AMM2FERT- Biochemical Enhancement of Ammonia Fertiliser Production with Sustainable and Low Carbon Principles

The summary of overall project findings is as follows.
• The concentrations of ammonia, urea, organic nitrogen and free available nitrogen in farm slurries and industrial fertilisers vary depending on the nature of the material in terms of its source, application and chemical composition. Pig slurry has different composition and characteristics to Cattle slurry. Pig slurries contain predominantly Ammonium Nitrogen, typically 70% and 30% Organic Nitrogen. Whereas Cattle slurry typically contains 60% Organic Nitrogen and 40% Ammonium Nitrogen. The age of the cattle slurry also has an impact on the nitrogen type available in the slurry with ageing resulting in a conversion of organic nitrogen to ammoniacal nitrogen. Total nitrogen contents in samples analysed during the laboratory and demonstrator trials on Harper Adams farm ranged from 650mg/l and up to 7000mg/l. However, once a solids settlement period was incorporated during sample trials the total nitrogen levels stabilised to within 2000 and 3000mg/l. Ammoniacal nitrogen levels varied as a proportion of the total nitrogen content of the slurry samples ranging from 8% and up to 75% of the nitrogen content.
• The restrictions on ammonia pollution in agriculture vary from region to region, but all are becoming more stringent. In the UK nitrogen fertiliser regulations typically discriminates according to nitrogen availability, materials with high levels of available nitrogen such as poultry manure, pig slurry, cattle slurry and broiler manure are in some cases subject to application timing restrictions and additionally to rules which dictate application methods. The imposition of regulations such as IPPC and Nitrate Vulnerable Zones (NVZ) in the UK have in recent years improved the utilisation efficiency of organic fertilisers; this has resulted in the reduced use of inorganic nitrogen sources, i.e. mineral fertilisers. In Denmark where similar regulation was imposed nitrogen fertiliser use has declined by 50% since 1990. The UN/ECE Gothenburg Protocol and the EU National Emissions Ceiling Directive have been implemented to control ammonia emissions (amongst other pollutants) at the national level. Both the Protocol and the Directive have national emission ceilings for 2010, and both are currently undergoing revision to include revised more stringent ceilings for 2020.
• Laboratory and demonstrator trials successfully proved the feasibility of utilising enzymatic treatment to enhance the conversion of organic nitrogen to ammoniacal nitrogen as a precursor to controlled volatilisation and absorption. Ammoniacal nitrogen contents within the slurry matrix were improved by up to 50%. Thus offering higher potential yields in subsequent stages of the process the air assisted volatilisation, absorption and neutralisation of ammonia into a liquid ammonium form.
• The DGC physical stripping and ammonia absorption method was proven to convert upto 85% of the ammonia in the slurry matrix into a liquid ammonium solution during early trials.
• Further efficiency improvements and increased yields may be possible. High solids in the slurry and foaming was a real issue during laboratory and demonstrator trials which impacted greatly on the process performance. Better control of solids content and redesigning vessels and piping design for foaming control would improve fluid flows and increase aeration rates essential to the stripping/volatilisation process performance.
• The CO¬2(eq) emissions associated with using (i) dairy slurry topped up with mineral fertiliser, (ii) mineral fertiliser alone, and (iii) ammonium nitrate recovered from dairy slurry as fertiliser on a crop of Winter Wheat grown on a medium soil with a soil nitrogen index (SNS) of 1 are presented in Section 2. The final emissions of the recovered Ammonium Nitrate from the AMM2FERT process are 3.26 tonnes CO2(eq)/ hectare which are lower than the emissions produced by using the standard farming practise of using slurry and topped up with mineral ammonium nitrate, but higher than those of mineral ammonium nitrate fertilisers alone. However, as described previously 98 % of the embodied emissions associated with recovered ammonium nitrate from AMM2FERT are due to the use of electricity in the system. Thus, a small reduction of the energy used in the process could reduce the total emissions dramatically. Further process optimisation work and incorporation of renewable energy supplies can potentially reduce the AMM2FERT process carbon footprint significantly.
• Several new applications have been identified for the AMM2FERT process including i) direct conversion of ammonia from pig and cattle slurry to concentrated liquid ammonium-N fertiliser; ii) post-anaerobic digestion conversion of readily available ammonium-N to liquid ammonium-N fertiliser and iii) the enhanced growth of Urease enzyme producing microorganisms for nutrient growth and stabilisation. These applications present real market potential for future exploitation of the AMM2FERT process.