Investigation of the potential effect of encapsulated metal nanoparticles on enhancement of thermophilic anaerobic digestion

The present work investigates the enhancement effect of seven different catalysts made of Cu/SiO₂, Pd/SiO₂, Pt/SiO₂, Ni/SiO₂, Co/SiO₂, Ag/SiO₂ and Fe/SiO₂ nanoparticles (NPs) on methane production during thermophilic anaerobic digestion. The tested NPs were synthesized by the sol-gel process and encapsulated in porous silica (SiO₂) to prevent their coagulation and agglomeration. Transmission electron microscopy (TEM) pictures confirmed the specific morphologies of all seven catalysts.

Then, these 7 NPs were tested first in batch experiments with acetate as a carbon substrate for bio-methane production. Ni/SiO₂ and Co/SiO₂ showed the best enhancement of methane production from acetate. From this part, both NPs were tested for bio-methane production on two different substrates: starch and glucose. With the starch substrate, the improvements of methane production were equal to 47% and 22%, respectively, for Ni- and Co/SiO₂ compared to control sample. In the last part of this work, the influences of NP concentration and thermal pre-treatment applied to the NPs on bio-methane production from glucose were investigated. The results showed that all forms of nickel and cobalt NPs enhance the methane production, and their effect increased with the increase of their concentrations. The best sample was the calcined nickel NPs at a concentration of 10^–4 mol L^–1, leading to a methane production rate of 72.5% compared to the control.