Long pipes and the sea

In the past there have been three main alternatives for cities to handle human waste: recycling for use in agriculture, treatment in a WWTP or pumping waste into the sea. The sewerage plan made for Copenhagen in the 1850s included an outlet into the Sound, Øresund, far off the shore. This system facilitated the transport of wastewater into the sea and the introduction of water closets.

Since 1903 most Copenhagen's wastewater was directed untreated straight into the Sound. However, small local WWTPs were constructed starting in 1910. The first central wastewater treatment plant began to operate in Copenhagen in 1972.