Optimization of Biological Sulphate Reduction to Treat Inorganic Wastewaters: Process Control and Potential Use of Methane as Electron Donor
This work investigated two different approaches to optimize biological sulphate reduction: to
develop a process control strategy to optimize the input of an electron donor and to study how
to increase the feasibility of using a cheap carbon source such as methane.
For the design of a control strategy that uses the organic loading rate (OLR) as control input,
feast and famine behaviour conditions were applied to a sulphate reducing bioreactor to excite
the dynamics of the process. Such feast/famine regimes were shown to induce the accumulation
of carbon, and possibly sulphur, storage compounds in the sulphate reducing biomass. This
study showed that delays in the response time and a high control gain can be considered as
the most critical factors affecting the application of a sulphide control strategy in bioreactors.
The delays are caused by the induction of different metabolic pathways in the anaerobic sludge
including the accumulation of storage products.
Polyhydroxybutyrate (PHB) and sulphate were found to accumulate in the biomass present in
the inversed fluidized bed bioreactor used in this study, and consequently, they were considered
to be the main storage compounds used by SRB. On this basis, a mathematical model was
developed which showed a good fit between experimental and simulated data giving further
support to key role of accumulation processes.
In order to understand the microbial pathways in the anaerobic oxidation of methane
coupled to sulphate reduction (AOM-SR) diverse potential electron donors and acceptors
were added to in vitro incubations of an AOM-SR enrichment at high pressure with several
co-substrates. The AOM-SR was stimulated by the addition of acetate which has not been
reported for any other AOM-SR performing communities. In addition, acetate was formed
in the control group probably resulting from the reduction of CO2. These results support
the hypothesis that acetate may serve as an intermediate in the AOM-SR process, at least in
some groups of anaerobic methanotrophic archaea (ANME) and sulphate reducing bacteria.