Biomass ash from combined heat and power plants as a sustainable soil amendment for the United Kingdom agriculture

Combined heat and power (CHP) plants generate around 65,000 tonnes of biomass combustion ash in the UK each year, with an estimated 52,000 tonnes of this being landfilled at a significant cost and environmental impact. This paper comprises a critical literature review and a detailed techno-economic evaluation to assess the potential of biomass ash from CHP plants as a soil amendment and partial fertiliser supplement for winter wheat (Triticum aestivum L.) in UK agriculture. The review summarises published information on biomass ash characterisation, elemental composition, heavy metal concentrations, and the effects of thermal calcination (400–800 °C) on nutrient availability and heavy metal immobilisation. Key findings include that calcined biomass ash can be used as a liming agent or a source of secondary macronutrients (Ca, Mg, K, and P), but cannot be used as a complete NPK substitute due to high levels of near-total nitrogen volatilisation during combustion. A full-scale commercial techno-economic model (20 years, 8% WACC) confirms that, under base-case assumptions, the project is financially viable (pre-Quality Protocol) at + £7.4 M (Scenario A) and + £24.1 M (Scenario B) after regulatory reclassification. The main commercial barriers identified are the absence of a UK Quality Protocol for biomass combustion ash, compliance requirements under SI 1989/1263, PTE threshold limits, and end-of-waste legislation. All quantitative data are presented as preliminary estimates that must be confirmed through multi-location field trials, soil incubation studies, and site-specific engineering evaluations.