ABSTRACT
Elevated phosphorus concentration levels in wastewater are responsible both for the deterioration of the water quality of natural water sources and for the formation of insoluble scale on the various equipment and parts of machinery used during the wastewater treatment processes. Phosphorus concentrations in wastewater, both municipal and industrial, may increase due to intensive soil fertilization and domestic and/or industrial processes. Treated wastewater is increasingly reused in the industry in order to cope with the lack of water resources. In some cases, phosphate concentration levels in treated water may be sufciently high to cause the formation of undesirable crystalline scale formed through the combination of the orthophosphate ions with metal ions such as calcium, magnesium, and iron, which may be present in excess in wastewater. Serious operational problems in wastewater treatment plants in operation for short time have been attributed to the formation of magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O or struvite, hereafter MAP) in pipes and aerators [1]. The presence of metal ions in excess in wastewater, including calcium and magnesium, is responsible for the formation of tenaciously adhering scale forming on various equipment parts (piping, pumps, heat exchanger, aerators, etc.), which is of variable composition depending on the metal phosphates that may form. Moreover, the presence of trace heavy metal ions, the level of concentration of which
9.1 Introduction .................................................................................................. 159 9.2 Experimental ................................................................................................ 161
9.2.1 Experiments in Batch Reactors ........................................................ 161 9.2.2 Fluidized Bed Experiments .............................................................. 163
9.3 Results and Discussion ................................................................................. 164 9.4 Summary ...................................................................................................... 170 Acknowledgments .................................................................................................. 171 References .............................................................................................................. 171
may be low enough to yield the respective phosphate salts, may lead to the formation of solid solutions of these metals into the MAP matrix. Carbonate and phosphate scale deposits are the most important priority for the maintenance of a wastewater treatment plant in the industry, especially in cases where elevated temperatures and alkaline pH are involved [2,3].
