WWTP Amersfoort (NL): conversion into an energy and nutrient factory – commissioning and performance

Parnowska, M.1 and Geraats B.2

1Eliquo UK, 2 Eliquo Water Energy, the Netherlands



To achieve improved efficiency and minimisation of operating costs, Water Board Vallei & Veluwe in the Netherlands set out to upgrade their assets at the Amersfoort WWTP by turning it into a regional sludge centre, processing sludges from a number of nearby plants in the most beneficial way. Eliquo Water Energy carried out the upgrade by incorporating a number of energy generating and phosphate recovering technologies with the existing assets.  An important consideration was to build and commission the additional equipment without disrupting the plant operations.

This paper presents:

  • The concept of Amersfoort WWTP ‘Energy and Nutrient Factory’ especially the conversion of traditional digesters to digesters fed with TPH sludge from a LysoTherm®
  • An assessment of the operational parameters and performance of the digesters and dewatering during period from April to September.Keywords

Nutrient recovery, struvite precipitation, thermal hydrolysis process


Amersfoort wastewater treatment plant (WWTP) in the Netherlands is owned and operated by the Dutch Water Board Vallei & Veluwe. In 2013 the Water Board 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 acts as a so-called ‘energy and nutrient factory’.

Before the changes, the sludge line was processing indigenous sludge and a small amount of raw sludge imported from Woudenberg WWTP. Digested sludges from two other local treatment plants – Nijkerk and Soest were brought to the site for dewatering.

Before the upgrade, the sludge line at Amersfoort WWTP consisted of three digesters, sludge buffer tanks and two centrifuges. The biogas generated was utilised in two old, inefficient CHP units. The two centrifuges were used for dewatering of the indigenous and imported sludges. The centrate produced was treated in a deamonification reactor (DEMON®). The main process stages of the sludge line at Amersfoort before the upgrade are presented in Figure 1.

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