Uncovering interactions among ternary electron donors of organic carbon source, thiosulfate and Fe0 in mixotrophic advanced denitrification: Proof of concept from simulated to authentic secondary effluent.

To offset the imperfections of higher cost and emission of CO2 greenhouse gas in heterotrophic denitrification (HDN) as well as longer start-up time in autotrophic denitrification (ADN), we synergized the potential ternary electron donors of organic carbon source, thiosulfate and zero-valent iron (Fe0) to achieve efficient mixotrophic denitrification (MDN) of oligotrophic secondary effluent. When the influent chemical oxygen demand to nitrogen (COD/N) ratio ascended gradually in the batch operation with sufficient sulfur to nitrogen (S/N) ratio, the MDN with thiosulfate and Fe0 added achieved the highest TN removal for treating simulated and authentic secondary effluents. The external carbon is imperative for initiating MDN, while thiosulfate is indispensable for promoting TN removal efficiency. Although Fe0 hardly donated electrons for denitrification, the suitable circumneutral environment for denitrification was implemented by OH- released from Fe0 corrosion, which neutralized H+generated during thiosulfate-driven ADN. Meanwhile, Fe0 corrosion consumed the dissolved oxygen (DO) and created the low DO environment suitable for anoxic denitrification. This process was further confirmed by the continuous flow operation for treating authentic secondary effluent. The TN removal efficiency achieved its maximum under the combination condition of influent COD/N ratio of 3.1-3.5 and S/N ratio of 2.0-2.1. Whether in batch or continuous flow operation, the coordination of thiosulfate and Fe0 maintained the dominance of Thiobacillus for ADN, with the dominant heterotrophic denitrifiers (e.g., Plasticicumulans, Terrimonas, Rhodanobacter and KD4-96) coexisting in MDN system. The interaction insights of ternary electron donors in MDN established a pathway for realizing high-efficiency nitrogen removal of secondary effluent.

An Oxidant-Free and Mild Strategy for Quinazolin-4(3H)-One Synthesis via CuAAC/Ring Cleavage Reaction.

An oxidant-free and highly efficient synthesis of phenolic quinazolin-4(3H)-ones was achieved by simply stirring a mixture of 2-aminobenzamides, sulfonyl azides, and terminal alkynes. The intermediate N-sulfonylketenimine underwent two nucleophilic additions and the sulfonyl group eliminated through the power of aromatization. The natural product 2-(4-hydroxybenzyl)quinazolin-4(3H)-one can be synthesized on a large scale under mild conditions with this method.

Organic carbon source excites extracellular polymeric substances to boost Fe0-mediated autotrophic denitrification in mixotrophic system.

Fe0-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe0 corrosion. The mixotrophic denitrification (MDN) coupling Fe0-mediated ADN with heterotrophic denitrification (HDN) can circumvent the weakening of Fe0-mediated ADN over operation time. But the interaction between HDN and Fe0-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO3--N ratio increased from 0.0 to 1.8-2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe0-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO3--N removal significantly, while accelerated the electron release originating from Fe0 corrosion. The bioorganic-Fe complexes were generated on Fe0 surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe0-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe0-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.

Discovering dominant ammonia assimilation: Implication for high-strength nitrogen removal in full scale biological treatment of landfill leachate.

Landfill leachate containing high-strength nitrogen is generated in domestic waste landfilling. The integration of anoxic and aerobic process (AO) based on nitrification and denitrification, has been a mainstream process of biological nitrogen removal (BNR). But the high-strength organics as well as aerobic effluent reflux might change the biochemical environment designed and operated as AO. In view of the nitrogen balance in a full scale landfill leachate treatment plant with two-stage AO, we found that approximately 90% removal of total nitrogen (TN) and ammonia (NH4+-N) focused on primary anoxic and aerobic stage. Meanwhile, the less nitrate and nitrite in the aerobic effluent were incapable of sustaining denitrification or anaerobic ammonia oxidation (anammox). The high reflux flow from aerobic to anoxic process enabled the similar microbial community and functional genes in anoxic and aerobic process units. However, the functional genes involving ammonia assimilation in all process units showcased the highest abundance compared to those correlated with other BNR pathways, including nitrification and denitrification, assimilatory and dissimilatory nitrate reduction, nitrogen fixation and anammox. The ammonia assimilation dominated the removals of TN and NH4+-N, rather than other BNR mechanism. The insight of dominant ammonia assimilation is favorable for illustrating the authentic BNR mechanism of landfill leachate in AO, thereby guiding the optimization of engineering design and operation.

Recycling sludge-derived hydrochar to facilitate advanced denitrification of secondary effluent: Role of extracellular electron transfer.

Sludge-derived hydrochar (SDHC) was recycled to enhance the denitrification of secondary effluent. Under different carbon to nitrogen (C/N) ratios, the nitrogen removal efficiency (NRE) and carbon source efficiency (CSE) of denitrification coupled with SDHC (DN-SDHC) were distinctly higher than that of denitrification alone (DN). Moreover, at the C/N ratios of 3.0-3.2 and 5.8-5.9, the nitrogen removal rate (NRR) of DN-SDHC was 3.6- and 1.5-fold that of DN, respectively. The characterization of SDHC before and after used in denitrification indicated that the metal ions and functional groups did not participate in denitrification. Although SDHC has no redox capacity to donate electron for denitrification, its higher conductivity enabled the acceleration of extracellular electron transfer from carbon source to denitrifiers. The abundance of denitrifying community and functional genes was synchronously promoted by SDHC. Especially, the significant increase of nosZ gene encoding nitrous oxide reductase was conducive to mitigating the emission of N2O greenhouse gas.

Influence of cell lysis by Fenton oxidation on cryptic growth in sequencing batch reactor (SBR): Implication of reducing sludge source discharge.

The cell lysis-cryptic growth was implemented by Fenton oxidation in sequencing batch reactor. Optimizing sludge lysis condition could maximize the release of nutrients and sludge disintegration degree. After Fenton oxidation, the extracellular polymeric substance was obviously destroyed with the sludge average particle decreased from 64 µm to 36 µm. After 5% of the settled sludge in sequencing batch reactor (SBR) was oxidized by Fenton and then returned to SBR, the mixed liquor suspended solids (MLSS) decreased by 19.3% at the end of 35 days operation, the average mixed liquor volatile suspended solids/mixed liquor suspended solids (MLVSS/MLSS) was promoted by 13.3% during the entire operation. Returning lysed sludge had no significant influence on the organics and nitrogen removal, but the total phosphorus removal was distinctly enhanced by generating FePO4 precipitate. Additionally, returning lysed sludge suppressed nitrifying bacteria and promoted denitrifying bacteria slightly. Consequently, the cell lysis-cryptic growth for reducing sludge source discharge from wastewater biological treatment could be achieved on the premise of ensuring effluent quality.

Performance of diatomite/iron oxide modified nonwoven membrane used in membrane bioreactor process for wastewater reclamation.

This study describes an approach for surface modification of a nonwoven membrane by diatomite/iron oxide to examine its filterability. Analysis results showed that nonwoven hydrophilicity is enhanced. Static contact angle decreases dramatically from 122.66° to 39.33°. Scanning electron micrograph images show that diatomite/iron oxide is attached on nonwoven fiber. X-ray diffraction analysis further proves that the compound is mostly magnetite. Fourier transformed infrared spectra results reveal that two new absorption peaks might be attributed to Si-O and Fe-O, respectively. Modified and original membranes were used in double nonwoven membrane bioreactors (MBRs) for synthetic wastewater treatment. High critical flux, long filtration time, slow trans-membrane pressure rise and stable sludge volume index confirmed the advantages of modified nonwoven. Comparing with original nonwoven, similar effluent qualities are achieved, meeting the requirements for wastewater reclamation.

[Relationship between mRNA expression of MnSOD and manganese neurotoxicity].

OBJECTIVE: To investigate the relationship between mRNA expression of manganese superoxide dismutase (MnSOD) and manganese neurotoxicity. METHODS: Thirty-one patients with occupational chronic manganese poisoning (case group), as well as 31 controls exposed to the same condition (control group), were included in the study. Whole blood RNA was extracted, and the mRNA expression of MnSOD was measured by RT-PCR; the two groups were compared in terms of the mRNA expression of MnSOD. PC12 cells were treated with 0, 100, 200, 400, 600, 800, and 1000 ümol/L MnCl2 for l, 2, 3, and 4 d; the cell viability was determined by MTT assay, and the mRNA expression of MnSOD was measured by RT-PCR. RESULTS: The case group had significantly lower mRNA expression of MnSOD than the control group (0.390 ± 0.080 vs 0.582 ± 0.219, P < 0.05). MnCl2 had a toxic effect on PC12 cells; the concentration of MnCl2 was positively correlated with the toxic effect but negatively correlated with the mRNA expression of MnSOD. CONCLUSION: MnSOD mRNA may be involved in the manganese-induced damage of nerve cells. It is hypothesized that high mRNA expression of MnSOD may play an inhibitory effect on manganese neurotoxicity.