Phosphorus speciation during anaerobic digestion and subsequent solid/liquid separation

• Published in: The Science of the total environment Vol. 734; p. 139284
• Main Authors: Mazzini, Stefania, Borgonovo, Gigliola, Scaglioni, Leonardo, Bedussi, Floriana, D'Imporzano, Giuliana, Tambone, Fulvia, Adani, Fabrizio
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10-09-2020
• Subjects: 31P NMR; Anaerobic digestion; Phosphorus speciation; Renewable fertilizers; TAN; BB; AD; D; PTFE; FM; DM; I; HRT; Anaerobic digestion; Phosphorus speciation; S/L; NMR; TKN; 31P NMR; Pi; SL; LF; Renewable fertilizers; ICP-MS; VS; TS; Po; P NMR
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.139284

This study aims to investigate the effect of anaerobic digestion (AD) on P species and how the different species are distributed in the digestate and digestate fractions, i.e. liquid and solid fractions. To do so, six full scale AD plants were used in this work and representative biomass samples were collected for investigation. P fractionation proceeded by adopting fractionation protocols consisting in step-by-step extraction with different solvents, (i.e. NaHCO3, HCl and NaOH-EDTA). Subsequently P species in the different fractions were identified by using 31PNMR. On average, AD did not substantially affect P speciation that depended on the P-fraction content of feeds. A high NaHCO3 fraction content in the ingestate determined, also, a high content of this fraction in the digestate, with consequently lower contents of both P-HCl and P-NaOH-EDTA, i.e. digestate P-fraction contents represented an inheritance of P speciation in the ingestate. A feed effect was observed in single plants. Highest pig/cow slurry content in the feeds seemed to decrease readily soluble P (extracted with NaHCO3) content and increased P associated with both organic matter and amorphous Fe/Al in the digestate. Again, using a large amount of digestate in the feed increased P-soluble content in the digestate. 31P NMR analyses revealed that inorganic P compounds dominated the spectra of all biomasses and fractions, with orthophosphate as the predominant species. When present, organic phosphorus compounds were typically represented by monophosphate esters, DNA and phospholipids, with a predominance of monophosphate esters.
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•Anaerobic digestion (AD) can affect P speciation.•P speciation was studied in six AD plants by P fractionation and 31P NMR.•On average AD did not affect P distribution into the different P-fractions.•AD feed seemed to affect P speciation when AD plants were studied singly.•31P NMR assessed that orthophosphate dominated P in digestate and its fractions.