The rise in global population has led to increased production of wastewater. The treatment of wastewater at wastewater treatment plants (WWTPs) results in excess sludge production and odor, which leads to difficulty in transportation and disposal. Hence, the stabilization of excess sludge through various techniques have been intensively studied to improve sludge management. Anaerobic digestion is one among the sludge stabilization techniques, wherein total solids, pathogens, and odor are minimized through the metabolic action of anaerobic microorganisms. However, conventional anaerobic digestion faces several operational challenges such as slow initial hydrolysis, poor biomethanation and low solid reduction. To overcome this, the current thesis work examined a combined technology involving a hybrid microwave-hydrogen peroxide (MW-H2O2) pre-treatment and two-stage anaerobic digestion for the biodegradation of waste activated sludge.

The hybrid (MW-H2O2) pre-treatment increased the solubilization of waste activated sludge compared to individual treatments. The increased sludge solubilization was characterized by microbial breakdown and dissolution of extracellular polymeric substances (EPS). Furthermore, a novel semi-continuous two-stage anaerobic digestion was developed for the current study. The two-stage digestion involved phase-I acidifier and phase-II methanizer, maintained at thermophilic and mesophilic conditions, respectively. The two-stage anaerobic digestion showed better performance compared to conventional single-stage digestion, in the biodegradation of waste activated sludge. Also, the application of hybrid pre-treatment enhanced the efficiency of two-stage digestion in terms of biogas production, biogas quality, pathogen removal and methanogenic activity. In addition, the efficiency of two-stage digestion was further examined by the co-digestion of activated sludge with highly acidifying fruit and vegetable wastes (FVW). The digester showed better performance in terms of biogas production and quality with 75 % activated sludge and 25 % FVW, than 50 % of each substrate, thereby signifying the importance of mixing ratio in digester stability. Moreover, the dewaterability of effluent digestate was observed to increase with the application of microwave and hybrid pre-treatments. Besides, the improvement in dewaterability was observed to be concurrent with the release of biopolymers by the pre-treatment.

Publications:

· H.W. Ambrose, L. Philip, G.K. Suraishkumar, A. Karthikaichamy, T.K. Sen, Anaerobic co-digestion of activated sludge and fruit and vegetable waste : Evaluation of mixing ratio and impact of hybrid ( microwave and hydrogen peroxide ) sludge pre-treatment on two-stage digester stability and biogas yield, J. Water Process Eng. 37 (2020) 101498. doi:10.1016/j.jwpe.2020.101498.

· H.W. Ambrose, C. Tse-Liang Chin, E. Hong, L. Philip, G.K. Suraishkumar, T.K. Sen, M. Khiadani, Effect of hybrid (microwave-H2O2) feed sludge pretreatment on single and two-stage anaerobic digestion efficiency of real mixed sewage sludge, Process Saf. Environ. Prot. 136 (2020) 194–202. doi:10.1016/j.psep.2020.01.032.

· H.W. Ambrose, L. Philip, T.K. Sen, G.K. Suraishkumar, The Effect of Combined Microwave and Hydrogen Peroxide Pretreatment on Sludge Characteristics and Oxidation Status of Waste Activated Sludge, in: B. Lefebvre (Ed.), Act. Sludge Process Methods Recent Dev., nova science publishers, 2019: pp. 105–141.