dws-waternet-horstermeer-schultz-bondt-outside-770pxDutch minister Melanie Schultz van Haegen (in the middle) for Infrastructure and Environment officially commissioned world's first full scale 1-Step filter at waste water treatment plant Horstermeer, the Netherlands on 20 November. The highly innovative filter combines three processes for the additional treatment of wwtp-effluent.

The 1-Step filter (one step total effluent polishing) has been developed for water company Waternet in cooperation with engineering firm Witteveen + Bos, activated carbon producer Cabot Norit, Delft University of Technology and water research foundation STOWA .

dws-waternet-horstermeer-1-step-compartment-350pxStringent effluent standards for nutrients
Wwtp Horstermeer discharges its effluent on the river De Vecht that is situated in an area that is sensitive to eutrophication. To be able to achieve a good ecological potential in the river, as prescribed by the European Water Framework Directive, the discharge of the wwtp is limited to 5 mg/l nitrogen and 0,5 mg/l phosphate.

The 1-Step filter is in full operation since January and has since been optimized. Under normal operating conditions the discharge of the wwtp now contains only 2,7 mg/l nitrogen and 0,21 mgl/ phosphate.

Further optimalization is expected to get the nutrient concentrations down further to resp. 2,2 mg/l and 0,15 mg/l.

The wwtp-effluent has no standards for micro-pollutants but special monitoring showed that a big group of substances from medicines was removed by 30 to 90% at the start of the runtime of the activated carbon filter bed. The adsorption capacity of the carbon decreasing to zero over a period of 6 months (based on 15.000 - 20.000 treated bed volumes).

Excellent example of cooperation
"This is a leap forward in the field of water treatment," said Minister Schultz van Haegen at the commissioning ceremony. "We need such innovation desperately in order to achieve our ambitions for good quality of surface and groundwater" The minister congratulated the parties on the short development time of only six years from idea to implementation. "It is an excellent example of cooperation within the Dutch water sector between water boards, private parties and knowledge institutes."

dws-waternet-horstermeer-1-step-scheme-350pxCombination of three processes in one filter
The 1-Step filter is a fixed bed filter operated with a downward flow. The filter medium is activated carbon.

Next to the removal of suspended solids, the filter also achieves simultaneous biological denitrification, physical/chemical removal of phosphate and removal of micro pollutants by adsorption to the activated carbon.

Compared to current available advanced effluent treatment methods, such as continuous sand filtration, 1-Step has - because of the activated carbon - an additional adsorption capacity for dissolved substances including many micro pollutants, resulting in a cleaner discharge.

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