There are over one thousand wastewater treatment plants in Australia. Most are owned by water utilities and local government authorities, but they also operated by mining companies, factories, industrial concerns and even jails and defence establishments. Many smaller operators like restaurants also do their best to purify the water they have used before discharging it in to the sewer system.
Treating wastewater is a major industry. Australia is a dry continent and returning clean water to the environment is a priority. One of the main reasons to treat wastewater is to reduce its acidity, or pH value, which is often caused by nitrification, often from effluent.
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 reduce acidity is to dose the water with an alkaline substance. Alkalis are the opposite of acids and the right dose will result in a neutral pH level.
But there is a problem. Over 90 per cent of Australia’s treatment of wastewater is done using caustic soda, otherwise known as sodium hydroxide. Other widely used alkalis are soda ash (sodium carbonate) or hydrated lime (calcium hydroxide). But all these materials are hazardous and require high dose rates to be effective. It is called ‘caustic’ soda for a good reason.
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 actual dosing of water with caustic soda is quite simple, but the substance must be handled with extreme care, with containment and OH&S measures, because it is very dangerous. Caustic soda is extremely corrosive and can cause severe burns on human skin, or even death if ingested.
Caustic soda is also bad for the environment. While it reduces the acidity of the water, it also raises its sodium level, which raises the salinity of any body of water it is discharged into. Soil salinity is a major problem in Australia.
A solution to the environmental problems of caustic soda
Fortunately, there is an alternative. An increasing number of water treatment plants have switched to magnesium hydroxide to reduce acidity in wastewater.
Magnesium hydroxide has similar effects to caustic soda in reducing pH levels, but is much more friendly to the environment. In fact, it is a nutrient, and can actually be beneficial.
Magnesium hydroxide has been around for a long time. It used to be called milk of magnesia, and was widely used as an antacid and a laxative. It is still often used as an active ingredient in both. In recent years it has been developed as a safer and more environmentally beneficial alternative to caustic soda and lime for reducing the pH levels of wastewater.
So, with all its benefits, why has it not been more widely adopted? We spoke to Ralph Lloyd-Smith, Technical Support Engineer with leading Australian wastewater treatment company, Calix.
“Many people think it is more expensive,” he explains. “When you look at it by volume or unit price, that might appear to be the case, but it is actually cheaper than caustic soda in most applications. The same volume of magnesium hydroxide provides almost twice as many moles of hydroxide as does caustic soda.”
There have been other things holding back usage of magnesium hydroxide, says Lloyd-Smith. “It’s a little more difficult to handle. Magnesium hydroxide is a slurry, with small particles of solid suspended in water, while caustic soda is a liquid.
“But that is more than counterbalanced by the fact that magnesium hydroxide presents no safety problems. Anybody who spills caustic soda has to report it immediately. Not so magnesium hydroxide. And then of course there are the many environmental benefits, which are becoming increasingly important.”
Calix, an Australian manufacturer of patented industrial sustainable solutions, has become a champion of magnesium hydroxide, which it manufactures and markets under its ACTI-Mag brand, for lowering the acidity of wastewater in Australia.
“It’s a no-brainer,” Lloyd-Smith says, “but many people are still using caustic soda because they don’t know there’s an alternative, or because they may be tied into a contract with a supplier.
“Some food processing plants use caustic soda to clean their equipment regularly, and figure they may as well also use it to reduce acidity. We’re trying to encourage the use of magnesium hydroxide because it is so much safer and because of its many environmental benefits.”
Calix’s efforts are having some success. An increasing number of municipal water treatment plants have switched to magnesium hydroxide and the company has been very successful in having it adopted in areas where environmental concerns are paramount, such as vineyards.
“It’s a case of getting the message out there,” Lloyd-Smith says. “It’s an education process. When we speak to environmental managers and the hands-on people at the wastewater facilities, it’s not a difficult story to tell. The penny drops. A lot of them had never realised there was an environmentally friendly and safer alternative to caustic soda.”
The use of magnesium hydroxide as an alkali for wastewater treatment was introduced into Australia by major chemical company Orica around 20 years ago, but it is only since Calix took on the technology six years ago that its usage in Australia has become more popular.
Calix was founded in Australia in 2005 to commercialise the calcination process, which involves grinding minerals to tiny particles and heating them at temperatures up to a thousand degrees. The process is ideally suited to the manufacture of magnesium hydroxide, which now constitutes the bulk of Calix’s business.
