for 43 % of SO42--S removal), and Dissimilatory sulfate-reducing (DSR) processes (contributing 57 % of SO42--S removal). Microbial analysis identified Desulfovibrio and Sulfurospirillum as key microbes, while metagenomic analysis highlighted crucial sulfur and nitrogen cycling pathways. The findings support Sulfammox and SDAD as promising eco-friendly strategies for treating ammonia- and sulfate-rich industrial wastewater.

Combining nonthermal N2 plasma with a denitrifying biofilm reactor for PFAS-contaminated wastewater remediation

Perfluoroalkyl and polyfluoroalkyl substances (PFAS), commonly known as ’forever chemicals,’ pose significant environmental threats to water bodies due to their persistence and toxicity. Traditional remediation methods are often ineffective or costly. In response, this study presents a novel two-step solution combining nonthermal nitrogen (N2) plasma degradation with a denitrifying biofilm reactor to treat PFAS-contaminated wastewater efficiently. Treatment by N2 plasma resulted into PFOA and PFDA degradation efficiencies up to 45% and 60%, respectively. The low cost of N2 gas makes N2 plasma more favorable (compared to e.g. Ar plasma) for practical applications. The biofilm reactor, inoculated with activated sludge and packed by expanded clay aggregates (ECA), could efficiently remove the inorganic nitrogen produced by N2 plasma. CH3COONa was utilized as a carbon source to supply energy for denitrifying bacteria. The total nitrogen (TN) removal efficiency was up to 90% at a C/N ratio of 4.0. Also, UV254 (40–50%), turbidity (80–90%) and COD (80–90%) were removed in the biofilm reactor. Due to the non-biodegradability of PFAS, their removal (initially up to 60–90%) in the biofilm reactor was attributed to ad- or absorption on sludge and ECA. The bioreactor offers a cost-effective solution to the issue of secondary inorganic nitrogen pollution caused by N2-containing plasma. This is beneficial for broadening the practical use of both N2 plasma and air plasma. The two-step process is not only applicable for treating PFAS-contaminated wastewater but can also be applied to various fields suitable for N2 and air plasma applications.

Robust PD/A biofilms sustain advanced real municipal wastewater treatment: Reinforcement of interspecific communication and electron transfer

In this study, a robust partial denitrification/anammox (PD/A) biofilm system was efficiently established within merely 83 days using solely conventional activated sludge as the inoculum, employing a multivariate regulation strategy involving the addition of biofillers, optimization of municipal wastewater feeding ratios, prolongation of hydraulic retention time, and introduction of hydrazine. The performance variability of PD/A system within a long-term, intricate mainstream substrate environment was further investigated by incrementally elevating municipal wastewater proportion (50 % → 75 % → 100 %). The results demonstrated that PD/A system ultimately achieved an impressive total nitrogen removal efficiency of 93.6 % and an effluent total nitrogen concentration of 8.6 mg/L, accompanied by anammox contributing over 85 % to nitrogen removal. The biofilm’s layered spatial structure nurtured Candidatus Brocadia, enabling it to reach an abundance of 2.5 % under high real municipal wastewater loading. Metabolic function analyses revealed that biofilm enhanced the abundance of genes associated with interspecies electron transfer and quorum sensing communication in PD/A consortia after prolonged exposure to municipal wastewater. These findings underscore the significances of interspecific interactions, bacterial communications, and synergistic metabolic traits within PD/A biofilm systems in the stabilization of real municipal wastewater treatment.

Removal of nutrients and bioelectricity generation from institutional wastewater using constructed wetland-microbial fuel cell

This study evaluated the removal of nutrients from institutional wastewater and the generation of bioelectric power using a microcosm-scale constructed wetland system integrated with a microbial fuel cell (CW-MFC). The research explored the impact of vegetation on both bioelectric production and wastewater treatment within the wetland matrix. Results indicated that the CW-MFC system with vegetation outperformed the unplanted system in terms of treatment efficiency. The planted modules achieved average total nitrogen (TN) and total phosphorus (TP) removal efficiencies of 94.6 % and 90.0 %, respectively, compared to 90.59 % and 83.5 % in the unplanted system. Notably, the CW-MFC planted with Scirpus atrovirens exhibited the highest average output voltage (0.648 V) and power density (232 mW/m³). In contrast, the unplanted CW-MFC produced a maximum voltage of 0.537 V and a power density of 220 mW/m³. These findings suggest that Scirpus atrovirens enhances both the treatment efficiency and bioelectricity generation by facilitating microbial activity involved in the biodegradation of organic compounds and improving electron flow from the anode to the cathode. The significant nutrient removal efficiencies and bioelectric power generation demonstrate the potential of using a vegetated CW-MFC system to achieve sustainable wastewater treatment while simultaneously producing renewable energy, thus contributing to more eco-friendly waste management practices

Comparation on the responses and resilience of single-Anammox system and synergistic partial-denitrification/anammox system to long-term nutrient starvation: Performance and metagenomic insights

Starvation disturbance was a common problem in biological sewage treatment processes. However, understanding about the responses and resilience of different active anammox biomass in autotrophic and heterotrophic systems to long-term nutrient starvation remains limited. This study compared responses and potential recovery mechanisms of autotrophic single-Anammox and heterotrophic synergistic partial-denitrification/anammox (PD/anammox) systems to prolonged starvation (31–40 days). After starvation, total inorganic nitrogen (TIN) removal efficiency of single-Anammox and synergistic PD/anammox systems decreased to 62.16 % and 78.52 %, respectively, of their original level. After the nutrient resupply, the performance of both systems gradually recovered to a similar-to-pre-starvation level at the rate of 1.26 %/day and 1.89 %/day, respectively. Compared with single-Anammox system, complex synergistic relationship of microorganisms and effective quorum sensing (QS) regulation strategies might mitigate the negative influences were caused by starvation and ensure the performance quickly return of synergistic PD/anammox system. This study would contribute to promote the application of Anammox technology.

Uncovering pathway and mechanism of simultaneous thiocyanate detoxicity and nitrate removal through anammox and denitrification

Thiocyanate (SCN−) exists in various industries and is detrimental to the ecosystem, necessitating cost-effective and environmentally benign treatment. In response to alleviate the bacterial toxicity of SCN−, this study developed a two-stage coupled system by tandem of anammox in reactor 1 (R1) and SCN−-driven autotrophic denitrification in reactor 2 (R2), achieving simultaneous removal of SCN− and nitrogen. The total nitrogen removal efficiency of the coupled system was 92.42 ± 1.98%, with nearly 100% of SCN− elimination. Thiobacillus was responsible for SCN− degradation. The deduced degradation pathway of SCN− was via the cyanate pathway before coupling, followed by the co-action of cyanate pathway and carbonyl sulfide pathway after coupling. Although scaling-up study is needed to validate its applicability in real-world applications, this study contributes to the advancement of sustainable and cost-effective wastewater treatment technologies, being an attractive path for low-carbon nitrogen removal and greenhouse gas emission-free technology.

Pollution resistance and removal efficiency of mesophytic plants of polluted water bodies

With the development of cities and economic growth, the eutrophication of urban park landscape water has become a hot topic in environmental governance and research at home and abroad. Using indoor water pollution simulation experiments, the decontamination and pollution resistance performance of six aquatic plants were studied. The research results found that all six aquatic plants can reduce the pH value of eutrophic water bodies. The pH of the Lythrum salicaria L. (Q) and Iris tectorum Maxim (Y) treatment systems was the lowest which are 7.34 and 7.48, respectively. They were significantly lower than the control group (CK). The content of nitrogen and phosphorus elements were reduced by six types of plants in the wastewater. After the completion of the experiment, the total nitrogen (TN) removal efficiency of Y was as high as 66.2%, and its content decreased from 9.49 to 3.21 mg/l. The removal rates of total phosphorus (TP) by six types of plants ranged from 59.1 to 81.3% and they were significantly higher than the CK. Among them, the removal rate of TP in wastewater by Y treatment exceeded 80%, which is superior to other plants and significantly different from CK. After the completion of the experiment, the content of chlorophyll a (chl a) in the water treated with Y was the lowest (6.6 mg/l). It was significantly lower than the other treatments (P&lt;0.05). The contents of chl a in Y decreased by 37.1% compared to the initial level. Compared to CK, it is 54.1% lower and the content of chl a in CK showed an increasing trend with time delay. Overall analysis shows that the microsystems formed by the six plants all have a certain improvement effect on water quality, effectively inhibiting the proliferation of algae in eutrophic water bodies. Among them, planting iris has the best effect. Bangladesh J. Bot. 53(3): 757-763, 2024 (September) Special

Directional Electron Transfer in Enzymatic Nano‐Bio Hybrids for Selective Photobiocatalytic Conversion of Nitrate

Semi‐artificial photosynthetic system (SAPS) that combines enzymes or cellular organisms with light‐absorbing semiconductors, has emerged as an attractive approach for nitrogen conversion, yet faces the challenge of reaction pathway regulation. Herein, we find that photoelectrons can transfer from the ‐C≡N groups at the edge of cyano‐rich carbon nitride (g‐C3N4‐CN) to nitrate reductase (NarGH), while the direct electron transfer to nitrite reductase (cd1NiR) is inhibited due to the physiological distance limit of active sites (&gt; 14 Å). By means of the directional electron transfer between g‐C3N4‐CN and extracted biological enzymes, the product of the denitrification reaction was switched from inert N2 to usable nitrite with an unprecedented selectivity of up to 95.3%. The converted nitrite could be further utilized by anammox microbiota and dissimilatory nitrate reduction to ammonia (DNRA) microorganisms, doubling the efficiency of total nitrogen removal (96.5 ± 2.3 %) for biological nitrogen removal and ammonia generation (12.6 mg NH4+‐N L‐1 h‐1), respectively. Thus, our work paves an appealing way for the sustainable treatment and utilization of nitrate for ammonia fuel production by strategically regulating the electron transfer pathway across the biotic‐abiotic interface.

Directional Electron Transfer in Enzymatic Nano-Bio Hybrids for Selective Photobiocatalytic Conversion of Nitrate.

Semi-artificial photosynthetic system (SAPS) that combines enzymes or cellular organisms with light-absorbing semiconductors, has emerged as an attractive approach for nitrogen conversion, yet faces the challenge of reaction pathway regulation. Herein, we find that photoelectrons can transfer from the -C≡N groups at the edge of cyano-rich carbon nitride (g-C3N4-CN) to nitrate reductase (NarGH), while the direct electron transfer to nitrite reductase (cd1NiR) is inhibited due to the physiological distance limit of active sites (> 14 Å). By means of the directional electron transfer between g-C3N4-CN and extracted biological enzymes, the product of the denitrification reaction was switched from inert N2 to usable nitrite with an unprecedented selectivity of up to 95.3%. The converted nitrite could be further utilized by anammox microbiota and dissimilatory nitrate reduction to ammonia (DNRA) microorganisms, doubling the efficiency of total nitrogen removal (96.5 ± 2.3 %) for biological nitrogen removal and ammonia generation (12.6 mg NH4+-N L-1 h-1), respectively. Thus, our work paves an appealing way for the sustainable treatment and utilization of nitrate for ammonia fuel production by strategically regulating the electron transfer pathway across the biotic-abiotic interface.

Urban wastewater treatment at ambient conditions using microalgae-bacteria consortia in a membrane high-rate algal pond (MHRAP): The effect of hydraulic retention time and influent strength

The effects of hydraulic retention time (HRT) and influent wastewater strength on microalgae-bacteria performance were studied in two sets of experiments in a 6-day biomass retention time membrane high-rate algal pond (MHRAP) pilot plant to assess its pollutants removal potential. In the first set of experiments, the MHRAP was continuously fed with effluent from primary settling and operated at 6-, 4- and 2-days HRT and in the second set, the MHRAP was operated at 4-, 2-, and 1-day HRT using pre-treatment effluent. Results showed a complex interaction between algae-bacteria consortium, ambient conditions and MHRAP operation. In set 1, the highest total nitrogen (T-N) and total phosphorus (T-P) removal efficiencies were reached with 6-day HRT (23.6±0.6 % and 32±4 %, respectively), partially due to free ammonia nitrogen stripping and phosphorus precipitation, because of abiotic factors, which reduces the activity of nitrite-oxidizing bacteria and led to partial-nitrification. On the other hand, the 4 and 2-day HRT T-N and T-P removal efficiencies were reduced (below 10 % and 5 %, respectively) because the abiotic factors limited the physicochemical processes, and less biomass was taken up. In set 2, a suitable equilibrium between the microalgae and bacterial communities at 2-days HRT achieved high T-N (91±5 %) and T-P (71±8 %) removal efficiencies. Mass balances indicated that the nitrogen was mostly removed by nitrification-denitrification (87 % of T-N) and T-P predominant removal mechanism was precipitation. The COD removal efficiencies were higher than 86 % in both sets, since the particulate COD and colloids were removed by ultrafiltration. The obtained results showed that MHRAP technology would allow reducing COD and nutrient loads in the effluent under certain operating conditions, demonstrating the potential for resource recovery and wastewater treatment of microalgae-bacteria consortia.