Thesis (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Lignocellulose is the principal form of biomass in the biosphere and therefore the predominant
renewable source in the environment. However, owing to the chemical and structural
complexity of lignocellulose substrates, the effective and sustainable utilization of
lignocellulose wastes is limited.
Many environments where lignocellulose residues are ordinarily stored can be highly acidic
(e.g. landfills), and under these circumstances biodegradation of the lignocellulose is slow and
unhygienic. Owing to the metabolic activities of the micro-organisms, the initially acidified
habitats rapidly undergoes self-neutralization. A number of pathogenic bacteria (coliforms
and Salmonella sp.) are present during this slow degradation process and it is therefore
imperative to improve the efficiency and hygienic effects of the biodegradation of the
lignocellulose.
Although the fundamentals of biodegradation of lignocellulose have been widely investigated,
many issues still need to be resolved in order to develop commercially viable technology for
the exploitation of these waste products. For example, owing to the complex, heterogeneous
structure of lignocellulose, the degree of solubilization, modification and conversion of the
different components are not clear. Likewise, the overall anaerobic degradation of
lignocellulose is not understood well as yet.
In this study, the emphasis was on the promotion of solid anaerobic digestion of lignocellulose
wastes for environmental beneficiation and waste reutilization. The degradation of
lignocellulose in landfill environments was first simulated experimentally. Once the microbial
populations and the degradation products of the system were characterized, the promotion of
anaerobic digestion by use of activated sludge was studied. This included acidogenic
fermentation, as well as recovery of the methanogenic phase. Moreover, special attention was
given to the further disposal of humic acids or humic acid bearing leachates formed in the
digestive system, since these acids pose a major problem in the digestion of the lingocellulose. With ultrasonication, approximately 50% of the lower molecular weight fraction of humic
acids could be decomposed into volatile forms, but the higher molecular weight fraction
tended to aggregate into a colloidal form, which could only be removed from the system by
making use of ultrasonically assisted adsorption on preformed aluminium hydroxide floes.
This was followed by an investigation of the microbial degradation of humic acids and the
toxicity of these acids to anaerobic consortia. Further experimental work was conducted to
optimize the biological and abiological treatment of lignocellulose in an upflow anaerobic
sludge blanket (DASB) reactor fed with glucose substrate. The humic acids could be partially
hydrolysed and decomposed by the acid fermentative consortia of the granules in the DASB
reactor.
Finally, solid mesothermophilic lignocellulose anaerobic digestive sludge can be viewed as a
humus-rich hygienic product that can improve the fertility and water-holding capacity of
agricultural soil, nourish plants and immobilize heavy metals in the environment as a bioabsorbent. / AFRIKAANSE OPSOMMING: Lignosellulose is die hoofbron van biomassa in die biosfeer en is daarom ook die belangrikste
hernubare bron in die omgewing. As gevolg van die chemiese en strukturele kompleksiteit
van lignosellulose substrate, is die doeltreffende en volhoubare benutting van lignosellulose
afval egter beperk. Die suurgehalte van die omgewings waar lignosellulose reste gewoonlik
gestoor word, soos opvullingsterreine, kan hoog wees en onder hierdie omstandighede is die
biodegradasie van die lignosellulose stadig en onhigiënies. As gevolg van die metaboliese
aktiwiteite van die mikro-organismes ondergaan die aanvanklik aangesuurde habitatte vinnig
self-neutralisasie. 'n Aantal patogeniese bakterieë (koliforme en Salmonella sp.) is deurgaans
gedurende dié stadige natuurlike proses teenwoordig en dit is dus van die grootste belang om
die effektiwiteit en die higiëne van die bioafbreking van die lignosellulose-substraat te
verhoog.
Alhoewel die grondbeginsels van die bioafbreking van lignosellulose reeds wyd ondersoek is,
moet verskeie probleme nog opgelos word ten einde kommersieel haalbare tegnologie te
ontwikkel vir die ontginning van afvalprodukte. Byvoorbeeld, as gevolg van die komplekse,
heterogene struktuur van lignosellulose, is die graad van solubilisering en die modifikasie en
omskakeling van verskillende komponente nog onduidelik. Net so word die algehele anaerobiese
afbreking van lignosellulose ook nog nie ten volle verstaan nie.
In hierdie ondersoek het die klem geval op die bevordering van soliede anaerobiese digestie
van lignosellulose afval vir omgewingsverbetering en die benutting van die afval. Die
afbreking van lignosellulose in opvullingsterreine is eers eksperimenteel gesimuleer. Nadat
die mikrobiese populasies en die afbrekingsprodukte gekarakteriseer is, is die bevordering van
anaerobiese digestie deur die gebruik van geaktiveerde slyk bestudeer. Dit het asidogeniese
fermentasie ingesluit, sowel as herwinning van die metanogeniese fase. Spesiale aandag is
gegee aan die verdere verwerking van humus sure en humussuurbevattende legate wat in die
digestiewe stelsel gegenereer is, aangesien die sure probleme veroorsaak het met die vertering
van die lignosellulose.
Met ultrasoniese straling is nagenoeg 50% van die lae-molekulêre massafraksie van die
humussure ontbind in vlugtige vorm, maar die hoë-molekulêre massafraksie het geneig om in 'n kolloïdale vorm te aggregeer, wat slegs uit die stelsel verwyder kon word deur middel van
ultrasonies ondersteunde adsorpsie op voorafgevormde aluminiumhidroksiedvlokkies.
Dit is gevolg deur 'n ondersoek na die mikrobiese afbreking van humus sure en die toksisiteit
van die sure ten opsigte van anaerobiese konsortia. Verdere eksperimentele werk is gedoen
ten opsigte van die biologiese en abiologiese behandeling van lignosellulose in 'n
opwaartsvloeiende anaerobiese slikkombersreaktor (OASK) gevoer met glukosesubstrate. Die
humus sure kon gedeeltelik gehidroliseer en ontbind word deur die suurgistende konsortia van
die granules in die OASK reactor.
Ten slotte kan die vaste termofiliese-mesofiliese anaerobiese lignosellulose verteringslik ook
gesien word as 'n humusryke higiëniese produk wat die vrugbaarheid en die waterhoudende
vermoë van landbougrond kan verhoog, plante kan voed en kan funksioneer as bioabsorbeerder
van swaarmetale in die omgewing.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52489 |
| Date | 03 1900 |
| Creators | Qi, Bing Cui |
| Contributors | Lorenzen, L., Aldrich, C., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 262 p. : ill. |
| Rights | Stellenbosch University |
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