Developing a suite of novel land conditioners and plant fertilizers from the waste streams of biomass energy generation

Soils provide, support and regulate fundamental processes in the environment, including nutrient cycling, plant growth, and have a strong influence on ensuring purity of the atmosphere, as well as water supply and quality. Through the delivery of these ecosystem services, vital global biodiversity and, ultimately, the sustenance of the human population is maintained. However, exploitation of soils through intensive agricultural practices such as the over application of phosphorus and nitrogen fertilisers, has resulted in their degradation and, as a result, a diminishment of soil fertility, threatening future global food security.
Phosphorus is a vital, non-renewable element required for crop growth, upon which agriculture is now almost entirely dependent to maintain current levels of food production. The extraction and processing of phosphorus, is also extremely environmentally damaging, and originates from a non-renewable source for which demand is rapidly increasing with no alternative available in the volume required. The production of nitrogen fertiliser is also a highly energy intensive and unstainable process, is tied strongly to the price and availability of fossil fuels. As the global population is expected to reach 9 billion by 2050, humanity faces an urgent need to balance an ever increasing demand for energy and natural resources, with the sustainable management of ecosystems and the vital services that they provide.
If managed correctly, the bioenergy sector presents a unique opportunity to, in part, address the challenges facing agriculture, energy generation, and waste disposal. Gasification, incineration, biomass boilers and anaerobic digestion (AD) are currently the dominant technologies being deployed to convert a wide range of biomass and waste biomass derived fuels into renewable energy. The by-products generated from these technologies themselves, such as ash (rich in phosphorus) from biomass thermal conversion and digestate (rich in nitrogen) from AD, have complimentary nutrient values and properties conducive to their use as soil conditioners and fertilisers. However, these waste streams are a typically undervalued, and frequently disposed of at a cost, with little consideration of best practice for environmental health due to the lack of quantitative evidence on which to base informed decisions at appropriate scales or across science disciplines.
It is the overarching aim of this research to mix ash and digestate waste materials to form a new, safe and sustainable source of nutrients for agricultural practice, thereby reducing pressure on natural resources and to address some of the challenges facing bioenergy waste disposal. This will be achieved through the following:
(i) To physically and chemically test the individual digestates and ashes and the resulting mixtures for consideration as soil amendments.
(ii) To compare the impact of selected digestates and ashes and mixtures against traditional fertilisers on soil properties, plant growth (winter wheat and pea) and the cycling of nutrients under carefully controlled conditions in glasshouses.
(iii) Following intensive glasshouse studies, the most promising of the blended soil amendments will be tested and compared to conventional fertiliser application in the field over two growing seasons for winter wheat and pea.
(iv) To engage with the Environment Agency about the way forward in developing the most promising soil amendments for use in agriculture as genuine alternatives to conventional fertiliser application.
Following extensive testing on selected crop types both in glasshouses and under field conditions, the final blended ash and digestate product(s) will be applicable for use in an agricultural setting as a direct substitute for traditional fertilisers. Benefits include a reduced dependence on phosphorus and nitrogen fertilisers, as well as maintenance of the physical chemical integrity of soil, thereby aiding long-term food security.

This research will contribute to paradigm-shift, to change in the way in which bioenergy 'waste' is perceived, from an expensive problem, to a truly sustainable substitute to traditional fertiliser products, with holistic environmental and economic value. Through providing a market for ash and digestate waste-streams from bioenergy generation, the development of a blended product will remove the cost burden, which is presently a significant disincentive to the generation of renewable biomass energy schemes, promoting further bioenergy developments. Direct benefit therefore, will extend from the commercial bio-energy operators by way of reduced waste disposal costs, waste management companies who can maximise the value of the materials by processing, through to the grower who can use lower cost and more sustainable products. Beyond immediate commercial beneficiaries, these benefits will transfer through the supply chain to the wider public, as food and power consumers, who will access more cost effective, sustainable and secure food products, as well as lower impact energy supply. Longer term, nutrient recovery will ensure that food production remains economically viable in the face of depreciating supplies of raw phosphate, and higher cost nitrogen, whilst a more viable and extensive network of low-carbon bio-energy production facilities will provide improved energy security. Both improved food and energy security will allow the UK to meet its obligations for carbon reduction under the Kyoto Protocol.
Looking globally, the use of rock phosphate reserves is increasingly geopolitically sensitive, with the mineral deposits under the control of a handful of countries such as China, the US and Morocco. China has recently imposed a 135% export tariff to ensure domestic supply. In addition, the import of P rock from Morocco is sensitive, as it currently occupies the Western Sahara, controlling its P reserves. Hence, trading with these regions is highly condemned by the United Nations. Further to these politically unstable sources, the USA is estimated to have less than 30 years of high quality rock phosphate reserves remaining. Hence, for countries such as the UK with no natural rock phosphate mineral reserves, political, legal and economic challenges related to primary P use are likely to become increasingly important issues as global supply declines. The UK, and indeed other countries, will therefore be increasingly dependent upon recycling of P to ensure economic competitiveness of agriculture.
With respect to nitrogen, the production of N fertilisers relies heavily on adequate supplies of methane from which hydrogen gas can be generated; hence it is tied strongly to the price and availability of fossil fuels. Reduced dependence on the Haber Process as a result of N formation from anaerobic digestion of waste materials will significantly reduce the UK's dependence on foreign gas imports for fertiliser production. The development and demonstration of efficacy of waste-derived fertilisers therefore presents a benefit to any user of fertilisers who is currently reliant on traditionally sourced products.
It is hoped that the proposed eventual End of Waste submission for the product, which will be derived from the "mixing" of two wastes in its simplest terms, will go some way to reframing and addressing the current perception of waste as a "disposal issue", and truly redefining waste as a resource. Although waste recycling and reuse has come a long way in recent years, the perception of wastes as ingredients to be blended and reused is not yet fully established as acceptable. This project will serve as a case study for future waste policy and legislation: The use of waste in food production is an application which is potentially highly sensitive to the end-user, and as such, success in this area will do much to promote movement and change in perceptions.