Degree Name

Doctor of Philosophy


School of Civil, Mining and Environmental Engineering


Activated sludge process-based biological wastewater treatment is widely used for the treatment of wastewater. It cleans wastewater by transforming the suspended and dissolved solids to biomass and gases. While cleaning the wastewater, this process also produces a huge quantity of sludge that requires costly management. Sludge management cost represents around 60% of the collective operational cost of a wastewater treatment plant. With increasing number of wastewater treatment plants to serve the growing population, sludge production is rapidly increasing each year and its disposal has emerged as a serious challenge for the operators of wastewater treatment plants.

Stringent regulations regarding pathogenic agents and other hazardous contaminants in sludge may restrict their disposal via conventional methods such as landfill, incineration, and agricultural reuse of biosolids. In the literature, various technologies have been considered to achieve sludge reduction while treating wastewater. One such option is the oxic-settling-anoxic (OSA) process where the main aerobic bioreactor is integrated with anoxic side-stream reactor and sludge is exchanged between these reactors maintaining different redox conditions. In this integrated process, sludge is retained for a temporary period in the side-stream reactors with low oxygen and substrate, and then it is recirculated to the main reactor for sludge reduction.

Membrane Bioreactor (MBR) is an advancement over the conventional activated sludge (CAS) process for wastewater treatment. MBR combines biodegradation with membrane filtration to produce suspended solids free biologically treated effluent in a single step with a smaller footprint than the CAS process. Because of these inherent characteristics of MBR, it is interesting to assess the combination of the MBR—side-stream anoxic reactors for sludge yield reduction during wastewater treatment. However, there are gaps in understanding the mechanisms of sludge reduction in this integrated process. Influence of operational parameters such as sludge interchange rate (SIR) and sludge retention time of external reactors (SRText. reactors), role of microbial community and trace organic contaminants (TrOCs) removal needs further investigation.

This study aimed to understand the mechanisms of sludge reduction in MBR—side-stream anoxic reactors (MBRside-stream) process. This initially involved investigating the influence of operational parameters such SIR and SRText. reactors on sludge yield reduction. Simultaneously the wastewater treatment performance, particularly the removal of TrOCs was studied.

FoR codes (2020)

400406 Powder and particle technology, 400409 Separation technologies, 400410 Wastewater treatment processes, 400411 Water treatment processes

This thesis is unavailable until Sunday, March 10, 2024



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.