Energy and nutrient factory at Amersfoort WWTP in The Netherlands

Geraats, B., Parnowska, M., Huntington, G., Eliquo Water & Energy B.V



The Amersfoort wastewater treatment plant (WWTP) in The Netherlands has been upgraded to become a regional sludge processing hub for a number of WWTPs in the area. By using a combination of innovative energy and nutrient recovery technologies, energy is recovered by the application of LysoTherm® thermal pressure hydrolysis technology which enables the plant to become energy positive. Phosphorus is also recovered, creating a valuable fertiliser product which will generate non-regulated revenue. This paper provides a description of the project which currently is in the commissioning phase.

Keywords: energy recovery; nutrient recovery; thermal pressure hydrolysis, anaerobic digestion, sludge treatment centre


Amersfoort wastewater treatment plant (WWTP) in The Netherlands is owned and operated by Dutch Waterboard Vallei & Veluwe. In 2013 it was decided to transform the plant into a regional sludge processing centre using innovative energy and nutrient recovery technologies. In line with the growing trend in The Netherlands and Western Europe, the focus was on the recovery of energy and nutrients from municipal wastewater and waste activated sludge; the upgraded plant will act as a so-called ‘energy and nutrient factory’. Eliquo achieved this objective by adding to the existing arrangement a number of innovative solutions: Wasstrip® reactor, LysoTherm® system and Pearl® 2000 reactor. Old CHP units have been replaced by 3 efficient 500 kW units. Sludge processing equipment has also been updated. This comprehensive upgrade has been carried out without disruption to the normal function of the WWTP. A process flow diagram of the new configuration is shown in figure 1.

Sludge from both Amersfoort WWTP and imported sludge from surrounding works is introduced into a Wasstrip® reactor, where the excess phosphate is stripped from the sludge. The sludge is pre-thickened and fed to 3 existing digesters. Each digester is equipped with a LysoTherm® sludge hydrolysis module. The heat needed for sludge hydrolysis is provided from the plant’s CHP engines operating on biogas. The centrate from the sludge dewatering and the filtrate from the Wasstrip® process is treated in a Pearl® reactor to produce Crystal Green® fertiliser.

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