Sludge digestion

Sludge digestion is a special category of digestion that we often encounter at sewage and wastewater treatment sites. The sludge produced at those sites is ideally suited to be used as input in a digester. In this article you will read all about sludge digestion.

How does sludge digestion work?

Sludge fermentation involves putting together a menu of products. These are weighed and mixed before being fed into the sludge digester. In some cases, a sludge digester has a pretreatment step. The purpose of the pre-processing step is to make the biomass easier to convert, thereby producing more biogas. 

After the pre-processing step, the input streams enter the digester. This can be a large stirred barrel, or it can be a system with several compartments. During this stage, the bacteria convert as much biomass as possible into biogas. 

This biogas is collected and then used in a Combined Heat and Power (CHP) system. This produces heat and electricity. Another option is to upgrade the biogas into green gas. This can be fed into the gas grid. In some cases, the biogas is used in a boiler to produce heat. 

Where is sludge digestion applied?

Sludge digestion is mainly applied at sites with Sewage and Wastewater Treatment. Sludge must be sold at high prices by water boards and other water treatment parties.  Fermentation converts some of the organic material in sewage sludge into biogas. This reduces the amount of sludge and the cost of disposal is also lower. 

At the same time, of course, green energy is produced. A lot of water boards and other purification parties are already applying this. There is a separate category within the SDE+ subsidy for sludge fermentation.


What does the development process look like?

At Ekwadraat we always start with an inventory of the various possibilities for sludge digestion. If this shows that there is sufficient potential, we draw up a business case for you. We then carry out a risk analysis, after which we start working to mitigate these risks. 

We then look for developments that increase the feasibility of a project, including:

Next, you need to apply for permits. Depending on your installation, you need to apply for different permits. As input for the permits, it is necessary to have the right drawings. Therefore, you should already have a good idea of the suppliers who will supply components for the installation. We will help you find the right suppliers.  Once the permits are in, we can apply for the SDE+ subsidy for your project.

We then help with the financing, maintain contact with RVO, can apply for innovation subsidies and draw up measurement protocols and measurement reports for you.


The possibilities for sludge digestion

Are you curious about the possibilities for sludge fermentation? Then we would like to help you. Ekwadraat is familiar with all developments and innovations in the field of digestion. This enables us to help you develop the best solution for your situation. We are also happy to guide you in realizing this solution. Please contact us for more information.

Fermentation and Ekwadraat in figures


>18 years of experience


Involved in the development of >75% of all Dutch installations


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Getting started with sludge digestion

Are you curious about the possibilities for sludge fermentation? Or do you want to realize a sludge digestion installation? Then get in touch.

Non-binding answer    Within 1-2 working days

"Curious about the possibilities for sludge digestion?"

Klaas de Jong

Senior adviseur/procestechnoloog