Evaluation of Sewage Digested Sludge Conditioning and Dewatering Through Qualitative and Quantitative Laboratory Methodologies Towards Process Monitoring

  • Ivo Miguel Delgado Bandeira Oliveira

    Student thesis: Doctoral Thesis


    This thesis reports on investigations that have contributed to an advancement in the applied and fundamental understanding on how the nature, related storage and processing of digested sewage sludge can influence polymer conditioning and dewatering. The work concentrated more specifically on evaluating the impact of thermal hydrolysis as a pre-treatment to anaerobic digestion (AD) of mainly secondary sewage sludges (Advanced AD, AAD plants) in comparison with conventional mesophilic AD (CMAD) on conditioning and dewatering of the digestate, as this knowledge seemed to be lacking for an AAD technology that is increasingly being implemented. An additional contribution to knowledge from this study relates to the evaluation of how polymer conditioning and dewatering of digested sludges could be monitored using rheometric measurements. It was concluded that digested sludge biofloc characteristics (size, shear viscosity and organic matter composition) affected the most the conditioning and dewatering results but these varied depending on the process conditions i.e. AAD versus CMAD and digestate handling conditions. The reduction in particle size and shear viscosity (η[0.1 s-1]) per g Total Solids as well as the increased solubilization of protein, organically bound nitrogen and chemical oxygen demand of the digestates which contributed to the increased conditioning requirements affected also the dewatering rate and the strength of the flocs produced after conditioning. The changes in the digested sludge biofloc characteristics were detected by rheometric measurements which were well correlated with changes in organic matter composition and polymer conditioning requirements (r of 0.9 and 0.8). It was proposed that the variations in η[0.1 s-1] and organic matter content such as soluble protein could be used to predict polymer dose requirements to achieve good filterability (R2 of 0.7; significance F and p<0.05). Future work is however required in order to consolidate these findings by monitoring conditioning, dewatering and η[0.1 s-1] of the digestate at full scale.
    Date of AwardJul 2017
    Original languageEnglish
    SupervisorSandra Esteves (Supervisor)


    • anaerobic digestion systems
    • digested sewage sludge
    • polymer conditioning
    • dewatering
    • secondary sewage sludges

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