Browsing by Author "Hamann, Martin Louis"

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    System hydrodynamics to reduce fouling of air-sparged immersed flat-sheet microfiltration membranes
    (Stellenbosch : University of Stellenbosch, 2010-12) Hamann, Martin Louis; Bradshaw, S. M.; Jacobs, E. P.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Immersed membrane systems hold many operational and environmental advantages in biological treatment of wastewater. However, immersed membrane filtration have only found application in niche markets to date because of higher capital and operating costs associated with membrane fouling. But with capital costs on the decline as membranes become less expensive, immersed membrane systems are increasingly considered as an attractive alternative to conventional treatment processes. Operating costs remain high however, since energy intensive techniques such as air-sparging are required to limit membrane fouling. Improving the air-scouring efficiency of air-sparged immersed membranes can significantly reduce operating costs and unlock the immersed membrane system technology to wider application. The aim of this study was to identify factors that will improve air-scouring efficiency in order to produce guidelines that will help in the development of an immersed microfiltration membrane system with a resulting lower operating cost. Although, the research was done on a flat-sheet microfiltration membrane, the guidelines obtained can be used for the development of any immersed microfiltration membrane arrangement. An airlift reactor set-up was chosen for this study. Six system hydrodynamic factors were evaluated in a factorial design to determine their effects on the cross-flow velocity profile. They were the downcomer area to riser area ratio, top clearance distance, bottom clearance distance, aeration intensity, water depth and air sparger location. It was found that the air-scouring efficiency was increased by generating a cross-flow velocity profile with increased magnitude and uniformity, but absolute uniformity of the cross-flow velocity profile was found to be a prerequisite for optimisation of air-scouring efficiency. Downcomer area to riser area ratio was found to be 99.9% significant in determining the magnitude of the cross-flow velocity profile. Two models were developed to respectively predict the relative magnitude and uniformity of the cross-flow velocity profile. By using these two models, a methodology was developed to design an airlift reactor set-up that would produce system hydrodynamics with an improved air-scouring efficiency.
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    Uncatalysed steam pretreatment regimes for bagasse and harvest residues in a sugarcane biorefinery
    (Stellenbosch : Stellenbosch University, 2020-03) Hamann, Martin Louis; Gorgens, Johann F.; Van Rensburg, Eugene; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Biorefining of sugarcane lignocellulosic wastes, i.e. bagasse and harvest residues, at existing cane sugar mills can diversify product ranges to potentially improve profitability. Bagasse is the fibrous residue after juice extraction from the cane and harvest residues are all agricultural wastes generated during sugarcane harvesting. Pretreatment, the first step in bioprocessing of lignocellulose, must ensure maximum yields of desired sugar intermediates (glucose, xylose and arabinose) according to lignocellulosic feedstock and downstream bioconversion requirements. This study chose steam pretreatment for its proven track record in largescale operations and availability of steam at sugar mills, and was studied uncatalysed to allow operation without chemicals addition. The originality of this study firstly included the direct comparison of bagasse and harvest residues pretreatment operability in the same equipment. Uncatalysed steam pretreatment of these feedstocks was optimised by response surface methodology in the ranges of 185 – 215 °C and 5 – 15 min for maximum digestibility (indication of cellulose accessibility to enzymes) of the solids, maximum combined sugar yield (CSY) and maximum hemicellulose recovery to identify preferred pretreatment operating regimes. Secondly, deacetylation (acetyl groups removed from lignocellulose with a mild alkaline extraction) upstream of uncatalysed steam pretreatment was proposed as a detoxification step to remove acetic acid in downstream fermentation. Uncatalysed steam pretreatment of raw and deacetylated bagasse and harvest residues was compared on digestibility, fermentability (portion of maximum theoretical ethanol yield that can be obtained) and dewaterability of the pretreated material. Thirdly, the contribution of the explosion step during steam pretreatment to improving digestibility of the pretreated solids was investigated by comparing material retained and released during the sudden depressurisation at the end of pretreatment. The most significant findings of this study included that sugarcane harvest residues were better suited than bagasse for biorefining via a sugar platform for the following reasons: (1) harvest residues allowed for robust uncatalysed steam pretreatment at a single condition (between 198 and 200 °C, and between 8 and 12 min) to obtain at least 95% of the maximum digestibility, CSY and hemicellulose recovery values, respectively; (2) maximum digestibility was obtained at lower severity (205.8 °C, 8.7 min as opposed to 215 °C, 15 min for bagasse); (3) pretreated harvest residues did not require detoxification at optimum pretreatment conditions; and (4) pretreated harvest residues displayed better dewaterability, especially when pretreated for maximum hemicellulose recovery, compared to bagasse. Furthermore, it was found that the mechanical impingement experienced by steam pretreated material as it is transported during depressurisation, has a significant contribution to improving digestibility. Also, it was found that deacetylation of feedstocks can be performed prior to uncatalysed steam pretreatment as a detoxification step that could potentially increase fermentability of pretreated pressed slurries (not washed). Consequently, it is proposed that bagasse continues to be used to generate steam and electricity in a sugar mill, while attention should be given to the recovery, collection and allocation of sugarcane harvest residues as an attractive sugarcane biorefinery feedstock.