7.2 Sean Case – University of Copenhagen

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WP 7.2: Nitrogen recycling from organic waste streams and biofertilizers, Sean Case, UCPH

This postdoctoral project consisted of a number of investigations of the feasibility and stakeholder acceptability of alternative biofertiliser solutions. In this summary, the studies are reported seperately. The main task was a farmer survey of organic fertiliser treatment technologies, whilst a second task was the screening of organic fertiliser treatment technologies. 

Farmer surveys

In order to prevent pollution and make better use of limited resources, there is an increasing need to retain and recycle waste in the European Union. One important waste stream is excess nutrients from animal and urban waste sources. 

Animal and urban waste can be treated in a number of ways in order to increase the retention of nutrients while ensuring they are suitable for agricultural application, and reducing climate change impact. To increase the adoption of organic fertiliser treatment technologies or new types of organic fertiliser on a large scale, a good understanding of the fertiliser market is required. One important aspect of this is the understanding of the current use of organic fertilisers by farmers, and their future interest in using them.

After a review of the literature, it was clear that the perceptions of farmers towards organic fertiliser products have not been adequately investigated. The key research question of this project was: What are the attitudes of farmers in the EU to mature and novel organic fertiliser products?

We surveyed farmers in several European countries (Denmark, Italy, Spain) to answer these research questions. In Denmark we successfully answered these research questions by surveying a representative selection of farmers across the country. We surveyed a representative sample of all farmers with > 10 Ha of land (specifically land permitted to receive fertiliser) in Denmark using a survey posted to 1 585 participants. We received a response from 452 farmers - a 28% response rate. The same survey design was used in Italy and Spain. The results from these countries differed from those of Denmark in that the respondents were not statistically representative of the country they come from; however, we were still able to derive many interesting insights into the opinions of farmers towards organic fertiliser use in these countries.

  • The attitudes of farmers across the EU towards novel and mature organic fertilisers. Paper in preparation.

Laboratory studies – screening of organic fertiliser treatment technologies

Alongside the survey work several laboratory incubations were performed in order to determine the efficacy of various organic fertiliser treatment technologies to improve the nutrient supply efficiency of these products. 

Biosolid drying: previous studies found that thermally-dried biosolids contained more mineralisable organic nitrogen (N) than the raw or anaerobically-digested (AD) biosolids they were derived from. However, the effect of thermal drying temperature on biosolids N availability is not well understood. This will be of importance for the value of the biosolids when used to fertilise crops.

We sourced an AD biosolids from a Danish waste water treatment plant (WWTP) and dried it in the laboratory at 70, 130, 190 or 250 °C to > 95% dry matter content. Also, we sourced biosolids from the WWTP dried using its in-house thermal drying process (input temperature 95 °C, thermal fluid circuit temperature 200 °C, 95% dry matter content). This incubation determined the effect of drying temperature on biosolids N mineralisation in soil, CO2 emissions, and N2O emissions.

  • The effect of thermally-dried sludges on nitrogen cycling in arable soil. Paper accepted. 

Laboratory screening of organic fertilisers

The Danish resource strategy presented targets to increase the recycling of organic materials in Denmark, specifically household and service sector organic waste, garden waste and sewage sludge. Recent increases in fertiliser prices, and an increasing interest in recycling organic waste, have made new types of waste residuals more commercially relevant to farmers. These materials are derived from a range of organic waste (e.g. enzymes, potato starch etc.), or from novel treatment techniques (such as biogasification). Many of these waste residuals are safe and suitable for application to agricultural land. However, there is a lack of knowledge regarding their efficient utilisation.

Several of these products have been tested in laboratory and field trials, however there is a lack of knowledge as to whether these products could be used more efficiently, or whether further processing could make them more valuable as fertilisers (due to enhanced nutrient release or availability, or improved handling).

The first incubation conducted in this project screened 16 different types of processed manures, urban wastes, and industrial wastes to compare their N mineralisation and P release properties. Based on the results of the first incubation, several fertilisers are now selected for a second experiment to ‘upgrade’ them via thermal/pressure treatment, alkalinisation, or sonification to improve their N and P release properties.

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