Industrial activities like textile processing and mining are typical sources of heavy metal-rich wastewaters. The sulfate reducing process has become an attractive method for the production of sulfide to precipitate metals since most of these streams also contain sulfate, which is the electron acceptor and, in less common cases, chemical oxygen demand which is the electron donor of sulfate reducing bacteria. The inverse fluidized bed (IFB) reactor is a system for the production of biogenic sulfide and metal precipitation in the same unit due to its configuration: the biomass floats on top of the reactor, whereas metal sulfide precipitates settle and thus can be recovered at the bottom.
The main objective of this thesis was to elucidate the factors affecting simultaneous sulfate reduction and precipitation of heavy metals in an IFB reactor in order to optimize the metal recovery from wastewaters such as acid mine drainage. Therefore, this thesis focused on varying different operational conditions to study their effect on the solid-liquid separation and purity of the metal sulfide precipitates as well as on their effect on the sulfate reducing process. Furthermore, one chapter was focused on the study of strategies for sulfide control in the IFB reactor. In addition, recommendations for further research to improve the recovery of the metal sulfides in bioreactors are given.
1 General introduction
2 Effect of sulfide concentration on the location of the metal sulfide precipitates in the IFB reactor
3 Influence of sulfide concentration and macronutrients on the metal sulfide precipitates characteristics
4 Effect of hydraulic retention time on the sulfate reduction process and the metal sulfide precipitates characteristics
5 Tuning strategies to control the sulfide concentration using a pS electrode in the IFB reactor
6 Effect of pH on the morphology, mineralogy and liquid-solid phase separation of Cu and Zn precipitates produced with biogenic sulfide
7 Factorial design and response surface analyses to understand the effect of process variables on the sulfate reduction process in the IFB reactor
8 General discussion and recommendations
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.