Micronutrients in the resource loop

Technology

In this project we aim to pay greater attention to micronutrients in the agro-food-waste system. In the past, research examined the reuse of organic residual streams, sludge streams and manure, but not from the perspective of the functional value of the micronutrients they contain. Micronutrients are – as in the case of phosphate – generally extracted from geological reserves and used in the food chain in a linear manner. The project partners strongly wish to work towards a circular use of micronutrients. The project approach includes determining the nutrient stream loads and concentrations in residual streams, the plant availability of these micronutrients, and the development of value chains for recycled micronutrients.

Challenge

This project’s objective is to establish a basis for closing the resource loop of essential micronutrients in the entire food chain (=agro-food-waste system). We aim to determine the balance (concentrations and loads) of micronutrients at the ‘back end’ (residual streams such as treatment sludge, KGW, livestock manure, drinking water sludge, residual streams from the animal-feed and food industry), and gain a better understand of their origin and current destinations. The focus will be on six to eight micronutrients that the project partners identified as the most relevant, for example, Manganese (Mn), Molybdenum (Mo), Boron (B), Magnesium (Mg), Iron (Fe), Copper (Cu) and Zink (Zn).

Solutions

This project will produce a set of working methods (combination of management and technology) for the use of promising residual streams with valorisation potential for the chain, through the development of innovative initiatives in the recycling of micronutrients. There are opportunities in waste and wastewater treatment for the optimal valorisation of residual streams, and thereby to contribute to the circular economy. For the agro sector, opportunities are seen that provide insight into the presence and role of the above-mentioned micronutrients in the cultivation of crops, and the development of scenarios for the recycling of the micronutrients from the waste and wastewater chains for use in agriculture.

 

Results

Data about micronutrients are relatively scarce. Field trials were conducted in 2018 and 2019 involving the application of ten different organic products before the cultivation of, respectively, potatoes and sugar beet (Report WPR-1024). The aim of the trial was to study the effect on soil resilience of applying different organic products. However, the study also measured micronutrients in the products, the soil and the crops. In Work Package 1 of this TKI project, these data were used to enhance our understanding of flows of micronutrients in agriculture. The analysis focused on the macro-element magnesium and the micronutrients boron, copper, cobalt, manganese and zinc. The aim of the study in WP1 was to acquire a clearer understanding of the influx, soil availability, levels in the crops, and the outflow of these compounds. More measurements were conducted for copper and zinc, and an analysis was conducted to determine how suitable the data are for the drafting of recommendations about copper and zinc in fertilisers for potatoes and sugar beet. The report can be found by clicking on the link below.

The project used the case of the sugar-beet chain to investigate the chances/possibilities for the reuse of micronutrients in the chain. The study began by mapping the position of micronutrients in the entire production chain, including the residual streams. This was followed by an identification of the solution paths to increasing the circularity of the micronutrient stream and/or enhancing the reuse of residual streams. The key conclusion is that the best possibilities for further enhancing reuse/recycling within the sugar-beet chain are offered by the treatment sludge. Currently, however, the treatment sludge cannot be recycled because of the prevailing legal provisions. A modification of these provisions to change the status of treatment sludge from agro-food processing would enable the reuse of this treatment sludge as a fertiliser in the agricultural sector. The report can be seen by clicking on the link below.

Work package 2 examined whether manganese from the drinking water sector can be used as a potential fertilizer. Manganese is only available to plants as the divalent ion Mn(II). Manganese can be extracted as manganese dioxide – Mn(IV) – from rinsing water sludge from drinking water production. The research has shown that there is potential to extract manganese in a high purity at some drinking water production locations. The separation of iron and manganese in the pre- and post-filters and the conversion to Mn(II) present a challenge. Because manganese is present in the raw groundwater as the divalent ion Mn(II) and is only oxidized to Mn(IV) in the filter, it is advisable to further investigate whether Mn(II) can be selectively removed from raw groundwater. That would save a lot of reprocessing costs and could yield a potentially interesting product.