No description available.

The quantitative relationship between the urinary excretion of <I>TBA</I> and the uptake of <I>PPA </I>and <I>CHCA</I> was examined by continuous intraruminal infusion of <I>PPA</I> (8, 16 or 24 mmol/d) either alone or with <I>CHCA </I>(8 or 16 mmol/d) in sheep nourished by intragastric infusions of all nutrients. The daily excretion of <I>TBA</I> was linearly correlated (<I>r</I> 0.99, <I>P</I><0.001) with the amounts of <I>PPA</I> and <I>CHCA</I> infused. The urinary recovery of infused <I>PPA</I> and <I>CHCA</I> as <I>TBA</I> was 0.79 (<I>s.e.</I> 0.01). Recovery of infused <I>SA</I> (8 mmol/d) as urinary total salicylic acid (<I>TSA</I>) was 0.89 (<I>SD</I> 0.08). Both <I>TBA</I> and <I>TSA</I> excretions were found to be exclusively of exogenous origin, with negligible faecal excretion. It is concluded that urinary <I>TBA</I> is a potential estimator of <I>PPA + CHCA</I> absorption from the digestive tract. <I>SA</I> may have potential as a marker of urine volume. The relationship between urinary excretion of <I>TBA</I> and forage intake was assessed with steers fed different amounts of fresh herbage from pastures comprising oat, rye, vetch and lucerne. Herbage samples collected daily were incubated <I>in vitro</I> with buffered rumen fluid for 48 h. The <I>PPA</I> production per unit of herbage <I>DM</I> incubated was fitted to the exponential function of time <I>Y </I>= <I>a +</I> [<I>b</I>. (1 - <I>e</I>^-<I>c.l</I>)]. Regression analysis showed that the <I>TBA:</I>creatine concentration ratio was a good explanatory variable (<I>r</I>²0.92-095; <I>P</I><0.001) of herbage intake. <I>TBA</I>:creatinine concentration ratio divided by the product <I>b.c</I>, both constants from the fitted curves of <I>PPA</I> production of herbage cultures, was another good index (<I>r</I>² up to 0.98). It is concluded that a method for the prediction of herbage intake for grazing animals based on <I>TBA</I> excretion in urine seems promising.

This study evaluates the enhancement of anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) by microwave pretreatment (MW) at high temperatures (115, 145 and 175°C). The highest level of solubilization was achieved at 175ºC, with a supplemental water addition of 30% (SWA30). Pretreatments combining two modalities; MW heating in presence or absence of hydrogen peroxide (H2O2) was also investigated. Biochemical methane potential (BMP) tests were conducted on the whole OFMSW, as well as on the liquid fractions. The whole OFMSW pretreated at 115 and 145 ºC showed little improvement in biogas production over control. When pretreated at 175 ºC, biogas production decreased due to formation of refractory compounds, inhibiting digestion. For the liquid fraction of OFMSW, the effect of pretreatment on the cumulative biogas production (CBP) was more pronounced for supplemental water addition of 20% (SWA20) at 145 ºC. Combining MW and H2O2 modalities did not have a positive impact on OFMSW stabilization and enhanced biogas production. Based on the BMP assay results, the effects of MW pretreatment (145 ºC) on the AD of OFMSW (SWA20) were further evaluated in single and dual stage semi-continuous digesters at hydraulic retention times (HRTs) of 20, 15, 12 and 9 days. Overall, MW pretreatment did not enhance the AD of the whole waste at the HRTs tested. However, the use of a dual stage reactor digesting non pretreated whole OFMSW had the best performance with the shortest HRT of 9 days. Conversely, for free liquid after pretreatment in two stage reactors at 20 day HRT methane production was tripled. In general, the performance of the dual stage digesters surpassed that of the single stage reactors. Cyclic BMP assays indicated that using an appropriate fraction of recycled effluent leachate can be implemented without negatively effecting methanogenic activity and biogas production. Based on the results obtained in this study, digestion of OFMSW by dual stage reactors without pretreatment appears to provide the best potential for waste stabilization in terms of biogas production and yield, process stability and volumetric loading rates.

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).

Thesis (M. App. Sc.)--University of Adelaide, Dept. of Animal Science, 1997? / Includes bibliographical references (leaves 107-130).

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.) - Carleton University, 2006. / Includes bibliographical references (p. 212-226). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Sydney, 2002. / Title from t.p. of PDF document (viewed Apr. 17, 2005). Includes bibliographical references (p. 242-264).

Thesis (M. Sc.)--University of Hong Kong, 1994. / Includes bibliographical references.