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According to research and the divalent cation bridging theory for bioflocculation, divalent cations can provide a benefit to flocs in activated sludge systems whereas high concentrations of monovalent cations can result in a deterioration in floc properties and treatment plant performance. Since many industrial plants have high concentrations of sodium due to either manufacturing processes or direct addition of sodium based chemicals to the activated sludge system, these plants may benefit from using alternatives to sodium based chemicals. The alternatives should be divalent cation based chemicals. A study was conducted to determine the effect of using Mg(OH)2 as an alternative to NaOH at a full-scale industrial wastewater treatment plant. Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition. In addition, a cost analysis of plant operation during NaOH and Mg(OH)2 use was performed. The results indicated that the settling, effluent quality, and dewatering were significantly better during Mg(OH)2 addition compared to NaOH addition periods. The alum and polymer dose used for clarification was significantly reduced during Mg(OH)2 addition. In addition, the dewatering at the treatment plant improved measured by CST, SRF, along with the cake solids from the SRF test. This led to a reduction in the volume of solids thickened by centrifuges which reduced solids disposal costs. Overall, the annual cost of using Mg(OH)2 was approximately 30,000 - 115,000 less than using NaOH, depending on the pricing of NaOH.

Document Type: Research Article


Publication date: January 1, 2000

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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