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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Toxic effects of terpinolene on Microcystis aeruginosa: Physiological, metabolism, gene transcription, and growth effects.

Bioherbicide terpinolene is widely employed in the agricultural field because of its unique phytotoxic properties. However, little is known about the toxicity of bioherbicide on harmful algal blooms (HABs) and its mechanisms. Therefore, in this study, the inhibiting effect of bioherbicide terpinolene on the growth and physiological change of Microcystis aeruginosa was determined. Results showed that the cell density and photosynthetic activity of microalgae were significantly inhibited by terpinolene. Activities of nitrate reductase (NR) and glutamine synthetase (GS) were decreased separately by 25.38% and 42.75% after 4 d of exposure to 1.47 mM terpinolene, suggesting the inhibiting effect of terpinolene on algal nitrogen metabolism. However, the transcript abundance of genes related to membrane protein cytochrome c oxidase subunit II (COX II) and ATP-binding cassette transporters (ABC transporter) were enhanced separately by 3.15 and 1.69-fold compared with control, suggesting the resistance response of cells to terpinolene stress. Additionally, terpinolene not only increased the content of endogenous phytohormones including indole-3-acetic acid (IAA), zeatin, and brassinolide, but also inhibited the expression of genes related to calcium-binding protein (CaBPs), one kind of calcium (Ca2+) sensors, suggesting its regulation on algal signal molecules. These findings helped to understand the ecotoxicity of terpinolene and guide the rational use of bioherbicide in agriculture.

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.

Metagenomic analysis reveals enhanced nutrients removal from low C/N municipal wastewater in a pilot-scale modified AAO system coupling electrolysis.

The conventional biological nutrients removal process is challenged by insufficient organic carbon in influent. To cross such an organic-dependent barrier, a pilot-scale electrolysis-integrated anaerobic/anoxic/oxic (AAO) process was developed for enhanced removal of nitrogen (N) and phosphorus (P) from low carbon/nitrogen (C/N) municipal wastewater. Average removal efficiencies of total nitrogen (TN) and total phosphorus (TP) in the electrolysis-AAO reached to 77.24% and 95.08% respectively, showing increases of 13.88% and 21.87%, as compared to the control reactor. Spatial variations of N and P showed that NH4+-N removal rate was promoted in aerobic zone of electrolysis-AAO. The intensified TN elimination, which was mostly reflected by abatement of NO3--N with the concomitant slight accumulation of NH4+-N and NO2--N, mainly occurred in anoxic2 compartment as the electrons supplied by electrolysis. Furthermore, minor P contents were measured and remained almost unchanged along the reaction units, indicating that chemical precipitation should be the dominant mechanism of P-removal in electrolysis-AAO. From the metagenomic-based taxonomy, phylum Actinobacteria was dramatically inhibited, and phylum Proteobacteria dominated the electrolysis-AAO. Particularly, nitrifying bacteria and multifarious autotrophic denitrifiers were enriched, meanwhile, a significant evolution of heterotrophic denitrifiers was found in electrolysis-AAO compared to control, which was mostly reflected by the inhibition of genus Candidatus Microthrix. Batch tests further confirmed that autotrophic denitrifiers using H2 and Fe2+ as essential electron sinks were mainly responsible for the electrolysis-induced denitrification. Differential metabolic capacities were revealed from the perspectives of functional enzymes and genes, and network analysis allowed insight of microbial taxa-functional genes associations and shed light on stronger relevance between autotrophic denitrifiers and denitrification-associated genes in the electrolysis-AAO system.

Coupling of thermophilic biofilm-based systems and ozonation for enhanced organics removal from high-temperature pulping wastewater: Performance, microbial communities, and pollutant transformations.

This study focused on the establishment of thermophilic biofilm-based systems (TBSs) coupled with ozonation for treatment of high-temperature pulping wastewater. The effects of the inoculum, sludge growth mode, and temperature were investigated. These factors played roles in the organics removal performance and microbial communities of pulping wastewater treatment systems. At 50 °C, the TBS inoculated with optimal inoculum achieved 59.12% and 37.96% reductions in COD and chromaticity, which were superior to the reductions achieved by other systems. In this TBS, thermophilic lignocellulolytic microorganisms (Chloroflexus, Meiothermus, norank_f_Caldilineaceae, and Roseiflexus) and carbohydrate-fermenting bacteria (norank_f_Anaerolineaceae) were predominant. Their relative abundances were 25.55% and 10.42%, respectively. For enhanced removal of COD and chromaticity, an integrated system consisting of a primary TBS, ozonation, and a secondary TBS was proposed. The total COD and chromaticity removal efficiencies increased to 90.48% and 87.89%, respectively. BOD5/COD increased from 0.20 to 0.40, and shifts of lignin-like and humic acid-like substances were observed during ozonation with the primary TBS effluent.

Effects of COD/TN ratio on nitrogen removal efficiency, microbial community for high saline wastewater treatment based on heterotrophic nitrification-aerobic denitrification process.

High salinity and high organic concentration impose negative impacts on autotrophic nitrification, which hinders efficient nitrogen removal. To achieve efficient nitrogen removal, high saline wastewater nitrogen removal systems with different COD/TN ratios based on heterotrophic nitrification-aerobic denitrification (HN-AD) process were established in this study. Results demonstrated that the COD/TN ratio had significant effects on nitrogen removal efficiency, microbial community structures and metabolic pathways. The optimal COD/TN ratio was 25 for nitrogen removal, with NH4+-N and TN removal rates of 11.86 mg·L-1·h-1 and 11.50 mg·L-1·h-1, respectively (3.65 and 3.31 times higher than those COD/TN ratio of 10). 16S rRNA high-throughput sequencing revealed that HN-AD functional bacteria (Pseudomonas, Bacillus, Paracoccus) with highest abundance (7.61%) played a key role in high saline wastewater treatment. And Halomonas, Nitrincola and Oceanimonas participated in the denitrification process. Moreover, the abundance of genes related to nitrogen removal was the highest (1.90%) revealed by functional genes prediction.