Effects of nanoparticles and ozone pre-treatments on dark fermentation of biosolids and wine vinasses

Abstract

This study investigates the impact of carbon-encapsulated zero-valent iron (ZVI) nanoparticles, both independently and in combination with ozone pre-treatment, on the batch and semi-continuous dark fermentation of biosolids and wine vinasses in a thermophilic reactor (55 °C). The study focuses on the production of volatile fatty acids (VFA) and hydrogen, as well as the dehydratability of the digestate.

The pre-treatment with ZVI nanoparticles does not result in an overall increase in total acid production. However, it does affect the VFA profile by promoting the formation of long chain acids (C ≥ 4), notably resulting in a 37 % increase in butyric acid yield (mg/gVS_added). In terms of hydrogen yield, the use of ZVI nanoparticles shows no discernible effect. However, a significant increase in carbon dioxide yield is observed, reaching a 129 % rise compared to the control, expressed as mL/gVS_added. When combining the dosage of ZVI nanoparticles with ozone, there was observed a noticeable effect on hydrogen yield, leading to an increase (e.g. 125 %). Regarding with the dehydratability of the digestate, the pre-treatments with ZVI nanoparticles, as well as the combination of the ZVI nanoparticles with ozone, enhanced the dehydratability of the digestate by reducing the specific resistance of the cake which facilitates the subsequent waste processing.