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Innovative sludge pretreatment technologies and enhanced anaerobic digestion Yi, Weigang


This dissertation reports the research findings from an investigation into the use of four technologies for municipal wastewater sludge pre-digestion treatment. The technologies explored include microwave, the microwave / hydrogen peroxide process, ultrasound and biological enzyme protease treatment. The general purpose of the sludge pretreatment applications is to improve anaerobic digestion efficiency in terms of biogas production, organic reduction and nutrient recovery. An examination was first carried out on the effects of these technologies on sludge solubilization (disintegration and hydrolysis), and the various factors influencing treatment efficiencies. Further detailed investigation was undertaken on the sludge macromolecule solubilization, biomass cell destruction and particle size alteration. Finally, an evaluation of the pretreatment impact on both mesophilic and thermophilic anaerobic digestion was done. This research work found that the degree of sludge solubilization is depending on a number of operating factors such as specific energy, temperature, power input, power density, treatment time, and specific oxidant dosage. In general, specific energy is the dominant factor. Substantial improvements in organic solubilization by the pretreatments were recorded (up to 43% increase in COD, 50% in protein solubilized, at specific energy 5000 kJ/g-DS). Different treatment methods resulted in variation in solubilization effect and digestion performance. Amino acid was found to be the key parameter in correlating to the mesophilic digestion improvements. Pretreatment improves biodegradability in mesophilic digestion (25% total biogas production increase). The mesophilic digestion reaction was found to fit second-order kinetics. Thermophilic digestion was inhibited initially by the large increase in soluble substrates, but recovered at the end of digestion period. The biogas production increase in mesophilic digestion was correlated to the increase in amino acids (R²=0.9216), not the increase in overall soluble COD. The inhibition in thermophilic digestion was correlated to the sum of increased soluble protein, polysaccharides and amino acids (R²=0.9822), regardless of the different pretreatment methods used. Overall, ultrasound pretreatment was found to be better energy efficient that other methods tested.

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