Molecular transformation pathway and bioavailability of organic phosphorus in sewage sludge under vermicomposting

Phosphorus reclamation from sewage sludge is essential for sustainable phosphorus management, as large quantities of phosphorus afflux into wastewater treatment plants and are finally enriched in sewage sludge via phosphorus removal technologies. Meanwhile, vermicomposting is a cost-effective biotechnique for sludge stabilization. This work unveiled the molecular transformation pathway and bioavailability of organic phosphorus (OP) in sludge under vermicomposting with solution 31P NMR, FT-ICR MS and enzymatic hydrolysis assay. In conclusion, vermicomposting transformed OP in two stages. In stage I (day 0 to 14), macromolecule CHONP such as phospholipids, phosphoproteins and nucleic acid were decomposed into orthophosphate and high bioavailability OP including flavin mononucleotide, flavin mononucleotide hydrate and N6-isopentenyladenosine 5′-monophosphate under the action of earthworm intestinal flora. This resulted in the bioavailability of OP reaching a maximum of 13.58 mg/L on day 14. In stage II (day 14 to 28), the enzyme in vermicompost began to dominate the transformation of OP. Under the catalysis of phosphate, high bioavailability orthophosphate monoester was decomposed into orthophosphate. Nitrogen-containing aromatic OP polymerization produced humic acid-like OP under the catalysis of ligase. And phytic acid-like OP were produced under the catalysis of transferase. These led to the OP bioavailability decreasing to 5.60 mg/L on day 28. This work provides a new perspective on sludge phosphorus recovery and use. [Display omitted] •In sewage sludge, organic phosphorus accounts for 32.7 % of the total phosphorus.•The transformation process of organic phosphorus was divided into gut associated process and cast associated process.•Macromolecular OP including phospholipids, phosphoproteins, DNA, and RNA was decomposed in gut associated process.•The nitrogen-containing aromatic OP was polymerized to produce humic acid-like OP in the cast associated process.•High bioactive orthophosphate monoester was produced under the action of earthworm intestinal flora on day 14.