Safety of common alkalis for wastewater treatment

Wastewater treatment presents a multitude of hazards, such as drowning; confined spaces; and exposure to hazardous chemicals or gases.

DOUG KELLEY \ November 25, 2020

Hazardous chemicals can pose a significant risk to health and safety if not managed correctly. Municipal and industrial plant managers have specific duties under increasingly stringent health and safety regulations to manage risks associated with using, handling, and storing hazardous chemicals.

Being a plant manager at a wastewater treatment plant is an enormous responsibility as you answer to many high authorities such as the Environmental Protection Agency (EPA) or Occupational Health and Safety Administration (OSHA) in the US, and WorkSafe in Australia.

In this article, we’ve compared three common alkalis for wastewater treatment, and explained why magnesium hydroxide products are the safest and most cost-effective options.

  1. Ca(OH)2 -> Calcium Hydroxide, lime slurry, hydrated lime
  2. NaOH -> Sodium Hydroxide, caustic soda
  3. Mg(OH)2 -> Magnesium Hydroxide, milk of magnesia

There are laws in each state or territory that set out the requirements for handling and transporting dangerous goods. Switching to safer chemical products mean you are not only protecting the health and safety of your people, but you are making cost savings for years to come.

Lime slurry – Ca(OH)2

Lime Slurry is an odourless, low viscosity suspension of calcium hydroxide in water. It is commonly used for municipal water treatment, pH adjustment, metals precipitation and odour control.

Lime slurry is not combustible or flammable but it can react violently with acids, and combustible materials. Prolonged and repeated skin contact with Lime Slurry can cause irritant dermatitis or alkaline burns.

If a large volume of lime dust (or slurry) is splashed into the eye alkaline burns can cause permanent damage.


Classification of the substance or mixture:

• Skin irritation, category 2
• Specific target organ toxicity following single exposure, category 3

• Serious eye damage, category 1

Signal word: Danger

Caustic soda – NaOH

Caustic soda (Sodium Hydroxide) is one of the most common alkalis used to provide alkalinity in wastewater treatment.

Caustic soda is very corrosive. At high concentrations, it is extremely hazardous to handle and several precautious must be in place to safely use in the treatment process.

It can cause irritation to the eyes, skin, and mucous membrane; an allergic reaction; eye and skin burns; and temporary loss of hair.

Workers may be significantly harmed from exposure to sodium hydroxide.


Classification of the substance or mixture:

• Skin irritation, , category 1B

• Serious eye damage, category 1

• Corrosive to metals, category 1

Signal word: Danger

Magnesium hydroxide – Mg(OH)2

Magnesium hydroxide is increasingly used as a substitute for caustic soda and lime. Not only is it less expensive but it is also the safest and most gentle-to-use alkaline chemical treatment available on the market for pH control applications.

Though magnesium hydroxide is much stronger for supplying OH- buffering, it is dramatically safer for operators to handle and for treating wastewater microorganisms. Magnesium hydroxide dissolves only when it encounters acidity, unlike NaOH which immediately releases OH- to burn operator’s skin and eyes. As a result no extra PPE or secondary containment is needed to handle magnesium hydroxide, thus reducing operating cost.

Not only it is safe, but magnesium hydroxide is also recognized as a skin-care essential.


Classification of the substance or mixture:

Not classified under GHS.
• Non-hazardous
• Non-corrosive

Disclaimer: This experiment was not performed in a controlled lab environment and is routinely performed safely as a benchtop demonstration to show that magnesium hydroxide provides more CaCO3 equivalent alkalinity on an equal weight basis when compared to caustic soda, which means less chemical consumption and can result in significant cost savings. Magnesium hydroxide is non-hazardous and non-corrosive which makes handling safer and easier.

ACTI-Mag for Caustic replacement

A safe and cost effective alternative to the use of sodium hydroxide (caustic soda) for wastewater alkalinity and pH adjustment.

Find out more about ACTI-Mag

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