Characterisation and agronomic evaluation of acidified food waste anaerobic digestate products.

Raw liquid anaerobic digestate was synthesised into nutrient-dense solid digestates via acidification and evaporation. Acidification retained ammonium in the digestate whilst also donating the anion to free ammonium to form an ammonium salt. Digestate was treated with the addition of sulphuric, nitric, and phosphoric acid resulting in the formation of ammonium sulphate, ammonium nitrate and ammonium phosphate, respectively then evaporated into a solid fertiliser product. FTIR, XRD and SEM-EDS collectively confirm that the addition of acids completely converted the free ammonium in the raw digestate into their respective ammonium salt counterparts. Compounds of potassium chloride, silicon dioxide, calcium carbonate, magnesium ammonium phosphate, sodium nitrate, and sodium chloride were identified in all solid digestate samples. Plant growth and grain yield was higher in urea ammonium nitrate, raw liquid digestate and acidified digestate products compared to control and unacidified solid digestate. Urea ammonium nitrate and ammonium nitrate solid digestate had the highest dry shoot, likely due to the high available nitrogen found in both fertilisers. Overall, acidification and evaporation of liquid digestate can efficiently transform it into a valuable solid fertiliser with a high nutrient density. This process not only has the potential to mitigate handling and storage constraints of low nutrient density digestate in anaerobic digestion facilities but also offers a sustainable alternative to conventional fertilisers.

The Synergistic Effect of High Intensity Focused Ultrasound on In-vitro Remineralization of Tooth Enamel by Calcium Phosphate Ion Clusters.

Background: Remineralization of dental enamel is an important intervention strategy for the treatment of demineralized lesions. Existing approaches have limitations such as failure to adequately reproduce both the ideal structural and mechanical properties of the native tooth. The ability of ultrasound to control and accelerate the crystallization processes has been widely reported. Therefore, a new approach was explored for in-vitro enamel remineralization involving the synergistic effect of high-intensity focused ultrasound (HIFU) coupled with calcium phosphate ion clusters (CPICs). Methods: The demineralized enamel was treated with CPICs, with or without subsequent HIFU exposure for different periods (2.5, 5, and 10 min). The specimens were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. The surface hardness and crystallographic properties of the treated specimens were evaluated using Vickers microhardness testing and X-ray diffraction (XRD), respectively. Results: SEM revealed distinct, organized, and well-defined prismatic structures, showing clear evidence of remineralization in the combined CPIC/HIFU treatment groups. AFM further revealed a decrease in the surface roughness values with increasing HIFU exposure time up to 5 min, reflecting the obliteration of interprismatic spaces created during demineralization. The characteristic Raman band at 960 cm-1 associated with the inorganic phase of enamel dominated well in the HIFU-treated specimens. Importantly, microhardness testing further demonstrated that new mineral growth also recovered the mechanical properties of the enamel in the HIFU-exposed groups. Critical to our aspirations for developing this into a clinical process, these results were achieved in only 5 min. Conclusion: HIFU exposure can synergise and significantly accelerate in-vitro enamel remineralization process via calcium phosphate ion clusters. Therefore, this synergistic approach has the potential for use in future clinical interventions.