Environmental Technologies for Contaminated Solids, Soils and Sediments
2nd cohort

Joana Cassidy

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.