Manganese-aided lime clarification of municipal wastewater

A preliminary study was carried out to assess the usefulness of manganese as an aid in the lime clarification of municipal wastewater. The approach was intended to take advantage of the potential sorption ability of manganese oxides for organic matter in the presence of divalent cations. In a batch clarification test, 94–95% and 75–77% reduction in turbidity and chemical oxygen demand (COD) from a municipal wastewater were observed with 800 mg l−1 of lime and 30 mg l−1 of manganese sulphate, whereas the corresponding reductions were 60–61% and 33–38% with lime alone (800 mg l−1). With ferric chloride (500 mg l−1), turbidity and COD reduction were 90–91% and 66–68%. Settled sludge volumes were 72, 70 and 128 ml l−1, respectively for the three treatments. Based on Ivesʹ filterability number, calculated using both turbidity and COD as measures of filtrate quality, supernatant from lime-manganese sulphate treatment appeared to be more filterable than that from either lime alone or ferric chloride treatment. Following coal-sand filtration, lime-manganese sulphate treatment showed a higher overall removal of turbidity (97%), COD (82%) and total phosphate (95%) than that by either lime alone (82, 52 and 79%) or ferric chloride (93, 68 and 92%) treatment. The study demonstrated the potential benefits of a lime-manganese sulphate combination in municipal wastewater treatment.