As a complex paleo-ocean located between the Tarim-North China and the Sibumasu/Baoshan blocks, the Proto-Tethys Ocean was opened from the rifting of the Supercontinent Rodinia and mainly closed at ...the end of the Early Paleozoic. The known studies suggest that there were many continents and/or micro-continents in the Proto-Tethys Ocean. During closure of the Proto-Tethys Ocean and assembly of these continents/micro-continents, some Early Paleozoic ophiolites and HP-UHP metamorphic rocks developed in East Asia similar to those Early Paleozoic orogens in Gondwana. However, some academic debates still remain on the boundaries of the Proto-Tethys Ocean and the nature, relationships and assembly processes of these continents/micro-continents to the Tarim-North China Continent to the north. These problems are important for revealing and reconstructing tectonic processes before the closure of the Proto-Tethys Ocean and the initial assembly of the Supercontinent Pangea. Not surprisingly, the Proto-Tethys tectonic domain is characterized by complex ocean-continent configurations, assemblies and dispersals of continents, from the rifting and drifting of the Supercontinent Rodinia to the assembly of the Supercontinent Pangea. Therefore, this paper mainly focuses on summarizing and discussing the northern part of the Proto-Tethys tectonic domain based on field geology, structural geology, magmatism, sedimentary formations, geochemical records, geochronology and tomography, in order to reveal three key aspects: 1) identifying the southern and northern boundaries of the Proto-Tethys Ocean; 2) establishing affinities of continents/micro-continents within the Proto-Tethys Ocean and its ocean-continent configuration; and 3) clarifying the temporal sequence and styles of micro-continental assembly and the closure of the Proto-Tethys Ocean. Integrated analysis results show that to the north the region is bounded by the paleo-Luonan-Luanchuan Suture (or Kuanping Suture) and its extension to West Kunlun; the southern boundary is marked by the Longmu Co-Shuanghu-Changning-Menglian Suture. The Tarim-Alax-North China Block to the north of the Proto-Tethys Ocean had a southward subduction polarity and collided with Gondwana along the northern margin of Gondwana in the Early Devonian. The southern branch of the Proto-Tethys Ocean may be closed, making the Greater South China Block, including the northern Qiangtang, Ruoergai, Yangtze and Cathaysia, Bureya-Jiamusi and Indochina blocks, southward subduction and accretion to the northern margin of Gondwana in the Early Devonian. The results also show that the North China Block had no clear affinity to Gondwana, whereas the other continental/micro-continental blocks, such as the Yangtze, Cathaysia, Tarim, Qaidam, Alax, North Qinling, Qilian, Oulongbuluke, South Qiangtang, Lhasa, Lanping-Simao and Indochina all have an affinity to Gondwana in the earlier part of the Early Paleozoic. During the interval 480–400Ma these series of continental blocks/micro-continental blocks experienced gradual southward subduction and accretion to the eastern segment of the northern margin of Gondwana, resulting in the closure of the Proto-Tethys Ocean and formation of the supercontinent called Proto-Pangea. The Greater South China Block and the Tarim-North China Block separated and drifted from Greater Gondwana of the Supercontinent Proto-Pangea since 380Ma, resulting in the formation of the Paleo-Tethys and the Mianlue oceanic crusts. After this minor adjustment and until 240–220Ma, they assembled northward gradually to develop Laurasia, which in turn resulted in the final formation of the Supercontinent Pangea.
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•Partial-denitrification is a feasible way to supply nitrite for anammox.•Nitrite accumulation rate (NAR) increased with pH during denitrification.•The higher NAR at pH 9.0 was ...correlated with an enrichment of Thauera.•Thauera harbored more nitrate reductase than nitrite reductase.•A process for achieving partial denitrification/anammox in WWTP was proposed.
Partial-denitrification (nitrate to nitrite) can supply nitrite for anammox which can reduce organic matter consumption in wastewater treatment plants (WWTPs). In order to achieve stable partial-denitrification, the effect of pH on denitrification were investigated for 420 days in three reactors with influent pH of 5.0, 7.0 and 9.0. The results indicate that the nitrite accumulation rate (NAR) increased with pH, with average effluent NARs being 21%, 38% and 57% in the above reactors, respectively. The sludge cultivated at a high pH of 9.0 was resistant to pH shock, with a high NAR being maintained at 83% when it was exposed to a low pH of 5.0. Metagenomic analysis showed that the higher NAR at pH 9.0 was correlated with an enrichment of Thauera, which harbored more nitrate reductase (8098 hits) than nitrite reductase (2950 hits). Based on these findings, a novel process was proposed for achieving partial-denitrification/anammox in mainstream WWTPs.
Sludge aggregation and biofilm formation are the most effective approaches to solve the washout of anammox microorganisms. In this study, the structure and composition of EPS (extracellular polymeric ...substances) were investigated to elucidate the factors for the anammox aggregation property. Anammox sludge taken from 18 lab-scale and pilot-scale reactors treating different types of wastewater was analyzed using EEM-PARAFAC (excitation–emission matrix and parallel factor analysis), FTIR (Fourier transform infrared spectroscopy) and real-time PCR combined with multivariate statistical analysis. The results showed that slime and TB-EPS (tightly bound EPS) were closely related with water quality and sludge morphology, and could be used as the indicators for anammox microbial survival ability and microbial aggregate morphology. Furthermore, slime secreted from anammox bacterial cells may be exhibited higher viscosity to the sludge surface and easily formed the gel network to aggregate. Large amounts of hydrophobic groups of protein in TB-EPS promoted the microbial aggregation. The mechanisms of anammox aggregation explored in this study enhanced the understanding of anammox stability in wastewater treatment processes.
The Mesozoic Western Pacific subduction system significantly impacted the North China and South China blocks along the East Asian continental margin and influenced the tectonic, magmatic, ...metallogenic and geomorphic evolution of the region. However, the dynamics and impact on the zone along the East Asian ocean-continent connection zone remain debated. Here we provide a comprehensive synthesis of the state-of-the-art information from deformation analysis, magmatism, geochronology, tomography and other fields from this region. We evaluate first the pre-Yanshanian (pre-Jurassic) final assembly of blocks and the Late Triassic formation of the unified continental margin in East China. We then focus on the Jurassic and Cretaceous geological processes in the East Asian ocean-continent connection zone. The temporal and spatial evolution of structural propagation, sedimentary depocentre, age zonation and migration of magmatism, as well as the large-scale tectono-morphological inversion in the Earth surface system combined with deep processes, are probed. In the early Yanshannian Period (Early and Middle Jurassic, 200–160 Ma), the destruction of the North China Craton (NCC) was mainly affected by the westward early-stage layered rollback, and stepwise delamination and thinning of its continental lithosphere, resulting in the early Yanshanian westward migration of tectonism and magmatism. Coevally, the combined effect of the closure of the Mongal-Okhotsk Ocean to the north and the subduction of the Bangong-Co- Nujiang Ocean to the south imparted an overall compressional setting in the East Asian Ocean-Continent Connection Zone (EAOCCZ). The centres of asthenospheric upwelling and mantle extrusion at depth continued to migrate eastward, driving the eastward lithospheric thinning with periodic and alternating extension and compression. The South China Block experienced a westward flat subduction during the early Yanshanian Period, resulting in the westward propagation of deformation and magmatism, followed by late two-stage delamination to induce the eastward tectono-magmatism. The difference in tectono-magmatic styles between the North China and South China blocks is a result of the different mechanisms and syles of the deep delamination processes under the superconvergence regime of the East Asian and adjacent plates. Especially delamination under North China generated the northwestward layered and fractured subcontinental lithospheric mantle, whereas under the eastern South China Block, were the oceanic lithospheric mantle of the Paleo- Pacific Plate that underwent flat subduction, or continental garnet peridotite mantle. In the middle Yanshanian Period (Late Jurassic to early Early Cretaceous, 160–125 Ma), the EAOCCZ underwent escape tectonics to form some basins related to strike slip faulting. Generally the extensional basins in the tails of the triangular-shaped escape blocks are perpendicular to the extrusion direction. The transtensional or transpressional basins are controlled by the strike slip faults distributed on both sides of the triangular block, and the flexural basins occur in front. In the late Yanshanian Period (late Early Cretaceous-Late Cretaceous, 125–65 Ma), the Paleo-Pacific (Izanagi) Plate subducted NNW-ward beneath the Eurasian continent, and the subduction angles changed gradually following eastward mantle extrusion induced by the closure of the Okhotsk Ocean to the north and Bangong-Nujiang Ocean to the south, as well as the rollback and subduction retreat of the Paleo-Pacific Plate to the east. The EAOCCZ gradually experienced lithospheric collapse and the formation of metamorphic core complexes, as well as obvious landscape reversal. During 70–45 Ma, the Izanagi-Pacific Ridge subducted beneath the EAOCCZ to induce wide uplift resulting in the formation of the Cenozoic dextral transtension-related basins.
Mainstream anammox still faces the challenges of non-ideal NO2−/NH4+ ratios and excess nitrate resulted from the instability of partial nitrification (PN) in municipal wastewater. To address these ...problems, in this study, we developed a novel two-sludge process that combined PN with synchronous anammox and endogenous partial denitrification (SAEPD); the process was tested with pre-treated domestic sewage at ambient temperatures for 205 d. High nitrogen removal efficiency of 91.2% was achieved with an influent C/N ratio of 1.7 at 15.4 °C; the success was attributed to the fact that EPD replenished the deficient nitrite by reducing nitrate and the excess nitrite was further reduced to nitrogen gas. With a non-ideal NO2−/NH4+ ratio of 0.89, the contribution of the SAEPD-sequencing batch reactor (SBR) during the anoxic stage reached 98.2% and the proportional contributions of the anammox and denitrification pathways were 77.2% and 22.8%, respectively. Although the low nitrite accumulation (66.1%) caused 10.8 mg N/L of nitrate to be transported into the SAEPD-SBR and the anammox reaction also converted 20% of nitrite to nitrate, only 1.1 mg N/L of nitrate remained in the effluent. High-throughput sequencing analysis revealed that although NH2OH was added, some genera of nitrite-oxidizing bacteria (0.73%) remained in the PN-SBR and potentially resulted in the oxidation of nitrite to nitrate. In the SAEPD-SBR, anammox and endogenous denitrifying bacteria co-existed and synergistically achieved the removal of ammonium, nitrite, and nitrate. Overall, the PN-SAEPD process has great potential for achieving cost-effective and energy-efficient municipal wastewater treatment.
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•EPD enhanced the robustness of mainstream anammox to cope with different NO2−/NH4+ ratios.•High TIN removal efficiency (91.2%) was achieved with a C/N ratio of 1.7 at 15.4 °C.•PN-SAEPD process has a unique advantage over the traditional PN/A process for treating nitrate.•Anammox and endogenous denitrifying bacteria synergistically achieved nitrogen removal.•PN-SAEPD process is an energy-efficient municipal wastewater treatment process.
This study presents a new method for energy-efficient wastewater treatment that synergizes the partial-denitrification, anammox, and in-situ fermentation (SPDAF) processes in an up-flow reactor. ...Nitrate-containing wastewater and actual domestic sewage were fed into this SPDAF system, which was operated for 180 days without the addition of external carbon sources and aeration. The total inorganic nitrogen (TIN) removal efficiency reached 93.1% with a low C/N ratio of 1.6, a NO3 ––N/NH4 +–N ratio of 1.13 and a TIN concentration of 92.5 mg N/L. The contribution of anammox to nitrogen removal accounted for 95.6%. Batch tests demonstrated that the partial-denitrification process was able to use organics from either the influent or those produced by fermentation, thus providing nitrite for anammox. Significantly, fermentation played a key role in using the slowly biodegradable organics and provided adequate electron donor for partial-denitrification. Metagenomic sequencing analysis showed that the genera related to partial-denitrification, anammox, and fermentation bacteria were coexisted in this SPDAF system. The key functional genes of anammox bacteria (Hzs, 3986 hits; Hdh, 2804 hits) were highly detected in this study. The abundances of cytoplasmic nitrate reductase (58 706 hits) and periplasmic nitrate reductase (70 540 hits) were much higher than copper nitrite reductase (16 436 hits) and cytochrome cd1 nitrite reductase (14 264 hits), potentially contributing to the occurrence of partial-denitrification. Moreover, different abundances of genes involved in fermentation metabolism suggested that fermentation likely generated easily biodegradable organics for partial-denitrification.
Lithospheric subduction prior to the assembly of the South China and North China blocks is traditionally considered to be directed northward. However, some critical geological and geochemical data ...cannot be reconciled with this northward subduction. This paper presents new lines of evidence against the traditional models and proposes a new and revolutionary tectonic model to explain the distribution and exhumation of high pressure (HP)-ultrahigh pressure (UHP) metamorphic rocks of the Dabie-Sulu Belt. We emphasize the following: 1) The Triassic tectonic environment of the southern margin of the North China Block was passive, not active, based on the stratigraphy; 2) In the southern margin of the North China Block no arc magmatism was recorded. 3) Many Paleoproterozoic slices of Jiaobei affinity of the Jiao-Liao-Ji Belt in the North China Block were located in the Triassic Sulu Orogen. 4) Many 1.85Ga metamorphic zircons are preserved in the Dabie-Sulu high pressure-ultra-high pressure (HP-UHP) metamorphic rocks. 5) The geometric asymmetry of many structural patterns in the HP-UHP slices indicates top-to-the northwest thrusting during the exhumation of HP-UHP slices. 6) Blueschists occur in the south of the UHP eclogite slices. 7) In the eastern segment of the North Qinling Orogen, no components with an affinity of the South China Block have been found. Along the Shangdan Suture of the Qinling Orogen has been recorded an apparent northward subduction. We consider that the suture is just a lateral subduction zone rather than a major collisional zone. Along the Shangdan Suture, the rarity of I-type plutonism can be attributed to a transform-type continental margin. The Bureya-Jiamusi-Khanka Block has an affinity to the South China Block based on its similarity regarding the Paleozoic history of deformation and Triassic blueschist metamorphic facies metamorphism. The Bureya-Jiamusi-Khanka Block could be the northern extension of the Dabie-Sulu Belt, and this gigantic belt could be interpreted as an orocline related to the southeastward subduction of the North China Block beneath the Greater South China Block.
lFloc aggregation (< 200 μm) results in a quick enrichment of AnAOB.lAggregated flocs alter the physio-morphology and microbial community in sludge.lFloc aggregates supply an initial carrier and ...anaerobic microenvironment for AnAOB.lAnAOB rapid enrichment further facilitates anammox granules maturation.
Rapid enrichment of anaerobic ammonia oxidation bacteria (AnAOB) is highly associated with the granulation process; however, the interactive mechanism remains unclear, especially for the initial granulation process. A single-stage partial nitritation-anammox (PN/A) bioreactor combined with granular/floc sludge was operated for 400 days. During the experimental period, the nitrogen removal rate increased from 0.60 to 1.21 kg N m−3d−1, and the nitrogen removal capability improved primarily during a transition period (days 200–250), which was accompanied by a particle size increase and AnAOB proliferation (4.9 ± 1.7 days). Moreover, as observed by the biomass physio-morphology, the size distribution, and the microbial community shift, small flocs (< 200 μm) aggregated due to the addition of excess sodium acetate. The emerging floc aggregates represented an early form of granules, providing the initial biological carrier and necessary anaerobic microenvironment for the growth of attached AnAOB, resulting in a high AnAOB growth-rate. These results are the first direct evidence that floc aggregates are essential to AnAOB enrichment, and that they can be affected by operational conditions. This study provides an in-depth understanding of the link between floc aggregations and AnAOB enrichment and broadens the feasibility of optimizing PN/A applications.
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•The novel two-stage PN/A process achieved high-efficient nitrogen removal.•Partial denitrifying in ANA-EGSB improved the system’s nitrogen removal efficiency.•AOB and anammox ...bacteria dominated in nitritation and anammox reactor.•Separating nitritation and anammox facilitated system’s stability and efficient.
This study focused on the long-term stability of a novel two-stage partial-nitritation/anammox (PN/A) process treating municipal wastewater with fluctuated water quality. Specifically, two parallel sequencing batch reactors (SBRs) were used for removing organic matters and achieving complete nitritation, while the expanded granular sludge bed (ANA-EGSB) was used for anammox. With the influent ammonium concentration varying from 32 to 79 mg/L and the average hydraulic retention time of 3.39 h in this system, more than 93% of ammonium was removed and the effluent TIN was 4.8–11.8 mg/L. The partial denitrifying occurring in the anammox reactor could reduce nitrate to nitrite that was reused by anammox bacterium, enhancing the TIN removal efficiency. Further, the “overconsumption of ammonium” under anaerobic conditions was observed in ANA-EGSB. Microbial community analysis showed that Nitrosomonas (AOB) were the dominant nitrifying bacteria in the nitritation SBR and Candidatus_Brocadia with the relative abundance of 6–13% dominated in ANA-EGSB.
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•PN/A-EPD/A process was developed in an IFAS-SBR treating real municipal wastewater.•High NRE of 90.1% was achieved under aerobic HRT of 8 h and DO of 0.4 ± 0.1 mg/L.•89.9% of TN was ...removed by anammox pathway in typical cycle.•Relative abundance of Candidatus Brocadia rose from 0% to 0.79% in suspended sludge.
In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.
