Thesis subject

Effect of sulphide and metals on the microbial composition of anaerobic sludge

Anaerobic digestion (AD) is a well-established process for waste and wastewater treatment, reconciling bioremediation to biogas production. Methane (one of the main components of biogas) is a renewable biofuel that can be used for the production of heat and electricity. It is desirable to have high methane yields in order to maximize the potential of AD processes for energy recovery. However, methanogenesis is normally the rate-limiting step of the whole AD process and is quite sensitive to inhibition by several compounds.

Inhibition of methanogenesis by sulphide has been reported. Sulphide can be formed from sulphate (often present in wastewaters, especially the ones resulting from industrial and mining activities) by sulphate-reducing bacteria (SRB). Heavy metals can also affect the anaerobic digestion since, unlike other toxic compounds, they are not biodegradable and they can accumulate to toxic concentrations. One of the most common methods for metal detoxification is the use of sulphide to precipitate the heavy metals. In this work we intend to study the effect of sulphide on methanogenic sludges and also how pH influence the metal toxicity and metal detoxification process using sulphide.

Aim and techniques

Differences in pH will affect the equilibrium between the different sulphide species (H2S, HS-, H+ and S2-) as well of the metals ions. These changes will influence the toxicity of sulphide and its ability to bind to metals and precipitate, which will have effects in biogas production and in the microbial community.

The main objective of this thesis is to analyse the changes in the microbial composition of anaerobic sludge induced by the presence of sulphide, metals and combination of both. DNA/RNA will be isolated from anaerobic sludge incubated with sulphide and metals. Changes in the microbial composition of bacterial and archaeal domains will be analysed by 16S rRNA gene based fingerprinting (Denaturing Gradient Gel Electrophoresis, DGGE). Predominant microorganisms in the sludge will be identified by 16S rRNA gene sequencing. Main players will be quantified using RT-qPCR (real-time quantitative PCR) or FISH (Fluorescence in situ hybridization) techniques.

More information:

The project is designed for a MSc thesis (6 months) for students with interest in Microbial Physiology. Please fill free to contact for more information.

Supervisors:

Lara Paulo (PhD)

Diana Sousa (Post-Doc)