The nitrogen removal capacity of sewage water treatment plants in the Netherlands is improving continuously. In 2006, the 75 percent barrier was broken for the first time. Purification efficiency is enhanced by new, high-capacity plants and the treatment process has been improved. European legislation regarding the protection of surface water quality has played an important part in this respect.
Removal of nitrogen from sewage water crucial to surface water quality
Too large amounts of nitrogen and phosphate in surface water are likely to disrupt the water fauna and flora. Since all Dutch water treatment plants discharge their treated water to surface water, efficient treatment of waste water is of paramount importance for surface water quality.
Removal of phosphate and nitrogen from sewage water
European target regarding nitrogen achieved for the first time
In 2006, sewage water treatment plants in the Netherlands have complied with the EU Urban Waste Water Treatment Directive for the first time. According to this directive, 75 percent of nitrogen and phosphate must be removed from waste water before it is discharged to surface water.
As early as in 1996, the Netherlands complied with the European phosphate directive. It took more time to comply with the European nitrogen directive, because the removal of nitrogen calls for more expensive and radical changes in the purification process.
Sewage water treatment plants
Sewage treatment capacity is growing continually
Since the early 1980s, the number of sewage water treatment plants has been reduced substantially from more than 500 in 1981 to approximately 370 in 2006. Despite the reduction, the overall sewage treatment capacity has increased in this period. The average capacity per unit has grown considerably.
The reason is that over the past decades, many smaller (and often technically obsolete) plants have been closed down and replaced by larger, high-capacity plants. Due to extra measures, these plants have better nitrogen removal facilities. More state-of-the-art technology and replacement of obsolete units by modern ones enhanced the nitrogen removal capacity.
Tjerk ter Veen, Ronnie Huwaë and Kees Baas