Global population is set to reach nine billion by 2050, and since the agricultural demand for mineral reserves is already exceeding availability the importance of a more sustainable circular economy is immediately apparent. Given recent increases in the number of biomass to energy conversion schemes, a circular economy utilising biomass by-products possess great potential as a sustainable alternative to traditional fertilisers. This study assesses the potential usefulness of bioenergy waste products as replacements for traditional fertilisers and the barriers that may oppose this change. Biomass thermal conversion involves the combustion of biological material such as poultry litter to generate low-carbon heat and power, and produces waste products in the form of ash as a result. Anaerobic digestion is a similar practice involving the bacterial digestion of organic material in an oxygen-free environment to produce energy rich bio-gas and waste digestate as a by-product. These waste products are rich in nutrients essential to plant growth and, furthermore, the nitrogen and carbon content of the digestate complements the lack of these elements in the bottom ash when both products are blended and applied together.

There are a number of hypothesised benefits to soil function as a result of ash and digestate application. In order to promote plant growth, certain nutrients defined as macro- (such as nitrogen) and micro-nutrients (such as potassium) must be present, both of which are contained in biomass waste. Additionally, the organic matter content within digestate increases soil density, which promotes water retention and reduces the loss of soluble nutrients through water runoff. It is important to note that while studies have been undertaken concerning application of the waste product individually, there is a scarcity of information on the application of mixtures of ash and digestate as a soil amendment.

Despite these merits, certain barriers exist that would make widespread use difficult, the most prominent of these revolving around the perception of the waste as a problem rather than a product with inherent value. In addition, biomass waste is captured under the strict waste regulations under the EU Waste Framework Directive (WFD) which, in the UK, is implemented by the Environmental Permitting Regulations (2010) by DEFRA. These regulations state that an environmental permit (or an exemption) is required in order to carry out land spreading activities. If mixtures of biomass by-products were to be used as alternatives to traditionally made fertilisers, then changes to environmental permitting regulations may need to be modified.

For further information

Read the Environment International original research article which this summary is based on ‘Harmonising conflicts between science, regulation, perception and environmental impact: The case of soil conditioners from bioenergy’ (February 2015).

Visit the profile of the research ambassador, Tim Gardner, who wrote this summary.

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