Title: A comprehensive study on autothermal thermophilic aerobic digestion process of waste activated sludge in a continuous stirred digester

Authors: Lobat Taghavi; Teimour Amani; Mohsen Nosrati

Addresses: Department of Environment and Energy, Science and Research Branch, Islamic Azad University, P.O. Box 14515-775, Tehran, Iran ' Chemical Engineering Group, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran ' Biotechnology Group, Chemical Engineering Department, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran

Abstract: In this research autothermal thermophilic aerobic digestion (ATAD) of a typical waste activated sludge (WAS) was investigated in a continuous stirred digester, precisely. Volatile solids (VS) reduction, energy audit, pathogen inactivation and sludge dewaterability during aerobic digestion were studied. Two processes with air and pure oxygen sparging were performed and their results were compared. In a continuous ATAD system working with WAS, feeds concentrated preliminary more than 30 g/L can provide stable temperatures above 40°C in aerobic digester. Similarly, sludge feeds concentrated initially above 20 g/L can provide stable temperatures above 43°C in an oxygen sparged aerobic digester. Sludge feeds with total solids concentrations of 60 and 10 g/L demonstrated the highest (57°C) and the lowest (24°C) reactor temperature, respectively. Feed sludges having thickest concentrations of 60 and 50 g/L which caused the thermophilic temperatures of 57°C and 51°C in the reactor, provided moderately dewaterable sludges. In oxygen sparged process, evaporation heat loss was reduced and temperature profiles were higher and also, pathogen removal was sensibly improved in compared with air sparged system.

Keywords: autothermal thermophilic aerobic digestion; ATAD; dewaterability; energy audit; pathogen inactivation; solid reduction; waste activated sludge; WAS; continuous stirred digesters; evaporation heat loss; temperature profiles; pathogen removal.

DOI: 10.1504/IJEWM.2015.068941

International Journal of Environment and Waste Management, 2015 Vol.15 No.2, pp.173 - 185

Accepted: 16 Oct 2014
Published online: 09 May 2015 *

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