Cost-effective technology for better water quality
Under the European Water Framework Directive, which aims to assure high-quality surface water and groundwater, wastewater treatment plants must treat their effluent more thoroughly to remove phosphate and other contaminants. In addition, the Urban Wastewater Directive requires a stricter approach to micropollutants. The 1-STEP® filter, put into operation at Horstermeer sewage treatment plant, is a proven, cost-effective technology that removes organic micropollutants, medicinal residues, suspended solids and heavy metals, in addition to these nutrients.
1-STEP® is a modular, compact filter with a fixed activated carbon filter bed that is used in conjunction with a relatively fast rate of downward flow. The filter combines four treatment processes in one step. In addition to removing suspended matter by filtration, nitrogen is simultaneously removed via biological denitrification (with a carbon source), phosphate is chemically removed by coagulation and flocculation (with a low dose of metal salt), and, if necessary, organic micropollutants can be removed via adsorption on the surface of the activated carbon.
Inexpensive and efficient
This post-treatment step - the four processes in a single reactor - represents a compact, robust and reliable effluent treatment solution. The filter produces filtrate of excellent quality over a long period of time (stability in production) and removes a broad spectrum of priority substances and emerging substances.
Moreover, this technology is characterised by a low level of investment and modest operating costs. Compared to conventional processes configured in sequential steps, the implementation of the 1-STEP® filter at the Horstermeer sewage treatment plant has resulted in savings of between 30% and 50% in terms of the investment outlay and operating costs. Some of these savings are achieved through the comparatively low consumption of chemicals and energy, and through effective filter bed cleaning.
Pioneering
In 2013, Water Authority Amstel, Gooi en Vecht put the very first 1-STEP® filter into service at the Horstermeer sewage treatment plant (population equivalent: 165,000). This sewage treatment plant is equipped with a complete 1-STEP® filter with a capacity of 1,550 m3/h, installed to meet the WFD standard of a maximum total nitrogen content of 5 mg/l and a maximum total phosphorous content of 0.3 mg/l. The filter was also installed with the intention of future-proofing the Horstermeer sewage treatment plant, as it is capable of meeting the future discharge limits for organic micropollutants specified in the Urban Wastewater Directive.
Circular approach
At the Horstermeer sewage treatment plant, the filter improves effluent quality in a cost-effective manner. Consequently, the 1-STEP® filter is an indispensable element in water reuse systems and also facilitates the implementation of a circular approach. Because the removal efficiency of micropollutants decreases over time (as the activated carbon slowly becomes saturated), the filter should ideally be used in conjunction with an ozone system, such as the O3-step filter. The set-up in Horstermeer follows this recommendation.
The 1-STEP® filter is a joint innovation initiated by Water Authority Amstel, Gooi en Vecht Water, Witteveen+Bos, Nijhuis Industries, Cabot Norit Activated Carbon and Delft University of Technology, and partly funded through STOWA and the Dutch Water Framework Directive Innovation Programme.
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