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Alce, Jessica

Gamaralalage, Disni

Gill, Andy

Mckechnie, Jon

Meredith, Will

Snape, Colin

West, Helen

English

Engineering Conferences International

BIOWASTE TO BIOCHAR: HYDROTHERMAL CARBONISATION & HIGH TEMPERATURE TORREFACTION OF FOOD WASTE ANAEROBIC DIGESTATE  Will Meredith, University of Nottingham william.meredith@nottingham.ac.uk Colin Snape, University of Nottingham, UK Disni Gamaralalage, University of Nottingham, UK Jon Mckechnie, University of Nottingham, UK Helen West, University of Nottingham, UK Jessica Alce, Severn Trent Green Power (STGP), UK Andy Gill, Coal Products Ltd (CPL), UK   Key Words: Biochar, hydrothermal carbonisation, torrefaction, food waste, anaerobic digestate  Biochar can potentially contribute as a Greenhouse Gas Removal (GGR) technology to achieve UK’s net zero emission target by 20501, but risks being constrained by the availability of conventional feedstocks such as wood. Biomass wastes which are less attractive in energy applications, particularly anaerobic digestate, can extend the scale of biochar deployment. Application of stable biochar in the soil is capable of achieving a long-term carbon storage with potential co-benefits for improving the soil quality2.  Anaerobic digestion (AD) plants treat numerous feedstocks including the current input of around 30% is from food waste. In 2019, over 4 million tonnes of food waste were treated in the operational 579 AD plants3. Future growth in the sector will be driven by food waste management, where AD is viewed as an environmentally favourable treatment method for unavoidable food waste. Our analyses indicate the biochar production from food waste digestate achieving a substantial net greenhouse gas (GHG) removals of approximately 1.6 t-CO2eq.t-biochar-1. Transport distance and soil effects are uncertain but are estimated to have a small impact on GHG emissions, highlighting that the majority of emissions reductions are from the physical storage of carbon in biochar (1.9 t-CO2eq.t-biochar-1). The use of 50% of UK’s projected available food waste digestate by 2030 can sequester around 85 kt-CO2eq p.a, requiring 28 individual 20 kt p.a biochar production facilities. Commercial biochar production from food waste digestate is able to provide cost-effective GHG removals of less than £100 t-CO2-1 avoided. Other wet wastes such as green waste will command a lower gate fee resulting in higher costs of avoiding CO2. Sensitivity analysis demonstrates the heavy influence of the gate fee and its importance for biochar process establishment. This work considers a highly promising opportunity in solving a waste disposal burden and simultaneously removing atmospheric GHGs. Multiple sources of biochar will be needed to make significant contributions to the UK’s GGR target.  The biochar will be produced at a demonstration facility at the CPL site in Immingham, UK by combining hydrothermal carbonization (HTC) with high temperature torrefaction (HTT) at temperatures of ca. 700°C, to char the biocoal produced by HTC of AD fibre provided by STGP. This will obtain very stable biochar with atomic H/C ratios <0.5 and stable polyaromatic carbon (SPAC)4 contents of over 90%. Further, the biochar produced will satisfy the voluntary European Biochar Certificate (EBC) environmental standard for biochar and have good adsorptive properties for moisture and nutrient retention. It constitutes a highly promising opportunity in solving a waste disposal burden and simultaneously removing atmospheric GHGs.  1. Simon R. et al. 2021. Greenhouse gas removal methods and their potential UK deployment. Department for Business, Energy and Industrial Strategy by Element Energy and the UK Centre for Ecology and Hydrology. 2. Oni BA, Oziegbe O. & Olawole OO. 2019. Significance of biochar application to the environment and economy. Annals of Agricultural Sciences vol. 64 222–236. 3. Department of Environemnt, Food & Rural Affairs. 2021. Area of crops grown for bioenergy in England and the UK:2008-2020. 4. McBeath MV, Wurster CM, Bird MI. 2015. Influence of feedstock properties and pyrolysis conditions on biochar carbon stability as determined by hydrogen pyrolysis. Biomass and Bioenergy 73, 155–173.  

Biowaste to biochar: hydrothermal carbonisation & high temperature torrefaction of food waste anaerobic digestate

https://dc.engconfintl.org/cgi/viewcontent.cgi?filename=0&article=1026&context=pyroliq_2023&type=additional

Biowaste to biochar: hydrothermal carbonisation & high temperature torrefaction of food waste anaerobic digestate

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Engineering Conferences International