Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system.

Three kinds of bioretention were designed to explore the effects of zero-valent iron (ZVI) and biochar on the nitrogen removal performance and to seek a more reasonable packing method in this study. The results showed that the effluent removal rates of nitrate, ammonium and total nitrogen were 53.30 ± 12.68%, 98.41 ± 0.38% and 64.03 ± 8.72% respectively in Bioretention-3 during the rainfall events, while the nitrate concentration decreased gradually with the increase of drying time. According to the batch experiment, it was found that zero-valent iron could release continuously and stably in Bioretention-3 and Bioretention-1 due to the interception effect of biochar on dissolved oxygen. In addition, biochar in soil layer could protect zero-valent iron from excessive oxidation while biochar in the substrate layer could release organic matter to promote heterotrophic denitrification. Microbial community analysis showed that the dominant phyla were Proteobacteria (20.92-40.81%) and Actinobacteriota (9.89-24.54%). The dominant nitrifying genera was Nitrospira while there were also aerobic denitrifying bacteria (Sphingomonas, Bradyrhizobium and Chryseolinea, etc.) in soil layer. In the substrate layer, there was more ferrous iron-mediated autotrophic denitrification process (Thiobacillus, Geobacter and Denitratisoma, etc.) in Bioretention-1 and Bioretention-3 while a larger proportion of Dissimilatory Nitrate Reduction to Ammonium process (DNRA) (Bacillus, Desulfovibrio and Pseudomonas, etc.) in Bioretention-2. In general, this study showed that biochar addition in soil coupled with mixing zero-valent iron and biochar as substrate layer was a more stable and efficient design through various aspects of evidence. It provides a new way for how to use zero-valent iron and biochar to improve nitrogen removal capacity in stormwater management.

Effects of ferrous addition to Vallisneria natans: An attempt to apply ferrous to submerged macrophyte restoration.

Restoration of submerged macrophytes is an efficient way for endogenous nutrient control and aquatic ecological restoration, but slow growth and limited reproduction of submerged macrophytes still exist. In this research, the effect of ferrous on the seed germination and growth of Vallisneria natans (V. natans) were studied through aquatic simulation experiments and its influence on the rhizosphere microbial community was also explored. The seed germination, growth, and physiological and ecological parameters of V. natans were significantly affected by the ferrous treatments. Ferrous concentration above 5.0 mg/L showed significant inhibition of seed germination of V. natans and the best concentration for germination was 0.5 mg/L. During the growth of V. natans, after ferrous was added, a brief period of stress occurred, which then promoted the growth lasting for about 19 days under one addition. The diversity and richness of the rhizospheric microbial were increased after the ferrous addition. However, the function of the rhizospheric microbial community showed no significant difference between different concentrations of ferrous adding in the overlying water. Ferrous addition affected the growth condition of plants (content of CAT, Chl a, Chl b, etc.), thus indirectly affecting the rhizospheric microbial community of V. natans. These impacts on V. natans and rhizosphere microorganisms could generalize to other submerged macrophytes in freshwater ecosystems, particularly which have similar habits. These findings would contribute to the ecological evaluation of ferrous addition or iron-containing water, and provide a reference for submerged macrophytes restoration and ecological restoration in freshwater ecosystems.

Efficient nitrogen removal pathways and corresponding microbial evidence in tidal flow constructed wetlands for saline water treatment.

The artificial tidal wetlands ecosystem was believed to be a useful device in treating saline water, and it played a significant part in global nitrogen cycles. However, limited information is available on nitrogen-cycling pathways and related contributions to nitrogen loss in tidal flow constructed wetlands (TF-CWs) for saline water treatment. This study operated seven experimental tidal flow constructed wetlands to remove nitrogen from saline water at salinities of 0-30‰. Stable and high NH4+-N removal efficiency (∼90.3%) was achieved, compared to 4.8-93.4% and 23.5-88.4% for nitrate and total nitrogen (TN), respectively. Microbial analyses revealed the simultaneous occurrence of anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), nitrification and denitrification, contributing to nitrogen (N) loss from the mesocosms. The absolute abundances were 5.54 × 103-8.35 × 107 (nitrogen functional genes) and 5.21 × 107-7.99 × 109 copies/g (16S rRNA), while the related genera abundances ranged from 1.81% to 10.47% (nitrate reduction) and from 0.29% to 0.97% (nitrification), respectively. Quantitative response relationships showed ammonium transformation were controlled by nxrA, hzsB and amoA, and nitrate removal by nxrA, nosZ and narG. Collectively, TN transformation were determined by narG, nosZ, qnorB, nirS and hzsB through denitrification and anammox pathways. The proportion of nitrogen assimilation by plants was 6.9-23.4%. In summary, these findings would advance our understanding of quantitative molecular mechanisms in TF-CW mesocosms for treating nitrogen pollution that caused algal blooms in estuarine/coastal ecosystems worldwide.

Molecular analysis of microbial nitrogen transformation and removal potential in the plant rhizosphere of artificial tidal wetlands across salinity gradients.

This study explored the microbial nitrogen transformation and removal potential in the plant rhizosphere of seven artificial tidal wetlands under different salinity gradients (0-30‰). Molecular biological and stable isotopic analyses revealed the existence of simultaneous anammox (anaerobic ammonium oxidation), nitrification, DNRA (dissimilatory nitrate reduction to ammonium) and denitrification processes, contributing to nitrogen loss in rhizosphere soil. The microbial abundances were 2.87 × 103-9.12 × 108 (nitrogen functional genes) and 1.24 × 108-8.43 × 109 copies/g (16S rRNA gene), and the relative abundances of dissimilatory nitrate reduction and nitrification genera ranged from 6.75% to 24.41% and from 0.77% to 1.81%, respectively. The bacterial 16S rRNA high-throughput sequencing indicated that Bacillus, Zobellella and Paracoccus had obvious effects on nitrogen removal by heterotrophic nitrifying/aerobic denitrifying process (HN-AD), and autotrophic nitrification (Nitrosomonas, Nitrospira and Nitrospina), conventional denitrification (Bradyrhizobium, Burkholderia and Flavobacterium), anammox (Candidatus Brocadia and Candidatus Scalindua) and DNRA (Clostridium, Desulfovibrio and Photobacterium) organisms co-existed with HN-AD bacteria. The potential activities of DNRA, nitrification, anammox and denitrification were 1.23-9.23, 400.03-755.91, 3.12-35.24 and 30.51-300.04 nmolN2·g-1·d-1, respectively. The denitrification process contributed to 73.59-88.65% of NOx- reduction, compared to 0.71-13.20% and 8.20-15.42% via DNRA and anammox, as 83.83-90.74% of N2 production was conducted by denitrification, with the rest through anammox. Meanwhile, the nitrification pathway accounted for 95.28-99.23% of NH4+ oxidation, with the rest completed by anammox bacteria. Collectively, these findings improved our understanding on global nitrogen cycles, and provided a new idea for the removal of contaminants in saline water treatment.

Simultaneous denitrification and iron-phosphorus precipitation driven by plant biomass coupled with iron scraps in subsurface flow constructed wetlands.

This study investigated the interaction between plant biomass and iron scraps and their influence on nitrogen (including nitrate and ammonia) and phosphorus removal in the subsurface flow constructed wetland. The results showed that with the addition of 0.5 g L-1 of plant biomass and 5.0 g L-1 of iron scraps, the nitrate, total nitrogen and total phosphorus removal were simultaneously improved. During 35 days of continuous operation, the plant biomass played main effect on the enhanced denitrification, accounting for about 57%, while iron scraps enhanced the other 43% of nitrogen removal and most phosphorus removal through precipitation inside the wetlands. Iron scraps could benefit the degradation of cellulose into low molecular carbohydrates by 10%, and the biomass could promote the oxidation of iron and increase the total phosphorus removal by 15%. Plant biomass coupled with iron scraps also improved simultaneously the richness, diversity and evenness of microbial community and promoted the abundance of Nitrospira (17.37%) and Thiobacillus (8.46%) in wetlands. In practice, putting iron scraps as matrix and placing plant biomass in the influent region would be a better choice. This research would provide a new method for effective utilization of plant biomass and iron scraps and further treatment of low-polluted wastewater in the wetlands.

Microbial response mechanism of plants and zero valent iron in ecological floating bed: Synchronous nitrogen, phosphorus removal and greenhouse gas emission reduction.

Iron-based ecological floating beds (EFBs) are often used to treat the secondary effluent from wastewater treatment plant to enhance the denitrification process. However, the impact and necessity of plants on iron-based EFBs have not been systematically studied. In this research, two iron-based EFBs with and without plants (EFB-P and EFB) were performed to investigate the response of plants on nutrient removal, GHG emissions, microbial communities and functional genes. Results showed the total nitrogen and total phosphorus removal in EFB-P was 45-79% and 48-72%, respectively, while that in EFB was 31-67% and 44-57%. Meanwhile, plants could decrease CH4 emission flux (0-3.89 mg m-2 d-1) and improve CO2 absorption (4704-22321 mg m-2 d-1). Plants could increase the abundance of Nitrosospira to 1.6% which was a kind of nitrifying bacteria dominant in plant rhizosphere. Among all denitrification related genera, Simplicispira (13.08%) and Novosphingobium (6.25%) accounted for the highest proportion of plant rhizosphere and iron scrap, respectively. Anammox bacteria such as Candidatus_Brocadia was more enriched on iron scraps with the highest proportion was 1.21% in EFB-P, and 2.20% in EFB. Principal co-ordinates analysis showed that plants were the critical factor determining microbial community composition. TN removal pathways were mixotrophic denitrification and anammox in EFB-P while TP removal pathways were plant uptake and phosphorus-iron coprecipitation. In general, plants play an important directly or indirectly role in iron-based EFBs systems, which could not only improve nutrients removal, but also minimize the global warming potential and alleviate the greenhouse effect to a certain extent.

The suitable biomass carbon source for improving nitrogen removal in surface flow constructed wetland system: Fresh vs. withered.

Plant biomass can be used as a carbon source to enhance the nitrogen removal effect. Related researches mainly focused on withered biomass, while little on fresh biomass. In this study, batch experiments revealed that the carbon release rate (60.5 mg TOC g-1) of fresh biomass was significantly higher than that of withered biomass (44.9 mg TOC g-1), while the nitrogen release rate showed the opposite trend. Compared with withered biomass, fresh biomass could release more sugar and less refractory humic acid, which means higher bioavailability. After adding fresh biomass, TN removal rate increased from 18.65% to 51.59%. The TN removal in the wetland adding withered biomass increased from 13.59% to 42.25%. The biomass addition had a slight impact on the effluent sensory quality in the first two days. After adding fresh biomass and withered biomass, the relative abundance of denitrifying bacteria like Flavobacterium and Pseudomonas in the system significantly increased. In general, fresh biomass was more suitable as a denitrification carbon source for surface flow constructed wetlands.

Comparison of microbial communities in different sulfur-based autotrophic denitrification reactors.

Sulfur-based autotrophic denitrification is a useful approach for the eutrophication control in lakes and rivers, yet the microorganisms in this process are still not clearly known. In order to reveal the bacterial composition in these denitrification reactors, high-throughput sequencing was performed over the sludge samples. And the results indicated that when using thiosulfate, elemental sulfur, and sulfide as electron donors, the microbial communities were clearly different. Besides the well-known Thiobacillus, many other genera of denitrifiers were identified. Chlorobaculum, Dechloromonas, and Acinetobacter were the most predominant genera in thiosulfate, elemental sulfur, and sulfide systems, respectively, while Janthinobacterium accounted for the most in the heterotrophic reactor with ethanol as electron donor. Thiobacillus existed abundantly in every system, even in the heterotrophic one. PCA comparison revealed that the microbial communities in the denitrification systems may vary greatly according to the electron donor, the running condition, sampling position, and other factors.

Application of light-weight filtration media in an anoxic biofilter for nitrate removal from micro-polluted surface water.

The research investigated nitrate removal from micro-polluted surface water by the single-stage process of anoxic biofilter using light-weight polystyrene beads as filtration media. In this study, sodium acetate was used as an external carbon source and the nitrate removal efficiency under different regimes of hydraulic loading rate (HLR), water temperature, and C/N ratio was studied. In addition, the effect of backwash on denitrification efficiency was investigated. The results show that the biofilter achieved a high nitrate removal efficiency in 2 weeks at water temperatures ranging between 22 and 25 °C at a C/N ratio (COD:NO3(-)-N) of 6:1. Besides, the average removal efficiency of nitrate at HLRs of 5.66, 7.07 and 8.49 m(3) m(-2) h(-1) were 87.5, 87.3 and 87.1%, respectively. The average removal efficiency of nitrate nitrogen was 13.9% at a HLR of 5.66 m(3) m(-2) h(-1) at water temperatures of 12-14 °C, then it increased to 93.7% when the C/N ratio increased to 10. It suggests that the optimal hydraulic retention time is at water temperatures of 8-10 °C. The water consumption rate of backwash was about 0.2-0.3%, and denitrification efficiency returned to the normal level in 12 h after backwash.

Sulfur-based autotrophic denitrification from the micro-polluted water.

Eutrophication caused by high concentrations of nutrients is a huge problem for many natural lakes and reservoirs. Removing the nitrogen contamination from the low C/N water body has become an urgent need. Autotrophic denitrification with the sulfur compound as electron donor was investigated in the biofilter reactors. Through the lab-scale experiment, it was found that different sulfur compounds and different carriers caused very different treatment performances. Thiosulfate was selected to be the best electron donor and ceramsite was chosen as the suitable carrier due to the good denitrification efficiency, low cost and the good resistibility against the high hydraulic loads. Later the optimum running parameters of the process were determined. Then the pilot-scale experiment was carried out with the real micro-polluted water from the West Lake, China. The results indicated that the autotrophic denitrification with thiosulfate as electron donor was feasible and applicable for the micro-polluted lake water.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system.

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.

Revealing sulfur-iron coupling mechanism for enhanced autotrophic denitrification in ecological floating beds.

A sulfur-iron coupled ecological floating bed (EFB-SFe) was developed to enhance the denitrification capability of sulfur-based ecological floating beds (EFB-S). The denitrification performance, kinetic process and microbial community composition were explored. Results showed that sulfur-iron coupling effectively enhanced the denitrification performance of EFB, surpassing the sum of their individual effects. The average total nitrogen removal rate ranged from 1.56 to 4.56 g·m-2·d-1, with a removal efficiency of 22-84 %. The k value for the S + Fe group increased from 0.04 to 0.18 d-1 to 0.40-0.46 d-1 relative to the S group. The sulfur-iron coupling promoted the enrichment of denitrifying bacteria (Thiobacillus and Ferritrophicum). The denitrification genes in EFB-SFe were upregulated, being 12-22 times more abundant than in EFB-S. Sulfur and iron autotrophic denitrification were identified as the main nitrogen removal processes in EFB-SFe. Overall, sulfur-iron coupling showed the potential to enhance the denitrification capacity of EFB-S for treating low-pollution water.

Boosting the denitrification efficiency of iron-based constructed wetlands in-situ via plant biomass-derived biochar: Intensified iron redox cycle and microbial responses.

Considering the unsatisfied denitrification performance of carbon-limited wastewater in iron-based constructed wetlands (ICWs) caused by low electron transfer efficiency of iron substrates, utilization of plant-based conductive materials in-situ for improving the long-term reactivity of iron substrates was proposed to boost the Fe (III)/Fe (II) redox cycle thus enhance the nitrogen elimination. Here, we investigated the effects of withered Iris Pseudacorus biomass and its derived biochar on nitrogen removal for 165 days in ICWs. Results revealed that accumulate TN removal capacity in biochar-added ICW (BC-ICW) increased by 14.7 % compared to biomass-added ICW (BM-ICW), which was mainly attributed to the synergistic strengthening of iron scraps and biochar. The denitrification efficiency of BM-ICW improved by 11.6 % compared to ICWs, while its removal capacity declined with biomass consumption. Autotrophic and heterotrophic denitrifiers were enriched in BM-ICW and BC-ICW, especially biochar increased the abundance of electroactive species (Geobacter and Shewanella, etc.). An active iron cycle exhibited in BC-ICW, which can be confirmed by the presence of more liable iron minerals on iron scraps surface, the lowest Fe (III)/Fe (II) ratio (0.51), and the improved proportions of iron cycling genes (feoABC, korB, fhuF, TC.FEV.OM, etc.). The nitrate removal efficiency was positively correlated with the nitrogen, iron metabolism functional genes and the electron transfer capacity (ETC) of carbon materials (P < 0.05), indicating that redox-active carbon materials addition improved the iron scraps bioavailability by promoting electron transfer, thus enhancing the autotrophic nitrogen removal. Our findings provided a green perspective to better understand the redox properties of plant-based carbon materials in ICWs for deep bioremediation in-situ.

Reveling the micromolecular biological mechanism of acetate, thiosulfate and Fe0 in ecological floating beds for treating low C/N wastewater: Insight into nitrogen removals and greenhouse gases reductions.

Selecting an appropriate electron donor to enhance nitrogen removal for treating low C/N wastewater in ecological floating beds (EFBs) is controversy. In this study, a systematic and comprehensive evaluation of sodium acetate (EFB-C), sodium thiosulfate (EFB-S) and iron scraps (EFB-Fe) was performed in a 2-year experiment on long-term viability including nitrogen removal and greenhouse gas emissions associated with key molecular biological mechanisms. The results showed that EFB-C (43-85 %) and EFB-S (40-88 %) exhibited superior total nitrogen (TN) removal. Temperature and hydraulic retention time (HRT) have significant impacts on TN removal of EFB-Fe, however, it could reach 86 % under high temperature (30-35 °C) and a long HRT (3 days), and it has lowest N2O (0-6.2 mg m-2 d-1) and CH4 (0-5.3 mg m-2 d-1) fluxes. Microbial network analysis revealed that the microbes changed from competing to cooperating after adding electron donors. A higher abundance of anammox genera was enriched in EFB-Fe. The Mantel's test and structural equation model provided proof of the differences, which showed that acetate and thiosulfate were similar, whereas Fe0 was different in the nitrogen removal mechanism. Molecular biology analyses further verified that heterotrophic, autotrophic, and mixotrophic coupled with anammox were the main TN removal pathways for EFB-C, EFB-S, and EFB-Fe, respectively. These findings provide a better understanding of the biological mechanisms for selecting appropriate electron donors for treating low C/N wastewater.

Unveiling the microplastic perturbation on surface flow constructed wetlands with macrophytes of different life forms: Responses of nitrogen removal and sensory quality.

Microplastics (MPs) discharging into constructed wetlands pose risks to these ecosystems. Nevertheless, the perturbation of MPs to different types of macrophytes, which play important roles in purifying pollutants of wetlands, has not been fully elucidated. In this study, polystyrene MPs (PS-MPs) perturbation on nitrogen removal and sensory quality of surface flow constructed wetlands planted with emergent and submerged macrophytes were investigated. PS-MPs enhanced N removal efficiencies temporarily, whereas the N removal rate constants were declined as exposure time was prolonged. The NH4+-N removal rate constants declined by 25.78 % and 34.03 % in E and S groups respectively. The NO3--N removal rate constants declined by 22.13 % in the S groups. Denitrifiers including Thiobacillus, Rhodobacter, and Sulfuritalea were stressed. The sensory quality deteriorated after PS-MPs exposure, which was significantly related to changes in Chlorophyll a, particle size distribution, and colored dissolved organic matter. Turbidity in E groups and chroma in S groups were greatly affected by PS-MPs. Overall, under MPs exposure, macrophytes in E groups were more suitable for nitrogen removal, and macrophytes in S groups better purified the turbidity. The study could provide the basis for better allocation of macrophytes in CWs to reduce the purifying risk by PS-MPs disturbance.

Removal of anaerobic soluble microbial products in a biological activated carbon reactor.

The soluble microbial products (SMP) in the biological treatment effluent are generally of great amount and are poorly biodegradable. Focusing on the biodegradation of anaerobic SMP, the biological activated carbon (BAC) was introduced into the anaerobic system. The experiments were conducted in two identical lab-scale up-flow anaerobic sludge blanket (UASB) reactors. The high strength organics were degraded in the first UASB reactor (UASB1) and the second UASB (UASB2, i.e., BAC) functioned as a polishing step to remove SMP produced in UASB1. The results showed that 90% of the SMP could be removed before granular activated carbon was saturated. After the saturation, the SMP removal decreased to 60% on the average. Analysis of granular activated carbon adsorption revealed that the main role of SMP removal in BAC reactor was biodegradation. A strain of SMP-degrading bacteria, which was found highly similar to Klebsiella sp., was isolated, enriched and inoculated back to the BAC reactor. When the influent chemical oxygen demand (COD) was 10,000 mg/L and the organic loading rate achieved 10 kg COD/(m3 x day), the effluent from the BAC reactor could meet the discharge standard without further treatment. Anaerobic BAC reactor inoculated with the isolated Klebsiella was proved to be an effective, cheap and easy technical treatment approach for the removal of SMP in the treatment of easily-degradable wastewater with COD lower than 10,000 mg/L.

Iron plaque formation and its effect on key elements cycling in constructed wetlands: Functions and outlooks.

Ecological restoration of wetland plants has emerged as an environmentally-friendly and less carbon footprint method for treating secondary effluent wastewater. Root iron plaque (IP) is located at the important ecological niches in constructed wetlands (CWs) ecosystem and is the critical micro-zone for pollutants migration and transformation. Root IP can affect the chemical behaviors and bioavailability of key elements (C, N, P) since its formation/dissolution is a dynamic equilibrium process jointly influenced by rhizosphere habitats. However, as an efficient approach to further explore the mechanism of pollutant removal in CWs, the dynamic formation of root IP and its function have not been fully studied, especially in substrate-enhanced CWs. This article concentrates on the biogeochemical processes between Fe cycling involved in root IP with carbon turnover, nitrogen transformation, and phosphorus availability in CWs rhizosphere. As IP has the potential to enhance pollutant removal by being regulated and managed, we summarized the critical factors affecting the IP formation from the perspective of wetland design and operation, as well as emphasizing the heterogeneity of rhizosphere redox and the role of key microbes in nutrient cycling. Subsequently, interactions between redox-controlled root IP and biogeochemical elements (C, N, P) are emphatically discussed. Additionally, the effects of IP on emerging contaminants and heavy metals in CWs rhizosphere are assessed. Finally, major challenges and outlooks for future research in regards to root IP are proposed. It is expected that this review can provide a new perspective for the efficient removal of target pollutants in CWs.

Key factors influencing sensory quality of scenic waters and its improvement by constructed wetlands.

Sensory quality is very important for scenic waters. It's necessary to find out the key factors influencing sensory quality of scenic waters and then take corresponding measures to improve it. In this study, transparency, turbidity and surface chroma were chosen as the main sensory quality indexes whose key influencing factors were analyzed by structural equation model (SEM). The results indicated that water's transparency, turbidity and surface chroma were all mainly influenced by suspended solid (SS). Meanwhile, transparency was also influenced by Chlorophyll a (Chl a), pH, dissolved oxygen (DO), particle size and nutrients. Turbidity was influenced by Chl a and particle size as well. To verify this result and improve water's sensory quality, three constructed wetlands (CWs) were set up and operated. CWs could effectively improve the sensory quality of water bodies. When hydraulic retention time (HRT) was 2 days, the water' transparency increased from 18.00 ± 2.83 cm to about 100 cm, the removal rate of turbidity was 56.26% âˆ¼ 97.11%, and the average removal rate of surface chroma of the three CWs was 72.56%, 70.31% and 63.36%, respectively. To get a better improvement effect, planting and extending HRT were feasible measures. The mechanism analysis showed that removing SS, especially large particles in water was the main reason for improving sensory quality by CWs, followed by removing Chl a. The operational results of CWs proved that SS was certainly the key influencing factor of water's sensory quality.

New insight and enhancement mechanisms for Feammox process by electron shuttles in wastewater treatment - A systematic review.

Ammonium oxidation coupled to Fe(III) reduction (Feammox) is a newly discovered iron-nitrogen cycle process of microbial catalyzed NH4+ oxidation coupled with iron reduction. Fe(III) often exists in the form of insoluble iron minerals resulting in reduced microbial availability and low efficiency of Feammox. Electron shuttles(ESs) can be reversibly oxidized and reduced which has the potential to improve Feammox efficiency. This review summarizes the discovery process, electron transfer mechanism, influencing factors and driven microorganisms of Feammox, ang expounds the possibility and potential mechanism of ESs to enhance Feammox efficiency. Based on an in-depth analysis of the current research situation of Feammox for nitrogen removal, the knowledge gaps and future research directions including how to apply ESs enhanced Feammox to promote nitrogen removal in practical wastewater treatment have been highlighted. This review can provide new ideas for the engineering application research of Feammox and strong theoretical support for its development.

Salinity effect on denitrification efficiency with reed biomass addition in salt marsh wetlands.

Five simulated salt marsh wetlands with reed were constructed to investigate the effect of salinity on denitrification efficiency and its enhancement by reed biomass addition. It was found that the salinity of 7 ‰ and 10 ‰ could promote the organic carbon release of reed biomass. Results showed that the nitrate removal was highest at the salinity of 7 ‰, and would be further enhanced from 54.06 ± 12.46 % to 74.37 ± 11.53 % after the addition of reed biomass. Meanwhile, the lowest nitrous oxide emission flux was also achieved, with 0.23 mg/(m2 h) at this salinity. Microbiological analysis showed that salinity changed the microbial community. The increasing salinity increased the relative abundance of Chloroflexi and Actinobacteria, but decreased that of Proteobacteria. Main functional genera of denitrification changed from Desulfuromonas to Azoarcus and Anaeromyxbacter when the salinity increased to 15 ‰. These results will help to understand the nitrogen removal capacity of salt marsh wetlands with reed biomass addition.