Anaerobic digestion of waste activated sludge can be improved if hydrolysis of particulate substrates is enhanced and available substrate is made more accessible by both breakup of the sludge matrix floc and rupture of the cell wall. Microwave (MW) pretreatment was suggested and studied as a way to improve digestion efficiency. The work done focuses on the effects of MW pretreatment on the characteristics of the sludge, due to thermal and athermal effects. It also evaluates the effects some process variables in the activated sludge process have on the pretreatment efficiency as well as the effect operating conditions in the downstream anaerobic digestion process have on the biodegradability efficiency of those sludges. Effects of athermal and thermal MW radiation were measured by use of a customized MW oven capable of providing MW radiation with uncoupled thermal and athermal effects. Athermal radiation was capable of increasing substrate present in the soluble phase of sludge, and had a positive effect in the digestion of athermal samples. The increases in biogas production and substrate solubilisation were smaller in magnitude than the increases measured for MW thermal tests. Further refining of the tests with athermal and thermal sludge, involved separation by size class of the solubilized substrate by means of ultrafiltration (UF), and revealed that changes in particle size distribution were significant not only for MW thermal tests, but also for athermal tests, with a particular emphasis in proteins in athermal tests. These changes had an effect on the biodegradability of the sludges by class size, with thermally pretreated sludge producing more biogas for smaller particles size classes but also exhibiting more inhibition. Tests were made with several combinations of sludge with different ages and subject to different MW pretreatment temperatures. The work showed that sludge age or solids retention time (SRT) has a significant effect on the pretreatment efficiency with maximum biogas improvements measured at different MW pretreatment temperatures depending on the SRT of the sludge tested, and with different behaviour for mesophilic and thermophilic digestion. Mesophilic tests showed greater improvements in terms of digestion effiency on average, but thermophilic tests showed more uniform performance, with a higher baseline efficiency. The presence of an optimum of MW pretreatment temperature and sludge SRT for maximal biogas production is more defined for mesophilic conditions than for thermophilic conditions. Semi-continuous studies were conducted with several combinations of single and two stage mesophilic and thermophilic digestors treating MW pretreated sludge and non-pretreated sludge. Staging and thermophilic digestion allowed the maintenance of a stable digestion process with high biogas productions and high solids removal efficiencies with production of sludge with good bacteriological characteristics for an very low residence time (5 d).

No description available.

Bacteriophytochromes (Bphs) comprise a family of protein photoreceptors that help bacteria sense changes in light. Bphs contain a chromophore that, upon absorption of red or far-red light, undergoes a cis-trans isomerization that leads to a conformational change in the holoprotein (photoconversion). In the active conformation, Bphs act as a kinase and regulate gene expression through phosphorylation of target proteins. Two putative Bph orfs (rpa0122 and rpa0990) in the Rhodopseudomonas palustris genome encode Bph-like proteins that have a conserved chromophore-binding cysteine residue. The hypothesis is that one or both of these unique Bph-like genes encode proteins that are capable of binding a chromophore and functioning to modulate the cell’s phenotype. I expressed and purified His-tagged RPA0990 in R. palustris, because proteolytic degradation was observed during overexpression in an E coli. expression system. The results show that RPA0990 contains a chromophore and is capable of photoconversion. The wavelengths of light absorbed by the Pr/Pfr forms of RPA0990, predicted to be active and inactive forms respectively, were determined to be 695 nm and 755 nm. Investigation into the phenotype of the bph mutants rpa0122 and rpa0990 revealed that both of these Bphs may have a small effect on light-harvesting complexes. Also, it was observed that the absence of O₂ does not inhibit the normal function of Bphs, although O₂ was thought to be needed to make a linear tetrapyrrole cofactor, by cleaving heme using heme oxygenase. I suggest that a linear tetrapyrrole can be made anaerobically, either through anaerobic heme cleavage by a novel enzyme, or directly from the heme precursor hydroxymethylbilane without ring cleavage. The activity of a divergent promoter region between the rpa1490 (bph3) and rpa1491 (pucBe) genes was evaluated by using the E. coli lacZ gene as a reporter. The results indicated that the pucBe promoter has much higher activity than the bph3 promoter. It was also found that double knockout of the regulatory genes ppsR1ˉ2ˉ led to an increase in bph3::lacZ expression and a decrease in pucBe::lacZ expression.

Thesis (M. Med. Sc.)--University of Hong Kong, 2007.

Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 221-244.

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 143-146). Also available in electronic format on the Internet.

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: Daniel K. Cha, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (doctoral)--Universität Konstanz, 1989. / Appended are reprints of two articles, in English, "Electromigration, a tool for studies on anaerobic ciliates," by Stefan Wagener, Claudius K. Stumm, and Godfried D. Vogels, and "Monoxenic culture of the anaerobic ciliate Trimyema compressum Lackey," by S. Wagener and N. Pfennig. Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Bibliography: leaves 203-219.

Thesis (M.Sc. (Clinical Pathology))--Mahidol University, 1982.