The primary treatment of livestock waste water is activated sludge, but ions such as phosphate, potassium, ammonium, nitrate, and sulphate remain in the effluent. In this research, the effects of residual ions on phosphorus recovery were investigated using the crystallisation of magnesium potassium phosphate (MPP). The potassium (K) to phosphorus (P) molar ratio (K/P) of the precipitate will deviate from the equimolar ratio if co-existing ions influence the materials. Containing 5.6-20.3 mM ammonium, 25.6 mM potassium, 6.5 mM phosphorus, 0-7.35 mM nitrate, and 0-3.06 mM sulphate, artificial wastewater test solutions were used. The optimum working pH and quantity of magnesium required for high phosphorus removal and recovery rates have been determined. A 10-L aerated and stirred reactor and a 5-L settling tank were utilised by the experimental apparatus. After using ideal conditions, the K/P ratio in the precipitate was approximately 1. A white precipitate containing about 30 g of needle-like crystals was produced by continuous 2-h therapy. The effects of differing concentrations of ammonium, nitrate, and sulphate ions in the artificial effluent were also studied. The K/P ratio decreased to around 0.7 and 0.5, respectively, due to an ammonium concentration of 8 mM or more and a sulphate concentration of 3 mM or more. Even at a nitrate concentration of 7.35 mM, the difference in nitrate concentration did not affect the K/P ratio. In the reaction tank, we also studied the generation of products and the actions in the settling tank. With mixing by air agitation in the reaction vessel, primary nuclei generation occurred within 60 s and growth to secondary nuclei was confirmed. The particle-containing suspension overflowed into a settling tank and broke into particles and treated water. K+ in the MPP crystal was found to be eluted by allowing the MPP crystal in the settling tank to stand for 7 h or more. It was therefore concluded that management of the interval between the removal of solids was critical in regulating the solid's composition.
Author (s) DetailsHiroyuki Harada
Department Local Resources, Prefectural University of Hiroshima, Shobara-shi, Hiroshima, Japan.
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