Removal of phosphate, magnesium and calcium from swine wastewater through crystallization enhanced by aeration

In order to confirm the possibility of removing PO4-P, Mg and Ca from swine wastewater through artificial crystallization by aeration, laboratory and pilot scale experiments were carried out using actual swine wastewater. The pH of swine wastewater increased up to approximately 8.5 with continuous aeration, and a large part of the soluble PO4-P, Mg and Ca was crystallized. The ingredients of the crystals were estimated as MAP and HAP according to their mole ratio of NH4-N, PO4-P, Mg and Ca. The sedimentation speed of crystals in swine wastewater was about 3 m h(-1), and over 90% of them had settled after standing I h. A pilot scale reactor with the dual functions of crystallization by aeration and settling was operated continuously using actual swine wastewater, with aeration conditions of HRT 4.1 h and 26 m(3) air h(-1) m(-2) cross section (18 m(3) air h(-1) m(-3) volume). During 50 days of operation, pH at the aeration column held stable at 8.0, and 65% Of PO4-P, 51% of Mg, and 34% of Ca were removed. (C) 2002 Elsevier Science Ltd. All rights reserved.