What kind of effects do Fe2O3 and Al2O3 nanoparticles have on anaerobic digestion, inhibition or enhancement?

Abstract

Fe2O3 and Al2O3 nanoparticles are widely used in products and find their way to wastewater treatment plants through the contact of water with these products. In this study, impacts of Fe2O3 and Al2O3 nanoparticles on methane potential of waste activated sludge (WAS) were investigated by comparing long and short term toxicity test results, modelling and FISH analysis. Methane production from the samples treated with the maximum concentration of Fe2O3 nanoparticles decreased 28.9% at the end of the long term BMP test. EC50 value for BMP test of the Fe2O3 nanoparticles was calculated as 901.94 mg/gTS with high coefficient of determination. Methane production from the samples treated with Al2O3 nanoparticles increased up to 14.8% (p > 0.05) at the end of the BMP test. However, short term toxicity tests for Fe2O3 and Al2O3 nanoparticles showed no impact on anaerobic digestion of WAS. Kinetic parameters obtained from models and captured FISH images were consistent with these results. Different impacts of nanoparticles on methane production suggested that anaerobic microorganisms can be affected from nanoparticles in various mechanisms. Hydrolysis (kH) and overall reaction rates (kR) values were determined as 0.0277 and 0.1441 d−1, respectively for each concentration of Al2O3 nanoparticles and raw WAS. Similarly, methane production from WAS containing 5, 50, 150 and 250 mgFe2O3/gTS were modeled with same kinetic values. However, kH constant was calculated as 0.0149 d−1 for 500 mgFe2O3/gTS. This means that Fe2O3 nanoparticles starting from this concentration inhibited the methanogenic consortium and caused decreased biogas production and spesific methane production rate.