Towards Circular Economy : Wood ash management for biomass CHP plants in the UK

Abstract: In response to climate change, the United Kingdom has committed to reach net zero greenhouse gas emissions by 2050. To reach the set target, the Committee on Climate Change is planning a notable increase of bioenergy up to 15% in the national energy mix and thus an increase of the amount of ash produced. Nowadays, ash is rarely recycled or reused but mostly landfilled, which is both costly for the industry and unsustainable. In parallel, agricultural land and forestry suffer both from soil acidification and nutrient depravation due to the intensive land utilization practices. This study reviews the potential of a circular economy of wood ash for application on land and forestry through a case study based on the ash generated by two biomass-fired CHP plants in the UK. It summarizes the general ash characteristics, the factors influencing its quality, and the optimal composition sought for application to land and forestry. The study also aims at defining the main concerns with regards to potential contamination of the environment and dangers to human health. Eventually, the process to evaluate and establish recycling of the ash for both plants was analysed in light of the above. The study found that ash is a remarkably variable co-product, depending mainly on the fuel input and combustion conditions. Ash is a good replacement for agricultural lime and conserves a notable part of the biomass fuel nutrients. It was estimated that ash could cover a significant part of the liming and fertilising demand in the UK by 2050, and deliver a substantial financial value to a power plant. However, contamination concerns are present, especially heavy metals, which could lead to damage on the environment and reduction of the growth rate. The study found that ash recycling in the UK is currently a challenging process, that should not be overlooked when designing a biomass project. When they exist, procedures are demanding with regards to testing, which can financially deter power plants to engage in ash recycling processes.