UBC Theses and Dissertations
The removal of heavy metals from municipal wastewaters by lime-magnesium coagulation MacLean, Byard H.
The evidence of heavy metal build up in the aquatic environment near sewage treatment plant outfalls around Vancouver,coupled with the generally held theory that secondary treatment is not required in this area, leads to the conclusion that a treatment method is required that is primarily aimed at heavy metal removal. In this study, jar tests were performed to evaluate the heavy metal removal efficiency of the lime-magnesium coagulation process. Five heavy metals (Cr³⁺ , Cu²⁺ , Pb²⁺ , Ni²⁺ and Zn²⁺ ) were all tested at initial concentrations of .5, 2.5 and 5.0 mg/1 individually and in combination. The experiments were performed on prechlorinated primary effluent and raw sewage at the natural alkalinity levels (120-130 mg/1 as CaCO₃), and some work was done at elevated alkalinity (190-200 mg/1). The need for filtration in the process was also researched. Results of the study indicated that the heavy metal removal efficiency was enhanced by the presence of Mg²⁺ at a given lime dosage for all of the heavy metals except nickel. A comparison indicated that intermediate lime treatment (220 mg/1) coupled with 33 mg/1 Mg²⁺ might be a more attractive process than just straight high lime treatment (400 mg/1).
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