Huijuan Li

Syntrophic interaction occurs during anaerobic fermentation of organic substances forming methane as the final product. H2 and formate are known to serve as the electron carriers in this process. Recently, it has been shown that direct interspecies electron transfer (DIET) occurs for syntrophic CH4 production from ethanol and acetate. Here, we constructed paddy soil enrichments to determine the involvement of DIET in syntrophic butyrate oxidation and CH4 production. The results showed that CH4 production was significantly accelerated in the presence of nanoFe3 O4 in all continuous transfers. This acceleration increased with the increase of nanoFe3 O4 concentration but was dismissed when Fe3 O4 was coated with silica that insulated the mineral from electrical conduction. NanoFe3 O4 particles were found closely attached to the cell surfaces of different morphology, thus bridging cell connections. Molecular approaches, including DNA-based stable isotope probing, revealed that the bacterial Syntrophomonadaceae and Geobacteraceae, and the archaeal Methanosarcinaceae, Methanocellales and Methanobacteriales, were involved in the syntrophic butyrate oxidation and CH4 production. Among them, the growth of Geobacteraceae strictly relied on the presence of nanoFe3 O4 and its electrical conductivity in particular. Other organisms, except Methanobacteriales, were present in enrichments regardless of nanoFe3 O4 amendment. Collectively, our study demonstrated that the nanoFe3 O4 -facilitated DIET occurred in syntrophic CH4 production from butyrate, and Geobacter species played the key role in this process in the paddy soil enrichments.

Direct or indirect exposure to inorganic arsenic (iAs) in the forms of AsIII (arsenite) and AsV (arsenate) through consumption of As-contaminated food materials and drinking water leads to arsenic poisoning. Rice (Oryza sativa L.) plant potentially accumulates a high amount of iAs from paddy fields than any other cereal crops. This makes it to be a major source of iAs especially among the population that uses it as their dominant source of diet. The accumulation of As in human bodies poses a serious global health risk to the human population. Various conventional methods have been applied to reduce the arsenic accumulation in rice plant. However, the success rate of these techniques is low. Therefore, the development of efficient and effective methods aimed at lowering iAs toxicity is a very crucial public concern. With the current advancement in technology, new strategies aimed at addressing this concern are being developed and utilized in various parts of the world. In this review, we discuss the recent advances in the management of iAs in rice plants emphasizing the use of nanotechnology and biotechnology approaches. Also, the prospects and challenges facing these approaches are described.

Revealing the role of engineered surface oxygen vacancies in the catalytic degradation of volatile organic compounds (VOCs) is of importance for the development of highly efficient catalysts. However, because of various structures of VOC molecules, the role of surface oxygen vacancies in different catalytic reactions remains ambiguous. Herein, a defective Pt/TiO2–x catalyst is proposed to uncover the different catalytic mechanisms of C3H6 and C3H8 combustion via experiments and theoretical calculations. The electron transfer, originated from the oxygen vacancy, facilitates the formation of reduced Pt0 species and simultaneously interfacial chemisorbed O2, thus promoting the C3H6 combustion via efficient C═C cleavage. The reduced Pt nanoparticles facilitate the robust chemisorption of bridging dimer O22– (Pt–O–O–Ti) species. This chemisorbed oxygen inhibits the C3H8 combustion by depressing C3H8 adsorption. This work offers insights for the rational design of highly efficient catalysts for activating the C═C bond in alkene or C–H bond in alkane.

Oxidation of ammonium to nitrite rather than nitrate, i.e., nitritation, is critical for autotrophic nitrogen removal. This study demonstrates a robust nitritation process in treating low-strength wastewater, obtained from a mixture of real mainstream sewage with sidestream anaerobic digestion liquor. This is achieved through cultivating acid-tolerant ammonia-oxidizing bacteria (AOB) in a laboratory nitrifying bioreactor at pH 4.5–5.0. It was shown that nitrite accumulation with a high NO2–/(NO2– + NO3–) ratio of 95 ± 5% was stably maintained for more than 300 days, and the obtained volumetric NH4+ removal rate (i.e., 188 ± 14 mg N L–1 d–1) was practically useful. 16S rRNA gene sequencing analyses indicated the dominance of new AOB, “Candidatus Nitrosoglobus,” in the nitrifying guild (i.e., 1.90 ± 0.08% in the total community), with the disappearance of typical activated sludge nitrifying microorganisms, including Nitrosomonas, Nitrospira, and Nitrobacter. This is the first identification of Ca. Nitrosoglobus as key ammonia oxidizers in a wastewater treatment system. It was found that Ca. Nitrosoglobus can tolerate low pH (<5.0), and free nitrous acid (FNA) at levels that inhibit AOB and nitrite-oxidizing bacteria (NOB) commonly found in wastewater treatment processes. The in situ inhibition of NOB leads to accumulation of nitrite (NO2–), which along with protons (H+) also produced in ammonium oxidation generates and sustains FNA at 3.0 ± 1.4 mg HNO2-N L–1. As such, robust PN was achieved under acidic conditions, with a complete absence of NOB. Compared to previous nitritation systems, this acidic nitritation process is featured by a higher nitric oxide (NO) but a lower nitrous oxide (N2O) emission level, with the emission factors estimated at 1.57 ± 0.08 and 0.57 ± 0.03%, respectively, of influent ammonium nitrogen load.