The challenges of anaerobic digestion and the role of biochar in optimizing anaerobic digestion

a b s t r a c t

“Biochar, like most other adsorbents, is a carbonaceous material, which is formed from the combustion of plant materials, in low-zero oxygen conditions and results in a material, which has the capacity to sorb chemicals onto its surfaces. Currently, research is being carried out to investigate the relevance of biochar in improving the soil ecosystem, digestate quality and most recently the anaerobic digestion process. Anaerobic digestion (AD) of organic substrates provides both a sustainable source of energy and a digestate with the potential to enhance plant growth and soil health. In order to ensure that these benefits are realised, the anaerobic digestion system must be optimized for process stability and high nutrient retention capacity in the digestate produced. Substrate-induced inhibition is a major issue, which can disrupt the stable functioning of the AD system reducing microbial breakdown of the organic waste and formation of methane, which in turn reduces energy output. Likewise, the spreading of digestate on land can often result in nutrient loss, surface runoff and leaching. This review will examine substrate inhibition and their impact on anaerobic digestion, nutrient leaching and their environmental implications, the properties and functionality of biochar material in counteracting these challenges.”

Conclusions

“The application of biochar has the potential to improve AD process by counteracting SII, improve digestate quality through nutrient retention, contributing to the buffering capacity of the system and create a surface area for the colonization of microbial cell. Comparatively, these functions can be achieved by another adsorbent like activated carbon with higher efficiency. However, the production of biochar is cost effective hence AD operators can afford to use the material without any need for recovery and this will further encourage the spreading of biochar and digestate on land. Biochar was not primarily designed for AD, hence future research in the interaction between biochar and AD microbes, buffering capacity of biochar during AD and sorption effect of biochar material on the AD using a continuous-fed digestion process should be investigated.”