Reuse of wastewater saves water and money

The Danish wastewa­ter treatment plant Fredericia Spildevand & Energi has, over 10 years, saved more than 5 million DKK by reusing wastewater for cleaning and other processes. The solution is to filter and disinfect the treated wastewater so that it can be used rather than clean drinking water.

Fredericia Spildevand & Energi has annually reused between 50,000-70,000 m3 of their treated wastewater for, among other things, cleaning the plant, flushing surfaces, and mixing. Previously, they would have used clean drinking water. The wastewater can only be used for these purposes because it is free of harmful bacteria – so-called ‘technical water’.  This is thanks to the disinfection generator from Danish Clean Water (DCW) that the wastewater plant installed several years ago.

Per Tandrup Dejgaard, engineer at Fredericia Spildevand & Energi, says: “The solution is good for both the environment and our accounts. We all have a responsibility to save drinking water where we can, and this is an obvious place where we are able to do that. The disinfection generator means that there are no harmful bacteria in the treated water and also no biofilm in the water pipes.”

Before Fredericia Spildevand & Energi installed the DCW generator, they tried a UV system to disinfect the water. However, this system did not work properly, which affected operations.

Simple ‘disinfect-and-reuse’ process

The DCW generator makes wastewater recycling a simple process. First, the treated wastewater goes through a water filter. Then a small amount of Neuthox disinfectant is injected into the storage tank and the technical water is ready for cleaning. The disinfectant is produced on site by the generator using common salt, water, and electricity. It kills potentially dangerous bacteria such as Legionella, salmonella and E. coli in the wastewater and eliminates biofilm in the pipes and system. The active substance in the disinfectant is hypochlorous acid (HOCl), which works effectively and at the same time is safe for humans to use and gentle on the environment in the low concentrations needed.

“Once the solution is installed and running, it’s almost as easy as turning on the tap. The only thing we have to remember is the weekly refill of salt for the generator, and the service twice a year. Otherwise, it pretty much takes care of itself,” says Per Tandrup Dejgaard.

Due to the DCW solution, Fredericia Spildevand & Energi has been granted an exemption to use technical water for spraying tasks in accordance with the Danish Working Environment Authority’s regulations on sewage work, etc.

Engineer Per Tandrup Dejgaard

Engineer Per Tandrup Dejgaard shows one of
the technical water taps.

Making great savings

The calculation for Fredericia Spildevand & Energi is made as an average per year over the 10 years they have had the DCW disinfection generator. The generator and technical water filtration system have been paid off, leaving only the operating costs, and making the savings even bigger. The price of the drinking water also plays a role, of course. In Fredericia Municipality, the price is low compared to other places in Denmark, where the profit from reusing wastewater would be correspondingly greater.

“Today, wastewater and sewage sludge are perceived as an important energy resource. It’s quite natural to also see technical water as an important water resource, and it makes good sense to expand its use – both from an economic and environmental point of view,” says Per Tandrup Dejgaard.

The wastewater is reused for:

  • Rough cleaning
  • Rinsing of surfaces and pipes
  • Automatic cleaning of machines such as inlet grates and dewaters
  • Mixing of substances, e.g., polymers, in the drainage
  • Dilution water/rinse water in pipe systems
  • Sludge vacuum trucks in the city

The savings on average per year (over 10 years):

  Purchase of drinking water (DKK)


DCW generator (DKK) Filtration system (DKK)
Saved drinking water 730,000
DCW generator, depreciation over 10 years (incl. interest) 60,000
Filtration system over 10 years 50,000
Salt 14,000
Electricity 31,000 5,000
Service/maintenance 17,000 5,000
Total 730,000 122,000 60,000
Savings per year   548,000
Savings over 10 years   5,480,000

The figures are excl. VAT.

The treated wastewater

Facts about Fredericia Spildevand & Energi

The facility receives and cleans approx. 10 million m3 of wastewater annually from households and industries in Fredericia Municipality. The capacity corresponds to the annual water consumption of 420,000 citizens. At the treatment plant, they also produce energy, heat, and technical water.