Efficient nitrogen and phosphorus removal performance and microbial community in a pilot-scale anaerobic/anoxic/oxic (AOA) system with long sludge retention time: Significant roles of endogenous carbon source.

Stringent wastewater discharge standards require wastewater treatment plants (WWTPs) to focus on enhancing nitrogen (N) and phosphorus (P) removal efficiency. Increasing sludge concentration by regulation of sludge retention time (SRT) would enhance wastewater treatment loads. However, phosphorus-accumulating organisms (PAOs) would be outcompeted by glycogen-accumulating organisms (GAOs) under long SRT, leading to a collapse of P removal. In this work, pilot-scale anaerobic-oxic-anoxic (AOA) and anaerobic-anoxic-oxic (AAO) systems with long SRT (30 d) were parallelly established for actual urban wastewater treatment. The results indicated that sludge reflux ratio, temperature, and C/N ratio significantly impact N and P removal performance of AOA and AAO systems with long SRT, and removal efficiency of AOA system significantly exceeded that of AAO system. AOA system with long SRT achieved the optimal performance at sludge reflux ratio of 200%, temperature of 25 °C, and C/N ratio of 8, with COD, NH4+-N, TN, and PO43--P removal ratio of 92.80±2.24%, 97.38±0.89%, 88.97±2.47%, and 94.33±3.27%, respectively. In addition, compared to AAO system, AOA system could save 23.08% of the aeration volume. This work highlighted that AOA system with long SRT included multiple coupled nitrogen and phosphorus removal pathways, such as autotrophic/heterotrophic nitrification, anoxic/oxic denitrification, endogenous denitrification, and denitrifying phosphorus removal. Among these, the synergistic effect of endogenous denitrification and denitrifying phosphorus removal driven by internal carbon sources contributed to satisfactory nitrogen and phosphorus removal efficiency in AOA system with long SRT.

The collaboration and competition between indigenous microorganisms and exogenous anaerobic digester sludge in anaerobic treatment of pickled mustard wastewater at different salinities.

The highly concentrated pickled mustard wastewater presents significant potential for energy recovery, but the stress effect of high osmotic pressure on cell integrity and activity seriously impedes the methane production by anaerobic microorganisms. The survival ability of indigenous microorganisms (IM) in pickled mustard wastewater supports the establishment of anaerobic treatment. Moreover, inoculation of anaerobic digester sludge is a common start-up strategy. However, the effects of exogenous anaerobic sludge on IM are unclear, especially in hypersaline environment. This research aimed to investigate the influence of exogenous anaerobic sludge on the construction, performance, and microbiota at 3% and 5% salinity. And the research focused on the collaboration and competition between exogenous anaerobic sludge and IM. The neutral community model (which explains the formation and evolution of biological communities) indicated that the interaction between exogenous digester sludge microorganisms and IM dominated community assembly. At 3%, the digester sludge collaborated with IM to increase daily COD reduction and biogas production compared with IM group. However, at 5%, the competitive relationship reduced daily COD reduction and biogas production compared with IM group. This study provides a new perspective for the selection of inoculation strategies for exogenous anaerobic digester sludge under different salinity, in order to realize energy conversion from salinity organic wastewater.

Co-doped Fe3O4/α-FeOOH for highly efficient peroxymonosulfate activation to degrade trimethoprim: Occurrence of hybrid non-radical and radical pathways.

Trimethoprim (TMP), as a widely used chemotherapeutic antibiotic agent, has caused potential risks to the aquatic environment. In this study, magnetic Co-doped Fe3O4/α-FeOOH was fabricated by a facile one-step ageing method and used for activation of peroxymonosulfate (PMS) in TMP degradation. It was found that low catalyst (0.5 g/L) and PMS addition (0.2 mM) led to the high degradation efficiency of TMP (97.2%, kobs = 0.11211 min-1) over a wide range of pH. The oxidation of active radical (SO4·-) and non-radical singlet oxygen (1O2) co-acted on TMP degradation. Besides, PMS was activated through the cycles between Co(II)/Co(III) and Fe(II)/Fe(III). Fifteen degradation intermediates of TMP were identified by LC-MS, and three possible degradation pathways including hydroxylation, demethylation, and cleavage were proposed. The recovered catalysts exhibited high stability and reusability, maintaining 80% TMP removal efficiency with inappreciable metal leaching (0.012 mg/L of Co, 0.113 mg/L of Fe) after six cycles. Besides, the Co-Fe3O4/α-FeOOH/PMS system was highly tolerant to inorganic anions and actual water bodies (river water, lake water, tap water, and sewage plant effluent). Overall, this work provided a promising way to the potential application of Fe-based binary metal oxide for PMS activation.

Denitrification and N2O Emission in Estuarine Sediments in Response to Ocean Acidification: From Process to Mechanism.

Global estuarine ecosystems are experiencing severe nitrogen pollution and ocean acidification (OA) simultaneously. Sedimentary denitrification is an important way of reactive nitrogen removal but at the same time leads to the emission of large amounts of nitrous oxide (N2O), a potent greenhouse gas. It is known that OA in estuarine regions could impact denitrification and N2O production; however, the underlying mechanism is still underexplored. Here, sediment incubation and pure culture experiments were conducted to explore the OA impacts on microbial denitrification and the associated N2O emissions in estuarine sediments. Under neutral (in situ) conditions, fungal N2O emission dominated in the sediment, while the bacterial and fungal sources had a similar role under acidification. This indicated that acidification decreased the sedimentary fungal denitrification and likely inhibited the activity of fungal denitrifiers. To explore molecular mechanisms, a denitrifying fungal strain of Penicillium janthinellum was isolated from the sediments. By using deuterium-labeled single-cell Raman spectroscopy and isobaric tags for relative and absolute quantitation proteomics, we found that acidification inhibited electron transfers in P. janthinellum and downregulated expressions of the proteins related to energy production and conservation. Two collaborative pathways of energy generation in the P. janthinellum were further revealed, that is, aerobic oxidative phosphorylation and TCA cycle and anoxic pyruvate fermentation. This indicated a distinct energy supply strategy from bacterial denitrification. Our study provides insights into fungi-mediated nitrogen cycle in acidifying aquatic ecosystems.

Stimulation of N2 O emission via bacterial denitrification driven by acidification in estuarine sediments.

Ocean acidification in nitrogen-enriched estuaries has raised global concerns. For decades, biotic and abiotic denitrification in estuarine sediments has been regarded as the major ways to remove reactive nitrogen, but they occur at the expense of releasing greenhouse gas nitrous oxide (N2 O). However, how these pathways respond to acidification remains poorly understood. Here we performed a N2 O isotopocules analysis coupled with respiration inhibition and molecular approaches to investigate the impacts of acidification on bacterial, fungal, and chemo-denitrification, as well as N2 O emission, in estuarine sediments through a series of anoxic incubations. Results showed that acidification stimulated N2 O release from sediments, which was mainly mediated by the activity of bacterial denitrifiers, whereas in neutral environments, N2 O production was dominated by fungi. We also found that the contribution of chemo-denitrification to N2 O production cannot be ignored, but was not significantly affected by acidification. The mechanistic investigation further demonstrated that acidification changed the keystone taxa of sedimentary denitrifiers from N2 O-reducing to N2 O-producing ones and reduced microbial electron-transfer efficiency during denitrification. These findings provide novel insights into how acidification stimulates N2 O emission and modulates its pathways in estuarine sediments, and how it may contribute to the acceleration of global climate change in the Anthropocene.

Effect of different hydrolytic enzymes pretreatment for improving the hydrolysis and biodegradability of waste activated sludge.

In this study, the effects of lysozyme, protease and α-amylase pretreatments for improving the hydrolysis and biodegradability of waste activated sludge (WAS) were investigated. The results showed that lysozyme was more effective in increasing the soluble chemical oxygen demand (SCOD) concentration in the liquid phase of sludge and improving the release of protein and carbohydrate from sludge flocculation to enhance sludge hydrolysis. After 8 h hydrolysis, the net SCOD increase in a reactor with lysozyme was 2.23 times and 2.15 times that of the reactors with protease and α-amylase, respectively. Meanwhile, lysozyme and protease could improve the lysis of microorganism cells and the dissolution of extracellular polymeric substances (EPS) to a certain extent, and lysozyme was more effective. Furthermore, the compositional characteristics of dissolved organic matter (DOM) and EPS were analyzed by EEM fluorescence spectroscopy and fluorescence regional integration (FRI) analysis. Tryptophan-like protein was the main component of sludge, which accounted for 31% and 38% of DOM and EPS, respectively. Lysozyme could decrease the percentage of non-biodegradable materials in sludge, such as humic acid-like substances and fulvic acid-like substances, so it could improve the biodegradability of sludge. This study can provide valuable information for future studies about hydrolytic enzyme pretreatments for WAS disposal.

α-(Fe, Cu)OOH/RGO nanocomposites for heterogeneous photo-Fenton-like degradation of ciprofloxacin under visible light irradiation.

Ciprofloxacin (CIP) is a third-generation fluoroquinolones (FQs) antibiotic, and the occurrence of CIP in the water environment has raised growing concerns owning to its environmental toxicity. In this paper, a novel α-(Fe, Cu)OOH/RGO nanocomposite was synthesized via a one-step reflux method for CIP degradation through a photo-Fenton-like process. When the RGO content was 1 wt%, CIP degradation ratio by the α-(Fe, Cu)OOH/RGO nanocomposite reached 100% under visible light irradiation within 120 min, and total organic carbon (TOC) removal ratio reached 60% within 180 min. The result of molecular fluorescence spectra highlighted that the loading of RGO on the α-(Fe, Cu)OOH significantly increased the content of hydroxyl radicals (·OH) in the heterogeneous photo-Fenton-like system and simultaneously inhibited the recombination of photogenerated electron and hole, which played critical roles in the enhancement of CIP degradation. In addition, 11 main intermediates were identified as the degradation products of CIP in the α-(Fe, Cu)OOH/RGO/H2O2/visible light reaction systems using liquid chromatograph-mass spectrometer (LC-MS) analyses. The results demonstrated that three degradation pathways for CIP removal by α-(Fe, Cu)OOH/RGO nanocomposite occurred, including (i) oxidation on the piperazine ring and dealkylation, (ii) defluorination and decarboxylation, and (iii) hydroxylation on the quinolone ring. This work would provide a novel insight of CIP degradation pathways in photo-Fenton-like processes.

Biologically induced phosphate precipitation in heterotrophic nitrification processes of different microbial aggregates: Influences of nitrogen removal metabolisms and extracellular polymeric substances.

Phosphorus (P) removal occurred in heterotrophic nitrification process, but its mechanism has not been fully explored. In this study, the P removal performances, pathways, and mechanisms in heterotrophic nitrification processes of different microbial aggregates (activated sludge and biofilm) were investigated. The results showed that the biofilm reactor had more efficient total nitrogen removal (98.65%) and phosphate removal (94.17%). Heterotrophic nitrification and denitrification processes generated alkalinity for biologically induced phosphate precipitation (BIPP), which contributed to 64.12%-78.81% of the overall P removal. The solid phase P content reached 48.03 mg/gSS with hydroxyapatite and calcium phosphate formation. The study clarified that biofilm was beneficial to BIPP because of the nitrogen removal metabolism and extracellular polymeric substance (EPS). Heterotrophic nitrogen removal metabolism was the driving force of BIPP, while EPS with abundant carboxyl and amide groups promoted the precipitation. The study would provide new insights into simultaneous nutrients removal and P recovery from wastewater.

Co-occurrence of autotrophic and heterotrophic denitrification in electrolysis assisted constructed wetland packing with coconut fiber as solid carbon source.

Aiming at the problems of lack of carbon sources for nitrogen removal and low phosphorus removal efficiency of constructed wetlands (CWs) in treating wastewater treatment plant (WWTP) effluent, an electrolysis assisted constructed wetland (E-CW) with coconut fiber as substrate and solid carbon sources was constructed. The synthetic secondary effluent was used as the influent of the E-CW with a wastewater treatment capacity of 140 L d-1. The total nitrogen (TN) and the total phosphorus (TP) removal efficiency of the E-CW with coconut fiber treating WWTP effluent were 69.4% and 93.3%, respectively, which were 54.3% and 88.2% higher than those of CW with coconut fiber and no electrolysis. The removal efficiency of TN was 39.9% higher than that of E-CW with gravel. The current intensity had significant effect on nitrogen removal efficiency and the release of carbon sources from coconut fiber. When current intensity increased from 0.25 A to 1.00 A, the TN removal efficiency and nitrate removal rate increased by 21.1% and 0.21 mg L-1 h-1, respectively, and the volatile fatty acids (VFAs) released from coconut fiber increased by 57.7 mg L-1. The 16S rRNA high-throughput sequencing results indicated that the main functional nitrogen-removing microbes were Hydrogenophaga, Thauera, Rhodanobacteraceae_norank, Xanthobacteraceae_norank, etc. Multiple paths including autotrophic denitrification with hydrogen and Fe2+ as electron donors and heterotrophic denitrification were achieved in the system. Meanwhile, the main functional lignocellulose degradation microbes were enriched in the system, including Cytophaga_xylanolytica_group, and Caldilineaceae. Because electrolysis created a favorable environment for them to release carbon sources from coconut fiber. This study provided a new perspective for advanced nutrients removal of WWTP effluent in CWs.

Enhanced degradation capability of white-rot fungi after short-term pre-exposure to silver ion: Performance and selectively antimicrobial mechanisms.

Azo dyes in wastewater have great threats to environment and human health. White-rot fungi (WRF) have broad-spectrum potential for such refractory organics bioremediation; however, their applications are largely restrained by the poor viability owning to microbial invasion under non-sterile conditions. In this study, short-term pre-exposure to silver ion (Ag+) was demonstrated to be a practical, economic, and green method to enhance the perdurability of azo dyes decoloration by WRF Phanerochaete chrysosporium under non-sterile conditions. In control (without Ag+ pre-exposure), decoloration deactivated since cycle 7 (<10%), whereas in Ag+ pre-exposure groups, the decoloration ratios remained 91.5%-94.7% after 7 cycles. Variations in decoloration-related extracellular lignin enzyme activities were consistent with the decoloration effectiveness. The enhanced decoloration capability in Ag+ pre-exposure groups under non-sterile conditions could be ascribed to the selectively antimicrobial action by Ag+. The released Ag+ from the self-assembled silver nanoparticles (AgNPs) could selectively "stimulate" the proliferation and viability of P. chrysosporium, and simultaneously inhibit the growths of invasive microorganisms. The pyrosequencing results indicated that genus Sphingomonas (24.1%-31.3%) was the main invasive bacteria in Ag+ pre-exposure groups after long-term operation owing to the AgNPs passivation. As control, the invasive fungi (Asterotremella humicola) and bacteria (Burkholderia spp.) occurred in control after short-term operation, and genus Burkholderia (74.9%) dominated after long-term operation, leading to decoloration deactivation. Overall, these findings offer a new insight into the bio-nano interactions between WRF and invasive microorganisms in response to Ag+ or biogenic AgNPs, and could extend WRF application perspective under non-sterile conditions in future.

High-temperature biofilm system based on heterotrophic nitrification and aerobic denitrification treating high-strength ammonia wastewater: Nitrogen removal performances and temperature-regulated metabolic pathways.

Conventional autotrophic nitrification process is difficult to treat high-temperature wastewater with high-strength ammonia. In this study, a high-temperature (50 °C) biofilm system based on heterotrophic nitrification and aerobic denitrification (HNAD) was established. The results showed that the HNAD process was high temperature resistant, and the nitrogen removal performance, pathway and microbial mechanism varied remarkably at different temperatures. The high-temperature system showed excellent nitrogen and COD removal capacities at 50 °C. Ammonia oxidation was mainly undertaken by heterotrophic nitrification, while anoxic and aerobic pathways worked in concert for denitrification. High-throughput sequencing indicated that heterotrophic nitrifying bacteria (8.58%) and denitrifying bacteria (52.88%) were dominant at 50 °C. Metagenomic analysis further suggested that the carbon metabolism was up-regulated in response to the increasing temperature, so more energy was generated, thereby promoting the HNAD-related nitrogen removal pathways. The study revealed the microbial mechanism of HNAD at high temperature and provided new insights into high-temperature biological nitrogen removal.

Mesophilic condition favors simultaneous partial nitrification and denitrification (SPND) and anammox for carbon and nitrogen removal from anaerobic digestate food waste effluent.

Three simultaneous partial nitrification and denitrification (SPND) bioreactors were established on ambient (30 °C), mesophilic (40 °C) and thermophilic condition (50 °C) at high dissolved oxygen levels (2-7 mg L-1) to remove nitrogen and carbon from anaerobic digestate food waste effluent (ADFE). The bioreactor performed best under mesophilic condition, with TN and COD removal efficiency of 96.3 ± 0.1% and 91.7 ± 0.1%, respectively. Free ammonia (FA) and free nitrous acid (FNA) alternately ensured selective inhibition of nitrite-oxidizing bacteria (NOB) in long-term operation of SPND systems. Candidatus Brocadia, known as anammox bacteria, was observed unexpectedly in the bioreactors. The analysis of microbial community and metabolic pathways revealed that mesophilic strategy stimulated SPND and anammox process. Mesophilic condition helped autotropic microbes resist the competitive pressure from heterotrophic bacteria, improving the balance between nitrifiers, anammox bacteria and other co-existing heterotrophs. Overall, this study offers new insights into the linkage among temperature, pollutant removals (carbon and nitrogen) and metabolic potential in the SPND bioreactors.

Estuarine plastisphere as an overlooked source of N2O production.

"Plastisphere", microbial communities colonizing plastic debris, has sparked global concern for marine ecosystems. Microbiome inhabiting this novel human-made niche has been increasingly characterized; however, whether the plastisphere holds crucial roles in biogeochemical cycling remains largely unknown. Here we evaluate the potential of plastisphere in biotic and abiotic denitrification and nitrous oxide (N2O) production in estuaries. Biofilm formation provides anoxic conditions favoring denitrifiers. Comparing with surrounding bulk water, plastisphere exhibits a higher denitrifying activity and N2O production, suggesting an overlooked N2O source. Regardless of plastisphere and bulk water, bacterial and fungal denitrifications are the main regulators for N2O production instead of chemodenitrification. However, the contributions of bacteria and fungi in the plastisphere are different from those in bulk water, indicating a distinct N2O production pattern in the plastisphere. These findings pinpoint plastisphere as a N2O source, and provide insights into roles of the new biotope in biogeochemical cycling in the Anthropocene.

Metagenomics reveals functional species and microbial mechanisms of an enriched thiosulfate-driven denitratation consortia.

In this study, thiosulfate-driven denitratation (TDD) system was successfully established under optimal S/N molar ratio of 1.00, with nitrite accumulation efficiency (NAE) of 82.24 ± 17.09%. This work highlighted that thiosulfate significantly preferred the reduction of nitrate than nitrite. However, after the depletion of thiosulfate, the in-situ formed intermediate product element sulfur (S0) served as the main electron donor, and significantly favored the reduction of nitrite than nitrate, which constrained nitrite accumulation and nitrate removal. In addition, metagenomic sequencing revealed that the functional denitratation species might be Thiobacillus_sp._65-29, but the occurrence of Nir-annotated species would decrease nitrite accumulation. Under S/N ratio of 1.00, the decreased abundant Nir-annotated species (e.g., Thiobacillus_sp.), as well as the down-regulated quorum sensing interactions between Nar- and Nir-annotated species were key microbial metabolisms of high NAE in the TDD system. Overall, this work provides new sight into the metagenome-base functional species and metabolic potential of thiosulfate-driven denitratation.

Hydraulic flow direction alters nutrients removal performance and microbial mechanisms in electrolysis-assisted constructed wetlands.

In this study, an electrolysis-assisted down-flow constructed wetland (E-DFCW) was successfully established, and achieved simultaneously efficient removal of PO43--P (93.6% ± 3.2%), NO3--N (97.1% ± 2.0%) and TN (80.6% ± 5.4%). When compared with electrolysis-assisted up-flow constructed wetland (E-UFCW), E-DFCW allowed significantly lower concentrations of PO43--P, NO3--N, total Fe and SO42--S in effluents. In addition, microbial community and functional genes prediction results indicated that hydraulic flow direction significantly altered microbial nitrogen, sulfur and carbon metabolisms in electrolysis-assisted constructed wetlands (E-CWs). Specifically, multi-path denitrification facilitated NO3--N reduction in cathodic chamber of E-DFCW, whereas autohydrogenotrophic denitrification might dominate NO3--N reduction in cathodic chamber of E-UFCW. More abundant and diverse denitrifiers in cathodic chamber of E-DFCW contributed to enhanced denitrification performance. Overall, this work provides microbial insights into multi-path nitrogen metabolisms in electrolysis-assisted denitrification systems in response to hydraulic flow direction.

Facilitating harmful algae removal in fresh water via joint effects of multi-species algicidal bacteria.

Harmful algae blooms posing serious threats to the ecological environment occur frequently across the world. Multi-species algicidal bacteria were enriched by utilizing immobilized carriers in a pilot scale experiment, which significantly promoted the effect of algal control in the reactors. Under the optimal condition, the algicidal ratio and chlorophyll a degradation rate reached 87.69% and 47.00 µg/(L·d), respectively. The growth of Cyanophyta, diatom, Dinoflagellate and Cryptophyta was inhibited significantly by the joint action of algicidal bacteria and light shading of fillers, accounting for 53.74% and 36.47%, respectively. The results of 16S rRNA high-throughput sequencing suggested algicidal bacteria (10.17%) belonging to 13 genera were enriched. Among the algicidal process, Bacillus and Pseudomonas played crucial roles. Fluorescence spectroscopy and UV254 were adopted to assess the release of dissolved organic matter (DOM) and the precursors of disinfection by-products (DBPs). Two efficient algicidal strains (C1, C4) were isolated which showed high homology with Enterobacter asburiae JCM6051(T) and Pseudomonas simiae oli(T), respectively. This study provided new insights into the in-situ bioremediation of eutrophication in fresh water.

Bacterial communities are more sensitive to ocean acidification than fungal communities in estuarine sediments.

Ocean acidification (OA) in estuaries is becoming a global concern, and may affect microbial characteristics in estuarine sediments. Bacterial communities in response to acidification in this habitat have been well discussed; however, knowledge about how fungal communities respond to OA remains poorly understood. Here, we explored the effects of acidification on bacterial and fungal activities, structures and functions in estuarine sediments during a 50-day incubation experiment. Under acidified conditions, activities of three extracellular enzymes related to nutrient cycling were inhibited and basal respiration rates were decreased. Acidification significantly altered bacterial communities and their interactions, while weak alkalization had a minor impact on fungal communities. We distinguished pH-sensitive/tolerant bacteria and fungi in estuarine sediments, and found that only pH-sensitive/tolerant bacteria had strong correlations with sediment basal respiration activity. FUNGuild analysis indicated that animal pathogen abundances in sediment were greatly increased by acidification, while plant pathogens were unaffected. High-throughput quantitative PCR-based SmartChip analysis suggested that the nutrient cycling-related multifunctionality of sediments was reduced under acidified conditions. Most functional genes associated with nutrient cycling were identified in bacterial communities and their relative abundances were decreased by acidification. These new findings highlight that acidification in estuarine regions affects bacterial and fungal communities differently, increases potential pathogens and disrupts bacteria-mediated nutrient cycling.

Intensified nutrients removal in a modified sequencing batch reactor at low temperature: Metagenomic approach reveals the microbial community structure and mechanisms.

To achieve efficient biological nutrients removal at low temperature, a modified sequencing batch reactor (SBR) was developed at 10 °C by extending sludge retention time (SRT), shortening aerobic stage and compensating anoxic stage. The average removal rates of ammonium (NH4+-N), total nitrogen (TN) and total phosphorus (TP) were 98.82%, 94.12% and 96.04%, respectively. Variation of carbon source in a typical cycle demonstrated the maximum synthesis of poly-ß-hydroxybutyrate (PHB) (60 mg/L) occurred after feast period. Furthermore, the TP in sludge reached 50.4 mg/g mixed liquor suspended solids (MLSS) (78.4% was inorganic phosphorus and 21.6% was organic phosphorus) after 120 days of operation, indicating an excellent P-accumulating capacity was achieved in this system. Ammonia oxidizing bacteria (AOB) activity inhibition test verified both AOB and ammonia oxidizing archaea (AOA) were involved in ammonia-oxidizing process and the latter accounted for 17%-19%. Metagenomic-based taxonomy revealed the dominant genera were Candidatus Accumulibacter (12.18%), Dechloromonas (7.54%), Haliangium (6.69%) and Candidatus Contendobacter (3.40%). As described from the denitrifying genes perspective, with the exception of nitrite reduction (performed by denitrifiers), denitrifying phosphorus-accumulating organisms (DPAOs) played a leading role in denitrification pathway, showing that poly-ß-hydroxyalkanoates (PHA)-driven nutrients removal was the dominate process.

Electron storage and resupply modes during sulfur cycle enhanced nitrogen removal stability in electrochemically assisted constructed wetlands under low temperature.

In this work, an electrochemically assisted vertical flow constructed wetland (E-VFCW) achieved efficient PO43--P (92.9-96.6%), NO3--N (50.8-91.8%) and TN (38.8-73.1%) removal from synthetic sewage effluent within 1-12 h at 12 °C. Abiotic reduction, Fe(II)-, S- and H2-dependent denitrification, as well as coupling of fermentation, acetogenesis and heterotrophic denitrification might facilitate NO3--N removal in the E-VFCW. Particularly, electron resupply for NO3--N reduction by the in-situ deposited FeS, FeS2 and S0 in the E-VFCW would occur during electron supply-demand disequilibrium situations (e.g., lower HRT or temperature). Stoichiometric results suggested that 21.7-278.7 mmol e- d-1 from the in-situ deposited S contributed to NO3--N reduction under HRT of 1-6 h at 12 °C, which improved the resilience capabilities of the E-VFCW to temperature and nitrogen loads fluctuations. Overall, this work provides new insights into the modes of S cycle mediating NO3--N conversions in the E-VFCW under low temperature.

Efficient nitrogen removal in a modified sequencing batch biofilm reactor treating hypersaline mustard tuber wastewater: The potential multiple pathways and key microorganisms.

This study first compared the efficiencies and mechanisms of the nitrogen removal in an aerobic sequencing batch biofilm reactor (SBBR) treating mustard tuber wastewater from high salt (30 gNaCl L-1) to ultra-high salt (70 gNaCl L-1). High-efficiency maintaining of nitrification was observed. Despite of high BOD5/TN (5.5-9), distinct denitrification decline for lack of carbon in response to salt stress was observed. Considering the high concentrations of sulfate in mustard wastewater, and the existence of sulfur-reducing bacteria (SRB) and sulfur-driven denitrifiers (DNSOB) in the aerobic SBBR, sulfate reduction-sulfur autotrophic denitrification process is a feasible idea to solve this problem. By modified to intermittent aeration mode, sulfur cycle was developed in SBBR. The average removal efficiency of COD, TN reached 85.20% and 98.56%, respectively. By batch activity tests and microbial community analysis, ammonia oxidation activity by ammonia-oxidizing archaea (AOA) was observed, and high abundance of AOA (Arch-amoA/AOB amoA: 2.38 × 102) together with ammonia-oxidizing bacteria (AOB) of Nitrosomonas_halophila (1.23%) ensured the high efficient nitrification. After running mode change, specific sulfur-driven NO3--N reduction rate increased and the abundance of dominant SRB and DNSOB rose from 3.95% to 10.79% and 2.22% to 9.95%, respectively. The sulfate-reducing process during anaerobic phase provided electron donors for subsequent autotrophic denitrification, making outlet NO3--N concentrations reduced from 18.26 mg L-1 to 1.93 mg L-1. The sulfur activity batch test showed that 73.80%∼80.92% of sulfate were circulation utilized, and rest of them conversed to the gaseous H2S and S0. In addition to DNSOB, anoxic denitrifier of Halomonas (22.91%), aerobic denitrifier of Phaeodactylibacter (2.75%) and endogenous denitrifier of Defluviicoccus (3.18%) were also dominant heterotrophic bacteria (all halophilic or halotolerant) in the intermittent aeration SBBR. Batch activity tests and periodic laws have also verified the existence of corresponding denitrification pathways. This study shows that the enrichment of special halophilic functional bacteria with multiple nitrogen removal pathways is a good idea for the efficient treatment of high-concentrated hypersaline industrial wastewater.