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Advanced slurry processing (anaerobic digestion, acidification and separation) is being promoted to generate renewable energy, reduce ammonia emissions and optimise storage and transport, respectively. However, these processes could affect slurry phosphorus (P) forms and bioavailability, and hence P dynamics in soil after application. This study investigated the effect of slurry processing, viz. separation, acidification and anaerobic digestion on P forms and distribution of cattle slurry, as well as P dynamics in soil following application of mechanically separated solid and liquid cattle slurry. The results showed that acidification and anaerobic digestion had little impact on TP distribution among particle fractions of slurry, but had substantial influence on P speciation and distribution. Acidification increased the dissolved inorganic-P (IP–H 2 O) proportion in cattle slurry, by reducing the mineral surface adsorbed (IP–NaHCO 3) and precipitated inorganic P (IP–HCl) proportion. Anaerobic digestion decreased OP-NaHCO 3 proportion by degradation and increased the IP-NaHCO 3 and IP-HCl proportion by adsorption and precipitation. Particles <63 μm accounted for over 65% of P present in cattle slurry. The above changes in whole slurry made by acidification and anaerobic digestion were dominated by the <63 μm fraction. Slurry-derived soluble inorganic-P in soil decreased with time, due to adsorption and microbial immobilisation. This decrease was slower in the soil amended with anaerobically digested slurry. Results suggest that anaerobic digestion and acidification change P speciation of separated solid and liquid slurry and the subsequent P dynamics in soil after application. • Acidification increased labile inorganic P in cattle manure by dissolution. • Anaerobic digestion increased labile inorganic P in cattle manure by degradation. • Particles <63 μm accounted for the majority of P present in cattle manure. • Anaerobic digestion increased mass proportion of the <63 μm particles. • Slurry processing controls soluble P in soil, but not the moderately labile P. [ABSTRACT FROM AUTHOR]

Highlights • The particulate fraction dominated the total P content of cattle slurry. • Slurry particulate fraction largely contributed to P leaching. • Anaerobic digestion altered the slurry particulates resulting in greater P leaching. Abstract Livestock slurry contains a large amount of particulate organic matter. When applied to soil these particles can act as carriers transporting phosphorus (P) through and over soils to watercourses. Little is known, however, about how slurry treatment (e.g. acidification and anaerobic digestion) may affect slurry particle size distribution and P forms within the particulate fraction. To characterize the small slurry particles, we separated untreated, acidified and anaerobically digested cattle slurry into 0.45–63 μm, <0.45 μm, <100 kDa and <3 kDa fractions and determined their P speciation. To understand the role of slurry particles on P leaching/translocation in soil, we applied the <63 μm, <0.45 μm and <100 kDa fractions of untreated and processed slurries to the surface of an unplanted agricultural, sand-textured soil in laboratory microcosms and studied P movement under a simulated rainfall regime. Results showed that the 0.45–63 μm particulate fraction accounted for >60% of total P content of the untreated and anaerobically digested cattle slurries. Acidification reduced the total P quantity of the 0.45–63 μm fraction by 26% through dissolution and desorption, resulting in a greater P in the <0.45 μm fraction. Anaerobic digestion increased the total P content of the 0.45–63 μm fraction, as the decomposition and breakdown of coarser particles transferred more P to this fraction. After application to soil, 3.3% of the added inorganic P and 1.7% of the added organic P was found in the leachate in the untreated <63 μm treatment. The 0.45–63 μm particulate fraction largely contributed to this P leaching, while the nanoparticulate fraction (3 kDa-0.45 μm) contained little P and had no appreciable effect on P leaching. Overall, acidification had no impact on P leaching. In contrast, anaerobic digestion increased inorganic P leaching by 67% and organic P leaching by 127%. In conclusion, our findings highlight the importance of the 0.45–63 μm fraction in P transport through soil, and the enhanced bioavailability and mobility of P following anaerobic digestion. These need greater consideration in future studies promoting the sustainable use of livestock waste and P recovery technologies. [ABSTRACT FROM AUTHOR]

Feed in tariffs (FiTs) and renewable heat incentives ( RHIs) are driving a rapid expansion in anaerobic digestion ( AD) coupled with combined heat and power ( CHP) plants in the UK. Farm models were combined with consequential life cycle assessment ( CLCA) to assess the net environmental balance of representative biogas, biofuel and biomass scenarios on a large arable farm, capturing crop rotation and digestate nutrient cycling effects. All bioenergy options led to avoided fossil resource depletion. Global warming potential ( GWP) balances ranged from −1732 kg CO2e Mg−1 dry matter ( DM) for pig slurry AD feedstock after accounting for avoided slurry storage to +2251 kg CO2e Mg−1 DM for oilseed rape biodiesel feedstock after attributing indirect land use change ( iLUC) to displaced food production. Maize monoculture for AD led to net GWP increases via iLUC, but optimized integration of maize into an arable rotation resulted in negligible food crop displacement and iLUC. However, even under best-case assumptions such as full use of heat output from AD- CHP, crop-biogas achieved low GWP reductions per hectare compared with Miscanthus heating pellets under default estimates of iLUC. Ecosystem services (ES) assessment highlighted soil and water quality risks for maize cultivation. All bioenergy crop options led to net increases in eutrophication after displaced food production was accounted for. The environmental balance of AD is sensitive to design and management factors such as digestate storage and application techniques, which are not well regulated in the UK. Currently, FiT payments are not dependent on compliance with sustainability criteria. We conclude that CLCA and ES effects should be integrated into sustainability criteria for FiTs and RHIs, to direct public money towards resource-efficient renewable energy options that achieve genuine climate protection without degrading soil, air or water quality. [ABSTRACT FROM AUTHOR]