There is good news for Denmark’s groundwater reserves and, thus, future drinking water. The Fehmarn connection and the many other giant construction projects we face can be realized with grey water. This is what Bent Grelk, who has over 30 years of experience as an advisor and consultant within concrete constructions, tells us:
– In principle, you can use purified wastewater, rainwater and water from drainage for concrete production, says Bent Grelk.
Water from different sources
He refers to the Danish concrete standard, which states, among other things, that the mixing water can come from different sources:
Suitability has been established for drinking water as well as recycled water from concrete production, groundwater as well as natural surface water and industrial wastewater, is stated in the concrete standard.
Requirements for the content
However, you cannot simply suck wastewater directly from the sewer into the mixing plant. The Danish Environmental Protection Agency requires that the content of heavy metals and other harmful substances must not be too high. Water recovered from process water in concrete production and industrial wastewater must also contain a maximum of two per cent dry matter.
May destroy curing
– As a starting point, there must therefore be no harmful substances in the mixing water to be used for concrete. People are often concerned about chlorides, but other substances can also destroy the concrete’s hardening and properties, says Bent Grelk.
FemernReport could tell on Tuesday that Lolland Municipality would like the tunnel element factory in Rødbyhavn to use grey water for concrete production. It will be able to take the peak of the industrial pressure on drinking water resources. And Bent Grelk, who has participated in several international research projects, believes that this can be done:
Continuous control
– My assessment is that, in most cases, you can use local surface water, treated wastewater/rainwater and groundwater. Normally, the harmful substances are often found in such small concentrations in such water that it does not damage the concrete. This must, of course, be ensured before use. There must also be continuous monitoring, as the composition and nature of the water can change relatively quickly – for example, during heavy rain, where polluted wastewater can be mixed with relatively clean rainwater, says Bent Grelk.
No concrete examples
However, the concrete expert is not familiar with concrete examples of grey water in concrete: – In most western countries, the same rules apply as in Denmark regarding mixing water for concrete. If you have to find examples of using contaminated surface water from lakes, streams, rainwater or groundwater, it is probably in countries where you don’t have easy access to clean drinking water, he concludes.
