Thermal hydrolysis of sewage sludge: Improvement in biogas generation and prediction of global warming potential.

Abstract

Anaerobic digestion (AD) is a prominent treatment method for the sludge produced from sewage treatment plants. Poor solid reduction and longer retention time are the main drawbacks of AD. Thermal hydrolysis (TH) is a potential pretreatment method for solubilization of sewage sludge (SS) solids thereby improving biogas production during AD post-treatment. In this study, the SS sample (total solids = 1.75 wt% and total chemical oxygen demand (COD) = 15,450 mg L-1) was subjected to TH pretreatment (temperature = 140-180°C and reaction time = 60 minutes) in a 0.7-L capacity stainless-steel high-pressure reactor. At a reaction temperature of 180°C, the maximum solid solubilization (total dissolved solids = 4652 mg L-1) and improved dewaterability (time to filter = 4.7 s.L g-1) were observed. The biochemical methane potential test results showed almost doubling of methane generation from 145 to 284 mL gCOD-1 after TH pretreatment at 180°C. The life cycle assessment approach was used to compare various SS treatment and disposal scenarios, two of which included hydrothermal pretreatment. The scenarios involving hydrothermal pretreatments showed the least global warming potential.