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Witteveen+Bos and Nijhuis Industries join forces to implement 1-STEP® filter worldwide


On Monday 5 March 2018, Karin Sluis, CEO of Witteveen+Bos and Menno M. Holterman, CEO of Nijhuis Industries, signed a Memorandum of Understanding agreeing a unique cooperation concerning the worldwide implementation and future development of the 1-STEP® filter. The 1-STEP® filter is the most cost-effective total tertiary treatment solution to improve the effluent quality of municipal sewage treatment plants. This revolutionary and game-changing treatment step treats total suspended solids, nitrogen, phosphorus, organic micro-pollutants and medical residues, all at the same time. The 1-STEP® filter combines four processes in a single treatment unit, ensuring a compact, robust, reliable and cost-effective effluent polishing solution to enable both a cleaner and protected environment, as well as least-cost treated effluent recycling schemes.

Waternet - innovator, co-developer and first ever 1-STEP® filter operator

Waternet is the water-cycle company for Amsterdam and the surrounding regions. From 2013 onwards, Waternet has operated the first ever 1-STEP® filter at their sewage treatment plant (STP) at Horstermeer (165,000 Population Equivalent). Horstermeer STP is equipped with a full scale 1,550 m3/h 1-STEP® filter which was installed to meet the stringent total nitrogen (5 mg/l) and total phosphorus (0.3 mg/l) limits imposed by the EU Water Framework Directive, whilst also future-proofing Horstermeer STP and enabling it to achieve possible future discharge limits for organic micro pollutants.

Extensive R&D efforts and field test

Based on extensive R&D efforts and field tests between 2009-2010, the Horstermeer STP 1-STEP® filter was constructed in 2011 and commissioned in August 2012. This 1-STEP® filter is the result of co-development by various companies involved, financially supported by STOWA and the Water Framework Directive Innovation Program. After it was put into operation on January 1st, 2013, it has been tested extensively under various load conditions, different water qualities, and across the full range of seasonal Netherlands’ weather events. The filter has been designed to treat up to 1.3 times the dry weather flow of the STP, whilst removing total nitrogen levels down to 2.2 mg/l and total phosphorous levels down to 0.18 mg/l; the lowest phosphorous level so far in practice. The successful implementation of the 1-STEP® filter at Horstermeer STP resulted in a 30-50 % saving in investment and operational costs when compared to conventional, successive processes.

About the 1-STEP® filter

The 1-STEP® filter is a modular and compact fixed bed activated carbon filter, operated at a relatively high rate downward flow. The 1-STEP® filter combines four treatment processes into one single treatment unit. In addition to the removal of suspended solids by filtration, nitrogen is simultaneously removed via biological denitrification (using a selective carbon source), chemical phosphate and heavy metals are removed by coagulation and flocculation (with a low dose of metal salt), and, if required, organic micro pollutants can be removed by adsorption onto the activated carbon.