Ultrasound Based Integrated Technique for Production of Sustainable Bio-crude from Domestic Sewage Sludge for Biorefinery

Generation of a tremendous amount of domestic sewage sludge pushes society to look for an alternate and viable option rather than its direct disposal. The organic-rich constituents of sludge make it an asset rather than waste. Sludge to energy conversion is a feasible option to combat the demand for renewable energy. Resource recovery from waste leads to socio-economic development by reducing fossil dependency with clean and green energy. This chapter mainly focuses on the potential of ultrasound-based techniques for the pretreatment of DSS to enhance bio-crude production. Thermochemical and biochemical treatment are two routes of sludge valorization with their advantages and limitations. Pyrolysis, gasification, combustion, and hydrothermal processing come under thermochemical treatment whereas, anaerobic digestion, aerobic digestion, and fermentation form the basis of biochemical treatment. Thermochemical routes demand energy, whereas biochemical routes are a time-consuming process. Pretreatment of sludge is a viable option to overcome these limitations. Ultrasound pretreatment increases COD solubilization, volatile suspended solids reduction, biogas production during AD, increases the yield and HHV of biocrude during thermochemical treatment, and favors lipid extraction for biodiesel production, and also promotes bioethanol production. Moreover, integrated ultrasound pretreatment positively affects the overall process by reducing the overall cost and increasing bio-crude production.