Clostridia Initiate Heavy Metal Bioremoval in Mixed Sulfidogenic Cultures

Sulfate reducing bacteria (SRB) are widely used for attenuating heavy metal pollution by means of sulfide generation. Due to their low metal tolerance, several SRB species depend on associated bacteria in mixed cultures to cope with metal-induced stress. Yet the identity of the SRB protecting bacteria is largely unknown. We aimed to identify these associated bacteria and their potential role in two highly metal-resistant mixed SRB cultures by comparing bacterial community composition and SRB activity between these cultures and two sensitive ones. The SRB composition in the resistant and sensitive consortia was similar. However, whereas the SRB in the sensitive cultures were strongly inhibited by a mixture of copper, zinc, and iron, no influence of these metals was detected on SRB growth and activity in the resistant cultures. In the latter, a Gram-positive population mostly assigned to Clostridium spp.initiated heavy metal bioremoval based on sulfide generation from components of the medium (mainly sulfite) but not from sulfate. After metal levels were lowered by the Clostridium spp. populations, SRB started sulfate reduction and raised the pH of the medium. The combination of sulfite reducing Clostridium spp. with SRB may improve green technologies for removal of heavy metals

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

Modelling of three phase sparged reactors

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Minor differences in sand physicochemistry lead to major differences in bacterial community structure and function after exposure to synthetic acid mine drainage

The formation of environmentally toxic acidic waste from mining activities is a world-wide problem. Neutralization of this waste can be accomplished by physicochemical and/or biological means. In this short-term study, synthetic acid mine drainage was added to sandfilled mesocosms containing silica-dominated (quartz) sand. Glucose was added as a carbon source for microbial iron and/or sulphate reduction. Replicates contained two separate batches of sand obtained from the same quarry site. The investigations used to assess and compare the chemical and biological functioning of the replicates included system hydraulic conductivity measurements, sand chemistry, effluent chemistry and bacterial community fingerprinting. Minor differences in composition of the sand, including the levels of available nutrients and micronutrients, resulted in major differences in measured parameters. Significant differences in effluent chemistry were found in systems containing different batches of sand. It was demonstrated that the characteristics of the sand and the presence of acid mine drainage impacted the bacterial community structure and function. The importance of the physical substrate on the selection of functional microbial communities in systems remediating AMD should not be under-estimated. The physical substrate should be carefully selected and it may be prudent to include small-scale comparative studies in each particular setting prior to full-scale implementation.Water Research Commission, Cape Peninsula University of Technology and the National Research Foundation of South Africahttp://link.springer.com/journal/12257hb201