Browsing by Author "Monteiro, Alexandre Gomes"
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- Phosphate recovery from manure digestatePublication . Monteiro, Alexandre Gomes; Silva, Paula Cristina PereiraEutrophication is the process by which a water body becomes excessively enriched with nutrients leading to excessive growth of algae and other aquatic plants, which depletes the oxygen in the water and can harm or kill other aquatic life. One of the causes of eutrophication is agricultural run-off, for example, resulting from the application of manure to soil, with phosphorus (P) from manure playing a significant role in this process. Phosphorus in manure is mainly present as magnesium phosphate (struvite) but its transformation into iron phosphate (vivianite) could have advantages for its recovery. Thanks to its paramagnetic properties, vivianite can be recovered using magnets which has been proven on a pilot scale from digested sludge. However, the high bicarbonate (HCO3-) content in manure makes vivianite formation less efficient because it leads to the formation of the iron carbonate (siderite). To further investigate the role of bicarbonate content in vivianite formation, two experiments were conducted: First, the digested manure went through a stripping process in which the high bicarbonate content was gradually reduced, followed by the addition of an iron solution to observe vivianite formation. Second, the formation of vivianite from struvite was studied at different bicarbonate concentrations in ultrapure water, as it is a less complex matrix. The digested manure was gradually stripped up to 130, 60, and 35 mM bicarbonate. Upon iron addition, vivianite formation efficiency was analysed with Mössbauer spectroscopy. The dissolution of struvite and formation of vivianite could be traced by the release of magnesium into the solution. The lower the bicarbonate content, the more struvite dissolved, and the more vivianite formed, with efficient vivianite formation below 50 mM bicarbonate. The struvite/iron/bicarbonate system in ultrapure water showed similar results to those observed in the manure samples, confirming that bicarbonate content is a barrier to vivianite formation in digested manure.