Free and Encapsulated Phosphate-Solubilizing Bacteria for the Enhanced Dissolution of Swine Wastewater-Derived Struvite—An Attractive Approach for Green Phosphorus Fertilizer

Struvite and hydroxyapatite are byproducts of phosphorus removal from wastewater that can be used as phosphate fertilizers. Due to their low water solubility, especially in alkaline soils, their use is currently limited. The use of phosphate-solubilizing bacteria to enhance the dissolution of struvite and hydroxyapatite could be an attractive solution for expanding their use, but literature reports on this are limited. In this study, Arthrobacter sp. (TBRC 5201), Azotobacter vinelandii (TBRC 7231), and Bacillus megaterium (TBRC 1396) were evaluated for their ability to dissolve struvite and hydroxyapatite on agar media with struvite or hydroxyapatite as the sole source of phosphorus. Only B. megaterium (TBRC 1396) was able to use struvite and hydroxyapatite for growth. After 14 d of incubation in liquid medium, B. megaterium (TBRC 1396) dissolved phosphorus from struvite up to 835.45 ± 11.76 mg P/l compared with 196.08 ± 3.92 mg P/l in a control without cells, whereas the dissolution of hydroxyapatite by B. megaterium was minimal. B. megaterium (TBRC 1396) was also capable of dissolving phosphorus from swine wastewater-derived struvite. Both free cells and alginate-encapsulated cells of B. megaterium (TBRC 1396) were able to rapidly dissolve phosphorus from swine wastewater-derived struvite, resulting in soluble phosphorus concentrations that reached 400 mg P/l within 2 days, compared with those without cells that required 12 days. In conclusion, the application of struvite with phosphate-solubilizing bacteria is a promising tool for green sustainable agriculture.