Technology Development of Flocculating Pretreatment of Livestock and Poultry Manure Slurry and of Phosphorus Recovery by MAP Crystallization

Flocculation was applied to the pretreatment of livestock and poultry manure fermenting slurry. Inorganic flocculants such as aluminium polychloride (PAC) and ferric sulfate(Fe₂(SO₄)₃), organic flocculants such as nonionic polyacrylamide (PAM), anionic polyacrylamide (APAM) and polyacrylamide (CPAM) were tested to remove suspended solid (SS) from the liquor. The results showed that CPAM was more efficient for SS removal than other flocculants. At SS of 13 500 mg/L, a CPAM dosage of 1.02 g/L could lower the SS to 148 mg/L, reaching a removal efficiency of 98.9%. After the flocculating pretreatment, the PO₄^3--P concentration was around 35 mg/L, and magnesium ammonium phosphate (MAP) crystallization process was used to recover phosphorus. It showed that at Mg:P molar ratio of 1:1, the optimum pH was 9.5, at which the phosphate removal efficiency was the highest; while at Mg:P molar ratios of 1.5-2:1, the optimum pH was 10.0. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to detect and analyze the crystallized product, and it showed that the product was MAP.