Phosphorus recovery and iron, copper precipitation from swine wastewater via struvite crystallization using various magnesium compounds

Abstract

Swine wastewater contains phosphorus, ammonia nitrogen, and heavy metals that affect the struvite purity produced from the wastewater and increase the ecological hazards. In addition, struvite crystallization process is highly dependent on the usage of magnesium sources. Thus, it is necessary to explore the effects of three magnesium sources, including MgCl2, Mg(OH)2 and MgO, on the phosphorus recovery and minimizing Cu and Fe contents via struvite crystallization process. The observations revealed that the predominant parts of Cu and Fe precipitate in the form of hydroxide during pH adjustment. Meanwhile, when using MgCl2 as the magnesium source, the optimal removal efficiency of phosphorus reached 94.55%, followed by MgO and Mg(OH)2. Simultaneously, 90.60% Cu and 98.80% Fe precipitate under MgCl2 as magnesium source. The redissolution behavior of Cu occurs when MgO and Mg(OH)2 are used as magnesium sources, increasing the Cu concentration. The smallest operation cost is from MgCl2 as magnesium source. The potential environmental impact analyzed by life cycle assessment method shows that MgCl2 in struvite crystallization process saves more fossil energy and protects resource while lessens the nature's eutrophication risk. The technical, economic, and environmental assessments confirm MgCl2 as a promisable source of magnesium in struvite crystallization process for achieving cleaner production goal.