The Ephyra® technology

Ephyra® is a compact and sustainable technology for sludge digestion. The concept is based upon a plug flow digestion in which the hydraulic retention time (HRT) and solids retention time (SRT) are separated. Small full-scale references of plug flow digestion are available.

Optimization of reactor design, process control and operations has led to significantly improved performances, which are part of the Ephyra® concept.

The distinguishing feature of Ephyra® is the horizontal compartmentalisation of sludge digestion. This means a separation of the hydraulic duration and sludge dwell time. In addition, an Ephyra® installation has a controller that completely controls the processes in the reactor.

Ephyra® results

In comparison to a conventional sludge digestion installation, the Ephyra® installation has demonstrated to break down 20% to 30% more organic substance for different sludge types. This results in more sustainable energy in terms of biogas and a lower amount of residual sludge.

Based upon full scale performance results, compact construction, ease-to-operate and a favorable energy balance of the Ephyra®, the payback time will often be only 2 to 5 years.


Advantages of Ephyra® compared to a WWTP with a traditional sludge digestion concept:

Enhanced (20% to 30%) biogas production, due to a higher breakdown of sludge
Lower use of chemicals (poly-electrolyte) for sludge thickening
Better dewaterability of the digested sludge
Smaller reactor, due to a higher sludge concentration in the reactors
Expansion of sludge processing capacity by 50-80% without placing reactor volume
Up to 20% improvement of the total energy balance of the WWTP


For more background information and results of the lab and pilot tests, read this online article in Water Matters.


‘Triple helix’ partnership

The innovative sludge digestion technology Ephyra® was developed by Royal HaskoningDHV in cooperation with STOWA (Foundation for Applied Water Research), Water board Zuiderzeeland. This project was co-financed with a contribution from the LIFE financial instrument of the European Union and with the Top Sector Energy subsidy from the Ministry of Economic Affairs.

To stimulate the innovation process of Ephyra®, the following parties have set up a ‘triple helix’ partnership: STOWA (Foundation for Applied WaterResearch), Waterboard Zuiderzeeland, Royal HaskoningDHV, TU Delft, Logisticon Water Treatment and Endress + Hauser.



The aim of this partnership is to gain knowledge and experience from joint (pilot) research. In 2016 we jointly realized the first practical installations (see the page Innovation process).

The research program is financially supported by the Netherlands Enterprise Agency (RVO) and European Union (LIFE+).

The parties involved have consciously opted for cooperation within the ‘triple helix’ of government, knowledge organizations and the business community. This was very successful, for example, in the development of the Nereda® technology for waste water purification from the National Nereda Research Program (NNOP).


In recent years there has been an increasing attention for extracting more energy and raw materials from wastewater globally. This is underlined by the realisation of numerous wastewater treatment plants worldwide.

In addition, in 2015, governments worldwide agreed on Global goals, also known as the Sustainable Developments Goals (SDGs). The following goals for access to affordable and clean energy by 2030 have been formulated:

Ensure universal access to affordable, reliable and modern energy services
Increase significantly the share of renewable energy in the global energy mix
Double the global rate of improvement in energy efficiency
Enhance international cooperation to facilitate access to clean energy research and technology, including renewable energy, energy efficiency and advanced and cleaner fossil-fuel technology, and promote investment in energy infrastructure and clean energy technology
Expand infrastructure and upgrade technology for supplying modern and sustainable energy services for all in developing countries, in particular least developed countries, small island developing States, and land-locked developing countries, in accordance with their respective programmes of support

Ephyra® contributes to the global sustainable energy goals. Also, it contributes to the reduction of waste from sewage treatment plants.

With the application of the Ephyra® technology, water boards reduce the operational costs for wastewater treatment and the costs for sludge processing, while the biogas yields increase.