Thermal and oxidative disintegration of anaerobic digested sludge by solution plasma process

Abstract

Solution plasma process (SPP) is promising for sludge disintegration, since the SPP only uses electric power and induces strongly oxidizing environments. In this study, the SPP using a capillary discharge that generating reactive oxygen species and heating solution was developed to assess the disintegration performance of anaerobic digested sludge. The SPP was compared with the thermal process (TP) which has only thermal contributions to evaluate the contributions of thermal and oxidative disintegration of sludge. Compared to the TP, under all tested conditions, the improved solubilization performance (up to 1.41, 1.84, and 6.55 times higher for overall COD, proteins, and carbohydrates, respectively) by the SPP was attributed to the oxidative effect (statistically significant, p < 0.01) with the thermal effect on the sludge disintegration. This oxidative effect became less significant as the temperature and incubation time without further plasma discharge increased. According to the particle size distributions and detailed characterization of dissolved organic matters, an increased release of biopolymers (proteins and carbohydrates), low molecular weight (LMW) substances (building blocks and neutrals), and the significant particle size reduction, suggested that the SPP induced floc disruption, cell lysis, and disintegration of sludge flocs even at the temperature of between 60 and 80 °C, while the TP was not favorable for releasing intracellular LMW substances and reducing the sludge floc size. Therefore, the SPP showed a synergistic impact of thermal and oxidative effects for improving the sludge disintegration. This study provides comprehensive insights for understanding the SPP and its possible application to sludge treatment.