In principle it will require authorisation to sell, import or use a product that acts as a biocide, i.e. controlling inter alia bacteria, algae or insects. The regulations are laid down in the Danish Chemicals Act and the Danish Pesticides Order, based upon the relevant EU legislation. You should ask yourself a number of questions before placing such a product on the market.
Use the menu items in the left column to find guidance on the different questions.Checklist
The Commission's website