Phosphorus recovery by struvite from anaerobic co-digestion effluents during residual biomass treatment

The residual biomass from agricultural activities has macronutrients and micronutrients, which could be recovered after an anaerobic co-digestion process. In this study, the effluents of the anaerobic co-digestion, which use coffee, cocoa mucilage, and pig manure, were evaluated to produce struvite. The effects of the Ca2+/PO43− ratio on the purity of struvite precipitation from synthetic and anaerobic co-digestion effluents was evaluated. The influence of pH, Ca2+/PO43− ration, and stirring speed on the efficiency of PO43− recovery and the removal of Ca2+ was studied. The phosphorus recovery increased from 85 to 99% with pH change from 8.5 to 10. The lowest removal of Ca2+ was 6.6% in the anaerobic effluent with the a ratio Ca2+/PO43− of 0.3:1 at pH 10. Struvite precipitate with high purity was obtained when the molar ratio was less than 0.3:1, and the pH was fixed to 10. X-ray diffraction analysis and scanning electron microscopy (SEM) confirmed the orthorhombic phases and morphology typical of struvite, respectively. In addition, the presence of K as a macronutrient and Ca and Na as micronutrients increases the viability of the struvite as fertilizer. The high recovery of phosphorus as struvite indicates it could be an alternative for nutrient recovery and utilization of these effluents.