The many benefits of continuous electrochlorination for water treatment

The small town of Horrocks is a five-hour drive north of Perth on Australia’s west coast and has a population of around 140 people.

Its drinking water is sourced from an aquifer a couple of kilometres inland via one of the country’s most groundbreaking water treatment plants. The new technologies deployed there are set to revolutionise the water industry and bring a range of sustainability benefits.

Engineers at Water Corporation, Western Australia’s principal supplier of drinking water, wastewater, drainage and bulk irrigation services, pioneered the Horrocks water treatment plant, which opened in June 2023. It’s the first ever benign full-scale continuous electrochlorination (CEC) treatment plant for aesthetics oxidation and disinfection.

CEC is the method of converting naturally occurring chloride in raw groundwater into hypochlorite by passing an electric current through it. It causes several beneficial reactions including oxidation of the dissolved metals iron and manganese, the removal of bacteria and viruses, a reduction in salinity and a slight increase in pH levels.

The ground water in WA is typically low in pH (less than ~5.6) and requires chemical treatment to boost the level up to acceptable drinking water guideline (6.5 – 8.5). This technology reduces or eliminates the need for pH correction using chemicals such as sodium hydroxide and soda ash.

“It’s the next step in the evolution of water treatment,” said Luke Zappia, Water Corporation’s Principal Water Treatment Engineer. “It chlorinates drinking water without producing sludge or by-products other than very small amounts of hydrogen.”

Reduced emissions

As no salt has to be added, the technique also reduces the amount of sodium hydroxide used by 64 per cent and eliminates entirely the need for operators to handle chlorine gas on site.

“The traditional chlorine gas method involves manufacturing and transporting chemicals and then having people on site to connect and use them, all of which obviously involves a great deal of energy and carbon emissions,” said Zappia, who’s been researching ways to transition away from chlorine gas for disinfection since 2007.

During the early stages of developing a CEC solution, the technology was found to reduce the concentration of nitrate in groundwater. 

“At the time, we didn’t know why, but we knew we had to explore it further to find out,” he said. “We liaised with the Northern Territory Power Water Corporation, the University of Queensland, Hydrodis Australia and Demetec to explore and further improve our understanding.” 

A novel spinoff project was established between the stakeholders and the results have been so successful that a pilot is currently in construction and will be deployed in the Northern Territory and Western Australia for further scaled testing.

A tough challenge

Once the technique was ready for real world testing, the team chose Horrocks for an unusual reason.

“We knew that if we could make it work there, it’d work anywhere,” Zappia said. “Its source water is anaerobic, has high salinity and contains over 10 mg of iron and 2 mg of manganese. Its pH level is 5.6, which is well below drinking water guidelines.”

The gamble paid off. In the nine months since CEC upgrades were commissioned, the results have been extremely encouraging – so much so that the plant won the Australian Water Association Western Australia’s Infrastructure Project Innovation Award (Regional), and will now compete in the national finals.

The judges were particularly impressed with the plant’s sustainability credentials.

“Our latest calculations show that using CEC is competitive compared to other chemicals like chlorine gas and hypochlorite. Current estimates based on energy demand alone show that it consumes about 9 kWh/kg CO₂ produced,” Zappia said. “There are also large reductions in scope-three greenhouse gas emissions that result from no longer manufacturing and transporting chlorine gas and liquid.”

Other benefits include:

1. Generating benign hydroxyl radicals that reduce the need for additional pH correction
2. Killing bacteria and viruses (up to 6Log) via dissipated energy between the anode and cathode
3. Reducing operations and maintenance costs by up to 80 per cent
4. Simplifying design by eliminating the ancillary components typically required for conventional chlorine gas and hypochlorite dosing systems
5. Improving community safety by removing the need for chlorine gas and buffer restrictions
6. Removing the need for emergency services responses and manifest requirements for potential chemical incidents

“It’s been a long but rewarding journey with progressive learning and improvement to overcome the many hurdles we’ve encountered,” Zappia said. “Our highly skilled teams have displayed an extraordinary level of resilience. They’ve been with us all the way through and really embraced the technology. Their commitment has been wonderful.”

Find out more about engineering careers with Water Corporation, and contact luke.zappia@watercorporation.com.au to find out more about CEC.