Significant environmental gains by reusing flocculents from drinking water

Flocculants extracted from iron sludge from drinking water extraction are cheaper and more environmentally friendly than commercial flocculants. And equally important: the removal efficiency is higher. This is the result of the HerCauWer project. In the follow-up, interesting applications in the market will be examined.

The production of drinking water always results in a sludge that contains a lot of iron: hydrated water. By dissolving this substance in acid, an iron salt is made, which can be reused as a flocculant or coagulant. The central question during the research project was: Is it feasible and interesting to use flocculants in wastewater treatment plants?

Roberta Hoffman, a senior researcher at KWR Institute for Water Research, talks about a nice circular solution. “You are using drinking water treatment waste to purify waste water. It is about removing phosphates.”

Higher removal efficiency
According to a preliminary lab study, reuse offers significant environmental benefits and a price that is at least 30 percent lower than commercial flocculant. The HerCauWer project, which ran between 2017 and 2021 – the acronym stands for “Reuse of Coagulant from Aquatic Water” – investigated whether these benefits could actually be demonstrated in practice.

This project was part of the Supreme Consortium for Knowledge and Innovation in Water Technology. Participants are AquaMinerals (partnership of drinking water companies and water boards to give materials from water treatment a second life), Feralco (producer of quality water treatment products), Brabantse Delta Water Board, KWR and drinking water companies Evides, WML, Vitens, Waternet and PWN.

The recently published final report shows that the flocculant extracted from drinking water does indeed have several advantages. Hofmann is one of the authors and explains: “The removal efficiency is higher. The flocculant removes more phosphate per iron molecule than using commercial flocculant. The impact on the environment is also 50 to 100 times lower. The flocculant is much cheaper.”

Aquafer is always available
However, the lower price of at least 30 percent cannot be confirmed by the previous study, Hoffman says. I tried to calculate this, but it wasn’t really possible because the prices of commercial flocculants in the market bounced around in all directions. There is no fixed amount attached to it.”

The KWR researcher mentions an additional feature. Commercial flocculants are currently scarce and therefore not always available. “This makes it very expensive. Aquafer, on the other hand, is always available.” The downside is that due to the low iron content, twice as much flocculant should be taken as commercial flocculant. “However, at a dilution factor of 3,000, that doesn’t matter much.”

The initial intention was to build an experimental facility at a drinking water treatment site that would dissolve and instantly give a dose of watery water. According to Hoffmann, that turned out to be impossible. “For drinking water, it is necessary to have a KIWA Watermark certificate. Of course we didn’t have that because it’s an experience.” It was therefore decided to carry out the test at the Delta Brabant Water Board’s sewage treatment plant in the village of Zeeland Bath. “There is no need for a watermark for this.”

More questions to explore
The HerCauWer project has been completed but there are still some issues that need further investigation. Hoffmann: “For example, 99 percent of the iron can be recovered from the sludge of the wastewater treatment plant in Gruppenfürst, while in the wastewater treatment plant in Ossendrecht we have not reached more than 40 percent. We do not yet know where it comes from This difference.”

Another question about where the flocculant is best produced: near where it will be used or in a more central location? “The first advantage is that the water indicator only needs to be transported a short distance. However, it may be more appropriate to produce the flocculant in a central location from a mixture of sludge from several wastewater treatment plants. Then the volume is always sufficient and the quality remains constant.”

Multiple requests under examination
Drinking water companies produce approximately 90,000 tons of water annually. “It’s now certainly useful to make a flocculant out of it,” says Hofmann. “We’re looking at a follow-up and whether we can raise enough money for that.”

When it comes to selling, AquaMinerals doesn’t want to bet on one horse. A large portion of the current flocculants goes to the brewing market. There is a lot of support on this and this is a risk. So we aim to expand sales to multiple applications.”

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