• Join AIWW 2021
  • Stay Up to Date
  • Login
Amsterdam International Water Web
  • Home
  • News
    • Latest
    • Agenda
  • Insights
  • About
    • About
    • Themes and topics
      • Subtheme #1. Clean Water and Ecosystem Restoration
      • Subtheme #2. Reuse, Recycle and Recover
      • Subtheme #3. Risk and Resilience
      • Subtheme #4. Community Engagement and Inter-sectoral Collaboration
    • PAC Members
    • AIWW team
  • What We Do
    • What we do
    • AIWW Activities
    • AIWW 2021: Blue green deals with integrated solutions
    • Water Solutions #1 – Clean Water and Ecosystem Restoration
    • Water Solutions #2 – Reuse, Recycle & Recover
    • Water Solutions #3 – Risk and Resilience
    • Water Solutions #4 – Community Engagement and Inter-sectoral collaboration
    • Amsterdam Agreements Overview
      • Amsterdam Agreements Introduction
    • AIWW Global Inventory
  • Programme AIWW2021
No Result
View All Result
  • Home
  • News
    • Latest
    • Agenda
  • Insights
  • About
    • About
    • Themes and topics
      • Subtheme #1. Clean Water and Ecosystem Restoration
      • Subtheme #2. Reuse, Recycle and Recover
      • Subtheme #3. Risk and Resilience
      • Subtheme #4. Community Engagement and Inter-sectoral Collaboration
    • PAC Members
    • AIWW team
  • What We Do
    • What we do
    • AIWW Activities
    • AIWW 2021: Blue green deals with integrated solutions
    • Water Solutions #1 – Clean Water and Ecosystem Restoration
    • Water Solutions #2 – Reuse, Recycle & Recover
    • Water Solutions #3 – Risk and Resilience
    • Water Solutions #4 – Community Engagement and Inter-sectoral collaboration
    • Amsterdam Agreements Overview
      • Amsterdam Agreements Introduction
    • AIWW Global Inventory
  • Programme AIWW2021
No Result
View All Result
Amsterdam International Water Web
No Result
View All Result
Home Insights

The result of 10 years of experience with Ephyra sludge digestion

André Visser, Eddie Koornneef and Danny Traksel (Royal HaskoningDHV)

January 18, 2022
in Insights, insights-articles

A new sludge digester has been in operation at the Tollebeek waste water treatment plant in Flevoland since 2017. The digester is an Ephyra system, developed by Royal HaskoningDHV since 2010. Instead of one reactor, there are 3 or 4 reactors connected in series, resulting in more complete digestion and more biogas.

The new method of sludge digestion was developed to give substance to ‘the Energy Plant’ or energy-neutral or even energy-positive sewage treatment. During development, specific attention was paid to:

  • Performance under different conditions, including with different types of sludge and varying dwell times;
  • Sludge digestion and biogas production and how they compare to the performance of other sludge digestion technologies;
  • Stability under different sludge loads.

In this article, we discuss the operation and performance of Ephyra in respect of the aforementioned questions, with particular focus on development from lab to practice scale.

Figure 1. Principle of the Ephyra technology, with 3 reactors as compartments in one digestion tank. Series connection of individual tanks is also possible.

 

Operation

The principle of Ephyra sludge digestion is the use of 2 to 4 digestion reactors or compartments connected in series, rather than a single reactor or tank (see Figure 1). This creates a plug flow type of digestion, unlike in the usual full mixed tank. When compared to a single full mixed tank, plug flow digestion produces fewer short-circuit currents, breakdown reactions occur more quickly, and the individual phases of the sludge digestion process are separated. All of this leads to better digestion with more sludge breakdown and more biogas.

Another important advantage is that average dwell times of 6 to 7 days are feasible, instead of the usual 15 to 20 days. As a result, the capacity of the system is high and more sludge can be processed with the same reactor volume. The shorter dwell times are possible thanks to, inter alia, (patented) recirculation from the last to the first compartment of the series circuit; this control strategy helps to prevent problems including acidification in the first reactor. 

From lab to practice

Development started around 2010, with the first ideas and creation of a computational model. The results of the first technical model calculations confirmed the expected benefits over a full mixed reactor, namely better sludge digestion and more biogas. To validate the model results, various tests with batch and continuous systems were carried out at Royal HaskoningDHV’s Technological Research Centre. A number of different sludge types were tested, with different proportions of primary sludge (from pre-sedimentation) and secondary sludge (from an activated sludge system). Comparison with conventional mesophilic digestion once again demonstrated that sludge breakdown was much higher. In Ephyra systems, when secondary sludge was digested, 15% more sludge was broken down, with 15% higher biogas production at the same time

 

2014-2016: pilot project at Tollebeek waste water treatment plant

The results of the technical and financial model calculations and the lab tests prompted Royal HaskoningDHV and the Zuiderzeeland Water Board to conduct a pilot at the Tollebeek waste water treatment plant. The idea was that, if the pilot project were to prove successful, Ephyra sludge digestion could be applied in this waste water treatment plant and sludge from Lelystad digested in the future. This would be facilitated by expanding the existing digestion at Tollebeek with an upstream Ephyra tank.

The pilot system consisted of four mechanically mixed reactors connected in series, with internally controlled recirculation from the last to the first reactor. The total dwell time was around 7 to 8 days, and the dwell time per reactor around 2 days.

The pilot showed that the sludge breakdown, averaging 40% dry matter, was in line with expectations.

During the pilot project, peak feeds were also tested, with the total dwell time reduced to 5 days for periods of 5 to 10 days. During these periods of peak load, the system continued to function stably; there was no noticeable drop in pH and sludge breakdown and biogas production remained steady; process control of the internal recirculation system functioned properly (see Stowa report 2016-34).

In addition to the pilot project, we also carried out model calculations involving various configurations and arrangements for use of the Ephyra digester at Tollebeek waste water treatment plant; examples are the number of reactors in series and the degree of internal recirculation.

 

From pilot to design

The results of the pilot and the model calculations have helped to produce a final design for the practical system envisaged for Tollebeek. The following changes have been made over the 2010 draft.

Use of horizontal mixed reactors

The original design was based on vertical reactors compartmentalised by partitions. This provided to have a number of drawbacks, however. The accessibility of the reactors (compartments) for maintenance was difficult, the reactors were higher than the building heights used in the Netherlands for sludge digesters, and the partitions were sensitive to blockages. The design was also expensive. A design with horizontal reactors connected in series did not have any of these drawbacks. This decision had already been taken prior to the pilot and the pilot system had been adapted to take these changes into account.

3 instead of 4 reactors in series

The model calculations indicated that there was almost no difference between the performance of 3 rather than 4 reactors in series. This was confirmed by exploratory lab tests. In view of the simplicity of the system and with cost considerations in mind, it was decided that 3 reactors in series (in a single tank) was most appropriate for Tollebeek. Using 3 reactors in series has since become the standard when constructing a completely new sludge digester. If converting existing systems, a different design is possible. The 3 reactors/compartments in the practical system at Tollebeek waste water treatment plant have been constructed as slices of pie, hydraulically connected in 1 reactor with a total volume of 1,500 m3.

 

Thickness of sludge requires adjustments

In addition to the aforementioned design aspects, the pilot study also indicated that sludge, and thicker sludge in particular (as used in sludge digestion), is a ‘special’ medium with a relatively high viscosity. This entails multiple minor adjustments to the design of mixers, pumps, heat exchangers and other equipment, piping and valves.

 

The Ephyra practical system at Tollebeek was completed at the end of 2017 and is functioning well. A second system has been operational since 2021 as an integral part of the Energy Plant at the Sleeuwijk waste water treatment plant. This is a completely new system (‘green pasture situation’) and also features 3 reactors connected in series in a single tank. In addition, two international systems are in the design and tendering phase, and a new pilot is due to start in Canada.

 

 

Figure 2. Organic matter removal (ODS) as a function of the proportion of excess sludge as measured on laboratory, pilot and practical scale. 100% means that only secondary sludge is digested. The tests were carried out at approximately 15 days or more of dwell time.

 

Figure 3. Organic matter (ODS) removal as a function of the dwell time for a sludge mixture of 50% primary and 50% secondary sludge. The graph is based on laboratory tests and model calculations.

 

 

How does the Ephyra sludge digester perform?

An important measure for sludge digestion performance is sludge breakdown, often represented as the return from the removal of organic dry matter (ODS) from the sludge. This return depends on the technology used and the sludge input – the latter because primary sludge breaks down more effectively than secondary sludge.

The relationship between sludge breakdown and the percentage of excess sludge to be digested is shown in Figure 2. From this, it can be deduced that if only secondary sludge is digested, approximately 45 to 46% of the organic matter is broken down. As the proportion of primary sludge increases, so too does its breakdown. For a sludge mixture of 50% primary and 50% secondary sludge, the breakdown is approximately 52 to 54%.

An important feature of Ephyra digesters is that they are stable in operation and digest sludge with shorter dwell times. This applies to a dwell time of around 5 days. Removal efficiency is less with shorter dwell times, however. The relationship between dwell time and return is shown in Figure 3. With dwell times in excess of 15 days, efficiency scarcely increases at all. The optimum lies between 10 and 15 days and depends on the composition of the sludge.

This new way of digesting sludge proved to be extremely stable and reliable throughout the entire development period – on laboratory scale, during the pilot project and now in practice.

 

SUMMARY

In 2010, RoyalHaskoningDHV began developing a new process for sludge digestion using the Ephyra principle. Digestion does not occur in just one reactor but in 3 or 4 reactors in series. Laboratory-scale tests, model calculations and a pilot study resulted in a design that was realised at Tollebeek waste water treatment plant in Flevoland in 2017. The new Ephyra sludge digester effects higher breakdown of organic matter and produces more biogas than conventional digesters.

 

Sources

Stowa 2016-34. Application of new Ephyra® and Themista® digestion concepts

Share76Tweet47Share13Send
Previous Post

Reduced variety of floodplain nature: a threat of uniformity

Next Post

Invasive fungus threatens Dutch salamander with extinction

Anniek Corporaal

Anniek Corporaal

Related Posts

‘This is what a river should look like’
Clean Water and Ecosystem Restoration

‘This is what a river should look like’

September 22, 2022
Effect of source location on the spread of groundwater contamination by open geothermal energy systems
Best Practices

Effect of source location on the spread of groundwater contamination by open geothermal energy systems

September 21, 2022
Image processing for automatic interpretation of drinking water mains inspections
Best Practices

Image processing for automatic interpretation of drinking water mains inspections

September 21, 2022
Groundwater drainage in New Orleans
Best Practices

Groundwater drainage in New Orleans

September 21, 2022
Drinking water treatments and their potential toxicity
Best Practices

Drinking water treatments and their potential toxicity

September 21, 2022
Next Post
Invasive fungus threatens Dutch salamander with extinction

Invasive fungus threatens Dutch salamander with extinction

AIWW Agenda

AIWW 2023

tba

Aquatech 2023

tba

Global Water Agenda

Browse by Category

  • Agri-food (5)
  • Amsterdam Agreements (7)
  • Best Practices (57)
  • Blue Green Deals with Integrated Solutions (53)
  • Cities (15)
  • Clean Water and Ecosystem Restoration (31)
  • Community engagement and inter-sectoral collaboration (12)
  • Conferentie (16)
  • Featured (109)
  • Future Water Leaders (19)
  • Global Inventory (4)
  • Industries (4)
  • Insights (27)
  • insights-articles (12)
  • News (109)
  • PAC (9)
  • Reuse, Recycle and Recover (19)
  • Risks and Resilience (25)
  • Sponsor (1)
  • Summit (7)
  • Utilies (5)
  • Water Solutions #1. Clean Water and Ecosystem Restoration (15)
  • Water Solutions #2. Reuse, Recycle and Recover (14)
  • Water Solutions #3. Risks and Resilience (16)
  • Water Solutions #4. Community engagement and inter-sectoral collaboration (3)

Browse by Tags

#groundwater AIWW AIWW 2021 AIWW2021 AIWW Conference Amsterdam Agreement Amsterdam International Water Web Amsterdam International Water Week clean water collaboration conference drinkable rivers drought EJWP Europe european investment bank flooding future water leaders Insights nature recover report resilience reuse risk risk managament risk management SDGs United Nations wastewater waste water wastewater management wastewater treatment water water event water managament water management Water Matters water recycle water sector water systems water youth network webinar wetskills youth for water

Contact information

Koningskade 40 | 2596 AA | the Hague |
the Netherlands

Phone :
+31 (0) 70 – 32 22 765

Email:
 info@amsterdamiww.com

Latest News

  • ‘This is what a river should look like’ September 22, 2022
  • Please join our FREE webinar on Aquathermy September 21, 2022
  • Effect of source location on the spread of groundwater contamination by open geothermal energy systems September 21, 2022

Subscribe To Our Newsletter

Latest Newsletters

  • AIWW – The Drop 💧 Check our Amsterdam Agreements | Apply now for the Willy Verstraete Award
  • AIWW – The Drop 💧 AIWW is the global leader in Blue-Green thinking
  • AIWW – The Drop 💧 All we want for X-mas 🎄, are Blue-Green deals with Integrated Solutions!
  • Thank you for making AIWW2021 a success – now let’s get to work! – Participants
  • Thank you for making AIWW2021 a success – now let’s get to work! – Speakers

© 2021 International Water Week       Disclaimer | Privacy Statement

No Result
View All Result
  • Home
  • News
    • Latest
    • Agenda
  • Insights
  • About
    • About
    • Themes and topics
      • Subtheme #1. Clean Water and Ecosystem Restoration
      • Subtheme #2. Reuse, Recycle and Recover
      • Subtheme #3. Risk and Resilience
      • Subtheme #4. Community Engagement and Inter-sectoral Collaboration
    • PAC Members
    • AIWW team
  • What We Do
    • What we do
    • AIWW Activities
    • AIWW 2021: Blue green deals with integrated solutions
    • Water Solutions #1 – Clean Water and Ecosystem Restoration
    • Water Solutions #2 – Reuse, Recycle & Recover
    • Water Solutions #3 – Risk and Resilience
    • Water Solutions #4 – Community Engagement and Inter-sectoral collaboration
    • Amsterdam Agreements Overview
      • Amsterdam Agreements Introduction
    • AIWW Global Inventory
  • Programme AIWW2021

© 2021 International Water Week       Disclaimer | Privacy Statement

Welcome Back!

Login to your account below

Forgotten Password?

Create New Account!

Fill the forms below to register

All fields are required. Log In

Retrieve your password

Please enter your username or email address to reset your password.

Log In
This website uses cookies. By continuing to use this website you are giving consent to cookies being used. Visit our Privacy and Cookie Policy.