There are more than 1,000 sewage treatment plants in Denmark and these take waste water from households, enterprises and institutions. The plants treat the waste water to remove substances harmful to the aquatic environment.
In Denmark, we clean the vast majority of waste water before it is discharged, to prevent the waste water from contaminating the aquatic environment or soil and groundwater with organic matter, nutrients and environmentally hazardous pollutants.
The treated waste water is either discharged into streams, lakes, the sea or used as fertilizer for agriculture. The discharge of waste water requires a permit. Among other things, the discharge permits set conditions on how much waste water may be discharged, and requirements for concentrations and quantities of pollutants. Normally, the waste water discharge is not allowed to contain pollutants in a concentration that can cause damage to the environment.
In Denmark, there are mainly three types of sewage systems:
- Joint systems, where waste water and rainwater are collected in one sewer, which is led to a treatment plant. This is the traditional system which is mostly present in older sewage systems.
- Separate systems, where waste water and rainwater are led in separate sewers to the treatment plant and recipient, respectively. Gradually implemented in systems that already have joint systems, and preferably used in newer developments.
- Decoupled sewage systems where only waste water is led to the sewer, and every property therefore must dispose of the rainwater that falls on the property themselves (e.g. by seepage on their own land). Mainly used in the open country and in summer house areas and sewage catchment areas where, according to waste water plans, it is possible to handle rainwater locally.
In 2015 there were approximately 281.500 properties without connection to a sewage system in Denmark.
The Danish Ministry of Environment and the Danish Environmental Protection Agency are responsible for Danish legislation on waste water.
The Danish Environmental Protection Agency have supervisory authority on waste water discharges, both in regards to administrative control, permissions and calculations of compliance with the permitted discharge amounts, and physically in regards to the condition of the discharge points. The Danish Environmental Protection Agency manages operational accidents at the treatment plants and rain-fed outlets that belong to the waste water utilities as well as pumping stations where waste water is discharged directly into an aquatic environment.
The Danish municipalities generally supervise the sewers, pumping stations without overflow, other machinery in the sewers without discharge/overflow and their condition, as well as all types of connections to the waste water utilites' facilities. The municipalities also supervise the physical and biological conditions of the local water streams in order to monitor compliance with the regulation regarding their quality.
The municipalities also manage operational accidents at pumping stations where waste water overflows into surrounding areas.
The municipalities is the authoritary body on planning the expanse of the loval sewage networks.
The waste water utilites are responsible for establishment, operation and maintenance of the public sewage systems up to the indvidual property lines. They are also responsible for treatment of the waste water from the public sewer, as well as treatment and discharge of rainwater in case a separated sewer system has been established.
The consumers are responsible for maintaining the sewage system within their own property.