Detoxification of water by semiconductor photocatalysis

An overview of the use of semiconductor photocatalysis for water purification is given. The basic principles of semiconductor photocatalysis are described along with the current understanding of the underlying reaction mechanism(s) and how it fits in with the major features of the observed Langmuir-Hinshelwood-type kinetics of pollutant destruction. These features are illustrated based on literature on the destruction of aqueous solutions of 4-chlorophenol as a pollutant, using titanium dioxide as the photocatalyst. The range of organic and inorganic pollutants that can be destroyed by semiconductor photocatalysis are reported and discussed. The basic considerations that need to be made when designing a reactor for semiconductor photocatalysis are considered. These include: the nature of the reactor glass, the type of illumination source, and the nature and type of semiconductor photocatalyst. The key basic photoreactor designs are reported and discussed, including external illumination, annular, and circular photoreactors. Actual designs that have been used for fixed and thin falling film semiconductor photocatalyst reactors are illustrated and their different features discussed. Basic non-concentrating and concentrating solar photoreactors for semiconductor photocatalysis are also reported. The design features of the major commercial photocatalytic reactor systems for water purification are reported and illustrated. Several case studies involving commercial photocatalytic reactors for water purification are reported. An attempt is made briefly to compare the efficacy of semiconductor photocatalysis for water purification with that of other, more popular and prevalent water purification processes. The future of semiconductor photocatalysis as a method of purifying water is considered

Guiding the development of a controlled ecological life support system

The workshop is reported which was held to establish guidelines for future development of ecological support systems, and to develop a group of researchers who understand the interdisciplinary requirements of the overall program

Master of Science

thesisAnaerobic Ammonia Oxidation (Anammox) has become an important topic in environmental microbiology and engineering in the last 15 years. The application of Anammox in wastewater treatment provides many beneficial advantages over traditional nitrogen removal processes, particularly in treating ammonium-rich waste streams. In this study, the Anammox process was applied to a fed-batch reactor to treat raw digester filtrate from a local treatment plant. During initial treatment, the filtrate was diluted and an external nitrite source was supplemented. After reaching stable removal, a partial-nitritation (PN) reactor was started-up and fed with the same raw filtrate (undiluted). The effluent from the PN reactor was then fed directly to the Anammox (in place of diluted filtrate). A very long solids retention time (SRT) of 200 days was maintained throughout the study via manual wasting and decanting in order to produce very little sludge and still maintain efficient nitrogen removal. Sequence analysis and fluorescence in-situ hybridization (FISH) were performed on the biomass communities from both reactors. Automated ribosomal intergenic spacer analysis (ARISA) was also conducted on the Anammox biomass throughout the study period. The reactor operated at a moderate loading rate (average 0.33±0.03 with a max of 0.4 g N (L day)-1) comparable with many other fed-batch reactors in literature. It also achieved significant N removal (average of 82±4%) and specific removal rates (average 0.28±0.05 with max of 0.35 g N (g VSS day)-1) likewise comparable with similar studies despite maintaining a very long SRT. Sequence analysis and FISH showed that K. stuttgartiensis dominated the enriched Anammox community (approximately 65% of the biomass) along with several unidentified, but seemingly enriched, potential Anammox strains. ARISA analysis of the Anammox community showed no noticeable shift in the community profile despite the change in feed composition during the study period. It has been found in other studies that the species K. stuttgartiensis is capable of dissimilatory nitrate reduction to ammonium (DNRA), which would give it a selective advantage in conditions created by maintaining a long SRT. Ammonia oxidizing bacteria (AOBs) of the N. europaea lineage dominated the community in the PN reactor, agreeing with literature showing that lineage to dominate in oxygen-limited, ammonium-rich conditions