Methanogens, sulphate and heavy metals: a complex system

Anaerobic digestion (AD) is a well-established technology used for the treatment of wastes and wastewaters with high organic content. During AD organic matter is converted stepwise to methane-containing biogasa renewable energy carrier. Methane production occurs in the last AD step and relies on methanogens, which are rather sensitive to some contaminants commonly found in wastewaters (e.g. heavy metals), or easily outcompeted by other groups of microorganisms (e.g. sulphate reducing bacteria, SRB). This review gives an overview of previous research and pilot-scale studies that shed some light on the effects of sulphate and heavy metals on methanogenesis. Despite the numerous studies on this subject, comparison is not always possible due to differences in the experimental conditions used and parameters explained. An overview of the possible benefits of methanogens and SRB co-habitation is also covered. Small amounts of sulphide produced by SRB can precipitate with metals, neutralising the negative effects of sulphide accumulation and free heavy metals on methanogenesis. Knowledge on how to untangle and balance sulphate reduction and methanogenesis is crucial to take advantage of the potential for the utilisation of biogenic sulphide as a metal detoxification agent with minimal loss in methane production in anaerobic digesters.The research was financially supported by the People Program (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013 under REA agreement 289193

Toxic effects exerted on methanogenic, nitrifying and denitrifying bacteria by chemicals used in a milk analysis laboratory

The toxic effects caused by the chemicals contained in wastewaters generated by laboratories involved in raw milk analyses were assessed using batch assays. These assays were carried out separately with methanogenic, ammonium-oxidizing, nitrite-oxidizing and denitrifying bacteria. Since sodium azide is one of the main components of the chemical mixture present in these streams, a set of assays was carried out with the whole chemical mixture, and another one was performed only with azide as the sole toxicant. The concentrations of all chemicals in the raw wastewaters (100%) were the fundamental references used to assess the relative concentrations corresponding to a decrease of 50% in bacterial activity (IC50). The results obtained showed that nitrite-oxidizing bacteria were the most sensitive microorganisms, with IC50 relative concentrations around 0.04%. The values obtained for the other groups were: 20, 20 and 33% for methanogenic, ammonium-oxidizing and denitrifying bacteria, respectivel

Comparison of PPCPs removal on a parallel-operated MBR and AS system and evaluation of effluent post-treatment on vertical flow reed beds

The presence in the aquatic environment of xenobiotics such as Pharmaceutical and Personal Care Products (PPCPs) has emerged as an issue of concern. Upgrading sewage treatment quality with modern technologies such as Membrane Bioreactors (MBRs) and/or implementing a further posttreatment might mitigate the release of xenobiotics into surface waters. The performance of two processes treating municipal sewage, a MBR and an Activated Sludge (AS) unit, have been compared in terms of PPCPs removal. Moreover, their effluents were treated using vertical flow reed beds. Both systems were operated under similar conditions, more specifically Hydraulic Retention Time (HRT), maintained at 8 hours, and Sludge Retention Time (SRT) set at 6 and 20 days. Pharmaceuticals belong to therapeutic groups such as antiepileptics (carbamazepine) and analgesics (ibuprofen, naproxen, diclofenac), whereas the personal care products are musk fragrances (galaxolide and tonalide). Xenobiotics removals achieved in the MBR showed better results, particularly for the acidic drugs ibuprofen (87% vs. 50%) and naproxen (56% vs. 6%) operating at low SRT. After filtration through vertical flow reed-beds, PPCPs content in effluents was decreased, below 1 ppb in most cases, improving the effluent quality and confirming reed-beds as an interesting low cost alternative in order to attenuate xenobiotics contamination

Critical Influence of Nanofaceting on the Preparation and Performance of Supported Gold Catalysts

A partial transformation of the {100} surfaces of ceria nanocubes into a set of nanometer-heighted, {111}- bounded, peaks was achieved by an oxidation treatment at 600°C. This particular type of surface nanostructuration allows the preparation of CeO2 nanoparticles in which {111} nanofacets contribute significantly to their surface crystallography. This transformation of the surface structure plays a key influence on the behavior of ceria as a support of gold catalysts. Thus, the appearance of well-developed {111}-nanofacets leads to a much higher efficiency in the usage of this noble metal in the synthesis of catalysts when prepared by the deposition-precipitation method. Moreover, gold catalysts supported on the surfacereconstructed oxide present an intrinsic (per gold surface atom) CO oxidation activity much higher than that of catalysts prepared on the nontreated oxide.Fil: Tinoco, Miguel. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Fernández García, Susana. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: López Haro, Miguel. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Hungría, Ana B.. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Chen, Xiaowei. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Blanco, Ginesa. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Pérez Omil, Jose. Universidad de Cadiz. Facultad de Ciencias; EspañaFil: Collins, Sebastián Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Okuno, Hanako. Grenoble Institute Of Technology; FranciaFil: Calvino, Jose J.. Universidad de Cadiz. Facultad de Ciencias; Españ