Adding granular activated carbon into anaerobic sludge digestion to promote methane production and sludge decomposition

Anaerobic digestion of waste activated sludge is frequently restricted with the slow fermentation rate due to its complex components. Carbon materials have been reported to enhance syntrophic metabolism of anaerobic wastewater treatment, but its function in anaerobic digestion of sludge has yet to be investigated. In this study granular activated carbon (GAC) was added into a batch-mode anaerobic sludge digestion reactor with an attempt to improve the sludge digestion. The results showed that with adding GAC from 0 to 5.0 g, the methane production increased by 17.4%, and the sludge reduction rate increased by 6.1 percent points (from 39.1% to 45.2%). In the 20 days’ digestion, GAC obviously enriched hydrogen-utilizing methanogens, Geobacter, and other methanogens capable of direct interspecies electron transfer, which could enhance the electron exchange between syntrophs and methanogens to accelerate substrate consumption and methane production.