Livestock wastewater is mainly treated with activated sludge, but ions such as phosphorus, potassium, ammonium, nitrate and sulfate remain in the effluent. In this study, the effects of residual ions on phosphorus recovery using the magnesium potassium phosphate crystallization method were investigated when magnesium was added to increase the pH. If co-existing ions affect the products, the phosphorus to potassium molar ratio (K/P ratio) of the precipitate will deviate from being equimolar. Artificial wastewater test solutions 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 sulfate were used. First, the optimum operating pH and amount of magnesium added to give a high phosphorus removal rate and recovery rate were determined. The experimental setup was a 10 L aerated and stirred reactor, and a 5 L settling tank. The K/P ratio in precipitate was approximately 1 using the optimum conditions. Continuous 2 h treatment allowed a white precipitate containing about 30 g of needle-like crystals to be obtained. Next, the effects of varying the ammonium, nitrate, and sulfate ion concentrations in the artificial effluent were investigated. Ammonium and sulfate ion concentrations of 8 mM or more and 3 mM or more, respectively, caused the K/P ratio to decrease to about 0.7 and 0.5, respectively. Varying the nitrate concentration did not affect the K/P ratio, even at a nitrate concentration of 7.35 mM.

Wastewaters containing phosphorus and nitric acid are produced during biological treatment processes. In this study, a material for treating such wastewaters was developed. Foamed glass was produced from waste glass and then heated with iron sulfate to prepare an adsorbent for phosphorus and carrier for reducing nitric acid. The adsorbent performance was evaluated in batch and continuous experiments. The saturated adsorption amount of phosphate was 6.23 mg/g for the product obtained from glass of size 3 to 12 mm; the amount adsorbed was relatively high, in spite of the large glass size. The denitrification by reduction of nitrate was around 25%.