On 19 December 2014, two Erasmus Mundus Joint Doctorate PhD defences took place. Mr. Lucian Staicu and Mr. Rohan Jain successfully presented and defended their PhD theses.
Piet Lens, Professor of Environmental Biotechnology at UNESCO-IHE, was their Promotor. The co-promotors were Dr. Esposito, Department of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, Italy and Dr. van Hullebusch, Associate Professor in Biogeochemistry at the University of Paris-Est, France. On the occasion of these two PhD defenses, UNESCO-IHE organized a mini symposium on the treatment of selenium rich wastewaters.
Lucian Staicu's thesis abstract
The thesis of Lucian Staicu is entitled ‘Production of colloidal biogenic selenium and removal by different coagulation-flocculation approaches’.
Selenium (Se) is a chalcogen element with a narrow window between essentiality and toxicity. Se oxyanions are water-soluble, bioavailable and toxic. In contrast, elemental selenium, Se(0), is solid and less toxic. Nevertheless, Se(0) is potentially harmful as particulate Se(0) has been reported to be bioavailable to bivalves, to fish and also prone to re-oxidation.
The solid-liquid separation potential of colloidal Se(0) generated by a mixed microbial culture was assessed by centrifugation, filtration, and coagulation-flocculation (by aluminum sulfate and ferric chloride). Centrifugation at different centrifugal speeds achieved 22% (for 1,500 rpm), 73% (for 3,000 rpm) and 91% (for 4,500 rpm) removal. Separation by filtration through 0.45 µm filters resulted in 87% Se(0) removal.
Additionally, aluminum sulfate achieved the highest turbidity removal (92%) at a dose of 10-3 M, whereas ferric chloride achieved a maximum removal efficiency of only 43% at 2.7 x 10-4 M. Colloidal Se(0) produced by the Pseudomonas moraviensis strain was sedimented using electrocoagulation (Fe and Al sacrificial anodes).
The best Se(0) turbidity removal (97%) was achieved using iron electrodes at 200 mA. Aluminum electrodes removed 96% of colloidal Se(0) only at a higher current intensity (300 mA). Because biogenic Se(0) is harmful to the environment, appropriate measures must be implemented for its solid-liquid separation using an efficient technology.
Rohan Jain's thesis abstract
The thesis of Rohan Jain is entitled ‘Biogenic nanoparticles of elemental selenium: Production, characterization and relevance in wastewater treatment’
This study was broadly divided into three different sub-sections a) production and characterization of biogenic elemental selenium nanoparticles (BioSeNPs), b) application of BioSeNPs in heavy metals removal and c) fate of BioSeNPs in upflow anaerobic sludge blanket (UASB) and activated sludge reactor.
This study demonstrated that extracellular polymeric substances (EPS) are capping the BioSeNPs and thus providing them colloidal stability. Production of biogenic selenium nanowires was also achieved in this study by reduction of selenite at thermophilic temperatures (55 and 65 oC).
BioSeNPs showed adsorption preference towards heavy metals in the following order: Cu>Zn>Cd. The interaction of heavy metals with BioSeNPs takes place through hydroxyl and carboxyl group, which were part of EPS, present on the surface of BioSeNPs. Thermophilic reduction of selenate in an UASB reactor showed better total selenium removal as compared to mesophilic reactor. The BioSeNPs trapped in activated sludge showed affects physico-chemical properties of BioSeNPs