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.

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.

Formation of trihalomethanes in swimming pool waters using sodium dichloroisocyanurate as an alternative disinfectant.

Disinfection is essential to preventing infection caused by microbial pathogens in swimming pool water. The most commonly used disinfection methods are chlorine disinfectant, including sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (SDIC, C3O3N3Cl2Na) with characteristics of available chlorine formation and stability. In this study, we estimate the formation of trihalomethanes (THM4) in indoor swimming pools filled with seawater that adopt these disinfection methods, and we investigated the factors influencing the formation of THM4. Formation of THM4 by free chlorine (FC) and SDIC respectively is 327.8 µg L-1 and 307.6 µg L-1; Br-THMs is 226.7 µg L-1 for FC, 198 µg L-1 for SDIC. SDIC has less THM4 formation than FC in the same molar Br- dosage (10 µM) and total chlorine dosage (20 µM), and bromoform is the main Br-THMs species. The occurrence of THM4 is inhibited at high dosages of natural organic matter and Br-. The total Br-THMs increase from 75 µg L-1 to 189.7 µg L-1 and from 64.6 µg L-1 to 190 µg L-1 by FC and SDIC at pH 5.0-9.0, both of which are highly dependent on pH. In real water, similar results were found in Br--containing water (1 mg-Br- L-1).

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.

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.

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.

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.

Effective abatement of 29 pesticides in full-scale advanced treatment processes of drinking water: From concentration to human exposure risk.

This study investigated the occurrence and removal of 29 pesticides in 4 drinking water treatment plants (DWTPs) with conventional and advanced treatment processes (i.e., ozonation + biological activated carbon, and ultrafiltration) in Shanghai, China from 2018 to 2019. The concentration levels of target pesticides in raw waters ranged from below the limit of quantification (

Accelerated oxidation of iopamidol by ozone/peroxymonosulfate (O3/PMS) process: Kinetics, mechanism, and simultaneous reduction of iodinated disinfection by-product formation potential.

Iopamidol (IPM) is a potential source of toxic iodinated byproducts (I-DBPs) during water disinfection. In this work, we determined the kinetics and mechanism of degradation of IPM by a combination of ozone (O3) and peroxymonosulfate (PMS, HSO5-), and assessed its effect on the formation of iodinated trihalomethanes (I-THMs) during chlorination treatment. The degradation of IPM was accelerated by the O3/PMS process, and the hydroxyl (HO•) and sulfate (SO4•-) radicals were major contributors to the degradation. Using identification of the second order reaction rate between SO4•- and IPM (kSO4•-, IPM = 1.6 × 109 M-1 s-1), the contribution of HO• to the degradation was determined to be 78.3%. The degradation of IPM was facilitated by pH > 7, and natural organic matter (NOM) and alkalinity had limited effects on the degradation of IPM in the O3/PMS process. The transformation products of IPM were determined and inferred by QTOF-MS/MS, and the degradation pathways were elucidated. These include amide hydrolysis, amino oxidation, hydrogen abstraction, deiodination, and hydroxyl radical addition. Interestingly, oxidation of IPM by O3/PMS also decreased its potential for formation of I-THMs. After oxidation of IPM, the I-THMs formed from 5-µΜ IPM decreased from 14.7 µg L-1 to 3.3 µg L-1 during chlorination. Although the presence of NOM provided the precursor of I-THMs during chlorination of IPM, the O3/PMS process decreased I-THMs formation by 71%, because oxidation of released iodide into iodate effectively inhibited I-THMs formation. This study provides a new approach for the accelerated degradation of IPM and control of the formation of I-DBPs.

Occurrences of 29 pesticides in the Huangpu River, China: Highest ecological risk identified in Shanghai metropolitan area.

To investigate the occurrence and risk of pesticides in the Huangpu River basin, spatial and temporal concentration variations of 29 commonly used pesticides and their risk quotient (RQ) values for three different trophic organisms (fish, daphnia, green algae) from 16 sampling sites were conducted in 2018-2019. These 29 pesticides include 4 carbamates, 2 benzimidazoles, 6 neonicotinoids, 2 organophosphates, 9 triazoles, and 6 others. Of the 29 pesticides analyzed, 18 were present in every sample taken from the Huangpu River. The concentration of target pesticides in water samples ranged from < LOQ (for buprofezin in summer, autumn, and winter) to 607.30 ng L-1 (for carbendazim in spring). From the source (i.e., Taihu Lake) to the estuary of the Huangpu River, with the exception of isocarbophos and isoprothiolane (gradual decrease), the spatial variation of target pesticide concentrations firstly exhibited an increasing trend and then a decreasing trend. Peak spatial variation was seen in metropolitan area, which is closely related to the type of land use and the discharge of tributaries. In addition, the total summed concentration of the 29 pesticides during winter (1037.60 ng L-1) was higher than summer (788.82 ng L-1) in rural and metropolitan areas. For the ecological risk assessments of fish, daphnia, and green algae, the triazoles, carbamates, neonicotinoids were risk-dominant pesticides, respectively. Notably, carbendazim had a 100% detection frequency and the highest concentration of the 29 pesticides analyzed, indicating its high consumption in the Huangpu River basin.