Mild hydrogen peroxide interceded bacterial disintegration of waste activated sludge for efficient biomethane production

Abstract

Regardless of the issue of sludge management all over the world, the role of phase separated pretreatment prior to anaerobic digestion are more promising in terms of energy efficient biomethane production. However, the effect of phase separated pretreatment (dissociation of extracellular polymeric substances (EPS) followed by biological pretreatment in a two-step process) must be sensibly evaluated from various perceptions to consolidate its effectiveness in sludge management and bioenergy recovery. In this study, mild hydrogen peroxide induced bacterial pretreatment (H2O2-BP) was employed as phase separated pretreatment to investigate the effectiveness of EPS dissociation prior to biological pretreatment on sludge solubilization and biomethanation. The novelty of this study is the application of mild dosage of hydrogen peroxide at sludge pH for the removal of EPS layer with lesser formation of recalcitrant substances which thereby enhances the disintegration by enzyme secreting bacterial and methane generation. The outcome confirmed that the higher EPS dissociation was achieved at H2O2 dosage of 8 μL per 100 mL of sludge with negligible cell lysis. An extractable EPS of 172.8 mg/L was obtained after H2O2 treatment. The higher sCOD solubilization of 22% and the suspended solid reduction of 17.14% were achieved in hydrogen peroxide followed by bacterial pretreatment (H2O2-BP) as compared to of bacterial pretreatment alone (BP) (solubilization-11% and suspended solids reduction-9.3%) and control (C) sludges (solubilization-5% and suspended solids reduction-4.3%). The methane generation for H2O2-BP sludge is 0.174 L/gCOD which is higher than BP (0.078 L/gCOD,) and C sludge (0.02175 L/gCOD). A higher biomass solubilization and increased biomethanation in H2O2-BP revealed that dissociation of EPS prior to bacterial pretreatment increases the surface area for bacterial pretreatment facilitating easier accessibility of substrate and enhanced biomethanation.