Rapid start-up strategy of partial denitrification and microbially driven mechanism of nitrite accumulation mediated by dissolved organic matter

Treatment of low-C/N nitrate wastewater using a partial denitrification-anammox granule system: Granule reconstruction, stability, and microbial structure analyses

Industrial wastewater discharged into sewer systems is often characterized by high nitrate contents and low C/N ratios, resulting in high treatment costs when using conventional activated sludge methods. This study introduces a partial denitrification-anammox (PD/A) granular process to address this challenge. The PD/A granular process achieved an effluent TN level of 3.7 mg/L at a low C/N ratio of 2.3. Analysis of a typical cycle showed that the partial denitrification peaked within 15 min and achieved a nitrate-to-nitrite transformation ratio of 86.9%. Anammox, which was activated from 15 to 120 min, contributed 86.2% of the TN removal. The system exhibited rapid recovery from post-organic shock, which was attributed to significant increases in protein content within TB-EPS. Microbial dispersion and reassembly were observed after coexistence of the granules, with Thauera (39.12%) and Candidatus Brocadia (1.25%) identified as key functional microorganisms. This study underscores the efficacy of PD/A granular sludge technology for treating low-C/N nitrate wastewater.

Anaerobic cyanides oxidation with bimetallic modulation of biological toxicity and activity for nitrite reduction

Cyanide is a typical toxic reducing agent prevailing in wastewater with a well-defined chemical mechanism, whereas its exploitation as an electron donor by microorganisms is currently understudied. Given that conventional denitrification requires additional electron donors, the cyanide and nitrogen can be eliminated simultaneously if the reducing HCN/CN- and its complexes are used as inorganic electron donors. Hence, this paper proposes anaerobic cyanides oxidation for nitrite reduction, whereby the biological toxicity and activity of cyanides are modulated by bimetallics. Performance tests illustrated that low toxicity equivalents of iron-copper composite cyanides provided higher denitrification loads with the release of cyanide ions and electrons from the complex structure by the bimetal. Both isotopic labeling and Density Functional Theory (DFT) demonstrated that CN--N supplied electrons for nitrite reduction. The superposition of chemical processes reduces the biotoxicity and enhances the biological activity of cyanides in the CN-/Fe3+/Cu2+/NO2- coexistence system, including complex detoxification of CN- by Fe3+, CN- release by Cu2+ from [Fe(CN)6]3-, and NO release by nitrite substitution of -CN groups. Cyanide is the smallest structural unit of C/N-containing compounds and serves as a probe to extend the electron-donating principle of anaerobic cyanides oxidation to more electron-donor microbial utilization.

Unraveling the mechanisms and responses of aniline-degrading biosystem to salinity stress in high temperature condition: pollutants removal performance and microbial community

To explore the intrinsic influence of different salinity content on aniline biodegradation system in high temperature condition of 35±1 °C, six groups at various salinity concentration (0.0%-5.0%) were applied. The results showed that the salinity exerted insignificant impact on aniline removal performance. The low-level salinity (0.5%-1.5%) stimulated the nitrogen metabolism performance. The G5-2.5% had excellent adaptability to salinity while the nitrogen removal capacity of G6-5.0% was almost lost. Moreover, high throughput sequencing analysis revealed that the g__norank_f__NS9_marine_group, g__Thauera and g__unclassified_f__Rhodobacteraceae proliferated wildly and established positive correlation each other in low salinity systems. The g__SM1A02 occupying the dominant position in G5 ensured the nitrification performance. In contrast, the Rhodococcus possessing great survival advantage in tremendous osmotic pressure competed with most functional genus, triggering the collapse of nitrogen metabolism capacity in G6. This work provided valuable guidance for the aniline wastewater treatment under salinity stress in high temperature condition.

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.

Microbial community evolution and individual-based model validation of biofilms in single-stage partial nitrification/anammox system

In this study, matrix degradation, microbial community development, and distribution using an individual-based model during biofilm formation on carriers at varying depths within a single-stage partial nitrification/anammox system were simulated. The findings from the application of individual-based model fitting, fluorescence in situ hybridization, and high-throughput sequencing reveal the presence of aerobic bacteria, specifically ammonia-oxidizing bacteria, as discrete particles within the outer layer of the carrier. Facultative anaerobic bacteria exemplified by anaerobic ammonia-oxidizing bacteria, are observed as aggregates within the middle layer. Conversely, anaerobic bacteria, represented by denitrifiers, are enveloped by extracellular polymeric substances within the inner layer. The present study extends the application of individual-based model to the formation of polyurethane-supported biofilms and presents valuable avenues for the design and advancement of pragmatic engineering carriers.

Impact of waste separation on the biological nitrogen removal in a MSW incineration leachate treatment plant: Performance and microbial community shift

After waste separation program was launched in China in 2019, incineration leachate treatment plants are facing a challenge of effective removal of nitrogen from leachate due to lack of sufficient carbon source. In this study, the performance of a biological incineration leachate treatment process (anaerobic digestion (AD) - two-stage anoxic/aerobic (A/O) process) was evaluated after adopting the waste separation program, and the changes in the microbial community and function was analyzed using 16S rRNA amplicon sequencing technology. Results showed that after the waste separation, the influent chemical oxygen demand (COD) concentration reduced by 90% (from 19,300 to 1780 mg L-1) with the COD/N ratio decreased from 12.3 to 1.4, which led to a decreased nitrogen removal efficiency (NRE) of <65% and a high effluent NO3- accumulation (445.8-986.5 mg N·L-1). By bypassing approximately 60% of the influent to the two-stage A/O process and adding external carbon source (glucose), the mean NRE increased to 86.3 ± 7.4%. Spearman's analysis revealed that refractory compounds in the bypassed leachate were closely related to the variations in bacterial community composition and nitrogen removal function in the two-stage A/O, leading to a weakened correlation of microbial network. KEGG functional pathway predictions based on Tax4Fun also confirmed that the bypassed leachate induced xenobiotic compounds to the two-stage A/O process, the relative abundance of nitrogen metabolism was reduced by 32%, and more external carbon source was required to ensure the satisfactory nitrogen removal of >80%. The findings provide a good guide for regulation of incineration leachate treatment processes after the waste separation.

Response of nutrients removal efficiency, enzyme activities and microbial community to current and voltage in a bio-electrical anammox system

The effects of different current intensities and voltage levels on nutrient removal performance and microbial community evolution in a Bio-Electrical Anammox (BEA) membrane bioreactor (MBR) were evaluated. The nitrogen removal efficiency increased with the current intensity within the range of 64-83 mA, but this improvement was limited at the current further increased. The phosphorus removal in the BEA MBR was attributed to the release of Fe2+, which was closely associated with the applied current to the electrodes. Heme c concentration, enzyme activities, and specific anammox activity exhibited a decreasing trend, while the functional denitrification genes showed a positive correlation with rising voltage. The nitrogen removal efficiency of the BEA system initially increased and then decreased with the voltage rose from 1.5V to 3.5V, peaking at 2.0V of 94.02% ± 1.19%. Transmission electron microscopy and flow cytometry results indicated that accelerated cell apoptosis/lysis led to an irreversible collapse of the biological nitrogen removal system at 3.5V. Candidatus Brocadia was the predominant anammox bacteria in the BEA system. In contrast, closely related Candidatus Kuenenia and Chloroflexi bacteria were gradually eliminated in electrolytic environment. The abundances of Proteobacteria-affiliated denitrifiers were increased with the voltage rising since the organic matter released by the cell apoptosis/lysis was accelerated at a high voltage level.

Differences in greenhouse gas emissions and microbial communities between underground and conventionally constructed wastewater treatment plants

Large quantities of greenhouse gases (GHGs) are emitted into the atmosphere during wastewater treatment. In this study, GHG and microbial samples were collected from four wastewater treatment plants (WWTPs), and their differences and relationships were assessed. The study showed that, compared with conventionally constructed WWTPs, well-established gas collection systems in underground WWTPs facilitate comprehensive collection and accurate accounting of GHGs. In aboveground WWTPs, capped anoxic ponds promote methane production releasing it at 2-8 times the rate of uncapped emissions, in contrast to nitrous oxide emissions. Moreover, a stable subsurface environment allows for smaller fluctuations in daily GHG emissions and higher microbial diversity and abundance. This study highlights differences in GHG emission fluxes and microbial communities in differently constructed WWTPs, which are useful for control and accurate accounting of GHG emissions.

Hydrogeochemical changes during artificial groundwater well recharge

Artificial groundwater recharge is a relatively economic and efficient method for solving shortages and uneven spatial-temporal distribution of water resources. Changes in groundwater quality during the recharge process are a key issue that must be addressed. Identifying the hydrogeochemical reactions that occur during recharge can be vital in predicting trends in groundwater quality. However, there are few studies on the evolution of groundwater quality during artificial recharge that comprehensively consider environmental, chemical, organic matter, and microbiological indicators. Based on an artificial groundwater recharge experiment in Xiong'an New Area, this study investigated the hydrogeochemical changes during groundwater recharge through a well. The results indicate that (1) as large amounts of recharge water (RW) were injected, the groundwater level initially rose rapidly, then fluctuated slowly, and finally rose again. (2) Water quality indicators, dissolved organic matter (DOM), and microbial communities were influenced by the mixture of RW and the background groundwater before recharge (BGBR), as well as by water-rock interactions, such as mineral dissolution-precipitation and redox reactions. (3) During well recharge, aerobic respiration, nitrification, denitrification, high-valence manganese (Mn) and iron (Fe) minerals reduction dissolution, and Mn2+ and Fe2+ oxidation-precipitation occurred sequentially. (4) DOM analysis showed that protein-like substances in the BGBR were the main carbon sources for aerobic respiration and denitrification, while humic-like substances carried by the RW significantly enhanced Mn and Fe minerals reduction dissolution. Therefore, RW quality significantly affects groundwater quality after artificial groundwater well recharge. Controlling indicators, such as dissolved oxygen (DO) and DOM, in the RW can effectively reduce harm to groundwater quality after recharge. This study is of theoretical and practical significance for in-depth analysis of the evolution of groundwater quality during artificial well recharge, prediction of trends in groundwater quality during and after recharge and ensuring groundwater quality safety.

Ecological mechanisms of biofilm development in the hybrid sludge-biofilm process: Implications for process start-up and optimization

The hybrid sludge-biofilm processes have been widely applied for the construction or upgradation of biological wastewater treatment process. Ecological mechanisms of biofilm development remain unclear in the hybrid ecosystem, because of the intricate interactive effects between sludge and biofilms. Herein, the establishment principles of biofilms with distinct coexisting sludge amounts were uncovered by varying sludge retention times (SRTs) from 5 to 40 days in the hybrid process. With the increasing of SRTs, biofilm biomass decreased with the increase of suspended sludge, resulting in lower biofilm proportion. As estimated by the Gompertz growth model, the increased sludge amounts (i.e., higher SRTs of 20 and 40 days) prolonged the initial colonization stage and decreased the specific development rate of biofilms when compared to lower sludge amounts with the shorter SRTs (i.e., 5 and 10 days). Null model analysis demonstrated that deterministic homogenous selection could facilitate the colonization and accumulation of biofilms with less coexisting sludge (SRT of 10 days). However, stochastic ecological drift and homogenizing dispersal dominated the colonization and accumulation stages of biofilms with more coexisting sludge (SRT of 20 days), respectively. The ecological networks reflected that positively-related taxa presented taxonomic relatedness, whereas high inconsistency of taxonomic relatedness was observed among aggregate forms or development stages as affected by varied SRTs. The high incidence of intra-taxa co-occurrence patterns suggested that taxa with similar ecological niches could be specifically selected in biofilms when being exposed with less coexisting sludge. This study uncovered ecological mechanisms of biofilm development driven by varying the SRTs of suspended sludge, which would help to propose appropriate strategies for the efficient start-up and optimization of the hybrid sludge-biofilm system.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.

The presence of copper ions alters tetracycline removal pathway in aerobic granular sludge: Performance and mechanism

This study investigated the removal characteristics of tetracycline (TC) in the presence of copper ions (Cu2+) in aerobic granular sludge by analyzing the TC removal pathway, composition and functional group changes of extracellular polymeric substances (EPS), and microbial community structure. The TC removal pathway changed from cell biosorption to EPS biosorption, and the microbial degradation rate of TC was reduced by 21.37% in the presence of Cu2+. Cu2+ and TC induced enrichment of denitrifying bacteria and EPS-producing bacteria by regulating the expression of signaling molecules and amino acid synthesis genes to increase the content of EPS and -NH2 groups in EPS. Although Cu2+ reduced the content of acidic hydroxyl functional groups (AHFG) in EPS, an increase in TC concentration stimulated the secretion of more AHFG and -NH2 groups in EPS. The long-term presence of TC presence of the relative abundances of Thauera, Flavobacterium and Rhodobacter and improved the removal efficiency.

The existence of ferric hydroxide links the carbon and nitrogen cycles by promoting nitrite-coupled methane anaerobic oxidation

Microorganism-mediated anaerobic oxidation of methane can efficiently mitigate methane atmospheric emissions and is a key process linking the biogeochemical cycles of carbon, nitrogen, and iron. The results showed that methane oxidation and nitrite removal rates in the CF were 1.12 and 1.28 times higher than those in CK, respectively, suggesting that ferric hydroxide can enhance nitrite-driven AOM. The biochemical process was mediated by the enrichment of methanogens, methanotrophs, and denitrifiers. Methanobacterium and Methanosarcina were positively correlated with Fe3+ and Fe2+, whereas Methylocystis and Methylocaldum were positively correlated with methane, and denitrifiers were positively correlated with nitrite. Metagenomic analysis revealed that the genes related to methane oxidation, nitrogen reduction, and heme c-type cytochrome were upregulated in CF, indicating that a synergistic action of bacteria and methanogens drove AOM via diverse metabolic pathways, within which ferric hydroxide played a crucial role. This study provides novel insights into the synergistic mechanism of ferric iron and nitrite-driven AOM.

Optimizing nitrogenous organic wastewater treatment through integration of organic capture, anaerobic digestion, and anammox technologies: sustainability and challenges

With China's recent commitment to reducing carbon emissions and achieving carbon neutrality, anaerobic digestion and anaerobic ammonium oxidation (anammox) have emerged as promising technologies for treating nitrogenous organic wastewater. Anaerobic digestion can convert organic matter into volatile fatty acids (VFAs), methane, and other chemicals, while anammox can efficiently remove nitrogen with minimal energy consumption. This study evaluates the principles and characteristics of enhanced chemical flocculation and bioflocculation, as well as membrane separation, for capturing organic matter. Additionally, the paper evaluates the production of acids and methane from anaerobic digestion, exploring the influence of various factors and the need for control strategies. The features, challenges, and concerns of partial nitrification-anammox (PN/A) and partial denitrification-anammox (PD/A) are also outlined. Finally, an integrated system that combined organic capture, anaerobic digestion, and anammox is proposed as a sustainable and effective solution for treating nitrogenous organic wastewater and recovering energy and resources.

Intensifying single-stage denitrogen by a dissolved oxygen-differentiated airlift internal circulation reactor under organic matter stress: Nitrogen removal pathways and microbial interactions

Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH₄⁺-N. During the operation, the COD/NH₄⁺-N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1-2 and AR = 1.4-1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.

Effect of COD/ NO3−-N ratio on nitrite accumulation and microbial behavior in glucose-driven partial denitrification system

COD/NO₃ ^--N ratio was considered to be one of the key factors achieving effective nitrite accumulation during partial denitrification. In two parallel reactors incubated with glucose as carbon source at COD/NO₃ ^--N of 3 and 5, respectively, the microbial community structure shift and the nitrite accumulation performance during long-term operation were investigated. The maximum nitrite accumulation ratios at COD/NO₃ ^--N of 3 and 5 were 17.9% and 47.04%, respectively. Thauera was the dominant genus in both reactors on day 220 with the relative abundance of 18.67% and 64.01%, respectively. Batch experiments with different electron acceptors suggested that the distinction in nitrite accumulation at COD/NO₃ ^--N of 3 and 5 might be caused by the differences in the abundance of Thauera.

Nitrite accumulation, denitrification kinetic and microbial evolution in the partial denitrification process: The combined effects of carbon source and nitrate concentration

The combined effects of carbon source (HAc, HPr, Glu, Glu + HAc) and nitrate concentration (40, 80 mg/L labeling as R₄₀, R₈₀) on partial denitrification (PD) were discussed at C/N ratio of 2.5 (COD = 100, 200 mg/L). The optimal NO₂^--N and NTR reached to 67.03 mg/L, 99.14% in HAc-R₈₀ system, and denitrification kinetics revealed the same conclusion, corresponding to higher COD utilization rate (CUR: 58.46 mgCOD/(gVSS·h)), nitrate reduction rate (N_aRR: 29.94 mgN/(gVSS·h)) and nitrite accumulation rate (N_iAR: 29.68 mgN/(gVSS·h)). The preference order was HAc > HPr > Glu + HAc > Glu in both R₄₀ and R₈₀ systems due to different metabolic pathways, however, the NO₂^--N accumulation and kinetic parameters of R₈₀ group were dramatically higher than those in R₄₀ for the same carbon source. The R₈₀ group facilitated more concentrated biodiversity (607-808 OTUs) with Terrimonas and norank_f_Saprospiraceae responsible for high NO₂^--N accumulation in HAc and HPr served systems, while norank_f_norank_o_Saccharimonadales and OLB13 dominated the Glu containing systems.

Micro and nano bubbles promoted biofilm formation with strengthen of COD and TN removal synchronously in a blackened and odorous water

Blackening and odorization of rivers (BOR) distributed widely in urban cities with high density of human beings. Amounts of pollution control methods have been developed for treatment of these contaminated rivers. Among them, artificial aeration is an effective method for BOR treatment. As a novel developed aeration approach, Micro and nano bubbles (MNBs) takes advances of high specific surface area, high oxygen transfer, long retain time and interface effect. Thus, MNBs aeration was used in an anoxic-oxic (AO) process with traditional activated sludge methods to treat water of BOR in this study. A special designed reactor was made to allow both MNBs and macro bubbles aeration of which mode could be altered easily. The results revealed that MNBs improved removal of COD, NH₄⁺-N and TN distinctly in water of BOR. MNBs provided high dissolved oxygen and promoted the transformation from floc sludge to biofilm. Significant difference between the microbial community of MNBs and macro bubbles sludges was revealed by 16S rRNA amplicon sequencing. Function predictions of MNBs and macro bubbles sludges indicated MNBs enhanced nitrification and aerobic ammonia oxidation without negative impact on denitrification. Moreover, biofilm formed bacteria were enriched by MNBs aeration. This study demonstrated MNBs would be a great potential for the combination of activated sludge and biofilm to treat BOR.

Recovery of anammox process performance after substrate inhibition: Reactor performance, sludge morphology, and microbial community

Most of the current studies have focused on the inhibition of anaerobic ammonium oxidation (anammox) by substrates, however, little attention has been paid to the recovery process of the reactor after inhibition. Therefore, we investigated the changes in reactor performance, granular sludge structure, and microbial community during the recovery phase after being inhibited by a high nitrogen load for 15 d. The nitrogen removal rate of the reactorwasrestored to pre-inhibition levels after 75 d of recovery, and the stoichiometric ratio converged to the theoretical value. The surface of the granular sludge developed into a broccoli-like structure, and the Ca and P contents of the granules increased from 6.88% and 4.39% to 24.42% and 13.88%, respectively. The abundance of the anammox bacterium Candidatus brocadia increased from 5.86% to 12.10%, and network analysis indicated that SMA102 and SBR1031 were positively correlated with the occurrence of Candidatus brocadia.

Metagenomics illuminated the mechanism of enhanced nitrogen removal and vivianite recovery induced by zero-valent iron in partial-denitrification/anammox process

In this study, a novel strategy of zero-valent iron (ZVI) combined with acetic acid was proposed to optimize partial-denitrification/anammox (PD/A) process, and enhanced nitrogen removal mechanism was elucidated through metagenomics. Results showed that the optimal nitrogen and phosphorus removal were as high as 99.50% and 98.37%, respectively, with vivianite being precipitated as the main byproduct. The occurrence of Feammox was a crucial link for enhanced ammonia removal and vivianite recovery. Metagenomic analysis further certified that long-term acclimation of optimization strategy triggered DNRA-based nitrate reducing genes (narY/Z and nrfA) assigned to Candidatus Brocadia, which allow direct uptake of nitrate by the anammox. Additionally, ZVI might act as a new electron donor to decrease organics dependence of PD by reducing the abundance of genes for electron production involved in carbon metabolism. However, FA addition enhanced the relative abundances of genes involved in anammox including nitrogen reduction and oxidation, thereby accelerating nitrogen removal.

Efficient nitrogen removal from stormwater runoff by bioretention system: The construction of plant carbon source-based heterotrophic and sulfur autotrophic denitrification process

The plant carbon source and sulfur were selected as the denitrification electron donors and filled in the internal water storage zone (IWSZ) of bioretention system to establish excellent mixotrophic denitrification system, which was beneficial to waste recycling and showed very high nitrate nitrogen removal efficiency (approximately 94%). The ammonia nitrogen, total nitrogen, and chemical oxygen demand removal efficiencies could reach 79.41%, 85.89%, and 74.07%, respectively. Mechanism study revealed the synergistic degradation effect was existed between acetic acid released from plant carbon source and the generated sulfate, which improved the S/CH₃COOH mediated nitrate nitrogen removal reactions. Autotrophic denitrification occurred mainly in the upper layer of IWSZ, and the dominant bacteria were Thiobacillus. While in the lower layer, the dominant bacteria were mainly related to organic matter utilization and heterotrophic denitrification. The abundance of narG, nirK, nirS, and nosZ functional genes in the upper layer was significantly higher than the lower layers.

Spatial Variation of Cladophora Epiphytes in the Nan River, Thailand

Cladophora is an algal genus known to be ecologically important. It provides habitats for microorganisms known to provide ecological services such as biosynthesis of cobalamin (vitamin B12) and nutrient cycling. Most knowledge of microbiomes was obtained from studies of lacustrine Cladophora species. However, whether lotic freshwater Cladophora microbiomes are as complex as the lentic ones or provide similar ecological services is not known. To illuminate these issues, we used amplicons of 16S rDNA, 18S rDNA, and ITS to investigate the taxonomy and diversity of the microorganisms associated with replicate Cladophora samples from three sites along the Nan River, Thailand. Results showed that the diversity of prokaryotic and eukaryotic members of Cladophora microbiomes collected from different sampling sites was statistically different. Fifty percent of the identifiable taxa were shared across sampling sites: these included organisms belonging to different trophic levels, decomposers, and heterotrophic bacteria. These heterogeneous assemblages of bacteria, by functional inference, have the potential to perform various ecological functions, i.e., cellulose degradation, cobalamin biosynthesis, fermentative hydrogen production, ammonium oxidation, amino acid fermentation, dissimilatory reduction of nitrate to ammonium, nitrite reduction, nitrate reduction, sulfur reduction, polyphosphate accumulation, denitrifying phosphorus-accumulation, and degradation of aromatic compounds. Results suggested that river populations of Cladophora provide ecologically important habitat for microorganisms that are key to nutrient cycling in lotic ecosystems.