Electronic Thesis and Dissertation Repository


Master of Engineering Science


Civil and Environmental Engineering


Dr. George Nakhla


This study aimed at assessing the impact of ultrasonication on the anaerobic digestibility of thickened waste activated sludge (TWAS) in anaerobic fluidized bed reactor (AnFBR), determining the unbiodegradable fraction of TWAS, and exploring co-digestion of food waste (FW) and TWAS. Two lab-scale AnFBRs treating TWAS were studied to explore the impact of ultrasonication (US) in the break down and reuse of scum for methane production. At an organic loading rate (OLR) of 4.7 kg COD/m3-d and 480 kJ of US energy, COD and VSS destruction efficiencies were 65% and 63%, respectively roughly 20% higher than the control reactor without US. To explore the specific methanogenic bacterial activity (SMA), the SMA test was conducted during OLR of 9.7 kg COD/m3-d and showed that the activity-based sludge retention time is higher for the ultrasonicated AnFBR (U-AnFBR) (7.1 days) compared to AnFBR (5.1 days). The investigation also indicated that the unbiodegradable fractions of PCOD and VSS were 0.28 based on PCOD and 0.26 based on VSS. However, to investigate the co-digestibility of FW as co-substrate, five semi-continuous flow anaerobic digesters were operated to explore the co-digestion performance treating a mixture of FW and municipal biosolids (primary sludge and TWAS) at an HRT of 20 days. Sixty days of steady-state operation at organic loading rates of 2.2 kgCOD/m3-d to 3.85 kgCOD/m3-d showed that COD removals were higher for the three co-digesters than for the two municipal biosolids digesters i.e. 61%-69% versus 47%-52%. Specific methane production per influent CODs were 1.3-1.8 folds higher in co-digestion than mono-digestion. Additional methane production through synergism accounted for the minimum 18%-20% of the overall methane production.