In this work package, we work on the separation and concentration of nutrients present in liquid waste resources with the aim to contribute to their successful recycling as upgraded sustainable waste-based fertiliser products

Our two main aims are:

1) to develop and optimise biotic and abiotic processes to concentrate nutrients from liquid waste streams, and

2) to assess the effect of sorbents in biogas processes during digestate post-treatment and utilisation.

We will explore and compare a selection of methods and processes to separate and up-concentrate nutrients from different secondary nutrient-rich resources, with particular focus on nitrogen and phosphorus.

 

Microalgae

Microalgae are microscopic, mainly aquatic organisms that can perform oxygenic photosynthesis like plants do, i.e. they obtain most of their energy from light and can use CO2 as their carbon source (Figure 1).

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Figure 1. Microscopic pictures of some microalgal strains that are used in our lab. Left picture: Haematococcus pluvialis (larger green cells to the left), Chlorella sorokiniana (small lucent cells to the right). Right picture: Arthrospira platensis (“Spirulina”). Photos: Thorsten Heidorn

In nature, microalgae have, together with land-based plants, the important function of recycling nutrients by converting inorganic molecules to organic with a higher energy content, which can then be used by e.g. animals and humans (carbohydrates, proteins, Figure 2).

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Figure 2. Microalgae within closed loops for carbon (C), phosphorus (P), and nitrogen (N)

The advantage of microalgae in comparison to plants in the context of a technical treatment system is the fact that they are suspended in water and therefore can more easily be integrated into an existing technical system such as a waste water treatment plant.

The cultivation of microalgae is one possibility to concentrate nutrients from liquid waste streams, just like it would happen in nature (e.g. algal blooms as a rather undesirable phenomenon).

Within this project we will study how microalgae can be used for taking up nitrogen and phosphorus from treated sewage and how the biomass can then be used as a fertiliser.

In our lab we have several advanced, continuous photobioreactor systems, which give us the possibility to closely control and monitor the process (Figure 3).

Click here for first results on microalgae

Sorbents

As an example for abiotic processes, we will study the effect of different sorbents to concentrate nutrients, which are present in liquid waste streams.

Sorbents are materials, which can bind nutrients and hence potentially extract them from liquid waste streams.

There are many different types of sorbents, all of which are characterised by different ways to bind nutrients (Figure 4).

When it comes to recycling, it is important to also ensure that the sorbents will release adsorbed nutrients when they are used as fertilisers, i.e. whether the nutrients will become available to plants. 

In this project, we will analyse the binding characteristics of different sorbents by different methods in order to identify appropriate sorbents for waste treatment. 

Since diluted waste streams are of low economic value, costs related to their treatment e.g. by sorbents must be accordingly low. We will therefore focus on sorbents, which are relevant for the treatment of diluted waste streams.   

We will also explore the effects, which sorbents can have during post-treatment of biogas digestate, or when digestate is used as fertiliser. For this, we will utilize the lab-scale biogas reactors, which NIBIO already possesses (Figure 5).

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Figure 5. Biogas laboratory. Photo: Kathrine T. Gulden
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Figure 3. Photobioreactor used to grow microalgae. Photo: Thorsten Heidorn

 

 

 

 

 

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Figure 4. Biochar can be used as sorbent. Photo: Anette Tjomsland