Workers in various industries routinely have to deal with and worry about the toxic substances they encounter while doing their jobs. But what about the substances that are most dangerous after they’ve been used? This is the case with spent caustics.

In this article, we’ll give you an overview of what spent caustic (or caustic waste) is and the hazards associated with it. Then, we’ll look at how to dispose of it to ensure the safety of workers and the protection of the environment.

What is Caustic Waste?

Caustic waste refers to industrial caustic solutions that have become exhausted and are no longer suitable for use. In other words, they're caustics that are spent. These solutions generally include sodium or potassium hydroxide, water, and contaminants that consume sodium and potassium hydroxide.

Caustic solutions are used in many different industries and for many different purposes, including cleaning, purifying, diluting, distilling, or other fluid-handling purposes.

Common acidic or caustic solutions include:

  • Caustic soda (also known as lye)
  • Nitric acid
  • Phosphoric acid
  • Sodium hypochlorite
  • Peracetic acid

Understanding the Hazards

Spent caustics are both hazardous and difficult to treat due to health, safety, and environmental concerns.

Those working with and around caustic waste must take proper care and precautions, as it is highly corrosive to skin and eyes. In cases of skin contact, untreated corrosion wounds are slow and difficult to heal. Contact with the eyes – even in small amounts – can cause irreversible tissue damage and blindness. Because of this, proper handling procedures are of the utmost importance.

Improper disposal of spent caustic can also have a devastating effect on the environment. It’s toxic to aquatic life and can harm fragile ecosystems, and even after being neutralized cannot simply be disposed of into waterways.

Finally, it can cause serious operational problems for wastewater treatment plants. Just a small amount of caustic waste can result in foaming, effluent toxicity, oil emulsification, and impaired bioflocculation (the clumping of fine, dispersed organic particles).

Key Things to Remember When Disposing of Spent Caustics

There are no specific regulations that govern the treatment of caustic waste, which means every company may do it a little differently. That doesn’t mean there are no best practices for safely eliminating spent caustic while preventing harm to workers and the environment. So with that said, here are some important things to remember when disposing of caustic waste.

Use Appropriate PPE

Since caustic waste is corrosive to the skin and eyes, workers who handle it must be equipped with PPE that provides adequate protection. This includes protective gloves, protective clothing, and eye and face protection to guard against splashes.

Know the Emergency Protocols

Workers who come into contact with the solution must immediately remove all contaminated clothing and rinse the skin in a safety shower (find out How to Select an Emergency Shower).

Workers who inhale the solution should be moved to fresh air to await medical assistance.

Workers who get the solution in their eyes should rinse at a safety station continuously while awaiting medical assistance.

Neutralize the pH and Dilute the Solution

The pH of all spent caustics should be raised or lowered to bring the substance back to a neutral state. Once this state is achieved, dilute the solution substantially. It’s important to note that even after spent caustics are neutralized and diluted, they are still not suitable for dumping in waterways.

Use Wet Air Oxidation

While there are various methods available for disposing of caustic waste, wet air oxidation is one of the best. Alternatives such as acid springing produce corrosive and toxic gases and doesn’t actually address any of the problems associated with spent caustics.

Rather than relying on hazardous and expensive liquid oxidizers, wet air oxidation uses things that are easily available at most sites: atmospheric oxygen, electricity, steam, and cooling water. In addition to producing an effluent that is not harmful once it is neutralized, the resulting solution is fairly simple for effluent treatment plants to handle – there are no foaming concerns, no foul odors, and no health and safety issues.

Wet air oxidation also involves lower operating costs when compared to other treatment methods, since the spent caustic provides the majority of the energy necessary to heat the wet air oxidation system.

Summary

Caustic waste must be disposed of carefully to ensure it doesn’t harm workers, the environment, or the operations at wastewater treatment plants. By using a wet air oxidation process and being prepared with the proper PPE and emergency procedures, however, you can dispose of spent caustics without complications.