Abstract
Many studies have been conducted on the anaerobic digestion of sewage sludge due to its enormous amount to collect and dispose of. Different methods to improve the process of anaerobic digestion of sewage sludge have been investigated, focusing on the increase of biogas production.
In this article, attention is focused on the use of two different carbon-rich products to boost the production of methane in the anaerobic digestion of sewage sludge. The investigation aims to underline the different outcomes that biochar and hydrochar show on methane yield. Both are carbon-rich products but there are differences in their properties and the processes from which they are derived. Biochar is a product of the pyrolysis treatment of biomass. This product can be different in composition and properties depending on the process conditions. Hydrothermal Carbonization (HTC) is an important mid-temperature thermochemical process that converts biomass into hydrochar. The solid HTC by-product seems to be a good accelerator of methane production. The tests are performed in batch reactors, with 0.5, 2, and 5 grams of the two products added to 60 grams of inoculum and 100 grams of sludge, based on the total volatile solids. Mesophilic Anaerobic Digestion was adopted, at a temperature of 35°C, for 34 days, until methane production was stopped. pH is an important parameter for the process, its value being maintained in the 6.8-8 range. The results show a significant increase in methane yield compared to the simple anaerobic digestion process.
