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

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

Wood ash effects on soil properties and Lactuca sativa growth in soils amended with digestate and poultry litter

The evaluation of the impact of wood ash, on metal uptake and transfer factor of lettuce grown on soil amended with poultry litter, digestate and its fraction was carried out. Positive (inorganic fertilizer) and negative (unamended soil) fertilization controls were included and impacts on soil fertility and crop productivity, as well as potential toxic elements’ levels, were assessed at pre and post planting period. Soil properties (e.g., plant available N and P, and water soluble elements), plant morphometry, elemental composition (e.g., total nitrogen, total carbon, total phosphorus) and nutrient uptake were determined using standard methods. There was higher nutritive content of the soil amended with whole digestate than fiber digestate resulting in its largest weight of lettuce. Ash significantly improved the impact of the amendments on the properties of the soil which was reflected in better lettuce productivity and was most applicable to the poultry litter. Based on the transfer factor and uptake of the trace metals, results show lower potential toxicity in the lettuce from the organic treatments in comparison to the inorganic fertilizer. Wood ash had positive ameliorative effects on the amended soils which makes it a suitable nutrient booster for organic fertilizers and alternative to inorganic fertilizers for leafy vegetables