The removal of organics from municipal wastewaters by lime magnesium coagulation

• Main Author: Leung, Yuk-ching
• Language: English
• Published: 2010
• Online Access: http://hdl.handle.net/2429/21156

In view of a potentially hazardous problem existing in municipal wastewater due to heavy metals and trace organics, this research attempted to find the removal efficiency of trace organics that could be achieved by chemical treatment (lime-magnesium coagulation) instead of by conventional biological treatment. Pesticides, polychlorinated biphenyls (PCB's) and phenols were chosen because of their high toxicity, existence in significant quantities, and ubiquitous nature. Extraction, concentration, derivatization and gas liquid chromatography (GLC) were employed to detect these compounds. Jar tests at pH 10.0, 10.7 and 11.4 with magnesium (Mg²⁺) dosages of 0, 8, 17, 33 and 50 mg/l were carried out to find the optimum removal condition. Very high removal of each from an initial concentration of 250 μg/l could be obtained, although not under the same experimental conditions. The highest removal efficiencies of Dieldrin, Aroclor 1254, Dichlorvos and Pentachlorophenol were 88.1%, over 95%, over 80% and 7 3.5% respectively. The two optimum dosages found were 8 mg/l Mg²⁺ at pH 10.7 and 33 mg/l Mg²⁺ at pH 11.4. The former combination of conditions is worthy of consideration when magnesium and lime recycle are not practised, especially with regard to sludge handling, chemicals used and final pH adjustment. The latter set of consideration when lime and magnesium recycle are included. Whether lime-magnesium coagulation can be a cost-effective treatment process for municipal wastewater, and how it can be instituted within existing treatment plants, still requires further investigation. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate