Simultaneous nitrification–denitrification and microbial community profile in an oxygen-limiting intermittent aeration SBBR with biodegradable carriers

To enhance the startup and efficient simultaneous nitrification and denitrification for sewage treatment, sequencing batch biofilm reactors (SBBRs) partially coupled with rice husk were established and operated under various intermittent micro-aeration cycles (IMCs) and COD/N ratios under oxygen-limiting intermittent aeration conditions. Experimental results showed that the increase of IMCs with non-aeration/micro-aeration mode of (8 h/4 h)₁ to (2 h/1 h)₄ in a 12 h-cycle accelerated the startup performance and improved NH₄⁺–N and COD removal. NH₄⁺–N, TN and COD removal efficiencies were 98.7?±?0.9, 89.2?±?5.2 and 82.9?±?6.7% at COD/N ratio of 7.6 with the highest IMCs in SBBR, respectively. Higher TN removal efficiencies of 87.2?±?4.0 and 58.1?±?3.5% were also achieved at lower COD/N ratio of 5.6 and 2.8, respectively. In SBBRs with various IMCs, facultative denitrifier like genus Acinetobacter and solid-phase denitrifier belonging to Comamonadaceae family were enriched. However, aerobic denitrifiers with function of heterotrophic nitrification like Paracoccus were favored to enrich under higher IMCs condition, and more anoxic denitrifiers like sulfur-based autotrophic denitrifier Thiothrix and heterotrophic denitrifiers like Pseudomonas and Methyloversatilis were observed at lower IMCs condition. Autotrophic nitrifier (Nitrosomonas and Nitrosipra) and heterotrophic nitrifiers both contributed to the efficient nitrification.     

Impacts of exposure to mine tailings on zooplankton hatching from a resting egg bank

In the last five years, two colossal environmental disasters involving iron-enriched mine tailings have occurred in Brazil, affecting many aquatic ecosystems over the short, medium and long-terms. This study investigated whether these iron-enriched mine tailings affect the main biotic strategy to restore zooplankton populations affected by severe stress, i.e., hatching of dormant stages. A 30 day hatching experiment was conducted, using a resting egg bank from a natural lake, exposed to 3 concentrations of mine tailings: control (0 g), T25 (25 g) and T50 (50 g). A total of 22, 15 and 16 species hatched in the control, T25 and T50, respectively. Conochilus sp., Filinia terminalis, Hexartha mira, Bosmina longirostris and Ceriodaphnia silvestrii hatched only in the control, which suggests that these species are sensitive to any concentration of mine tailings. A gradual decrease in richness and hatchling abundance was recorded, from the control (8.0?±?1.0 SE species and 1597?±?73.9 hatchlings) to T25 (4.6?±?1.2 species and 1279?±?136.5 hatchlings) and then to T50 (2.3?±?1.2 species and 603.3?±?61.9 hatchlings). Our results suggest that exposure of zooplankton resting eggs to iron-enriched mine tailings may negatively impact these egg banks in natural ecosystems, with potential impacts on the restoration of zooplankton communities after even short-term exposures.

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Characterisation of recombinant thermostable manganese-superoxide dismutase (NeMnSOD) from Nerium oleander

Superoxide dismutase is one of the key antioxidant enzymes accountable for the eradication of free radicals generated during various metabolic processes. This is first study reporting a thermostable MnSOD obtained from a xerophytic plant, Nerium oleander. The full-length gene identified using Rapid amplification of cDNA ends revealed an open reading frame of 699 bp flanked by 5′UTR and 3′UTR of 134 bp and 198 bp respectively. The corresponding NeMnSOD protein was cloned and expressed in Escherichia coli. The purified protein yields a band of 25.4 kDa, which established a specific activity of 2617 units mg^?1 of protein and under native condition yield bands of 52 kDa and 110 kDa, confirming the dimeric and tetrameric state of the protein. The Km and V_max of 0.078?±?0.008 mM and 1052.3?±?33.59 units mg^?1 of protein, respectively. The purified enzyme demonstrated thermostability by retaining more than 20% activity at a temperature 70 ℃. The enzyme functioned at pH range of 4–9.0 with maximum activity at pH 7.4. Sodium azide, effectively inhibited the activity of enzyme confirming it to be MnSOD. The enzyme activity was least affected on treatment with strong denaturants (Urea, guanidine HCl and SDS) and harsh chemicals (DTT, CHAPS and β-mercapto-ethanol) These experimental data validated with Insilco analysis revealed that NeMnSOD possessed thermo as well as kinetically stable moiety which can be further exploited with its applications in the field of pharmaceutical, food and cosmetic industry, which urge for such thermostable enzyme.

Graphic Abstract

     

Silver Nanoparticles and Nanorings for Surface-Enhanced Raman Scattering

Silver (Ag) nanoparticles (NPs) and Ag nanorings (NRs) have been fabricated. Due to the inherent features of Ag NPs and Ag NRs, strong electromagnetic (EM) near-field distributions were expected, and hence surface-enhanced Raman scattering (SERS) activity was demonstrated. Size and interparticle gaps distribution of Ag NPs were estimated to be 48.14?±?10.14 nm and 14.11?±?5.24 nm respectively along with estimated coverage density of?~?4?×?10¹⁰ cm^?2. On the other hand, Ag NRs were found to consist of Ag clusters and of various shapes and sizes, instead of a perfect ring structure. High-resolution FESEM revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were connected to form the edge of the NR. However, the coverage density of Ag NRs was estimated to be?~?5.6?×?10⁶ cm^?2. Based on the scenarios, it was speculated that the local EM near-field distribution would excel and thus led to enhanced SERS signals. SERS enhancement of R6G was estimated as high as 2.18?×?10⁴ and 2.78?×?10⁴ at 610 cm^?1 (C???C ring bending mode in phenyl rings) for Ag NPs and Ag NRs respectively. FDTD analysis was carried out to elucidate the EM near-field distributions.

Graphical abstract

Ag NPs and Ag NRs from an ultrathin layer of Ag on ZnO/Glass (middle pane) confirming high EF of R6G adsorbed on Ag NRs (right pane) and Ag NPs (left pane) supported by corresponding EM near-field distributions.

     

Soybean Hull Insoluble Polysaccharides: Improvements of Its Physicochemical Properties Through High Pressure Homogenization

Soybean hull is an agroindustrial waste which has not been fully studied as a food ingredient. The aims of this work were to obtain insoluble fibers from soybean hull and to evaluate the effect of high pressure homogenization (HPH) on its physicochemical properties. Hull insoluble polysaccharides (HIPS) were obtained in a single step, as the insoluble residue after pectin removal. FTIR showed bands corresponding to cellulose and hemicellulose in HIPS, and thermogravimetric analysis showed two degradation events at 236.3 °C and 325.6 °C, corresponding to cellulose and hemicellulose, respectively. HIPS dispersions (pH 3.00) were subjected to HPH by three cycles at increasing pressures (up to 1000 bar), obtaining soybean hull nanofibers. SEM images show that HPH at 1000 bar reduced the dimensions of the fiber bundle from 30 to 90 μm in length and 9–15 μm in diameter to nanofibers of 10–30 μm in length and 100–400 nm in diameter. AFM further confirms a heterogeneous distribution of sizes in HIPS₈₀₀ and HIPS₁₀₀₀, evidencing the presence of individual nanofibers with diameters around 50 ± 10 nm and 40 ± 10 nm, respectively, with several μm in length. Furthermore, an increase in water holding capacity from 2.1 to 61 g_water/g_{dry matter} and viscosity from 0.39 to 34,945 Pa.s were achieved as HPH at 1000 bar treatment was applied. HPH increased the interfacial area and promoted the interconnection of fibers in a hydrated gel-like structure. This explains flow behavior, which was extensively studied in this work: three-region viscosity profile (shear-thinning, plateau or shear-thickening and shear-thinning) and a pronounced hysteresis loop. Oscillatory rheology was used to study the viscoelastic behavior of HIPS dispersions. HIPS are a source of nanofibers, easy to obtain through a single step of chemical treatment followed by the application of high pressures. It is remarkable that the use of few chemical solvents is favorable from an environmental point of view. This work also suggests a potential application of HIPS to improve physicochemical and structural properties in acidic foods.

Graphical Abstract

     

Effect of temperature,pH and ionic strength on hydroxyapatite stabilised Pickering emulsions produced in batch and continuous mode

Oil-in-water (O/W) Pickering emulsions are attracting attention as carriers of lipophilic active compounds with clear advantages over traditional systems. Having in view their effective use it is important to study their stability against environmental stresses impacting manufacture, storage, and application conditions. In this work, hydroxyapatite nanoparticles (n-HAp) Pickering emulsions produced in continuous mode using a mesostructured reactor (average size?~?7, 11 and 18 µm) and in batch mode using a rotor–stator device (average size?~?18 µm) were studied concerning their behaviour at different temperatures (5–90 ºC), pH (2–10) and ionic strength (0–500 mM), conditions with relevance for food applications. Droplet size, morphology, and zeta-potential were analysed after 1 and 7 days under storage. In general, and despite the droplet size, the n-HAp Pickering emulsions were stable within the tested ionic strength range, at relatively high pH environments (6–10), and at temperatures up to 70 ºC. Pickering emulsions undergo complete phase separation at very low pH (2) due to n-HAp particle's disruption. A clear tendency to aggregation and coalescence was observed for high temperatures (70–90 ºC). Results indicate no significant differences related to the used production method. From an industrial perspective, this work also corroborates that the scale-up to a continuous process using a mesostructured reactor, NETmix, from a batch laboratorial process is feasible without impacting stability.

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Intriguing Plasmonic and Fluorescence Duality in Copper Nanoparticles

Dendrimeric copper nanoparticles (CuNPs) were prepared by the reduction of [Cu₂(CH₃CO₂)₄] with ascorbic acid at 75 °C in the presence of ranelate ions. The metallic nanoparticles exhibited a strong plasmonic band centered at 581 nm, and their average size distribution was typically in the range of 20–30 nm. By adding polyvinylpyrrolidone to the reaction mixture, the growth of the initial copper nanoparticles was hindered. Their sizes were stabilized around 1.8 nm, leading to spherical agglomerates of about 50 nm. Upon green light excitation, the agglomerates exhibited yellow-orange fluorescence emission, keeping the surface plasmon resonance band at 581 nm. This dual behavior suggested the occurrence of collective plasmonic resonance and efficient energy transfer within the agglomerated nanoparticles, in order to account for the observed fluorescence in the system.

Graphical Abstract

     

Studies in nitrification of municipal sewage in an upflow biofilter

The upflow aerated biofilter with polyurethane foam cubes as the supporting medium was used for the investigation of nitrification studies on municipal sewage (secondary treated as well as untreated domestic sewage). In case of secondary treated sewage effluent, a synthetic composition of NH₄ ⁺-N and COD of each 50?mg/l was studied for a HRT variation of 24, 12, 8 and 6 hours. The ammonium removal efficiencies were found to be in the range of 98 to 100% with the steady-state effluent concentrations of NH₄ ⁺-N and NO₂ ^?-N in the range of 1–4 mg/l and 0.1–0.2?mg/l respectively. In case of domestic sewage system, nitrification studies along with suspended solids removal study was carried-out on untreated sewage for a HRT variation of 24, 12 and 6 hours. The ammonium removal efficiencies of 100% were observed for all the three HRT values at very high COD/NH₄ ⁺-N ratio of 15. The suspended solids removal efficiencies of 95 to 98% were observed with the average effluent suspended solids concentration of 5.9 to 15.9?mg/l. The experiments were conducted in non-backwash conditions of the biofilter. The study has revealed the best use of the upflow biofilter system for nitrification applications and suspended solids removal.     

In vitro organogenesis and plant regeneration of Thymus serpyllum L.: an important aromatic medicinal plant

An efficient in vitro propagation system has been developed for the rapid micropropagation of Thymus serpyllum L. (Banajwain), an aromatic medicinal herb from nodal explant on MS medium. Phenolic leaching and high rate of contamination was the most significant problem in establishing in vitro culture of Thymus serpyllum which was overcome by preparing explants in an antioxidant ascorbic acid (1000 ppm) at 6°C for 45 min and addition of the same antioxidant (50 mgl⁻¹) to the MS medium. The frequency of shoot production was influenced by different cytokinins (Kn, BAP, and Kn + BAP) and 95.56% shoot induction was observed when MS medium was supplemented with 1.0 + 2.0 mgl⁻¹ (Kn + BAP). The maximum average number of shoots 16.93 ± 2.15 and average length (3.98 ± 0.55) was recorded when MS medium have 0.5 + 2.0 mgl⁻¹ (Kn + BAP). The in vitro regenerated microshoots were rooted on MS and half strength MS medium and there was significant difference in root induction on both media under the influence of auxins (IAA, IBA, and NAA). The maximum average number (11.67 ± 3.03) and average root length (3.88 ± 0.71) was reported in half MS medium having 1.0 mgl⁻¹ IBA. The complete regenerated plantlets were acclimatized under growth chamber before transferring to the earthen pots and showed 90% survival.

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Effect of Foliar Application of Silicon and Salicylic Acid on Regulation of Yield and Nutritional Responses of Greenhouse Cucumber Under High Temperature

Plant nutrition management is known as an efficient strategy to control environmental constraints. This experiment was conducted in a climate control greenhouse with a hydroponic system. The high temperature (36 °C?±?1) was imposed on the pots after fruit formation. The studied factors were silicon in 2 concentrations (0 and 4 parts per thousand (ppt)) and salicylic acid in 3 concentrations (0, 0.5, and 1 mM). They were sprayed on cucumber plants 3 times and under high-temperature conditions to evaluate if they can regulate and improve the yield and quality of cucumber fruit under high-temperature conditions or not. The results showed that all treatments significantly improved the nutritional status, total yield, and fruit quality (including marketable yield (i.e., fruits that can be sold due to their good shape) and nitrate content). Under high-temperature conditions, foliar application of silicon had the highest effect on the increase of total yield and marketable fruit yield (respectively, 36.14% and 40.29% increase compared to the control treatment). Micro-nutrients concentrations in the leaf were significantly increased by Si but a reverse status happened for salicylic acid. Under high temperatures, both treatments also significantly decreased the nitrate content of the fresh matter of fruit but silicon was the superior treatment. Silicon and salicylic acid, respectively, had positive effects on mitigation of adverse effects of high temperature on cucumber plants. These findings suggest the use of these treatments under high-temperature conditions in greenhouse cucumber production.

Graphical Abstract

N–No₃ content in dry matter of leaf (left) and fresh matter of fruit (right) affected by different treatments. *SaA0–SiA4: 4 ppt Si; SaA0.5–SiA0: 0.5 mM SA; SaA0.5–SiA4: 0.5 mM SA?+?4 ppt Si; SaA1–SiA0: 1 mM SA; SaA1–SiA4: 1 mM SA?+?4 ppt Si; control: without any SA and Si applications. Means in the same column followed by the same letter are not significantly different according to DMRT at (P?≤?0.05)

     

Impacts of vegetation and temperature on the treatment of domestic sewage in constructed wetlands incorporated with Ferric-Carbon micro-electrolysis material

Ferric-Carbon Micro-Electrolysis (Fe/C-M/E) material had been widely used for the pretreatment of wastewater. Therefore, we hypothesized that Fe/C-M/E material could enhance the treatment of domestic sewage when it was integrated into constructed wetlands (CWs). In this study, CWs integrated with Fe/C-M/E material were developed. Druing the experiment of effect of vegetation on the performance of CWs, percentages of NH₄⁺-N, NO₃^?-N, total nitrogen (TN), and Chemical Oxygen Demand (COD) removed in polyculture (W1) were up to 91.8%, 97.0%, 92.3%, and 85.4%, respectively, which were much higher than those in Lythrum salicaria monoculture (W2) and Canna indica monoculture (W3). In the experiment of temperature influences on the removal efficiency of CWs, temperature substantially influenced the performance of CWs. For example, NO₃^?-N removal percentages of W1, W2, and W3 at high temperature (25.5°C and 19.8°C) were relatively stable and greater than 85.4%. At 8.9°C, however, a sharp decline of NO₃^?-N removal percentage was observed in all CWs. Temperature also influenced the Chemical Oxygen Demand (COD) removal and soil microbial activity and biomass. Overall, the polyculture (Lythrum salicaria +Canna indica) showed the best performance during most of the operating time, at an average temperature ≥ 19.8°C, due to the functional complementarity between vegetation. All the CWs consistently achieved high removal efficiency (above 96%) for TP in all experiments, irrespective of vegetation types, phosphorous loadings, and temperatures. In conclusion, polyculture was an attractive solution for the treatment of domestic sewage during most of the operating time (average temperature ≥ 19.8°C). Furthermore, CWs with Fe/C-M/E material were ideally suitable for domestic sewage treatment, especially for TP removal.     

Kinetics of pollutant removal from domestic wastewater in a tropical horizontal subsurface flow constructed wetland system: Effects of hydraulic loading rate

The treatment capacity of constructed wetlands is expected to be high in tropical areas because of the warm temperatures and the associated higher rates of microbial activity. A pilot scale horizontal subsurface flow constructed wetland system filled with river sand and planted with Phragmites vallatoria (L.) Veldkamp was set up in the southern part of Vietnam to assess the treatment capacity and the removal rate kinetics under tropical conditions. The system received municipal wastewater at four hydraulic loading rates (HLRs) of 31, 62, 104 and 146 mm day^?1. Removals of TSS, BOD₅ and COD were efficient at all HLRs with mean removal rates of 86–95%, 65–83% and 57–84%, respectively. Removals of N and P decreased with HLRs and were: NH₄-N 0–91%; TN 16–84% and TP 72–99%. First-order area-based removal rate constants (k, m year^?1) estimated from sampling along the length of the wetland from inlet to outlet at the four HLRs were in the range of 25–95 (BOD₅), 22–30 (COD), 31–115 (TSS), 5–24 (TN and TKN) and 41–84 (TP) at background concentrations (C*) of 5, 10, 0, 1.5 and 0 mg L^?1, respectively. The estimated k-values should not be used for design purposes, as site-specific differences and stochastic variability can be high. However, the study shows that domestic wastewater can be treated in horizontal subsurface flow constructed wetland systems to meet even the most stringent Vietnamese standards for discharge into surface waters.     

Irradiance-driven 20-hydroxyecdysone production and morphophysiological changes in Pfaffia glomerata plants grown in vitro

Pfaffia glomerata possesses potential pharmacological and medicinal properties, mainly owing to the secondary metabolite 20-hydroxyecdysone (20E). Increasing production of biomass and 20E is important for industrial purposes. This study aimed to evaluate the influence of irradiance on plant morphology and production of 20E in P. glomerata grown in vitro. Nodal segments of accessions 22 and 43 (Ac22 and Ac43) were inoculated in culture medium containing MS salts and vitamins. Cultures were maintained at 25 ± 2 °C under a 16-h photoperiod and subjected to irradiance treatments of 65, 130, and 200 μmol m⁻² s⁻¹ by fluorescent lamps. After 30 days, growth parameters, pigment content, stomatal density, in vitro photosynthesis, metabolites content, and morphoanatomy were assessed. Notably, Ac22 plants exhibited 10-fold higher 20E production when cultivated at 200 μmol m⁻² s⁻¹ than at 65 μmol m⁻² s⁻¹, evidencing the importance of light quantity for the accumulation of this metabolite. 20E production was twice as high in Ac22 as in Ac43 plants although both accessions responded positively to higher irradiance. Growth under 200 μmol m⁻² s⁻¹ stimulated photosynthesis and consequent biomass accumulation, but lowered carotenoids and anthocyanins. Furthermore, increasing irradiance enhanced the number of palisade and spongy parenchyma cells, enhancing the overall growth of P. glomerata.

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A theoretical study on the coordination behavior of some phosphoryl,carbonyl and sulfoxide derivatives in lanthanide complexation

The selectivity of phosphoryl P(O)R₃, sulfoxide S(O)R₂, and carbonyl C(O)R₂ (R?=?NH₂, CH₃, OH, and F) derivatives with lanthanide cations (La³⁺, Eu³⁺, Lu³⁺) was studied by density functional theory calculations. Theoretical approaches were also used to investigate energy and the nature of metal–ligand interaction in the model complexes. Atoms in molecules and natural bond orbital (NBO) analyses were accomplished to understand the electronic structure of ligands, L, and the related complexes, L–Ln³⁺. NBO analysis demonstrated that the negative charge on phosphoryl, carbonyl, and sulfoxide oxygen (O_P, O_C, and O_S) has maximum and minimum values when the connected –R groups are –NH₂ and –F. The metal–ligand distance declines as, –F?>?–OH?>?–CH₃?>?–NH₂. Charge density at the bond critical point and on the lanthanide cation in the L–Ln³⁺ complexes varies in the order –F?<?–OH?<?–CH₃?<?–NH₂, due to greater ligand to metal charge transfer, which is well explained by energy decomposition analysis. It was also illustrated that E⁽²⁾ values of Lp(N)?→?σ*(Y–N) vary in the order P=O ? S=O ? C=O and the related values of Lp(N)?→?σ*(Y=O) change as C=O ? S=O ? P=O in (NH₂)_nYO ligands (Y?=?P, C, and S). Trends in the L–Ln³⁺ CP–corrected bond energies are in good accordance with the optimized O_Y?Ln distances. It seems that, comparing the three types of ligands studied, NH₂–substituted are the better coordination ligands.

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Graphical Abstract Density functional theory (B3LYP) calculations were used to compare structural, electronic and energy aspects of lanthanide (La, Eu, Lu) complexes of phosphine derivatives with those of carbonyls and sulfoxides in which the R– groups connected to the P=O, C=O and S=O are –NH₂, –CH₃, –OH and –F.

     

Performance evaluation of an integrated constructed wetland used to treat a contaminated aquatic environment

The treatment performance of an integrated constructed wetland (ICW) that was in operation for 3 years was evaluated. Artificial neural network modeling was used to predict contaminant treatment efficiencies based on easily measured field parameters. The estimates for average yearly removals of total phosphorus (TP), total nitrogen (TN), chemical oxygen demand (COD), and total suspended solids (TSS) were 0.81 ± 0.18, 7.17 ± 1.62, 63.80 ± 17.41, and 126.12 ± 48.61 g m^?2 d^?1, respectively. Removal velocities of contaminants were determined from analyses of inlet–outlet datasets. The areal removal rate constants were 0.46, 0.73, 0.44, and 0.82 m d^?1 for TP, TN, COD, and TSS, respectively. The presence of high background concentrations of contaminants (TP: 0.01 mg L^?1, TN: 0.13 mg L^?1, COD: 6.43 mg L^?1, TSS: 14.83 mg L^?1) indicated that the water in the ICW was mesotrophic. Statistical methods (i.e., principal component analysis (PCA), forward selection, and correlation analysis) were used to select optimal input subsets for different contaminants. These data subsets were subsequently used for model development. To find the optimal network architectures, a genetic algorithm was introduced to the learning processes. The models were competent at providing reasonable matches between the measured and the predicted effluent concentrations of TP (R² = 0.9711), TN (R² = 0.8875), COD (R² = 0.9359), and TSS (R² = 0.9164). The results of the models provided information that will be useful for the design and modification of constructed wetlands.     

One-stage partial nitritation/anammox at 15 °C on pretreated sewage: feasibility demonstration at lab-scale

Energy-positive sewage treatment can be achieved by implementation of oxygen-limited autotrophic nitrification/denitrification (OLAND) in the main water line, as the latter does not require organic carbon and therefore allows maximum energy recovery through anaerobic digestion of organics. To test the feasibility of mainstream OLAND, the effect of a gradual temperature decrease from 29 to 15 °C and a chemical oxygen demand (COD)/N increase from 0 to 2 was tested in an OLAND rotating biological contactor operating at 55–60 mg NH₄ ⁺–N?L^?1 and a hydraulic retention time of 1 h. Moreover, the effect of the operational conditions and feeding strategies on the reactor cycle balances, including NO and N₂O emissions were studied in detail. This study showed for the first time that total nitrogen removal rates of 0.5 g N?L^?1?day^?1 can be maintained when decreasing the temperature from 29 to 15 °C and when low nitrogen concentration and moderate COD levels are treated. Nitrite accumulation together with elevated NO and N₂O emissions (5 % of N load) were needed to favor anammox compared with nitratation at low free ammonia (<0.25 mg N?L^?1), low free nitrous acid (<0.9 μg N?L^?1), and higher DO levels (3–4 mg O₂?L^?1). Although the total nitrogen removal rates showed potential, the accumulation of nitrite and nitrate resulted in lower nitrogen removal efficiencies (around 40 %), which should be improved in the future. Moreover, a balance should be found in the future between the increased NO and N₂O emissions and a decreased energy consumption to justify OLAND mainstream treatment.     

Chemical oxygen demand,nitrogen and phosphorus removal by subsurface wetlands with Phragmites vegetation in different models

To improve the removal efficiency of subsurface wetlands vegetated mainly by Phragmites, pilot‐scale gravel‐based wetlands were used to treat sewage characterized by chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) pollution. For Phragmites vegetation, COD, TP and TN removal loads of wetland vegetation with Phragmites australis–Typha angustata–Scirpus validus as main species reached 0.517 g m^?2 d^?1, 0.277 g P m^?2 d^?1 and 0.023 g N m^?2 d^?1. The COD removal loads in pilot‐scale and medium‐scale (260 m² in area) wetlands with Phragmites‐monoculture vegetation were 0.62–0.64 g m^?2 d^?1, while that of P. australis–T. angustata–S. validus wetland reached 0.974 g m^?2 d^?1. Thus, the preferable poly‐culture model for Phragmites wetland vegetation was P. australis, T. angustata, S. validus and Zizania latifolia with stem density ratio of 8:1:5:1. After harvest, nitrogen and phosphorus standing stocks of wetland vegetations ranged only 2.2–9.93 g N m^?2 and 5.39–13.5 g P m^?2, respectively, as both the above ground biomass and the nitrogen and phosphorus contents of the wetland vegetation harvested in late autumn were low.     

Partial nitrification and nutrient removal in intermittently aerated sequencing batch reactors treating separated digestate liquid after anaerobic digestion of pig manure

The performance of an intermittently aerated sequencing batch reactor (IASBR) technology was investigated in achieving partial nitrification, organic matter removal and nitrogen removal from separated digestate liquid after anaerobic digestion of pig manure. The wastewater had chemical oxygen demand (COD) concentrations of 11,540 ± 860 mg/L, 5-day biochemical oxygen demand (BOD₅) concentrations of 2,900 ± 200 mg/L and total nitrogen (TN) concentrations of 4,041 ± 59 mg/L, with low COD:N ratios (2.9) and BOD₅:COD ratios (0.25). Synthetic wastewater, simulating the separated digestate liquid with similar COD and nitrogen concentrations but BOD₅ of 11,500 ± 100 mg/L, was also treated using the IASBR technology. At a mean organic loading rate of 1.15 kg COD/(m³ d) and a nitrogen loading rate of 0.38 kg N/(m³ d), the COD removal efficiency was 89.8% in the IASBR (IASBR-1) treating digestate liquid and 99% in the IASBR (IASBR-2) treating synthetic wastewater. The IASBR-1 effluent COD was mainly due to inert organic matter and can be further reduced to less than 40 mg/L through coagulation. The partial nitrification efficiency of 71–79% was achieved in the two IASBRs and one cause for the stable long-term partial nitrification was the intermittent aeration strategy. Nitrogen removal efficiencies were 76.5 and 97% in IASBR-1 and IASBR-2, respectively. The high nitrogen removal efficiencies show that the IASBR technology is a promising technology for nitrogen removal from low COD:N ratio wastewaters. The nitrogen balance analysis shows that 59.4 and 74.3% of nitrogen removed was via heterotrophic denitrification in the non-aeration periods in IASBR-1 and IASBR-2, respectively.     

Simultaneous energy recovery and autotrophic nitrogen removal from sewage at moderately low temperatures

This study assessed the technical feasibility of treating sewage with a combination of direct anaerobic treatment and autotrophic nitrogen removal, while simultaneously achieving energy recovery and nitrogen removal under moderately low temperatures. The concentrations of ammonia, nitrite, and COD in effluent were below 1, 0.1, and 30 mg/L, respectively. In the up-flow, anaerobic sludge fixed-bed, there was no obvious change observed in the total methane production at temperatures of 35?±?1 °C, 28?±?1 °C, 24?±?3 °C, and 17?±?3 °C, with the accumulation of volatile fatty acids occurring with decreasing temperatures. The control strategy employed in this study achieved a stable effluent with equimolar concentrations of nitrite and ammonium, coupled with high nitrite accumulation (>97 %) in the partial nitrification sequencing batch reactor system at moderately low temperatures. In the anaerobic ammonium oxidation (anammox) reactor, a short hydraulic retention time of 0.96 h, with a nitrogen removal rate of 0.83 kgN/(m³/day) was achieved at 12–15 °C. At low temperatures, the corresponding fluorescence in situ hybridization image revealed a high amount of anammox bacteria. This study demonstrates that efficient nitrogen removal and energy recovery from sewage at moderately low temperatures can be achieved by utilizing a combined system. Additionally, this system has the potential to become energy-neutral or even energy-producing.     

A comparative study of surface and subsurface flow constructed wetlands for treatment of combined sewer overflows: A greenhouse experiment

The use of surface flow (SFCWs) and subsurface flow constructed wetlands (SFCWs) for the treatment of combined sewer overflows was assessed at pilot scale. Synthetic wastewater was applied in three batches with decreasing concentrations to mimic concentration profiles that are obtained in the field during overflow events. Three simulated combined sewer overflows were applied on each wetland. Composite water samples (60 in total) were taken for a period of 8 days to study the removal of total nitrogen (Ntot), NH₄–N, NO₃–N, total COD (CODtot) and total phosphorus. Redox potential, which was monitored at various locations along the wetlands, was more negative in the SSFCWs. In general, removal occurred faster in the SSFCWs and the final concentrations were lower. The removal of Ntot was only 36.6 ± 3.3% in the SFCWs due to nitrification-limiting conditions. The conditions in the SSFCWs, in contrast, seemed to promote Ntot removal (removal efficiency 96.7 ± 1.9%). The removal of P was hampered in both wetland types by reducing conditions. P that was initially removed was released again from the substrates later on. First-order removal rate constants were derived for the removal of both CODtot (SSFCWs: 1.1 ± 0.3 m d^?1; SFCWs: 0.17 ± 0.06 m d^?1) and Ntot (SSFCWs: 0.4 ± 0.1 m d^?1; SFCWs: 1.7 ± 0.5 m d^?1).