Effect of magnesium and calcium precipitation on coagulation-flocculation with lime

Coagulation-flocculation studies were carried out to identify and quantify the organic matter (TOC) fraction removed by Mg (OH) 2 precipitation and the fraction removed due to CaCO 3 precipitation in lime treatment of wastewater. Most experiments were carried out with domestic sewage and some with a tannic acid solution simulating coagulable organics in wastewater. The experiments showed a clear relation between the amount of TOC removed and the amount of Mg (OH) 2 formed. This relation between TOC removal and Mg(OH) 2 precipitation can be expressed in terms of an adsorption isotherm. The coagulation-flocculation tests of sewage with lime as a coagulant indicated that about 26% of the removable TOC in sewage is eliminated by Mg(OH) 2.