We investigated the quality and amount of swine wastewater from feces-and-urine separate type piggery and examined the possibility of recovering phosphorus using struvite crystallization from swine wastewater. The quality investigation revealed a clear relation between swine wastewater and pH in the form of negative correlation between pH in swine wastewater and concentration of soluble PO₄-P and Mg. When the quality of swine wastewater was investigated for one year, pH and soluble PO₄-P and Mg concentration changed according to the season. The pH was low and soluble PO₄-P and Mg concentration was high in summer. Conversely, pH rose and the concentration of these soluble ingredients became low in winter. As for the composition rate of phosphorous, soluble PO₄-P was most prevalent in summer, while crystallized PO₄-P was most prevalent in winter. Although soluble PO₄-P in swine wastewater and the molar ratio of soluble Mg/PO₄-P were one or more in winter, they were less than 1 in summer. The amount of swine wastewater in the phosphorus recovery test from a feces-and-urine separate type piggery was investigated from September to May. The amount of swine wastewater decreased from September to January with the fall of temperature. In January and afterwards, the temperature began to rise, and the amount of swine wastewater also increased.
Although the soluble PO₄-P concentration was low, the phosphorus recovery by crystallization was possible from swine wastewater from a feces-and-urine separate piggery. When the soluble Mg/PO₄-P ratio was less than 1, the need for soluble Mg became clear.

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A simple MAP reactor made with PVC pipe was built as an experiment. The phosphorous removal and recovery by the struvite crystallization method were tried using swine wastewater taken from a feces-and-urine separate type piggery. It was possible to raise the pH of swine wastewater in the MAP reactor by aeration from the reactor's lower part and to make soluble PO₄-P into crystallized PO₄-P. During that process the pH rose for a short time, so the aeration intensity was high. With a reactor capacity of 200l, a wastewater holding time of 1 hour was required with an aeration of 30m³ h⁻¹ m^-3. Throughput was about 4.8m³/day. When the swine wastewater of pH 7.7 and the soluble Mg/PO₄-P ratio of 0.48 was used, the crystallization rate of soluble PO₄-P in this MAP reactor, 41% of the soluble PO₄-P was removed by the crystallization. When the source of magnesium was added and soluble magnesium concentration in treated water became 40mg/l, the removal ratio of PO₄-P increased to 75%. The amount of phosphorous recovery by the simple MAP reactor using the swine wastewater of pH 6.94 involved a soluble Mg/PO₄-P ratio of 0.56 and a soluble PO₄-P concentration of 63mg/l. The reactor was equipped with stainless steel nets for MAP adhesion. A solution of 30% MgCl₂ (0.1% of the volume of swine wastewater) was added, and the HRT in a reactor was set to 1 hour. The examination was carried it out for 44 days. The MAP weight adhering to the nets was 5.3kg. 0.61kg per soluble PO₄-P, and 1kg MAP supplied in the MAP reactor was recovered. Using this equipment, the crystallization rate of soluble PO₄-P can be raised to 70% or more by adding a source of Mg and raising the pH by aeration from the MAP reactor lower part. Moreover, 38g of MAP per 1m³ of swine wastewater supplied in the MAP reactor was recovered.

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