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Don't be so caustic!

Sustainability Matters

November 30, 2020

Magnesium hydroxide is much better than caustic soda or lime for treating wastewater. Why aren’t its advantages better known?

Treating wastewater from food manufacturing and processing industries is about to be turned on its head thanks to a benign but extremely effective ingredient.

One of the primary reasons to treat wastewater is to reduce acidity and raise the pH level. Balancing the pH is vital in preventing harm to the environment or to infrastructure such as pipes and storage facilities, and to minimise odour.

The best way to neutralise acid in wastewater is to dose with an alkali, with the right dose resulting in a neutral pH level. Most manufacturers treat acidic wastewater using caustic soda, otherwise known as sodium hydroxide. Other widely used alkalis are soda ash (sodium carbonate) or hydrated lime (calcium hydroxide).

However, all these materials are hazardous and require high dose rates to be effective. Caustic soda is often used instead of powdered alkalis like lime or soda ash because it is easier to handle and requires less maintenance. The dosing of water with caustic soda is quite simple, but the substance must be handled with extreme care, abiding by containment and occupational health and safety measures, because it is very dangerous. Caustic soda is extremely corrosive and can cause severe burns on human skin.

Caustic soda is also bad for the environment. While it reduces the acidity of the water, it also raises its sodium level, which increases the salinity of any body of water it is discharged into.

A solution to the problems of caustic soda

Fortunately, there is an alternative. An increasing number of companies treating wastewater have switched to magnesium hydroxide (MHL) to raise pH levels. This compound produces similar effects to caustic soda in raising pH levels but is much more friendly to the environment. In fact, it is a nutrient that can be beneficial.

Ralph Lloyd-Smith, technical support engineer with leading Australian wastewater treatment company Calix, said that the product is becoming more popular because it can be cheaper than caustic soda in most applications.

“The same volume of magnesium hydroxide provides 60% more alkalinity than concentrated caustic soda.”

Calix is an Australian manufacturer of patented industrial sustainable solutions including magnesium hydroxide, which it markets as ACTI-Mag, for neutralising acidic wastewater in Australia.

“Earlier generic magnesium hydroxide products used in wastewater treatment were difficult to use due to clogging and drop-out of slurry particle solids. Whilst many saw the benefits of the chemistry and removal of sodium, the product caused frustration due to blockages. We’ve done a bit of tricky chemistry to ensure that doesn’t happen with our product,” Lloyd-Smith said.

“Some food processing plants use caustic soda to clean their equipment regularly and figure they may as well also use it to raise the pH of their wastewater. We encourage the use of magnesium hydroxide because it is so much safer and because of its many environmental benefits.

“We are gradually educating plant managers as a lot of them had never realised there was an environmentally friendly and safer alternative to caustic soda. We are also adding value to their wastewater treatment (a non-core function for most industrial customers) by sharing our expertise in areas like diagnostics and problem-solving.”

Since Calix entered the water market six years ago, MHL usage in Australia has become more popular. In recent years there has been increased emphasis on environmental concerns and on OHS issues, which explains why more wastewater treatment plant operators, vineyards and food and beverage manufacturers are switching to magnesium hydroxide and more particularly ACTI-Mag.

Counting the advantages

As well as being perfectly safe for people to work with, magnesium hydroxide is a slow-release alkali which naturally buffers at a pH level of 8.5 to 9. This makes it an ideal choice for dosing in the sewer system for odour control, as this pH range holds hydrogen sulphide (rotten-egg gas) in solution. It automatically stabilises at this level, which makes it almost impossible to lose control of the treatment process, as can happen with caustic soda.

Lloyd-Smith says there is another problem with caustic soda: “In colder climates or in winter, it crystallises. The only way to prevent that is to dilute it more, which makes it less effective. That doesn’t happen with magnesium hydroxide.

“Magnesium hydroxide also offers a range of other benefits such as sludge compaction and dewatering, which means a reduction in other chemical additions and thus further cost savings. It also creates the perfect pH balance for good bacteria to thrive.”

Calix’s unique calcination process involves grinding minerals to tiny particles and heating them at temperatures up to a thousand degrees. This produces a high surface area magnesium oxide, which is then hydrated to produce the unique and highly reactive ACTI-Mag magnesium hydroxide.

Because Calix owns and operates a raw material mine, and controls the production, processing, testing and manufacturing facilities in different states, it can offer exceptional service, reliability and performance to its customers. Its success has seen ACTI-Mag exported to Europe and North America.

The company has won dozens of awards for its sustainability, innovation, technological excellence and export success.

Calix is at the leading edge of global research and development into environmentally sustainable wastewater, agricultural, CO2 mitigation and battery technology.

For more information: https://www.calix.global/solutions/solution-for-wastewater-treatment/.

Image credit: ©stock.adobe.com/au/stockphoto-graf

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Waste Management & Recycling