The bio-disposal of lignocellulose substances with activated sludge

[摘要] ENGLISH ABSTRACT:Lignocellulose is the principal form of biomass in the biosphere and therefore the predominantrenewable source in the environment. However, owing to the chemical and structuralcomplexity of lignocellulose substrates, the effective and sustainable utilization oflignocellulose 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 andunhygienic. Owing to the metabolic activities of the micro-organisms, the initially acidifiedhabitats rapidly undergoes self-neutralization. A number of pathogenic bacteria (coliformsand Salmonella sp.) are present during this slow degradation process and it is thereforeimperative to improve the efficiency and hygienic effects of the biodegradation of thelignocellulose.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 forthe exploitation of these waste products. For example, owing to the complex, heterogeneousstructure of lignocellulose, the degree of solubilization, modification and conversion of thedifferent components are not clear. Likewise, the overall anaerobic degradation oflignocellulose is not understood well as yet.In this study, the emphasis was on the promotion of solid anaerobic digestion of lignocellulosewastes for environmental beneficiation and waste reutilization. The degradation oflignocellulose in landfill environments was first simulated experimentally. Once the microbialpopulations and the degradation products of the system were characterized, the promotion ofanaerobic digestion by use of activated sludge was studied. This included acidogenicfermentation, as well as recovery of the methanogenic phase. Moreover, special attention wasgiven to the further disposal of humic acids or humic acid bearing leachates formed in thedigestive 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 humicacids could be decomposed into volatile forms, but the higher molecular weight fractiontended to aggregate into a colloidal form, which could only be removed from the system bymaking use of ultrasonically assisted adsorption on preformed aluminium hydroxide floes.This was followed by an investigation of the microbial degradation of humic acids and thetoxicity of these acids to anaerobic consortia. Further experimental work was conducted tooptimize the biological and abiological treatment of lignocellulose in an upflow anaerobicsludge blanket (DASB) reactor fed with glucose substrate. The humic acids could be partiallyhydrolysed and decomposed by the acid fermentative consortia of the granules in the DASBreactor.Finally, solid mesothermophilic lignocellulose anaerobic digestive sludge can be viewed as ahumus-rich hygienic product that can improve the fertility and water-holding capacity ofagricultural soil, nourish plants and immobilize heavy metals in the environment as a bioabsorbent.

[发布机构] Stellenbosch University