Phosphorus conversion during anaerobic digestion of high-calcium chicken manures and phosphorus recovery as struvite

Livestock and poultry waste contain large amounts of phosphorus (P). Recycling phosphorus from manure solves environmental pollution and reduces the consumption of phosphate rock. Most P existed in an insoluble form in chicken manure and was challenging to utilize further. When the carbon source (rice straw in this study) was added to adjust the C/N ratio, the release of P was greatly improved by up to 2-3 fold within 5 days, and Ruminococcaceae became dominant in the microbiota. In the presence of sufficient amounts of carbon, microorganisms can generate organic acid and decrease the pH value, thereby improving the dissolution of phosphorus. After examining the changes in phosphorus species in the system, carbon addition facilitated the dissolution of amorphous calcium phosphate, and hydroxyapatite remained the major residual P species. After decalcification and pH adjustment, nearly 100% phosphate released to the solution could be recovered as struvite.