Drinking Water Saved with Technical Water
The sewage treatment plant in Ystad aimed to stop wasting potable water and instead contribute to ensuring the municipality’s access to drinking water. They decided to use hypochlorous acid to reuse wastewater in their processes instead of using drinking water, saving 75 million liters of drinking water per year.
It almost feels like you have taken a wrong turn, heading to the beach instead of Ystad’s Sjöhög sewage treatment plant. In a way, you have, as the plant is virtually located on the beach with a stunning view over the southern Baltic Sea. Just outside the gates, the waves crash against the shore with a deafening roar, while seagulls defy boundaries and rest on the fence around the treatment basins.
Sjöhög treatment plant dates back to the 1960s but has been renovated several times, with the current version in use since 2016. The plant has a capacity of over 38,000 PE and serves both Ystad and parts of Skurup, receiving about 13,000 cubic meters of wastewater per day.
This summer, the latest change was made, making the plant self-sufficient in technical water. This means they purify outgoing wastewater from microorganisms and reuse it within the plant.
“We use 75,000 cubic meters of drinking water, or 75 million liters, annually and are thus one of the municipality’s largest water consumers. It felt so unnecessary to waste potable water, especially when it doesn’t even need to be drinking water used in the processes,” says Elias Molin, operations engineer at Sjöhög.
Drinking water is used for machine and gas cleaning, sludge thickening, and as flushing water. Elias Molin describes it as a large constant consumption year-round, providing a chance to save on the equivalent of over 360 households’ annual consumption.
“It’s important to conserve resources. A family in a house uses about 250 cubic meters of drinking water per year. We use 220 cubic meters per day here at the treatment plant. That’s a lot of people’s water we’re using.”
As the idea to produce technical water emerged, the Skåne County Administrative Board announced that municipalities and municipal companies could apply for support to improve water management and secure access to drinking water. The support for producing water at Sjöhög’s treatment plant amounted to one million SEK and could cover up to half the cost of the measures.
To purify the wastewater to technical water, they chose to filter the outgoing water through a drum filter and then use hypochlorous acid to kill bacteria. Hypochlorous acid is produced from electricity and common salt. Membrane filters were initially considered but discarded as they often require strong chemicals for cleaning. Another option was to use UV light, but this method could not guarantee the removal of all types of microorganisms in this application. Other alternatives were rejected as they were not safe enough for the staff’s work environment.
“We started thinking about this during the COVID-19 pandemic when another Ystad company, Anolytech, became quite hyped for making and distributing hand sanitizer. We contacted them, and they presented the hypochlorous acid method,” says Elias Molin.
The method of using hypochlorous acid to disinfect water is well-known and tested, used in agriculture and food production. The method is also popular, albeit in a smaller version, among property owners to disinfect showers against Legionella. However, this was the first time Anolytech was asked to install the technology at a treatment plant.
Possibly, the popularity stems from the fact that hypochlorous acid is harmless, occurring naturally in our stomachs, and does not produce any by-products. Another advantage is that hypochlorous acid can be produced on-site.
“Our requirements were that it should be easy to install, easy to use, and easy to service,” says Elias Molin.
However, the ease of installation seemed applicable only after necessary renovations of the facility had taken place. Among other things, the roof had to be raised to accommodate an associated drum filter, and an old storage building was converted to store filtered water awaiting disinfection. The renovations, combined with delays due to delivery problems caused by the war in Ukraine, meant it took over a year and a half to get everything in place.
“We’ve been under time pressure. The support from the County Administrative Board has a set deadline, and everything had to be reported by the end of October. When the situation in Europe changed this spring, we were a bit worried as it was uncertain whether the filter would arrive on time. But since the beginning of autumn, we’re finally up and running,” says Sanna Nilsson, operations manager at Sjöhög.
Another factor causing some delay was obtaining approval for the planned change in operations from the County Administrative Board. The original plan was to produce more technical water than needed for the treatment plant and offer the surplus to the parks department for watering municipal flowerbeds. However, the County Administrative Board considered each flowerbed watered to be an individual discharge point, which imposed stricter requirements and regulations. This made the project too complicated, so it was put on hold.
“It started with a citizen proposal suggesting that treated wastewater could be used to water the municipality’s flowerbeds and parks. We thought it was a good idea and wanted to explore the possibilities, but it seems we have to wait with that. I know similar ideas have been considered within Österlen VA, and VA Syd has been interested. It would have been nice if it could have been implemented,” says Sanna Nilsson.
The plan is to set up a so-called water kiosk where the VA unit’s own flushing truck can come and refill water for maintenance flushing of wastewater pipes. This way, all water returns to the treatment plant. The technical water is also used in the toilets and sinks at the treatment plant.
Elias Molin shows a noisy room where the production of hypochlorous acid takes place. Today, about a thousand liters of hypochlorous acid are produced per day from about 25 kilograms of salt.
“Or one cubic meter of hypochlorous acid for 220 cubic meters of water. We’ve started off strong to ensure we remove as many microorganisms as possible,” says Elias Molin.
The plan is to reduce the concentration in the future. They take water samples and send them for analysis weekly, but due to long response times, they have chosen to overdose to be on the safe side.
“But we also monitor to ensure there isn’t too much chlorine in the water. We don’t want free chlorine in the system that can harm the biology in the treatment plant.”
Sanna Nilsson cannot yet give an exact answer on the investment cost but estimates they planned for costs of 2.5 million SEK, including renovations. She estimates the final bill will be between 2.5 and 3 million SEK, including the support from the County Administrative Board. In the end, it balances out, she says.
“Considering the cost of the drinking water we used previously, the amount quickly equals the investment we’ve now made. This means the facility will likely pay for itself in one to two years. Additionally, we see a significant environmental benefit as we don’t consume drinking water to the same extent, while also helping to secure the municipality’s drinking water supply.”
Anolytech installerar sitt system i Ystads reningsverk.
