More phosphate and nitrogen removed from waste water

27/03/2007 15:00

An increasing number of sewage treatment works take additional measures to minimise the discharge of phosphate and nitrogen in waste water. European legislation regarding protection of surface water played an important part.

Sewage treatment works with additional facilities

Sewage treatment works with additional facilities

Sewage treatment works put in extra effort

The Netherlands has approximately 370 sewage treatment works. In 2005, seven in every ten had taken additional measures to remove phosphate from waste water and six in ten had taken additional measures to remove nitrogen. In 1990, fewer than one in ten had taken additional measures to facilitate the removal of phosphate and nitrogen.

Huge increase in sewage treatment efficiency

Sewage treatment works put in extra efforts to achieve higher treatment efficiency. In 2005, over 81 percent of the total amount of phosphate in waste water was removed, as against 57 percent in 1990. The treatment efficiency rate for nitrogen increased to 74 percent in 2005.

Treatment efficiency rates

Treatment efficiency rate

European targets within reach

The European requirement to the effect that each member state should realise a treatment efficiency rate of 75 percent on an annual basis was already realised in 1996. The same requirement regarding nitrogen is expected to be met for the first time in 2006.

Biological method to remove phosphate gains ground

Water treatment works have traditionally used chemicals to remove phosphate. This is an expensive method, because the chemicals used in the treatment process are expensive. The biological method which involves phosphate-absorbing bacteria has rapidly gained ground in recent years. In 2005, the biological method was applied in 42 percent of waste water treatment works, as opposed to only 7 percent in 1995. Nitrogen removal is an entirely biological process.

Methods for removal of phosphate

Methods for removal of phosphate
 
Tjerk ter Veen, Ronnie Huwaë and Kees Baas