Impact of Nanoparticles on Biogas Production from Anaerobic Digestion of Sewage Sludge

Since anaerobic digestion (AD) is the preferred procedure for sludge treatment and disposal, it is constrained by the hydrolysis and acidogenesis stages.Nanomaterials have an impact on the AD process due to their unique properties (large specific surface areas, solubility, adsorp-tion reduction of heavy metals, degradation of organic matter, reduction of hydrogen supplied and catalytic nature) which make them advantageous in many applications due to their effective-ness in improving the AD efficiency.Magnetic Nanoparticles (MNPs) were used in the present study to improve the biogas production.The experiments were divided into two stages to evaluate the effect of adding MNPs to two types of sewage sludge (SS): attached growth process (AG) and activated sludge (AS).The first stage consists of 15 tests divided into three experiments (A, B, and C).Doses of MNPs (20,50, 100, 200) mg/l were added to all digesters in the same experiment except for one digester (the control).Experiments A, B and C achieved the highest biogas production when 100 mg/l of MNPs was added.They were 1.9, 1.93 and 2.07 times higher than the control for A, B and C respectively.The second stage consists of 12 tests with a pretreatment for some of SS.It was divided into two experiments (D, E), where the chemical pretreatment was applied to experiment D and the thermal pretreatment was applied to experiment E except for the control.For digester D4, which had 100 mg/l of MNPs after a chemical pretreatment at pH = 12, the biogas production increased by 2.2 times higher than the control (D0) and 1.5 times higher than the untreated sludge with the addition of 100 mg/l MNPs (DN).Thermal pretreatment at 100 °C with addition of 100 mg/l MNPs (E4) achieved a biogas yield 2 times higher than the control (E0), and 1.39 times higher than untreated sludge with 100 mg/l MNPs (EN).The previous results indicate that the integration of magnetite can serve as the conductive materials, promoting inherent indirect electron transfer (IET) and direct interspecies electron transfer (DIET) between methanogens and fermentative bacteria which lead to a more energy-efficient route for interspecies electron transfer and methane productivity.This study demonstrated the positive effect of magnetite on organic biodegradation, process stability and methane productivity.