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The recycled fertilizers produced in Lohja offer their users huge emissions reduction potential. 

Sanni Mallat Gasum

Sanni Mallat, master’s thesis author

  • Environmental Technology, LUT University, Lappeenranta

  • Master’s major: Sustainability Science and Solutions

  • Title of thesis: Biokaasun ja kierrätyslannoitteiden tuotannon ilmastovaikutus (Climate impact of biogas and recycled fertilizer production)


Using recycled fertilizers can deliver significant environmental advantages

The study used life cycle assessment to investigate the climate impacts of recycled fertilizer products made at the Lohja biogas plant. Sanni Mallat’s master’s thesis shows that the fertilizers produced in Lohja offer their users huge emissions reduction potential.

How did you end up writing a master’s thesis for Gasum and what is your thesis about?

Interest in the energy company and its aims towards cleaner energy and a cleaner future made me apply to Gasum for a job. I started at Gasum working in customer service with consumers of transport gas. I became more and more interested in biogas and ended up enquiring about the possibility of doing my theses for my environmental technology studies.

The subject of the master’s thesis was to study the climate impacts of the biogas and recycled fertilizer produced at Gasum’s biogas plant in Lohja. The objective was in particular to increase knowledge about the climate impacts of recycled fertilizers and to compare the emissions originating from the production of these with emissions in the production of mineral fertilizers.

How was the research carried out?

The study used life cycle assessment (LCA) to investigate the climate impacts of the recycled fertilizer products made at the Lohja biogas plant. LCA can be used identify the environmental impacts of a product, process or service throughout its life cycle. This study used SULCA software to calculate the emissions.

The study took into account the stages in biogas production, starting from the transport of biowaste to the biogas plant and ending with the injection of the biogas into the system and the transport of fertilizers to users. For fertilizers, the focus was on the main plant nutrients: nitrogen (N), phosphorus (P) and potassium (K).

What are fertilizers?

Fertilizers are any organic or inorganic substances that are used to improve crop growth. Fertilizers play an important role in food production, and it has been estimated that population growth will increase the need for them by 30% between now and 2050.

Mineral fertilizers are inorganic fertilizers, which among other things contain nitrogen (N), phosphorus (P) and potassium (K).

The manufacture of mineral nitrogen in particular consumes a lot of energy and causes emissions since fossil natural gas or coal is used to make it. In addition, phosphorus is a non-renewable resource, which is extracted from mined phosphate rock.

Recycled fertilizers, on the other hand, often originate as a by-product in a process, like biogas production. For example, Gasum’s biogas plant in Lohja uses the digestion of waste to produce biogas for use as a road vehicle fuel and two recycled fertilizers: liquid Perus fertilizer and solid Humus fertilizer. Both fertilizers are also suitable for organic farming. Like mineral fertilizers, both types contain nutrients, but they also include organic matter that benefits the soil.

Why is this an important issue?

The issue is important because from the climate change perspective, every sector needs to monitor and reduce emissions. The manufacture of mineral fertilizers is energy intensive, causing a lot of emissions and since, for example, phosphorus resources are beginning to be depleted, consideration needs to be given to alternatives to mineral fertilizers.

The markets for recycled fertilizers are just emerging and this makes it interesting to compare these two alternative fertilizers from the environmental aspect.

What are the benefits of the recycled fertilizers produced in Lohja compared to mineral fertilizers?

The study shows that the emissions from recycled fertilizers produced at the Lohja biogas plant are many times lower than the emissions from the production of mineral fertilizers containing a similar amount of nutrients.

Besides the low-emission production process, recycled fertilizers have the advantage of having an organic matter content that has positive impacts on soil condition and properties. The raw materials are locally sourced, and the fertilizers are used locally.

Another advantage is that unlike industrial fertilizers, their price is not linked to the price of fossil energy. For example, in autumn 2021, the natural gas price resulted in a huge hike in prices of mineral fertilizers. On the other hand, prices of recycled fertilizers can be assumed to remain more stable.

The fertilizers produced in Lohja offer their users huge emissions reduction potential. Emissions in the production of recycled fertilizers are more than 90% lower than emissions in the production of a mineral fertilizer containing a similar amount of nutrients. Use of recycled fertilizers can avoid the emissions originating in the production of mineral fertilizers while promoting the recycling of nutrients and action to prevent climate change.

A comparison between a recycled fertilizer from Lohja and an imaginary mineral fertilizer containing the same amount of nutrients:

Gasum fertilizers comparison 02.png

(The study calculated the nitrogen (N), phosphorus (P) and potassium (K) contained in Perus and Humus fertilizers based on their product data sheets. The mineral fertilizers shown here are imaginary fertilizers that contain the same amount of nitrogen (N), phosphorus (P) and potassium (P) as recycled fertilizers. The emissions for mineral fertilizers have been calculated based on the emission factors obtained from the Ecoinvent database.)

Blue = Gasum’s recycled fertilizer, Grey =Mineral fertilizer


How does the use of recycled fertilizers promote the circular economy?

Gasum’s biogas plants promote the circular economy at its best. Renewable biogas produced from waste is used as a transport fuel and in the case of the Lohja plant, two nutrient-rich recycled fertilizer products are obtained from the digestate arising as a by-product in the process. These fertilizer products can be used in organic farming on local farms.

This means that the energy contained in the waste is utilized and the nutrients are efficiently recycled onto the fields.

How can the consumer promote the circular economy? What is the role of the consumer from the perspective of biogas and recycled fertilizer production?

Everyday consumer choice is of great importance from the perspective of biogas and recycled fertilizer production as well as from the climate change aspect. For example, consumers can contribute to the circular economy and climate change mitigation by putting food waste into the biowaste bin instead of the general waste bin.

The energy contained in biodegradable waste is utilized as energy in the form of biogas and important nutrients contained in the waste ultimately end up benefitting plants by being recycled as fertilizers. Important nutrients and organic matter in general waste would be lost from the cycle. Effective recycling of nutrients can reduce the use of non-renewable natural resources like energy and nutrients.


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