Green Mineral Mining Centre
In the concept of the Green Mineral Mining Centre, flows like manure, sewage sludge, food and feed waste and other organic residues are used as a source to produce new Bio-Based Fertiliser (BBF) such as mineral fertilisers, organic fertiliser or organic soil improvers and energy (by digestion). At Green Mineral Mining Centres, businesses, governmental bodies and knowledge institutes work together on the development of a circular nutrient economy by new concepts for the processing of biomass waste streams into valuable products. The central goal is to close nutrient cycles and to provide a sustainable solution for surpluses of minerals in agriculture as illustrated in the following figure.
Green Mineral Mining Centres are demonstration locations where operational and potential new sustainable cost-effective solutions are developed, tested and implemented for the processing of biomass waste streams. In this development, the following four pillars are of key importance: technology, market, economical business benefits, and environmental benefits.
The first example of a Green Mineral Mining Centre is the nutrient recovery initiative at the digestion plant Groot Zevert Vergisting (GZV), in Beltrum, the Netherlands. GZV was set up in 2004 as an answer to solve the surplus of manure in the region and the profitable conditions for biogas production. To date, GZV processes, through mesophilic digestion, over 100,000 tonnes per year of pig slurry (80%) and different types of agro-industrial organic waste. The plant is extended with a novel nutrient recovery installation processing and separating the digestate into phosphorus (P) fertilisers, nitrogen-potassium (NK) fertilisers, organic soil improvers and clean water (see figure below).
This processing at GZV will bring an end to current digestate disposal practices including transport of digestate over distances up to 300-500 kilometres to farmers in Germany. In the Netherlands, manure production by livestock farming is greater than the amount that can be applied on agricultural soils. A limited amount of nitrogen and phosphorus is allowed to be applied to agricultural soil due to European and national legislations. These legislations are necessary to reduce the environmental pollution from fertilisers to soil, water and air. In the Netherlands in regions with intensive husbandry there is a surplus of animal manure in terms of mainly P. This surplus has to be set aside outside the Dutch agricultural sector, for example by export to neighbouring countries. Besides export of P rich manure and digestate also large amount of nitrogen (N) and carbon (C) are exported.
In collaboration with Nijhuis Industries (NI) and Wageningen University and Research, GZV developed a solution for both the nitrogen and phosphorus challenge (see figure). This is now implemented as nutrient recovery and reuse (NRR) systems using digested pig manure as a resource. The GENIUS approach of NI is for the recovery of nitrogen and potassium from the liquid fraction. The RePeat (recovery P to eat) approach of WUR is for the recovery of phosphorus from the solid fraction.
The GENIUS system has been started up in 2019 and is now producing NK-concentrate which is already being used by the farmers in the region. In this GENIUS system, the digestate is separated into a solid and a liquid fraction by means of a decanter centrifuge. The NK-rich liquid fraction is processed into a NK-concentrate and clean water through a combination of Dissolved Air Flotation (DAF) and a membrane filtration system, including micro filtration (MF), reverse osmosis (RO) and ion-exchange (IX). The separation of the liquid digestate fraction into NK-concentrate and clean water is expected to generate substantial cost savings for the plant by allowing local spreading of the NK-concentrate and discharge of water to a nearby surface waters.
The NK concentrate is further blended with other inorganic N materials/fertilisers which are recovered at other nutrient recovery plants in order to meet with the crop requirements of grass, maize and potato in the region of the Achterhoek. The fertilising product is used by farmers who have signed up to join the ‘Bio-based Fertilisers Achterhoek‘ pilot project which allows them to use the NK-concentrate blend as a substitute for mineral nitrogen fertiliser. This is above the N application standard of manure but within the N application standard of mineral N fertiliser.
The residual phosphorus rich solid fraction will be treated with the RePeat P-stripper system through an ‘acid-base’ process. Sulphuric acid is applied to release the phosphate from the solid fraction and a base (magnesium or calcium hydroxide) is added to precipitate the solubilised P. If magnesium hydroxide is used, mainly crystalline struvite (magnesium ammonium phosphate) is formed in which also a part of the nitrogen is enclosed. If calcium hydroxide is used, an amorphous calcium phosphate is produced which needs to be further dewatered. After phosphate recovery from the solid fraction a P-poor organic material remains which can potentially be used as soil conditioner or natural peat replacement for the pot soil industry. Part of the sulphate (added as sulphuric acid) can be recovered as an organic gypsum fertiliser.
Since dewatering of calcium phosphate at large scale is still a problem, GZV will start with the production of struvite (more crystalline) for which the system is designed with specific retention times. Engineering of the RePeat system is now completed and an extensive period of testing and optimisation will start in 2020. Per day, the installation will convert 50 tonnes of solid fraction of digestate into organic soil improver, organic gypsum sludge and struvite.
SYSTEMIC project demonstration plant
The Green Mineral Mining Centre contributes is one of the five demonstration plants of the EU SYSTEMIC project. The overall goal is to demonstrate the technical feasibility of nutrient recovery technologies and to determine the quality of the end-products in Europe. Scientific information on the agronomic performance and environmental quality of bio-based fertilisers is the key to stimulate the use of these new fertilisers by farmers or industry. Policy makers also require this kind of information in order to adapt European or national legislation to overcome legal barriers.
The development of the nutrient recovery and reuse technology and manufacturing at GZV has been funded by:
- Ministry of Agriculture, Nature and Food Quality
- Province of Gelderland
- Topsector Agri & Food (A&F) and Bio-based Economy (BBE)
- European Union’s Horizon 2020 Framework Programme for Research and Innovation under Grant Agreement no. 730400
- Groot Zevert Vergisting B.V.