• Energy Research

This work studied the effects on the anaerobic digestion of sewage sludge by zero valent iron nanoparticles (NZVI) dosage. Biochemical methane potential tests were carried out with 5-9 mg/gVS (99.7%, 40-60 nm). The biogas yield increased from 132 (control) to 310 mL/gVS with 9 mg/gVS. The methane content increased from 63.2% (control) to 77.6% with NZVI, which corresponded to a maximum yield of 238 mLCH4/gVS with 9 mg/gVS. The maximum VS reduction was 19.6%. The highest INT-ETS activity (20.1-37.1 µgINTred/gVS·h) corresponding to the maximum values of sCOD was reached within the first days. NZVI decreased the ORP to -300 mV and increased the VFA's concentration (+2000 mg/L). The ORP-VFA-pH analysis showed that NZVI promoted the acidogenesis-acetogenesis without acidification. That is, NZVI was effective in intensifying the performance and stability of the process.

This work studied the effects on the anaerobic digestion of sewage sludge by zero valent iron nanoparticles (NZVI) dosage. Biochemical methane potential tests were carried out with 5-9 mg/gVS (99.7%, 40-60 nm). The biogas yield increased from 132 (control) to 310 mL/gVS with 9 mg/gVS. The methane content increased from 63.2% (control) to 77.6% with NZVI, which corresponded to a maximum yield of 238 mLCH4/gVS with 9 mg/gVS. The maximum VS reduction was 19.6%. The highest INT-ETS activity (20.1-37.1 µgINTred/gVS·h) corresponding to the maximum values of sCOD was reached within the first days. NZVI decreased the ORP to -300 mV and increased the VFA's concentration (+2000 mg/L). The ORP-VFA-pH analysis showed that NZVI promoted the acidogenesis-acetogenesis without acidification. That is, NZVI was effective in intensifying the performance and stability of the process.

Abstract Waste activated sludge (WAS) is a polluting waste with severe management problems that must be treated to prevent pollution and human health risks. Anaerobic digestion (AD) is the most used process to stabilize sludge; however, it must be improved because the biomethanation of sludge entails low biodegradability, pathogen inactivation, and biogas production. This study investigated the effects of ultrasonic pretreatment (USp) of WAS as a strategy to improve AD. Macromolecule solubilization, heavy metal behavior, pathogen inactivation and biogas production were evaluated. USp was applied at a range of 5000–35000 kJ/kg TS (total solids). The maximum solubilization degree of soluble chemical oxygen demand was 26%, and 22.9% of proteins at 35000 kJ/kg TS. The highest USp reduced only 2 log units of pathogens; nevertheless, a high inactivation was obtained when TS were reduced to 2% and continuous stirring was applied. AD of raw and sonicated WAS were compared with biochemical methane potential tests, and a biogas overproduction of 31.43% (219.5 mL/g VS) was achieved at highest USp. A modified Gompertz model was used for kinetic study of biogas production. The kinetic parameters at highest energy were: biogas production potential, G 0 = 634.2 mL; maximum biogas production rate, R max = 57.23 mL/day.

Abstract Waste activated sludge (WAS) is a polluting waste with severe management problems that must be treated to prevent pollution and human health risks. Anaerobic digestion (AD) is the most used process to stabilize sludge; however, it must be improved because the biomethanation of sludge entails low biodegradability, pathogen inactivation, and biogas production. This study investigated the effects of ultrasonic pretreatment (USp) of WAS as a strategy to improve AD. Macromolecule solubilization, heavy metal behavior, pathogen inactivation and biogas production were evaluated. USp was applied at a range of 5000–35000 kJ/kg TS (total solids). The maximum solubilization degree of soluble chemical oxygen demand was 26%, and 22.9% of proteins at 35000 kJ/kg TS. The highest USp reduced only 2 log units of pathogens; nevertheless, a high inactivation was obtained when TS were reduced to 2% and continuous stirring was applied. AD of raw and sonicated WAS were compared with biochemical methane potential tests, and a biogas overproduction of 31.43% (219.5 mL/g VS) was achieved at highest USp. A modified Gompertz model was used for kinetic study of biogas production. The kinetic parameters at highest energy were: biogas production potential, G 0 = 634.2 mL; maximum biogas production rate, R max = 57.23 mL/day.