Bioenergy Production From Sewage Sludge Via Enhanced Anaerobic Digestion And Dark Fermentation

Energy demands have dramatically increased over the last decade, and a revolution in technology and lifestyles has led to the use of fossil fuels to cover this demand, negatively impacting our environment and causing an increase in greenhouse gases (GHG) and global warming. Aside from their environmental impact, fossil fuels are an unsustainable source of energy. Hence, researchers have focused for many years on finding new sources of energy. Sewage sludge is a sustainable source of energy production and has long been used as feedstock for anaerobic digestion (AD) systems for biogas production. Ever stricter environmental restrictions on sewage sludge discharge/disposal and the reliance of wastewater treatment plants (WWTPs) on AD (as the preferred technology for sewage sludge handling) has led to an increase of sewage sludge volume in recent years. This situation is challenging for WWTP; moreover, AD increases GHG (30–40% of produced biogas is carbon dioxide). Therefore, current sewage sludge management needs to upgrade the produced biogas by increasing methane yield and reducing carbon dioxide. There is potential to upgrade the biogas through hydrogenotrophic pathway by addition of hydrogen gas into AD to be combined with carbon dioxide and produces extra methane gas and, therefore, achieving higher energy output, sewage sludge utilisation and volume reduction. This study investigates the hydrogen potential of sewage sludge by using the dark fermentation (DF) process, a promising biological hydrogen production method. Results reveal need to apply an upgraded method of optimising biogas production and increasing methane yield; the need for an inoculum pre-treatment prior to DF; and the importance of a substrate pre- treatment, such as enzymatic hydrolysis (EH). Further investigation and assessment of the DF process is required to create other opportunities to use sewage sludge as feedstock for sustainable hydrogen production.