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•Mainstream anammox system was started up in 75 days at ambient temperature.•The ratio of the seeding anammox sludge and nitrification sludge was only 1:25.•The average TN removal ...efficiency was 80.3% despite fluctuating influent quality.•High AOB activity and intermittent aeration promote anammox bacterial enrichment.•Anammox reaction was the primary nitrogen removal pathway in SNAD reactor.
The difficulties in enriching anammox bacteria and maintaining stable partial nitrification during start-up phase limit the application of mainstream anammox process. In this study, the feasibility of starting up simultaneous partial nitrification, anammox and denitrification (SNAD) reactor treating municipal wastewater by inoculating ordinary nitrification sludge (96.2%) and a small amount of anammox sludge (3.8%) was investigated. A sequencing batch reactor with intermittent aeration was used for the SNAD process. The SNAD reactor was started up in 75 days with a nitrogen removal efficiency of 85.4% at ambient temperature. The nitrogen removal performance maintained stable despite the fluctuating inflow. Anammox bacterial activity exponentially increased although nitrite oxidizing bacteria (NOB) activity in seeding sludge was high. The enhanced ammonium oxidizing bacterial activity and partial denitrification provided sufficient nitrite for anammox bacteria. Moreover, NOB was inhibited by intermittent aeration, anammox bacteria had competitive advantage on nitrite. The improved particle size and settleability of activated sludge also favored the anammox bacterial enrichment. This study provided an improved and easily-implemented start-up strategy for mainstream anammox. The seeding sludge was easily obtained and the operation strategy was simple. These findings were meaningful to the engineering application of mainstream anammox.
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•Stable sewage nitrogen removal was obtained in a PNA-SBBR at low temperatures.•Microbial community structure in the PNA biofilm system remained reasonably stable.•Psychrotolerant ...microbes were enriched at low temperature, improving system stability.•Increased secretion of TB-EPS favored the stable nitrogen removal at low temperatures.
Stable sewage nitrogen removal with nitrogen removal efficiency of 87.5 ± 2.2% was achieved in a partial nitrification-anammox (PNA) biofilm system at low temperatures (12.8–16.3 °C). High-throughput sequencing analysis indicated that the microbial community structure in the sequencing batch biofilm reactor (SBBR) remained reasonably stable. Candidatus Brocadia was the only detected anammox genus and remained stable at 0.3–0.5%. Some psychrotolerant microorganisms that could secrete cryoprotective extracellular polymeric substances (EPS), including Flavobacterium and Thermomonas, were enriched at low temperatures. This could be conducive to the stable operation of the PNA-SBBR. Moreover, according to the EPS composition and characteristics analysis, the secretion of tightly-bound EPS that bound to the cell surface containing plentiful protein was stimulated at low temperatures, further improving the system stability. Overall, the reasonably stable microbial community structure, enrichment of psychrotolerant microorganisms, and increased secretion of EPS could play important roles for stable sewage nitrogen removal at low temperatures.
The conversion pathway of NH4+ in deterioration and restoration periods. Display omitted
•Intermittent aeration restored single-stage PN/A process from nitrate build-up.•NOB accumulated under ...continuous aeration mode, Nitrospira was the dominant NOB.•Reducing DO to 0.17±0.08mg/L was failed to inhibited the NOB activity.•Sewage PN/A reactor was quickly started up by inoculating anammox sludge.
A single-stage partial nitrification-anammox (PN/A) reactor treating low-strength swage was operated for 288days to investigate the recovery of nitrogen removal from nitrate accumulation. The reactor was quickly started up by inoculating anammox sludge. However, nitrite oxidizing bacteria (NOB) abundance gradually increased on day 25, leading to high effluent nitrate concentration. Two strategies were executed to control the effluent nitrate. In strategy I, dissolved oxygen (DO) concentration was kept low (0.17±0.08mg/L), but nitrate production increased from 4.71 to 38.18mg-N/L. In strategy II, intermittent aeration operation mode (aeration 7min/anoxic 21min) was adopted, which significantly lowered the nitrate concentration to 1.3mg-N/L, indicating the NOB was inhibited. The high nitrogen removal rate of 73mg-N/(L·d) was achieved. The evolution of bacterial activity and abundance verified the changes of the nitrogen removal performance and proved the intermittent aeration strategy could successfully solve the problem of nitrate build-up in the PN/A process.
In the long history of development and elimination, the creatures have derived a variety of exquisite structures and unique properties, typically natural nacre, marine mussel and Glycera to adapt to ...the environment and resist the predation of the enemy. Hence, inspired by the combination of special structures and properties of multiple creatures, a novel type of graphene-based micro/nano architecture was proposed, and the related bioinspired nanocomposites were fabricated, Polydopamine coated Graphene oxide/Nanocellulose/Polydopamine (P-GCP). Apart from replicating the layered structure of natural nacre, P-GCP also introduced copper ions and polydopamine to simulate the hardening mechanism of the Glycera's jaw and the composition of adhesive proteins in mussels to further improve the tensile strength and conductivity of nanocomposites, respectively. The test results showed that the tensile strength of P-GCP reached 712.9 MPa, which was 5.3 times that of natural nacre. The conductivity of artificial nacre was as high as 207.6 S/cm, which was equivalent to that of reduced graphene oxide (rGO). Furthermore, the material exhibited outstanding electrical conductivity when it connected as wires in a circuit, demonstrating the practical application prospects in aerospace, supercapacitors, biomaterials, artificial bones and tissue engineering.
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•AOB played a main role in SPN/A nitrogen performance.•Anammox bacterial activity increased with AOB activity despite high NOB activity.•Combining intermittent aeration and ...bio-augmentation enhanced SPN/A stabilization.
Intermittent aeration and bio-augmentation were integrated to enhance single-stage partial nitrification-anammox (SPN/A) stability over 235-day operational period treating low-strength sewage. The effect of bio-augmentation sludge (with different abundances of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB)) was determined. Partial nitrification sludge based bio-augmentation increased the total nitrogen (TN) removal efficiency from 29.1% to 70%, followed by the nitrification sludge (from 38.1% to 65.4%), then the denitrifying phosphorus sludge (from 42.1% to 54.4%). The evolution of bacteria activity and communities showed that anammox activity increased with the enhancement of AOB activity, and higher AOB abundance led to higher anammox bacterial abundance despite high NOB abundance. The enhancement of AOB activity produced more nitrite, anammox bacteria gained more nitrite than NOB since intermittent aeration selectively inhibited NOB, thus the reactor stability enhanced substantially. This study highlights the significance of enhancing AOB activity to ensure long-term operational stability of SPN/A processes.
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•Applications of intermittent aeration in N removal are critically reviewed.•Strategies and mechanisms of enhanced N removal efficiency are presented.•Variations in N transformation ...and microbial interactions are discussed.•Advantages of intermittent aeration in the integrated anammox process are outlined.•Directions for future work in N removal with intermittent aeration are suggested.
Intermittent aeration has been shown to be one of the most effective and cost-effective strategies for biological wastewater treatment. This review presents an overview of the application and advantages of intermittent aeration, with the mechanisms of improvement in process stability discussed. Intermittent aeration was applied to maximize the utilization of organic carbon for denitrification rather than oxidized by O2. Under that condition, advanced nitrogen removal and sludge settleability were achieved and the energy consumption and N2O emissions were reduced. With the discovery that nitrite oxidation bacteria are selectively inhibited while ammonium oxidation bacteria are less affected under intermittent aeration conditions, intermittent aeration has been applied to the partial nitrification process. Furthermore, the non-aerated phases of intermittent aeration have been found to facilitate the synergism of anaerobic ammonium oxidizing bacteria (AnAOB) and denitrifying bacteria, providing a suitable environment for AnAOB growth. Therefore, intermittent aeration is considered to be an effective operational strategy for anammox-based processes, such as single-stage partial nitrification-anammox. In addition, simultaneous nutrient removal and sludge reduction could also be achieved. In order to regulate the synergism of microbial species, dissolved oxygen (DO) concentrations and the durations of aerated and non-aerated periods can be adjusted based on the monitored parameters such as nitrogen concentrations, pH and oxidation reduction potential profiles. Finally, the current limitations, gaps in knowledge and the areas requiring further research are proposed.
With the aid of the reciprocal transformation and the associated equation, we study the inverse scattering transform with a matrix Riemann–Hilbert problem for the modified Camassa–Holm (mCH) equation ...with nonzero boundary conditions (NZBC) at infinity. In terms of a suitable uniformization variable, the direct and inverse scattering problems are presented for the associated modified Camassa–Holm (amCH) equation. By means of the reciprocal transformation and the reconstruction formula for the potential of the amCH equation, we present the
-soliton solution for the mCH equation with NZBC. As applications, various solutions including both bright and dark types, smooth soliton solutions, singular soliton solutions, and multi-valued singular soliton solutions of the mCH equation and their interactions are exhibited.
Rubia yunnanensis is an important medicinal plant with various bioactive secondary metabolites. In order to reduce the dependence on wild populations of the species, we aim to establish in vitro ...culture system that can produce Rubiaceae-type cyclopeptides (RAs) and quinones. Agrobacterium rhizogenes-mediated transformation of stem segments of in vitro grown R. yunnanensis plants using four A. rhizogenes strains was studied and transformation conditions were optimized. Hairy roots appeared with the highest frequency (68.89%) when stem segments (with leaves) without pre-culture were immersed in A. rhizogenes A4 strain bacterial suspension for 30 min, co-cultured on Murashige and Skoog (MS) solid medium in the dark for three days, and afterwards incubated in darkness. PCR analysis of rolB and rolC genes confirmed transformed nature of six hairy root clones. The hairy roots grew rapidly, especially showing the highest accumulation of biomass in MS liquid medium compared to in vitro grown plants and calli. Histological observation of hairy root revealed anatomical difference in vascular cylinder, where the cells exhibited high mitotic activity characterized by vigorous growth. The UPLC-MS/MS analysis revealed that the amount of RAs in the hairy roots grown in ½MS liquid medium (4.611 μg g−1 DW) was higher than that in in vitro grown plants (0.331 and 4.096 μg g−1 DW for shoots and roots respectively) and calli (1.082 μg g−1 DW), but still far lower than that in the roots of seed-borne plants (80.296 μg g−1 DW). However, the hairy roots accumulated high level of quinones (2320.923 and 5067.801 μg g−1 DW for MS and ½MS liquid media respectively), of the same order of magnitude as the roots of seed-borne plants (7409.973 μg g−1 DW). Hairy root culture of R. yunnanensis, with high accumulation of biomass and production of quinones, may offer an attractive perspective for the production of the RAs and quinones that could be further optimized for pharmaceutical use.
•Hairy root culture of Rubia yunnanensis was established.•Seven Rubiaceae-type cyclopeptides and sixteen quinones were quantified.•High accumulation of quinones was achieved in hairy roots of R. yunnanensis.•Anatomical structure of hairy root was characterized.
With increasing energy demand driving the need for eco-friendly and efficient energy storage technology, supercapacitors are becoming increasingly prevalent in wearable devices because of their ...portability and stability. The performance of these supercapacitors is highly dependent on the choice of electrode material. The high capacitance and mechanical properties needed for these materials can be achieved by combining graphene's stable electrical properties with renewable cellulose's excellent mechanical properties into porous aerogels. In this study, graphene-cellulose hydrogels were prepared by a one-step hydrothermal method, with porous, ultra-light, and mechanically strong graphene-cellulose aerogels then prepared by freeze-drying. These composite aerogels possess excellent mechanical strength and high specific capacitance, capable of bearing about 1095 times the pressure of their own weight. Electrochemical tests show the specific capacitance of these composite aerogels can reach 202 F/g at a scanning rate of 5 mA/cm
. In view of their high surface area and fast charge transport provided by their 3D porous structure, graphene-cellulose aerogels have great potential as sustainable supercapacitor electrodes.
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