In 2003 there were 378 sewage water treatment plants in the Netherlands. In total, more than 1.7 billionm³ of waste water was treated, 14 percent less than in 2002 and the smallest volume of waste water since 1997.
Sewage water treatment plants and precipitation at weather station De Bilt
Less waste water because of drought
The volume of waste water entering treatment plants partly depends on the amount of precipitation; 2003 was a dry year, compared to 2002. Weather station De Bilt measured only 613 mm of precipitation in 2003, the smallest amount since1996.
Output sewage treatment plants
More efficient treatment
In 2003 sewage water treatment plants were operating more efficiently, resulting in a larger amount of pollutants being removed from sewage sludge. High amounts of nitrogen and phosphor were removed from sewage sludge and the upward trend of recent years continued. In 2003 80 percent of phosphor and 72 percent of nitrogen was removed from waste water. The respective rates for 1995 were 74 and 57 percent.
Treatment efficiency of biologically degradable substances has been around 97percent for a longer period.
The increase in treatment efficiency is caused by improved treatment technology and prolonged dry periods. In yearsof drought a smaller amount of sludge is transported through the sewage systemto the plants. And because the amount of rainwater entering the sewer systemdeclines, other waste water can be stored longer in the sewer system making thepurification process more efficient.
Electricity use of sewage water treatment plants
Lower electricity use
Electricity use of sewage water treatment plants dropped, because a smaller amount of waste water entered the plants. The 2003 electricity use was 683 million kWh, 2 percent down on 2002. The amount of electricity needed to remove1 kg of biologically degradable material from waste water appeared to be lower in 2003 than in 2002. The purification process was apparently more efficient but it is still too early to conclude that the efficiency increase is permanent.
Tjerk ter Veen and Kees Baas.