Development of an alkaline/acid pre-treatment and anaerobic digestion (APAD) process for methane generation from waste activated sludge

Abstract

Anaerobic sludge digesters are biorefineries for energy recovery from waste activated sludge (WAS) via methane production, in which disintegration of floc structure and microbial cells is a major challenge in releasing extracellular polymeric substances (EPS) and cytoplasmic macromolecules for subsequent hydrolysis and fermentation. Here, we developed a new process combining alkaline/acid pre-treatments and anaerobic digestion (APAD) to improve sludge digestion. Both alkaline and acid pre-treatments effectively disintegrated the floc structure and microbial cells to release sludge organic contents. Under the optimized alkaline/acid pre-treatment condition, carbon removal achieved 52.8 ± 1.7% in APAD digesters, in contrast to 30.9 ± 2.2% and 42.4 ± 1.6% in anaerobic digesters fed with fresh WAS (control-AD) and thermal pre-treated sludge (thermal-AD), respectively. Both alkaline/acid and thermal pre-treatments largely shifted sludge community composition and function, but in distinct ways, possibly due to their different sludge constitutes (i.e., dissolved organic matter and NaCl). Correspondingly, microbial network analysis identified three modules with varied keystone taxa and interaction patterns in the three digesters. Life cycle assessment showed the comparable environmental impacts of APAD, thermal-AD and control-AD. In all, this study provided a new solution for WAS treatment and insights into impact of sludge pre-treatments on sludge digestion microbiome.