Search

Methanogens play an important role in global carbon cycle. There exists a range of unknown methanogenic archaea in acidic peat lands, among which, acidophilic methanogens have attracted increasing research interests because of their special metabolic characteristics. To introduce acidophilic methanogens in the anaerobic digestion process of high concentration organic wastes or waste water could essentially overcome the inhibition of acid accumulation on the methanogens and help reduce the operation cost, broadening the industrial application of anaerobic bio-treatment technology. In this paper, we reviewed the recent researches on acidophilic methanogens, with the focus on enrichment and isolation methods, physiological and biochemical characters, metabolic characteristics, and application of molecular biology. The potential applications of acidophilic methanogens in anaerobic digestion process were analyzed and proposed, and the directions for further researches were suggested. [ABSTRACT FROM AUTHOR]

Composting is an effective way to realize livestock manure treatment and recycling. However, the nitrogen loss during manure composting is relatively serious. Studies on this nitrogen loss and its control could provide theoretic bas is and practical reference for efficient nitrogen loss control. This paper described the nitrogen transformation and the main nitrogen loss ways during the composting, and summarized the main factors (including raw material characteristics, environment factors, and technological conditions) affecting the nitrogen loss in the composting. In addition, the research progress in the nitrogen loss control, including adjusting carbon and nitrogen metabolism, changing nitrogen form, adding ammonia adsorbent, and controlling pile aeration and temperature, was reviewed, and the prospects for future research were presented. [ABSTRACT FROM AUTHOR]

Schwertmannite is usually naturally found in acidic mining wastewater and frequently used in the adsorption of heavy metal anions from water and wastewater. Schwertmannite was synthesized through a facile chemical method and utilized to remove Cr(Ⅵ) from contaminated groundwater. The kinetics, thermodynamics and isotherms, as well as the effects of environmental factors on the Schwertmannite adsorption processes were investigated. The experimental results showed that the synthesized Schwertmannite had a strong adsorption capability of Cr(Ⅵ) from aqueous solution. At the pre-set initial concentrations of Cr(Ⅵ), the Schwertmannite adsorption of Cr(Ⅵ) achieved equilibrium within 24 h, and the Lagergren's second-order model fitted the adsorption process better compared to Lagergren's first-order model and intraparticle diffusion model. Langmiur equation fitted the adsorption isotherms better than Freundlich equation. The Cr(Ⅵ) adsorption on Schwertmannite mainly involved ion exchange reaction between Cr(Ⅵ) and anions such as OH - and SO 4 2- and surface complexation reactions. The Δ H θ and Δ G θ were 6.368 kJ·mol -1 and -1.215 kJ·mol -1 , respectively, therefore the adsorption of Cr(Ⅵ) was a spontaneous and endothermic process. The removal of Cr(Ⅵ) from aqueous solution increased with increasing Schwertmannite dosage at pH=4.5. Acidic pH in the range of 4.5-6 favored Cr(Ⅵ) removal with Schwertmannite compared to that under basic conditions. Under the conditions of 5 mg·L -1 of initial Cr(Ⅵ) concentration, 0.5 g·L -1 of Schwertmannite dosage, pH=6, maximum Cr(Ⅵ) removal of 93.1% was achieved and the adsorption capacity of Cr(Ⅵ) with Schwertmannite reached up to 40.4 mg·g -1 . Batch tests showed that the presence of HCO 3 - and SO 4 2- inhibited the adsorption of Cr(Ⅵ) while Cl - had no significant impact. Cations and natural organic matter had a pH-dependent impact on Cr(Ⅵ) removal:at pH=8 natural organic matter and cations would significantly inhibit the Cr(Ⅵ) sorption, while the impact could be neglected at weak acidic conditions (pH=6).

As the first step of nitrification, ammonia oxidation is the key process in global nitrogen biogeochemical cycling. So far, the autotrophic ammonia-oxidizing bacteria (AOB) in the beta- and gamma-subgroups of proteobacteria have been considered as the most important contributors to ammonia oxidation, but the recent researches indicated that ammonia-oxidizing archaea (AOA) are widely distributed in various kinds of ecosystems and quantitatively predominant, playing important roles in the global nitrogen biogeochemical cycling. This paper reviewed the morphological, physiological, and ecological characteristics and the molecular phylogenies of AOA, and compared and analyzed the differences and similarities of the ammonia monooxygenase (AMO) and its encoding genes between AOA and AOB. In addition, the potential significant roles of AOA in nitrogen biogeochemical cycling in aquatic and terrestrial ecosystems were summarized, and the future research directions of AOA in applied ecology and environmental protection were put forward.