You ask and we answer! MgWater Technical Director Matt Madolora offers solutions to common water treatment problems.

QUESTION: How does magnesium hydroxide slurry compare to the lime slurry I am using for wastewater treatment?

ANSWER: Many facilities rely on lime slurry as an alkalinity supplement in wastewater treatment, often because lime is already familiar from its use in potable water softening. In drinking water treatment, lime is added to remove hardness minerals like calcium and magnesium. During this process, these minerals precipitate out as calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃). While this helps prevent scaling in distribution systems, it also removes natural, soluble alkalinity from the water.

This background is important because the role of alkalinity in wastewater is very different. Biological treatment systems need consistent, available (soluble) alkalinity to support nitrification, maintain stable pH, and protect microorganisms from process upsets. While lime physically adds alkalinity, its softening chemistry can create the unintended consequence of converting available soluble alkalinity to unavailable solids alkalinity when used in wastewater environments. 

One issue is that lime tends to form calcium carbonate sludge, which can accumulate, increase solids handling requirements, and create operational inefficiencies. More critically, the way lime reacts can cause sharp pH swings. These rapid changes may temporarily raise pH above biological tolerance levels, risking nitrifier inhibition or full biological upset. Additionally, lime’s tendency to remove magnesium and calcium hardness means it can actually reduce the pH stability that biological and physical processes rely on for efficiency.

Magnesium hydroxide behaves differently. It provides slow-release, highly effective alkalinity that buffers pH gently and consistently, supporting biological processes without overshooting. It avoids the sludge buildup associated with lime and helps maintain stable conditions even during high loading events. For facilities struggling with pH swings, high solids, or nitrification instability, magnesium hydroxide often delivers a more reliable and cost-effective solution.

Would you like to connect with one of our technical experts at Premier Magnesia to talk about the superior quality of our magnesium hydroxide? Click here for more info or contact us today.