The Impact of Enzymatic Hydrolysis of Sewage Sludge as a Pre-treatment for Dark Fermentation

Abstract

For many years, sewage sludge has been processed for methane production in anaerobic digestion reactors at wastewater treatment plants around the world. Sewage sludge is produced in large quantities and is rich in biodegradable organic materials, from which sugars (e.g., glucose) can be produced, recovered and used as a substrate to support hydrogen production through the Dark Fermentation (DF) process. DF is one of several methods used for bio-hydrogen production, whereby fermentative bacteria are used to hydrolyse organic substrates to produce hydrogen gas. Carbohydrates (sugars) is one of the main fermentable substrates for hydrogen production, and they are considered the most favourable substrate for fermentative bacteria (e.g., Clostridium bacteria). Although sewage sludge is rich in organic materials, still the complexity of its structure and low carbon/nitrogen ratio limits the bio-hydrogen production via DF processes. Therefore, this paper addresses the impact of Enzymatic Hydrolysis (EH) as a pre-treatment of sewage sludge on enhancing the biodegradability and glucose content in sewage sludge. The result shows that using the EH process as pre-treatment for sewage sludge, enhanced the glucose content in sewage sludge and converted some of the macro sewage flocs to easy digestible micro flocs (glucose). Therefore, the substrate being more favourable and easier to digest by bacteria in the DF reactor, enhanced the production of hydrogen and VFAs. More research needs to be done to find the optimum enzyme dosage, initial substrate concentration and operation temperature (especially when the enzyme is used inside the DF reactor).