Synthesis of amorphous-MnO2/Clinoptilolite and its utilization for NH4+-N oxidation in an anoxic environment.

Mediating the anoxic ammonia oxidation with manganese oxide (MnOx) can reduce the requirements of dissolved oxygen (DO) concentrations in constructed wetlands (CWs) and improve the removal of ammonium nitrogen (NH4+-N). Recent studies that employed natural manganese ore and/or mine waste as substrates in CWs may develop potentially negative environmental effects due to leachates. However, removing NH4+-N by anoxic ammonia oxidation is influenced by the crystal form of MnOx. In this study, a novel clinoptilolite-based amorphous-MnO2 (amorphous-MnO2/clinoptilolite) was synthesized by the sol-gel method as an alternative substrate to improve the efficiency of anoxic ammonia oxidation and reduce the impact of Mn ion leaching. According to the anoxic ammonia oxidation experiment of clinoptilolite, amorphous-MnO2/clinoptilolite, and manganese ore on NH4+-N, the amounts of NH4+-N removed were 24.55 mg/L/d, 44.55 mg/L/d, and 11.04 mg/L/d, respectively, and the initial NH4+-N concentration was 49.53 mg/L. These results indicated that the amorphous-MnO2/clinoptilolite had both the adsorption and the anoxic ammonia oxidation performance. The recycling experiment demonstrated that the effect of anoxic ammonia oxygen mediated by amorphous-MnO2 would not diminish with the gradual saturation of clinoptilolite for NH4+-N. Furthermore, the anoxic ammonia oxidation consumed NH4+-N in the clinoptilolite, which restored the adsorption capacity of the clinoptilolite and simultaneously decreased the leakage of manganese ions in the process, making it environmentally friendly. Therefore, the amorphous-MnO2/clinoptilolite provided an excellent substrate material for the constructed wetland under an anoxic environment, which greatly improved the nitrogen removal capacity compared to existing substrate materials.

Mn(VII) enhanced by CaSO3 to remove trace organic pollutants in high salt organic wastewater: Further enhancement of salinity.

The high concentration of salt in organic wastewater has a strong inhibitory effect on the removal of pollutants. A method for the efficient removal of trace pollutants in high-salinity organic wastewater was developed. This study investigated the effect of the combination of permanganate [Mn(VII)] and calcium sulfite [S(IV)] on pollutant removal in hypersaline wastewater. The Mn(VII)-CaSO3 system removed more pollutants from high-salinity organic wastewater than from normal-salinity wastewater. Chloride (increasing from 1 M to 5 M) and low concentration of sulfate (increasing from 0.05 M to 0.5 M) significantly enhanced the system's resistance to pollutants under neutral conditions. Despite the fact that Cl- can combine with the free radicals in the system and reduce their efficiency in removing pollutants, the presence of chloride ions greatly enhances the electron transfer rate in the system, promoting the conversion of Mn(VII) to Mn(III) and significantly increasing the reaction rate of Mn(III) as the primary active species. Therefore, chloride salts can greatly enhance the removal of organic pollutants by Mn(VII)-CaSO3. Although sulfate does not react with free radicals, a high concentration of sulfate (1 M) will affect the formation of Mn(III), which greatly weakens the removal effect of the entire system on pollutants. The system can still have a good pollutant removal effect with mixed salt. Altogether, this study demonstrates that the Mn(VII)-CaSO3 system offers new possibilities for the treatment of organic pollutants in hypersaline wastewater.

Pretreatment of septic tank wastewater by packed anaerobic baffled reactor: Pollutant degradation and microbial community succession in different compartments.

Anaerobic baffled reactor (ABR) is widely used in rural sewage treatment due to its unique structure, strong impact load resistance, and low energy consumption. However, there is a lack of research on pollutant degradation patterns and microbial community succession patterns in each compartment of ABR. In this study, a packed anaerobic baffled reactor (PABR) was constructed. The effects of T and HRT on the pollutant removal performance of PABR were investigated, and the pollutant degradation and microbial community succession in different compartments of PABR were studied. The results show that the removal rates of COD, NH4+-N, and TN of PABR can reach 85.54 ± 1.08%, 16.94 ± 1.01%, and 5.64 ± 1.18% respectively, and PABR has a good pollutant removal effect. With the extension of HRT, the COD removal rate of PABR increases steadily, and the NH4+-N and TN removal rate of PABR increases to a certain extent. The recommended HRT is 72 h. T has a significant impact on the COD removal effect of PABR. The increase of T in a certain range is conducive to the removal of pollutants by PABR. The COD removal rate of PABR decreases gradually along the flow direction, and the removal of organic matter is mainly concentrated in the first compartment. PABR has good removal capacity for CODss and better nitrogen removal capacity compared with traditional ABR. The richness and diversity of the microbial community in PABR increased gradually along the flow direction. The bacterial species in each compartment were similar but the proportion was different, showing the characteristics of multi-stage and separated phase operation. This study provides a new reference for the application of ABR in rural sewage treatment.

The importance of rest phase and pollutant removal mechanism of tidal flow constructed wetlands (TFCW) in rural grey water treatment.

This paper explored the effects of the rest phase of tidal flow constructed wetlands (TFCW) on pollutant removal and microbial communities, and further analyzed the mechanism of TFCW removal of pollutants from grey water. The results showed that the removal rate of organic matter was 69.91 ± 2.44% in the control group (NR-TFCW) without the rest phase, 94.95 ± 1.17% in the experimental group (TFCW), and 96.95 ± 2.43% in the control group (P-TFCW) with the ventilation pipe enhanced rest phase. Limiting and enhancing the oxygen supply in the emptying stage of TFCW will enhance the overlap rate of microorganisms in the upper, middle and lower layers of the reactor. Enhancing the rest phase of TFCW leaded to better aerobic removal of organic matter in the microbial community, while limiting the rest phase of TFCW results in the opposite. In addition, the species overlap rate of the top, middle and bottom layers of NR-TFCW (69.98%) and P-TFCW (54.29%) was higher than that of TFCW (11.34%). The removal of organic matter by TFCW mainly relied on the adsorption of biochar in the flood phase, and the microorganisms aerobic degraded the organic matter adsorbed on the biochar in the rest phase. And thus form a continuous cycle of adsorption and biological regeneration. The microbial community in TFCW did not have the ability to nitrify, but had the ability to remove phosphorus. Ammonia nitrogen in the influent was adsorbed by biochar or converted into cytoplasm. While the phosphorus in the influent was adsorbed by the biochar, it was also being biologically removed.

Effects of iron-based substrate on coupling of nitrification, aerobic denitrification and Fe(II) autotrophic denitrification in tidal flow constructed wetlands.

The aerobic properties of nitrification and the anaerobic properties of denitrification in constructed wetlands are difficult to reconcile. In this study, two constructed wetlands were constructed with pyrite and steel slag in combination with zeolite, and their respective nitrification and denitrification capacities were evaluated under different tidal strategies. The steel slag wetland achieved 70.89 % and 46.04 % removal rates of NH4+-N and total nitrogen (TN), and the carbon consumption of denitrification was 1.51 mg BOD/mgN, which was better than pyrite wetland. Microbial analysis showed that Fe(II) autotrophic denitrification and aerobic denitrification occurred in both wetlands, and they were coupled with nitrification to achieve simultaneous removal of NH4+-N and TN. Microbial co-occurrence network and k-core decomposition analysis indicated that the core genus of steel slag wetlands was nitrifying bacteria. This study provides new insights into the application of tidal flow wetlands to treat rural sewage.

Denitrification performance and characteristics of untreated corncob for enhanced nitrogen removal of municipal sewage with low C/N ratio.

Unpretreated corncob was applied in denitrification bio-filter (DNBF) and anoxic tank of AAO system, respectively, to treat sewage with low C/N ratio, and both two approaches achieved good denitrification performance. Although shorter HRT could effectively decrease effluent chroma and COD of corncob-DNBF, nitrogen removal efficiency declined unexpectedly. Higher internal reflux ratio was beneficial for corncob-AAO without damage to anoxic environment for denitrification, while there was no risk of effluent chroma and excessive COD. Different supplement modes could realize same denitrification effect with distinct advantages, which were higher specific denitrification rate and biomass amount, respectively. The latter mode, applying corncob at secondary treatment, was preferable for its operational stability and convenience. Stoichiometry analysis indicated the unit COD demand of AAO decreased from 5.70 to 5.04 g COD/g N after adding corncob, and the oxygen demand (or energy consumption of aeration) decreased as well. The dominant substrates decomposer in corncob-AAO altered to Kouleothrix (affiliated to phylum Chloroflexi), and the main denitrifying bacteria were unclassified_f__Methylophilaceae and Azospira. Accordingly, functional enzymes for degrading glucan, xylan and lignin and processing denitrification showed satisfying abundance in the integrated system, especially in the newly formed biofilm.

Enhancing ammonia oxidation mediated using different crystalline Mn-oxides in an anoxic environment.

A recent study found that the nitrogen cycle in marine sediments can occur under oxygen-limited conditions, and this is associated with a reduction of Mn (IV). However, the effect of MnO2 mediated anoxic ammonia oxidation in different sediments field test results are controversial. In this study, based on the fact that the crystal form and morphology of MnO2 in marine sediments are affected by geochemistry, α-, ß-, γ-MnO2 and amorphous MnO2 were prepared to explore the effect of the different MnO2 crystals on nitrogen removal under oxygen-limited conditions. The experimental results showed that the anoxic ammonia oxidation process was mediated by microorganisms, and the reaction was affected by pH and temperature. The optimal pH was 7 in the range of pH 4-9 and the optimal temperature was 25 °C in the range of 10 °C-40 °C. When the initial concentration of NH4+-N was 50 mg/L, the removal amounts of NH4+-N under an anoxic condition by α-, ß-, γ-MnO2 and amorphous MnO2 were 18.97 mg/L/d, 6.12 mg/L/d, 10.68 mg/L/d and 24.89 mg/L/d, respectively. During the anoxic oxidation between MnO2 and NH4+-N, the adsorption process occurred. In addition, the oxidation process produced both NOx--N (nitrification reaction) and gaseous nitrogen (ammonia oxidation reaction). The kinetic study showed that the NH4+-N removal process conformed to the pseudo-second-order rate model, and the removal rates were ranked as amorphous MnO2 > α- > Î³- > ß-MnO2. Together, these results showed that the amorphous MnO2 crystal structure was conducive to improve anoxic ammonia oxidation and nitrogen removal under oxygen-limited conditions.

Glycine- and Alanine-Intercalated Layered Double Hydroxides as Highly Efficient Adsorbents for Phosphate with Kinetic Advantages.

Phosphate is the main cause of eutrophication. Layered double hydroxides (LDH) are considered to be promising phosphate adsorbents due to their high affinity and large capacity. In this study, we partially intercalated zwitterionic glycine and alanine into Cl-LDH (corresponding to MgAl-LDH with interlayer anion Cl-) and synthesized efficient inorganic-organic nanohybrids for phosphate removal with kinetic advantages. Gly-Cl-LDH, Ala-Cl-LDH and Cl-LDH were characterized, and their phosphate adsorption performances under the influence of environment factors (e.g., solution pH, coexisting anions, contact time and phosphate concentration) were investigated. The results show that Gly-Cl-LDH and Ala-Cl-LDH had larger specific surface areas and larger interlayer spaces than Cl-LDH, and exhibited better adsorption performance at a lower pH and better adsorption selectivity against SO42-. Kinetic experiments indicated that Gly-Cl-LDH and Ala-Cl-LDH can reduce phosphate concentrations to a lower level in a shorter time. The pseudo-second-order kinetic constants of Gly-Cl-LDH and Ala-Cl-LDH were 1.27 times and 3.17 times of Cl-LDH, respectively (R2 > 0.996). The maximum adsorption capacities derived from a Langmuir model of Cl-LDH, Gly-Cl-LDH and Ala-Cl-LDH are 63.2 mg-P/L, 55.8 mg-P/L and 58.2 mg-P/L, respectively, which showed superiority over the prevailing phosphate adsorbents. This research provides highly efficient adsorbents for removing phosphate from aqueous solutions.

Denitrification performance and mechanism of denitrification biofilm reactor based on carbon-nitrate counter-diffusional.

This study researched denitrification performance and mechanism of denitrification biofilm reactor with different HRTs and carbon sources dosages. Experimental group (EG) had better nitrate and COD removal performance than control group (CG) with different HRTs or carbon doses, and the maximum nitrate-to-nitrite transformation ratio (NTR) of them reached 7.91 ± 1.60% and 17.50 ± 1.92%, respectively. Because organic carbon sources were added to the carrier's interior in EG, forming high local concentrations in biofilms and counter-diffusional with nitrate. By contrast, carbon sources and nitrate were provided from the aqueous phase in CG. Thus, the EG system has more active regions of the biofilm than CG. In addition, EG had higher proportions of microorganisms and enzymes related to denitrification and carbon metabolism. The most dominant phylum, genus, and species were Proteobacteria, Thaurea, and Thauera_sp._27, respectively. The transcript of acetyl-CoA synthetase (K01895) and denitrification (M00529) was mainly originated from unclassified_g__Pseudomonas and unclassified_g__Thauera, respectively.

Removal of micro organic pollutants in high salinity wastewater by comproportionation system of Fe(VI)/Fe(III): Enhancement of chloride and bicarbonate.

The high concentration of salt in industrial wastewater has a strong inhibitory effect on the removal of pollutants by free radicals. A method has been developed to effectively remove micro organic pollutants in industrial high-salinity wastewater. This study investigated the combination of ferrate(VI) (FeVIO42-, Fe(VI)) and Fe(III) on the reduction of the pollutants in synthetic high-salinity wastewater, while focusing on the effects of major inorganic substances. Whether in synthetic wastewater with or without salinity, Fe(VI)-Fe(III) process exhibited higher pollutants removal rates than Fe(VI). Both chloride (increasing from (2.2 ± 0.1) × 10-2 min-1 to (1.1 ± 0.03) × 10-1 min-1) and bicarbonate (increasing from (2.2 ± 0.1) × 10-2 min-1 to (1.1 ± 0.02) × 10-1 min-1) significantly enhanced the removal of pollutants by the Fe(VI)-Fe(III) process. Chloride changed the ionic strength of Fe(VI), but Fe(III) strengthened the formation of Fe(V)/Fe(IV) from FeO42-, which offset the effect of the decrease of HFeO4-. Bicarbonate complexed Fe(V)/Fe(IV), these complexes enhanced the oxidizing ability of Fe(V)/Fe(IV). Based on the Program Kintecus, Fe(IV) was proposed as the main iron species in Fe(VI)-Fe(III) system, and its concentration was 2 to 3 orders of magnitude higher than Fe(V) at pH 9.0. The enhancement of Fe(VI)-Fe(III) system was observed in the oxidation of pollutant in real wastewater. Overall, the Fe(VI)-Fe(III) process is a new option for treating organic pollutants in industrial high salinity wastewater.

Constructed wetlands for rural domestic wastewater treatment: A coupling of tidal strategy, in-situ bio-regeneration of zeolite and Fe(â ¡)-oxygen denitrification.

Constructed wetlands (CWs) offer a promising method to treat domestic wastewater in rural areas, but CWs usually limiting in nitrogen removal and large area. In this study, zeolite and pyrite were used to construct tidal wetlands to address the problems of insufficient oxygen supply and carbon source. The results show that the fully drained wetland achieved the highest ammonia removal load of 34.67 ± 1.72 g/(m2·d) with 8.57 ± 1.13 mg/L of effluent. Pyrite was found to compensate for the lack of carbon source in the denitrification process in half-drained wetland, which achieved a 78.36 ± 5.3% TN removal rate with 7.09 ± 1.85 mg/L effluent concentration. Pyrite released Fe(II) to promote nitrate reduction for denitrification in the subsequent flooded period. Microbial community analysis indicates that the tidal flow constructed wetlands simultaneously achieved nitrification and denitrification by the coupling of in-situ zeolite regeneration and Fe(II) oxidation denitrification.

Removal of diclofenac and oxytetracycline from synthetic urine by furfuryl alcohol-derived mesoporous carbon.

In this study, using furfuryl alcohol as the precursor carbon and mesoporous silica as the template, and furfuryl alcohol-derived mesoporous carbon (FMC) was prepared. The specific surface area of FMC was 1022.61 m2/g, the pore volume was 1.71 cm3/g, and the mesoporous volume was 98.8%. Based on the adsorption kinetics of pharmaceuticals onto the FMC in synthetic urine, equilibrium adsorption was reached in 120 min, and it followed a pseudo-second-order model. The adsorption isotherms were well-fitted by the Sips isotherm model, and the saturated adsorption capacities of diclofenac and oxytetracycline in fresh urine were 411.8 mg/g and 465.9 mg/g, respectively. Batch experiment results showed that pharmaceutical removal was strongly influenced by urine components such as sodium chloride, urea, and ammonium hydroxide. The adsorption of diclofenac and oxytetracycline was influenced by many factors including π-π interactions, hydrogen bonds, and electrostatic forces. FMC exhibited excellent reusability and retained urine nutrients during pharmaceutical adsorption.

The metabolic patterns of the complete nitrates removal in the biofilm denitrification systems supported by polymer and water-soluble carbon sources as the electron donors.

In this study, two denitrification bio-filters adopted polycaprolactone (PCL) and sodium acetate (NaAc) as polymer and water-soluble carbon sources respectively. With the increasing influent nitrate concentrations, NaAc bio-filter always had shorter HRT to achieve complete nitrate removal. Furthermore, the optimal volumetric denitrification rate in NaAc bio-filter was 0.728 g N/(L·d), which was higher than 0.561 g N/(L·d) in PCL bio-filter. For nitrates removal, the costs of bio-filters supported by NaAc and PCL were 24.93 and 120.25 CNY/kg N respectively. Although Proteobacteria in PCL bio-filter was abundant with 83.98%, NaAc bio-filter had better denitrification performance, due to the appropriate ratio of nitrate removal microorganisms and organic matters degradation organisms. The total abundance value of the denitrification genera is NaAc (16.06%) < PCL (41.19%). However, PCL bio-filter had poor denitrification performance, due to the lower adequacy of PCL depolymerization enzymes and the low expression of the key genes for denitrification.

Accelerated degradation of pharmaceuticals by ferrous ion/chlorine process: Roles of Fe(IV) and reactive chlorine species.

In this study, we determined the mechanisms and kinetics of the degradations of ibuprofen (IBP) and sulfamethoxazole (SMX), and identified the active species contributions in ferrous ion (Fe(II))/free chlorine (FC) system. Reactive chlorine species (RCS) were the major contributor to the degradations of IBP (73.0%) and SMX (59.3%), respectively, at pH 3. Due to the low reaction rates between Fe(IV) and target pollutants (kFe(IV), IBP = (1.5 ± 0.03) × 103 M-1 s-1 and kFe(IV), SMX = (4.8 ± 0.2) × 103 M-1 s-1) and the low [Fe(IV)]ss ((5.0 ± 0.6) × 10-8 M), Fe(IV) was not the main contributor and only contributed 0.17% and 0.86% to the degradation of IBP and SMX, respectively, at pH 3. The degradations of pharmaceuticals were facilitated by acidic conditions. Chloride (Cl-) accelerated the degradation of SMX and had a weak effect on the degradation of IBP. Natural organic matter limited the degradation of IBP and SMX. Overall, we demonstrated that multiple active oxidants (Fe(IV) and RCS) are produced by Fe(II)/FC and elucidated the mechanism of active oxidants degradation of pollutants.

Visible-to-UVC driven upconversion photocatalyst sterilization efficiency and mechanisms of ß-NaYF4: Pr3+, Li+@BiOCl with a core-shell structure.

UVC (wavelength < 280 nm) has a wide range of applications in the field of water disinfection due to its excellent bactericidal performance. In this work, we synthesized an upconversion luminescent material, ß-NaYF4: Pr3+, Li+ (NYF), which can generate UVC, and compounded it with a BiOCl photocatalyst to synthesize ß-NaYF4: Pr3+, Li+@BiOCl (NYF-Bi) with a core-shell structure. The NYF-Bi composite material can be driven under visible light and has high photocatalytic activity. The bactericidal performance of NYF and NYF-Bi were evaluated using Escherichia coli, Staphylococcus aureus, Shigella and Salmonella. The NYF-Bi composite material killed 99.99% of E. coli under visible light (λ ≥ 420 nm) within 180 min and maintained high germicidal efficacy after 4 cycles. Finally, we deduced the sterilization mechanism of the NYF-Bi composite material through carrier dynamics studies and catching agent experiments. The death of bacteria was mainly caused by UVC light and active species, including h+, OH, and O- 2. This research provides a new material for water disinfection.

First-Principle Insight Into the Effects of Oxygen Vacancies on the Electronic, Photocatalytic, and Optical Properties of Monoclinic BiVO4(001).

In this paper, first-principle calculations were performed to investigate the effects of oxygen (O) vacancies (Ovac) on the crystal structure, electronic distribution, adsorption energies of O2 and H2O and the density of states (DOS) of monoclinic bismuth vanadate (m-BiVO4). Ovac were stable when incorporated into m-BiVO4(001) and increased the adsorption energy of O2. Ovac changed the V3d orbitals of m-BiVO4(001) by adding a new band gap level, causing the redundant electrons of V atoms to become carriers and promoting the separation efficiency of electrons and holes. To verify the first-principle calculations, m-BiVO4 with different Ovac levels was prepared via hydrothermal synthesis. X-ray diffraction (XRD) patterns confirmed the existence of the (001) crystal surface of m-BiVO4. In addition, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectroscopy of m-BiVO4 confirmed the presence of Ovac and demonstrated that, as the Ovac level increased, the number of superoxide radicals ( O 2 - · ) and hydroxyl radicals (·OH) produced increased. In addition, m-BiVO4 with a higher Ovac level possessed superior photocatalytic properties to and degraded rhodamine B (RhB) dye nearly 2-fold faster than m-BiVO4 with a lower Ovac level. Finally, the removal rate of RhB increased from 23 to 44%. All experimental results were in good agreement with the first-principle calculated results.

Functional microorganisms and enzymes related nitrogen cycle in the biofilm performing simultaneous nitrification and denitrification.

Simultaneous nitrification and denitrification (SND) is a potential energy-saving process in wastewater treatment while the nitrogen removal mechanism is still unclear due to the lack of information about the functional microbes and enzymes. Sequencing batch biofilm reactors were implemented to achieve efficient SND. Eight nitrogen removal related microorganisms out of the top abundant 20 microbial community and reference species were used to construct a phylogenetic tree. Functional enzymes and modules analysis were investigated to reveal the SND pathway: in the aerobic part of the biofilm, ammonia oxidation was catalyzed by complete ammonia oxidizers while in the inner anoxic part, denitrification, dissimilatory nitrate reduction (DNRA) and nitrogen fixation (NF) cooperated to stimulate nitrate removal. These results provide a practical aeration control strategy to achieve SND and indicate that DNRA and NF are important nitrogen removal pathways that should not be ignored in the SND mechanism.

The influence mechanism of temperature on solid phase denitrification based on denitrification performance, carbon balance, and microbial analysis.

In this work, the influence mechanism of temperature on solid phase denitrification (SPD) was investigated using a pilot-scale reactor supported with polycaprolactone (PCL). The results showed that under nitrate loads of ~31.5 mg N/(L·h), as temperature decreased from 30 °C to 13 °C, the nitrate removal efficiency declined from 94% to 57%. Furthermore, denitrification rate constants were input into Arrhenius equation and the resulting temperature coefficient was 1.04. Significantly nitrite accumulation and less effluent COD residue occurred at low-temperatures. Via stoichiometry, the sludge yield coefficient and COD demand for nitrate removal both increased as a function of increasing temperature; and were calculated at 20 °C as 0.069 g MLVSS/(g COD·d) and 3.265 g COD/g N, respectively. Carbon balance analysis indicated that the COD release rate (υ) at 30 °C was twice that at 13 °C. LEfSe analysis demonstrated that Desulfomicrobium, Desulfovibrio, and Meganema were abundant at low-temperature, while Simplicispira, Aquabacterium, and Acidovorax were enriched at high-temperature. Besides, carboxylesterase (PCL depolymerase) was more abundant at high-temperature, implying an association with a fast υ. Moreover, nar was enriched at low-temperature, while nir was depleted, which led to nitrite accumulation. These results provide reference for SPD design parameter estimation and/or optimal operation strategy.

Denitrification performance and microbial diversity using starch-polycaprolactone blends as external solid carbon source and biofilm carriers for advanced treatment.

Enhanced nitrate removal from the secondary effluent in municipal wastewater treatment plants (WWTPs) is essential for avoiding water eutrophication. To this end, a vertical baffled solid-phase denitrification reactor (VBSDR) was developed using a starch and polycaprolactone (PCL) blend plate (S-PCL) as a carbon source and biofilm carrier. In this study, we evaluated the denitrification performance and microbial diversity of the VBSDR. The results of the Fourier transform infrared spectroscopy (FTIR), carbon leaching experiment, and scanning electron microscopy (SEM) demonstrated that the S-PCL structure can be attached and degraded more rapidly. Furthermore, the denitrification performance under varied operational conditions, i.e., influent nitrate loading rate (NLR) and operating temperature, was also investigated. Herein, when treating low C/N ratio and low-strength wastewater, a high denitrification rate (DR) [0.33 gN/(L·d)] was achieved. The effect of temperature on DR can be described by the Arrhenius-type equation, which shows that low temperature has a negative influence on DR and nitrate removal efficiency. Furthermore, DR was simultaneously affected by the NLR and temperature. The microbial diversity and community structure were determined by Illumina high-throughput sequencing. The special carbon source led to Acidovorax (denitrifying bacteria) and Flavobacterium (hydrolysis acidifying bacteria) being the VBSDR biofilm's most predominant functional bacteria at the genus level.

Developing the new kinetics model based on the adsorption process: From fitting to comparison and prediction.

In this study, an intrinsic kinetics model was proposed to simulate the adsorption process. The kinetics model was established based on the collision theory, where the available adsorption site and residual adsorbate concentration were considered. The model specifically highlights the significance of initial conditions in its equation. The initial reaction condition is expressed by the model parameter ξ, which includes four factors: concentration, volume, adsorbent dosage and adsorption capacity. The applicability of this model was mainly explored with the phosphate adsorption process by layered double hydroxides (LDH). Experimental results indicate that, at a certain initial condition, the intrinsic kinetics rate coefficient exhibits a superior stability, making the adsorption rate become comparable among different materials. On this basis, the kinetics rate coefficients of 60 materials were compared, and the LDH was proved to be advantageous in phosphate removal rate. Additionally, the intrinsic kinetics model was successfully applied to predict the phosphate adsorption kinetics under a wide range of initial conditions. The predicted concentration throughout the entire adsorption process is well consistent with the evolution of experimental data. This model is an effort to advance the kinetics analysis from fitting to comparison and prediction.