Synthesis of bifunctional NiFe layered double hydroxides (LDH)/Mo-doped g-C3N4 electrocatalyst for efficient methanol oxidation and seawater splitting.

To boost the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) of pristine NiFe-layered double hydroxides (LDH), the NiFe-LDH/Mo-doped graphitic carbon nitride (NiFe-LDH/MoCN) heterojunction was synthesized herein through hydrothermal method. The establishment of built-in electric field in NiFe-LDH/MoCN heterojunction enhanced the electrochemical oxidation activities towards both seawater splitting and methanol oxidation, via the improving electrocatalyst surface wettability and conductivity. Almost 10-fold enhancement of turnover frequency (TOF) and electrochemical active surface area (ECSA) than pure NiFe-LDH implied more active sites to participate in catalytic reactions via Mo doping and the formation of heterostructure. Moreover, the local charge redistribution demonstrated in the NiFe-LDH/MoCN interface region may favor the adsorption of methanol and OH- in the seawater. The present work may expound the strong coupling interaction and the establishment of built-in electric field in the interface between NiFe-LDH and semiconductor to enhance both methanol oxidation and seawater oxidation for NiFe-LDH.

Revealing the mechanisms of polypyrrole (Ppy) enhancing methane production from anaerobic digestion of waste activated sludge (WAS).

Anaerobic digestion (AD) is a promising method for treating waste activated sludge (WAS), but the low methane yield limits its large-scale application. The addition of conductive nanomaterials has been demonstrated to enhance the activity of AD via promoting the direct interspecies electron transfer (DIET). In this study, novel conductive polypyrrole (Ppy) was prepared to effectively improve the AD performance of WAS. The results showed that the accumulative methane production was enhanced by 27.83% by Ppy, with both acidogenesis and methanogenesis being efficiently accelerated. The microbial community analysis indicated that the abundance of bacteria associated with acidogenesis process was significantly elevated by Ppy. Further investigation by metatranscriptomics revealed that fadE and fadN genes (to express the key enzymes in fatty acid metabolism) were highly expressed in the Ppy-driven AD, suggesting that Ppy promoted electron generation during acid production. For methanogenesis metabolism, genes related to acetate utilization and CO2 utilization methanogenesis were also up-regulated by Ppy, illustrating that Ppy facilitates the utilization of acetate and electrons by methanogenic archaea, thus potentially promoting the methanogenesis through DIET.

Enhanced photodegradation of doxycycline (DOX) in the sustainable NiFe2O4/MWCNTs/BiOI system under UV light irradiation.

In this study, a magnetic NiFe2O4/MWCNTs/BiOI composite were fabricated and applied for enhanced and sustainable photocatalytic degradation of doxycycline (DOX) under UV light irradiation. The as-synthesized material was characterized by a series of techniques and its photocatalytic property was assessed via a couple of batch tests. With the pH at 3.0 and NiFe2O4/MWCNTs/BiOI loading of 1.5 g L-1, the DOX degradation (at 45 mg L-1) efficiency could achieve 92.18% with the reaction rate constant k of 0.0072 min-1. The high mineralization of DOX suggests the strong oxidation of both the parent pollutant and the intermediary products in the ternary catalyst system. DRS spectra indicated that compared with BiOI, the introduction of NiFe2O4 and MWCNTs reduces the band gap energy of the NiFe2O4/MWCNTs/BiOI. The quenching test illustrates that h+, OH and O2- all functioned in the developed photocatalytic system, where O2- and h+ play the dominant roles in DOX degradation. The more efficient electron-h+ separation and more oxidizing species induced by UV light resulted in the significant improvement of DOX abatement in the developed coupling system compared with that on either BiOI or NiFe2O4/MWCNTs. The magnetic property of NiFe2O4/MWCNTs/BiOI enables its easy separation of the solid catalyst from the reaction solution and the sustainable application in the photocatalysis. Based on the intermediates of DOX decomposition identified by UPLC-MS, the possible degradation routes were proposed accordingly.

Achieving rapid thiosulfate-driven denitrification (TDD) in a granular sludge system.

Sulfur-oxidizing bacteria (SOB) can drive a high level of autotrophic denitrification (AD) activity with thiosulfate (S2O32-) as the electron donor. However, the slow growth of SOB results in a low biomass concentration in the AD reactor and unsatisfactory biological nitrogen removal (BNR). In this study, our goal was to establish a high-rate thiosulfate-driven denitrification (TDD) system via sludge granulation. Granular sludge was successfully cultivated by increasing the nitrogen loading rate stepwise in thiosulfate-oxidizing/nitrate-reducing conditions in an upflow anaerobic blanket reactor. In the mature-granular-sludge reactor, a nitrate removal rate of 280 mg N/L/h was achieved with a nitrate removal efficiency of 97.7%±1.0% at a hydraulic retention time of only 15 minutes, with no nitrite detected in the effluent. Extracellular polymeric substance (EPS) analysis indicated that the proteins in loosely bound and tightly bound EPS were responsible for maintaining the compact structure of the TDD granular sludge. The dynamics of the microbial-community shift were identified by 16S rRNA high-throughput pyrosequencing analysis. The Sulfurimonas genus was found to be enriched at 74.1% of total community and may play the most critical role in the high-rate BNR. The batch assay results reveal that no nitrite accumulation occurred during nitrate reduction because the nitrate reduction rate (75.90±0.67 mg N/g MLVSS/h) was almost equal to the nitrite reduction rate (66.06±1.28 mg N/g MLVSS/h) in the thiosulfate-driven granular sludge reactor. The results of this study provide support for the establishment of a high-rate BNR system that maintains its stability with a low sludge yield.

Thiosulfate as the electron acceptor in Sulfur Bioconversion-Associated Process (SBAP) for sewage treatment.

The sulfur bioconversion-associated processes (SBAP) for sewage treatment have been extensively reported so far. In this study, biological thiosulfate reduction (BTR)-driven biotechnology for high rate sulfidogenesis and organic removal was explored to further close the gap of our knowledge on the sulfur cycle-based sewage treatment bioprocess. With thiosulfate as the electron acceptor, the sulfidogenic rate in the UASB rector is 105.6 mg S/L/h with the sludge yield of only 0.044 g MLVSS/g CODsubstrate. Thus providing sufficient electron donors or chemical sources (i.e. HS-) for the downstream autotrophic denitrification or for the cost-effective heavy metal precipitation. Thiosulfate disproportionation was not observed in BTR reactor. High-throughput pyrosequencing analysis reveals that Desulfobulbus and Desulfomicrobium are the predominant thiosulfate-reducing genera and the thiosulfate disproportionation-bacteria were at much lower genus level. The specific thiosulfate-reducer i.e. Dethiosulfatibacter which could utilize thiosulfate but not sulfate as the electron acceptor was also identified. Batch testing results indicate that the sulfidogenic activity on thiosulfate was 1.5 times that on sulfate. The optimal pH for BTR activity was between 7.0 and 8.0, a typical pH range of the municipal sewage. Thiosulfate can be efficiently recovered in the sulfide-driven denitritation reactor enriched with abundant sulfide-oxidizing genera (mainly including Thiobacillus and Sulfurimonas). Finally, a conceptual model of the sulfur cycle based on the biotransformation between thiosulfate and sulfide was established, offering new insights into the sustainable SBAP with sludge minimization.