ENHANCEMENT OF BIOGAS GENERATION BY UTILIZING RAW AND MODIFIED WITH HNO3 BIOCHAR OBTAINED FROM PYROLYSIS OF BIOMASS AND DIGESTATE

Biomass- and digestate-derived biochars were modified with nitric acid solution and examined in biochemical methane potential (BMP) tests to determine the effect of pretreatment on each of the different materials capability to improve the biogas production from the anaerobic digestion of conventional substrates such as corn silage. Methane yields from corn silage (0.308 m3kgVS-1) were over the average value for the specific type of lignocellulosic material. Addition of digestate-derived biochar (BCD) in AD process improved the methane production 1.13-fold. However, the sawdust-derived biochar (BCS) resulted in an even greater methane release of 0.374 m3kgVS-1. Chemical treatment reduced the pH of BCs from 10.29 and 11.54 to 3.10 and 2.81 for BCS and BCD, respectively while had a significant impact on materials composition almost removing the ash and metal elements from BCS and markedly decreasing 1.43-fold the ash fraction and by 70-75 % the minerals proportion in BCD. The presence of modified digestate-derived biochar (M-BCD) in a culture led to an enhanced methane production (0.402 m3kgVS-1) indicating that the specific additive exhibited a higher potential than all BCs to promote the efficiency of AD of a biomass feedstock. M-BCD also possessed the greatest capability to lessen an inhibition caused by H2S retaining the concentration of the toxic gas at levels lower than 100 ppm. On the other hand, modified BCS provoked a 9% abatement in methane yields providing evidence that nitric acid could have a neutral or slightly negative effect on the capability of a BC to improve the AD process.