Anaerobic digestion of thermal pre-treated sludge at different solids concentrations – Computation of mass-energy balance and greenhouse gas emissions

• Published in: Journal of environmental management Vol. 157; pp. 250 - 261
• Main Authors: Pilli, Sridhar, More, Tanaji, Yan, Song, Tyagi, Rajeshwar Dayal, Surampalli, Rao Y.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2015; Academic Press Ltd
• Subjects: Bacteria, Anaerobic - metabolism; Bioreactors; Comparative analysis; Conservation of Energy Resources; Emissions; Energy ratio; Greenhouse Effect; Hot Temperature; Humans; Mixed sludge; Models, Theoretical; Net energy; Performance evaluation; Primary sludge; Secondary sludge; Sewage - chemistry; Sludge; Solids; Thermal energy; Thermal pre-treatment; Waste Disposal, Fluid - methods; Water treatment; Mixed sludge; Energy ratio; Thermal pre-treatment; Primary sludge; Net energy; Secondary sludge
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2015.04.023

The effect of thermal pre-treatment on sludge anaerobic digestion (AD) efficiency was studied at different total solids (TS) concentrations (20.0, 30.0 and 40.0 g TS/L) and digestion times (0, 5, 10, 15, 20 and 30 days) for primary, secondary and mixed wastewater sludge. Moreover, sludge pre-treatment, AD and disposal processes were evaluated based on a mass-energy balance and corresponding greenhouse gas (GHG) emissions. Mass balance revealed that the least quantity of digestate was generated by thermal pre-treated secondary sludge at 30.0 g TS/L. The net energy (energy output-energy input) and energy ratio (energy output/energy input) for thermal pre-treated sludge was greater than control in all cases. The reduced GHG emissions of 73.8 × 10−3 g CO2/g of total dry solids were observed for the thermal pre-treated secondary sludge at 30.0 g TS/L. Thermal pre-treatment of sludge is energetically beneficial and required less retention time compared to control. •Energy sustainability of the thermal pre-treatment and anaerobic digestion is evaluated.•Energy and greenhouse gas emissions are considered as criteria in evaluating the process.•Thermal pre-treatment of sludge followed by anaerobic digestion is energetically sustainable.•Greenhouse gas emissions are reduced with thermal pre-treated of sludge followed by anaerobic digestion.