Sludge Thermal Hydrolysis - William Barber

Around the world, the production of sewage sludge is increasing. This is due to numerous factors including growing population, increasing urbanization and investments in wastewater infrastructure. In addition, the composition of sewage sludge is evolving because of stricter environmental regulation. Sludge is changing composition towards the production of activated or biological sludge produced during oxidation of wastewater to destroy nutrients, away from primary sludge produced during initial settlement of the incoming solids in wastewater influent. Unfortunately, the processing of activated sludge is notoriously difficult and has been widely lamented by the scientific literature within fifteen years of the commercialization of the activated sludge process in 1914. The principle difference between activated and primary sludge is the high content of extracellular polymer material in activated sludge. This material makes the sludge viscous and difficult to transport. It also retains water which drastically limits the dewaterability potential for the sludge. Additionally, this material makes activated sludge difficult to degrade during anaerobic digestion. As the use of anaerobic digestion of sludge has been growing in interest due to the production of renewable energy amongst other benefits, so has the interest in improving the anaerobic biodegradability of activated sludge, often seen as the rate limiting step in overall digestion performance of municipal sludge. Decades of
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