35 research outputs found
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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Effects of heavy metal pollution on the soil microbial activity
The effects of heavy metals on soil microbial processes were
investigated over a period of six weeks. Analytical grade (Sigma)
sulphate salts of copper, zinc and nickel were added individually and
in combinations to soil samples and incubated in different plastic
pots. Samples were taken from the pots forthnightly and the rates of
microbial carbon and nitrogen mineralization, microbial biomass carbon
and respiration were measured. The results showed the effect of metals
on the measured parameters were significant (P<0.05.). By the 6th
week postreatment, the rates of carbon accumulated were high in the
copper (6.03 %) and copper:zinc (5.80 %) treatments but low in the
nickel and zinc (4.93 % and 5.02 % respectively). The rates of nitrogen
mineralization were 0.41 and 0.44 % in samples treated with copper and
copper:zinc compared to 0.22 %-0.24 % obtained at the beginning of the
experiments. Soil microbial biomass carbon declined from average value
of 183.7 185.6 mg/g before treatment to as low as 100.8 and 124.6 mg/g
in samples treated with copper:zinc and copper respectively.The rate of
respiration of the soil microbial populations was equally inhibited by
the metals. From an average rate of 2.51-2.56 mg of C/g respiration of
the soil microbes declined to 0.98, 1.08 and 1.61 mg of C/g in the
copper:zinc, copper and zinc treated soils by the end of the
experiment. The results suggest additive or synergistic effects of the
metals